Some comparative attributes of unspoiled lotic vs. lentic freshwater ecosystems. Low-gradient (slow-moving) lotic waters often create, and remain connected to, accompanying riverine wetlands (a lentic freshwater ecosystem). These swamps, marshes, and ditches absorb, purify, and infiltrate flood waters while supporting a diverse number of plant and animal species.
We frequently perceive all waterfowl migration to be synchronized with the conspicuous movements of familiar species like Snow Geese, Tundra Swans, and Canada Geese—big flights coming south in October and November, then a return to the north in late February and March. And we’re all quite aware of the occurrence of large gatherings of some of these migrants while they make stopovers on some of our largest lentic (still) waters—the man-made lakes and reservoirs created by damming local streams. But did you know that there are populations of colorful waterfowl with dynamic migrations that extend throughout the winter and early spring with movements that are often continuous. Under favorable conditions, these birds favor the lotic (flowing) waters of the river and its larger tributaries as they transit the lower Susquehanna valley. That’s because unpolluted lotic freshwater ecosystems support a greater diversity of plants and animals than lentic waters, and therefore offer more opportunities for hungry migrating waterfowl to find food. Let’s have a look at some of the species that visit the river during their seasonal journeys…
While the urge to head south in the autumn is largely stimulated by the shortening of the photoperiod, it is the presence of ice, particularly on glacial lakes throughout the lands to the north of the lower Susquehanna River basin, that pushes many diving ducks to finally make their way south toward the guarantee of open-water feeding areas along the coast. This movement may occur at anytime between November and late February or, as we have seen during some of the mild winters of recent decades, it may scarcely be noticed at all.Common Mergansers often lead they way when it comes to migratory diving ducks. They regularly move south in conspicuous numbers by late November and December and are regularly pushing north as soon as the ice begins to melt. During a typical year, it is not unusual for some populations of these large diving birds to remain north of us during the winter. Then, in the days after a sudden rush of frigid polar air, an appreciable increase in ice cover will force a mid-winter movement of birds down the Susquehanna.Temperatures in lotic fresh waters vary over the length of the stream or river. They are largely determined by the collective impact of the numerous sources of heat flux depicted in this graphic. (Environmental Protection Agency image)Buffleheads begin passing through the lower Susquehanna region in Novemeber on their way to coastal saltwater bays for the winter. Lingering populations feed by diving in the river’s pools and riffles for benthic invertebrates including snails and insect larvae. Lesser quantities of aquatic plant matter supplement their diet.Many Common Goldeneyes will remain on shallow, ice-free waters of the northern lakes and rivers sculpted by the most recent glacial event, but only until they are forced south into and through the lower Susquehanna valley by the encroachment of freezing conditions. On the river, they are among the dozen or so species of diving ducks we see visiting or passing through during the typical late fall and early river.
During their visits to the lotic (also known as riverine) fresh waters of the Susquehanna and its largest tributaries, benthic-feeding waterfowl make short dives to take advantage of the plants, small fish, invertebrates, and other food sources inhabiting the stream bottom in the riffles and pools of the free-flowing waterway. Substrates, listed here by size (in descending order), along with other parameters influenced by this zonation determine the variety and abundance of the forage available to migrating waterfowl and other consumers. Ice or high water and poor visibility due to flooding can render the riffles and pools of the channel unusable for feeding. The birds must then choose to either linger and rest without feeding or leave the lotic freshwater habitat to seek sustenance. During a flood, this may require relocation to a nearby lentic (still) body of fresh water such as a lake or reservoir. The presence of ice will almost invariably force the birds to fly on to the Atlantic Coastal Plain and the tidal waters of its bays and estuaries.Hooded Mergansers are one of the few species of diving ducks likely to utilize flooded shoreline timber and riverine (fluvial) wetlands as refuge from high water on Susquehanna.A Pied-billed Grebe and a pair of Canvasbacks on an ice-free stretch of the lower Susquehanna in mid-winter feed and loaf in a riffle-flanked pool where a large mat of American Eelgrass, a submerged aquatic plant also known as Tapegrass or Wild Celery, grows during the summer. The vast mosaic of riffles and pools in a river this size offers tremendous opportunities for a diverse array of aquatic species to find their niche wherein they can survive and flourish.The presence of ice forces Buffleheads and other diving ducks to gather in turbulent open water, often below a riffle or dam. Another alternative is to continue on toward the salty bays and estuaries of the coast. High water may push these birds into the shallows among the flooded woods to feed, but they seldom utilize heavily forested riparian wetlands as a refuge due to their need for a running start to get airborne.
Riffle and Pool Characteristics of High Gradient (A) and Low Gradient (B) Streams. This graphic illustrates the change in deposition characteristics of a stream or river as its gradient decreases. A high-gradient stream (A) has a rapid velocity, often forms falls, and tends to carry away a high volume of all but the largest of particles of potential substrates as they erode from the surrounding landscape. On a low-gradient stream, the loss in water velocity reduces the water column’s ability to transport even the smallest of substrate particles. Deposition of this gravel, sand, silt, and clay forms lateral bars that over time create the familiar meandering path of a naturally flowing lowland stream. (National Park Service image)Benthic substrates in lotic freshwater pools and riffles support an abundance of life forms ranging from colorful diatoms on rocks and cobble, to invertebrates including snails and insect larvae, to fishes like this young Channel Catfish. Free of accumulations of sediment, this river bottom not only provides habitat for a healthy fishery, it facilitates the bidirectional exchange of water between the Susquehanna and its underlying aquifer.On the lower Susquehanna, populations of young Quillback suckers are found almost exclusively in clear, high-gradient pools.The Harlequin Duck winters along the rocky shores and man-made jetties of the Atlantic coast. In summer, they nest on fast-moving, headwater streams well to our north. Very rare on the Susquehanna, this is the first of two individuals found during March and April of 2025. It was observed feeding in the swift waters of the high-gradient riffles and pools where the river cuts through Blue Mountain north of Harrisburg. During previous weeks, Harlequin Ducks were being seen along the coast as far south as the mouth of the Chesapeake at Cape Charles, Virginia. It’s very possible that some of these birds traveled north through the bay area and up the Susquehanna on their way north.
Fluvial Geomorphology of a Stream. Many of the Susquehanna’s tributaries pass through each of these three erosional zones. Along the way, they carry out the process of breaking down the mountains formed by the Allegheny orogeny, the collision of North America and Africa that created the supercontinent Pangea about 325 to 260 million years ago (during portions of both the Carboniferous and Permian periods). Today’s main stem of the lower Susquehanna passes through a transfer zone (Zone 2), carrying eroded materials to a depositional zone (Zone 3) located within the ancient Susquehanna canyon stretching from Havre de Grace, Maryland, to Norfolk Canyon on the edge of the continental shelf. Within this zone, more than a 10,000-year accumulation of post-glacial sediments lies submerged by the rising waters of the Atlantic Ocean and Chesapeake Bay. Although the present-day lower Susquehanna is largely a transfer zone, some deposition occurs along low-gradient segments of the river, particularly where its course parallels the watershed’s ridges both above and below the high-gradient rapids where its path has eroded passage through the highlands. (National Park Service image)Although the present-day lower Susquehanna is largely a transfer zone, some deposition occurs along low-gradient segments of the river, particularly where its course parallels the watershed’s ridges both above and below the high-gradient rapids where its path continues to erode passage through the bedrock. On this 1908 map of the Susquehanna at Conewago Falls, alluvial terraces of gravel, sand, silt, and clay can readily been seen as pale areas nearly lacking brown contour lines along the shorelines and islands of the river. Deposits within most of these terraces date back to the melt period following the most recent glacial event and beyond. The delta shown at the mouth of Conewago Creek (west) includes massive volumes of material deposited by both the creek and the river. This delta is currently known as Brunner Island, much of it developed as the site of a coal/gas-fired electric generating station. Terrace deposits along the Susquehanna’s shorelines created extensive perched marshes and swamps (wooded marshes) fed by rains, high river water, small streams, and springs, the latter often seeping from the base of the rocky escarpments carved by the ancient Susquehanna and defining the present-day inland border of the floodplain. We call these sites “Alluvial Terrace Wetlands”. Few of these critical components of river morphology survive. Those not drained for farmland were obliterated by urbanization and canal, railroad, and highway construction. (United States Geological Survey base image: Middletown, PA, quadrangle, 1908)Water Willow is a familiar emergent plant that colonizes lateral bars and other alluvial deposits in low-gradient segments of the Susquehanna.The fine roots of Water Willow collect sediment and absorb nutrients while creating dense cover for young fish and numerous species of invertebrates including the Virginian River Horn Snails seen here.
Prior to the nineteenth century, the low-gradient flow regime of the river both above and below the riffles at Chiques Rock (lower right on map) created prime wildlife habitat. The natural accumulations of nutrients and substrates carried into and through the lotic waterway’s pools and riffles were cycled into an ideal growing medium for extensive mats of American Eelgrass and other aquatic plants. This underwater forest hosted a seemingly endless abundance of invertebrates and fishes (both resident and migratory)—supporting a variety of consumer species including various populations of humans. But soon after the mass clearing of much of the watershed’s land for farming and lumber, the mill ponds created by dams constructed on streams to power saw and grain mills became brimful with sediments eroded from the unprotected ground. During storm events, torrents of these sediments then flowed full bore toward the Susquehanna, and began accumulating in the low-gradient segments of the river.
Sediments left behind after the removal of mill dams are known as legacy sediments. They disconnect the stream from its historic floodplain and riverine (fluvial) wetlands, thus intensifying the impact of high water in the surrounding landscape. As these nutrient-charged deposits wash away, they become a source of pollution in the waters of the Susquehanna and Chesapeake.A mat of American Eelgrass growing in the flowing waters of the Susquehanna below Conewago Falls. Eelgrass and other submerged aquatic plants provide essential habitat for a wide variety of small fish and invertebrates while also consuming nutrients deposited in the cobble, gravel, and sand substrate of the river’s pools. Excess quantities of smaller particles of silt and clay can clog the substrate and thus inhibit the hyporheic exchange of water between the stream channel and the underlying aquifer, often diminishing the biomass and diversity of organisms inhabiting this benthic habitat. Buried in these life-choking sediments, the river bottom becomes inhospitable to growth of submerged aquatics including eelgrass.This low-gradient stretch of the Susquehanna at Marietta flows parallel to the Chickies Quartzite “Hellam Hills” before making a sharp right turn to punch through the ridge as a series of rapids at Chiques Rock. Formerly a fully functional lotic ecosystem and a paradise for migrating waterfowl, this river segment is now impaired by accumulations of nutrient-laden sediments from agricultural and urban runoff.Nutrient and sediment-loaded flood waters roar across the diabase boulders at the York Haven Dam and Conewago Falls, a high-gradient segment of the Susquehanna.They continue past Brunner Island (left power plant stacks) and through Haldeman Riffles and the Shocks Mills Railroad Bridge……into the stretch of river known as the “Marietta broads” along the base of the Chickies Quartzite “Hellam Hills”. The low stream gradient here produces a slower current and increased deposition of sediments.As the flood surges through the riffle and pool complex at Chiques Rock, the high stream gradient maintains a velocity in the water column sufficient to keep additional sediments in suspension until they reach the low-gradient river segment just downstream at Washington Boro, site of a naturally occurring lateral bar area known as the Conejohela Flats. These bars now lie within the man-made depositional zone known as “Lake Clarke”. Created nearly a century ago by construction of the Safe Harbor Dam, this impoundment is accumulating astounding volumes of nutrient-loaded sediments that continue to encapsulate the flats within a stream-impairing delta.Anytime from November to April on the lower Susquehanna, a group of Redheads, Canvasbacks (3 birds to right of the middle of the picture), and a Horned Grebe (lower left) is a welcome sight in a riverine pool known to have a summertime growth of American Eelgrass. Noted Dr. Herbert Beck in 1924 when describing the Canvasback, “Like all ducks, …, it stops to feed within the county (Lancaster) less frequently than formerly, principally because the vast beds of wild celery which existed earlier on broads of the Susquehanna, as at Marietta and Washington Borough, have now been almost entirely wiped out by sedimentation of culm. Prior to 1875 the four or five square miles of quiet water off Marietta were often as abundantly spread with wild fowl as the Susquehanna Flats are now. Sometimes there were as many as 500,000 ducks of various kinds on the Marietta broad at one time.”Today, seeing just dozens of Aythya genus ducks (Redheads, Canvasbacks, scaup) on the lower Susquehanna is a notable event. If they happen to be forced down by inclement weather while migrating through, you might get lucky enough to see several hundred.While the recovery of eelgrass/wild celery beds on the Susquehanna is trivial in scale and offers little support for numbers of waterfowl to return to historic levels, restorations on the upper Chesapeake in the vicinity of the Susquehanna Flats between Havre de Grace and Aberdeen Proving Grounds may have helped refuel a gathering of mostly Aythya genus ducks during the final days of February. This mass of ducks, many of which were forced south from the frozen Great Lakes during the previous weeks (some by way of the ice-choked Susquehanna) were apparently making an abrupt turn to make their way back north. Their stay was brief, but estimates by local birders put their numbers as high as one half million. The vast majority of the concentration consisted of Aythya species: Redheads, Canvasbacks, Ring-necked Ducks, and both Lesser and Greater Scaup. It probably included a mix of birds including both northbound migrants from further down the coast and the aforementioned refugees that had just arrived to pay a quick visit while escaping the late-season ice before turning around.During the past two centuries, as food supplies in the Susquehanna grew increasingly compromised for benthic feeders like these Lesser Scaup and other diving ducks, a change in distribution was necessary for survival.As individual species, Lesser Scaup and other waterfowl that fail to adapt to natural or man-made changes in their habitats and food supplies may see their overall global numbers falter.
Despite being located in the transfer zone, the lower Susquehanna has become a significant depositional zone along much of its length, mostly courtesy of the placement of sediment-trapping man-made dams.
Following construction of the mill dams and ponds on nearly every mile of the lower Susquehanna’s low-gradient tributary streams, enterprising parties moved on to the river. The first significant spans were constructed using wide timber cribs filled with large rock. They were placed to create water deep enough to allow canal boats to cross the Susquehanna at both Clark’s Ferry at the mouth of the Juniata River in Dauphin County and at Columbia/Wrightsville. These dams also diverted water into the newly excavated canals—the Pennsylvania Eastern Division Canal (completed in 1833) which followed the river’s east shore from Clark’s Ferry to Columbia, and the Susquehanna and Tidewater Canal (completed in 1840) along the west shore from Wrightsville to Havre de Grace, Maryland. Placement of these sediment-trapping man-made dams began a process of converting vast mileage of the lower Susquehanna from a transfer zone into a deposition zone. In addition, layout of the canals and locks followed the contours along the base of the riverside ridges, seriously altering most of the alluvial terrace wetlands that the river had created as a feature of its floodplain during the post-glacial period.
Construction of the canal dams was just the beginning. During the twentieth century, more massive dams would be added to the main stem of the river for hydroelectric energy production at York Haven, Safe Harbor, Holtwood, and Conowingo. Upon their completion, the days of unassisted anadromous fish migrations were over. On both the river and its tributaries, smaller dams including dangerous low-head dams maintain water levels for boating and recreation. They too create current-diminishing, pseudo-lentic waters that blanket the lotic riffle and pool substrates with polluted sediments.
MAN-MADE DAMS TURN LOTIC WATERS INTO UNFLUSHED TOILETS
The construction of dams on the lower Susquehanna has converted vast mileage of the river from a lotic freshwater system into a series of man-made lentic freshwater lakes. These areas have lost their function as a lotic transfer zone and are now a sort of dysfunctional series of depositional zones collecting vast volumes of sediment containing nutrients and other pollutants. Within each impoundment, the reduced velocity of the river causes it to drop suspended sand first, then the finer particles of silt and clay closer to the dam. The flow regime of riffles and pools is lost and the hyporheic zone that exchanges water between the river and the underlying aquifer is clogged. These impaired segments of river become ripe for eutrophication: algal blooms followed by die offs that can lead to a fatal reduction of dissolved oxygen in the water column.Deposits of lateral bars of sediment in low-gradient segments of the Susquehanna can create shallow water feeding habitat for puddle/dabbling ducks like these Gadwall. Where sediment pollution is severe, benthic foods in these areas often consist mostly of invertebrates and plant matter deposited by the current, the buried substrates devoid of a functioning ecosystem and the waters subject to eutrophication.Common Goldeneyes on a patch of open water on an otherwise ice-covered “Lake Clarke”, the impoundment created by Safe Harbor Dam. While they may find this spot advantageous for loafing, the food supply over the sediment-buried substrate will be limited.By the end of the twentieth century, accumulations of polluted sediments behind lower Susquehanna dams were nearing capacity. There is no working plan to attenuate the massive release of these pollutants that may be triggered by a catastrophic flood. The effort to reduce nutrient and sediment runoff remains the focus so that new loading is kept to a minimum and won’t add to the capacity problems at the dams or continue downriver to the Chesapeake at full strength when the dams are full. Alleviating the sediment aggregation problem within the river’s impoundments is a tall order and a dilemma not easily solved. (United States Geological Survey image)Common Mergansers will feed where benthic substrate supports the small fish and invertebrates they prefer. They will, however, gather in extraordinary numbers on the “lakes” created by riverine dams. Though they can only feed on what floats in with the current, hundreds or sometimes thousands of Common Mergansers will concentrate on “Conowingo Pond” during the late fall or early winter. There, safety in numbers gives them some guarantee of protection against the multitudes of eagles that simultaneously frequent the vicinity. Another advantage of staging on “Conowingo Pond” is its close proximity to favorable feeding areas on upper Chesapeake Bay and stretches of the Susquehanna where lotic riffles and pools offer abundant opportunities below the river’s dams.Fortunately for everything else living in the benthos, Common Mergansers are big enough to devour invasive, non-native Rusty Crayfish when they find them in our lotic waterways.
TIME TO CLEAN UP OUR ACT
WHERE DOES YOUR STORMWATER GO?
Channelized Urban/Suburban Streams Function as Sewers. They have no attached lowlands or floodplains to absorb, purify, and infiltrate runoff from rain events. Pollutants including litter, pet waste, lawn chemicals, tire-wear particles, hazardous fluids, and sometimes untreated human excrement flush unchecked from the municipal storm drainage system into the waterway. Thermal shock from summer downpours washing across sun-heated pavements can kill temperature sensitive fishes and other aquatic life. Nutrient and sediment loads from these impaired tributaries later accumulate downstream in low-gradient segments of the Susquehanna, turning the river into an open-air cesspool. Aggressively working to implement projects that eliminate these sources of pollution are the only effective way to keep the problem from getting worse. Making things better requires a lot more dedication and effort. (United States Geological Survey image by Frank Ippolito)
RIPARIAN BUFFERS MAKE A DIFFERENCE…WIDER IS BETTER
To sequester sediment and cycle nutrients (primarily nitrogen and phosphorus) contained in farm runoff, the U.S.D.A. recommends installing riparian buffers between streams and lands used for grazing and raising crops. To protect pollinating species including bees and butterflies from pesticide drift and eroding soils rich in fertilizers, they further recommend installing a stand of wind-pollinating plants such as conifers, oaks, and birches between the field and streamside plantings. These same conservation practices improve water quality and wildlife habitat on waterways located in residential and commercial areas as well. (United States Department of Agriculture image, click to enlarge)
FLOODPLAIN RESTORATION
Regardless OF HOW LONG YOU’VE BEEN CONDITIONED TO THINK OTHERWISE, THIS IS A DYSFUNCTIONAL, POLLUTED CREEK—AND IT NEEDS HELP
A channelized low-gradient stream eroding a path through deposits of legacy sediments displaces flood waters into previously unaffected areas and provides a continuing source of nutrient and sediment pollution during storm events. These impaired waters have a diminished capacity for supporting aquatic life including fishes.
RESTORED TO ITS HISTORIC FUNCTIONS
On an adjacent segment of the same creek, this legacy sediment removal project restored a braided meandering channel and connected it to its newly liberated, historic floodplain. In just their second year, the fluvial wetlands are effectively absorbing stormwater and sequestering nutrients as an attached component of the stream’s riffle and pool complex. During our visit earlier this week, we found American Toads, Northern Leopard Frogs (Lithobates pipiens), and Northern Spring Peepers breeding here. It’s just as Castor canadensis would have it!
“STOP HEMMING AND HAWING AROUND ALREADY”
“HEY COWBOY, HOW ‘BOUT GETTIN’ THEM FILTHY LITTLE DOGIES OUTTA DAT CRICK?”
Here’s a polluted stream in a pasture with grazing livestock. The site is a former mill pond within which the creek eroded a channel following removal of the dam. The animals defecate and urinate where access to water is gained at a broken down embankment of the nutrient-loaded legacy sediments deposited in the pond more than a century ago. It’s a haphazard form of animal husbandry and a reminder that all it takes is just one stubborn jackass to foul up the whole waterway.
DIRECT SOURCES OF NITROGEN (AMMONIA) POLLUTION IN STREAMS
DID YOU KNOW that a dairy cow produces about 80 pounds of waste (excrement and urine) every day?
DID YOU KNOW that a horse produces about 50 pounds of waste (excrement and urine) every day?
DID YOU KNOW that a human produces about 3 to 4 pounds of waste (excrement and urine) every day? The exceptions, of course, are those who continue to insist that raising farm animals in and alongside a body of water is okey-doke—a harmless practice. These individuals tend to retain the former constituent of human waste and are thus full of it.
“ATTABOY TEX, THAT’S MORE LIKE IT!”
Now that’s better. Legacy sediments have been removed to reconnect the stream to its floodplain. A livestock crossing and exclusion fencing has been installed, and a nutrient-consuming riparian buffer has been planted. This creek segment’s pollution woes have been mitigated. Do you have a neighbor needing this type of remedial work on their farm? Have them call your local conservation district office for advice. Some programs include financial assistance covering the costs of installation as well as monetary incentives for helping to clean up the water.
AND FINALLY
WHEN IT COMES TO BUILDING DAMS ON LOTIC FRESH WATERS…
…LEAVE IT TO THE BEAVERS
North American Beavers (Castor canadensis) create habitats that connect the riffle and pool regime of a low-gradient stream to a surrounding fluvial wetland that retains sediments, cycles nutrients, and provides essential habitat for hundreds of plant and animal species. Floodplains are for flooding. And if a beaver floods an area, you can be guaranteed that it was already part of a floodplain. You see, beavers don’t encroach upon humans, it’s humans doing the encroaching upon beavers. (National Park Service image)
MAD HATTERS
DID YOU KNOW that even before the landscape was cleared for farms and a supply of timber, and before mill dams on local creeks began accumulating soil runoff from the consequently barren hillsides, all the North American Beavers, the keystone species of lower Susquehanna stream ecology, were killed and sold to make hats? It’s no wonder things are fubar!
COMING SOON…
Horned Grebes are regular migrants and sometimes winter residents on ice-free stretches of the lower Susquehanna. They spend their time plying the benthic substrate of the river’s clear riffles and pools for a variety of invertebrates and small fish. Look for them moving north in coming days sporting this beautiful breeding plumage.April and early May are prime time for observing Common Loons on the Susquehanna as they undertake a journey from the Atlantic surf where they spent the winter to nesting sites on northern lakes. For this migrant in breeding plumage, clear water for sighting plenty of benthic life in the river’s riffles and pools assures a successful dive in search of energy-replenishing forage.
It all started rather innocently as a typically cold early January with sheets of ice covering the river and with soils on the lands in the remainder of the lower Susquehanna watershed frozen solid. Then came the “Blizzard of ’96”, blanketing much of the valley with between 20 and 30 inches of wind-driven snow.
Snowfall totals for the “Blizzard of ’96”, January 6-8, 1996. (NOAA/National Weather Service image)
In affected areas of Pennsylvania, Governor Tom Ridge closed all state roads for the duration of the snowfall event. Many would remain closed for much of the following week as drifting hampered exhaustive efforts to get impassable routes open.
In congested, high-density neighborhoods, cars remained buried for lack of anywhere to go with the snow. (Vintage 35 mm image)In more suburban areas, it was often a day-long chore to excavate a path to the street. (Vintage 35 mm image)
Just as the recovery entered its second week, a change in the weather pattern took hold as milder air and spring-like rains hastened the melt. Clogged by snow often several feet in depth, storm sewer inlets and other drainage features failed to collect the runoff. Street and urban flooding became widespread. Some buildings, particular those with large flat roofs, experienced structural damage due to any remaining snow soaking up the additional weight of the rain. As local creeks swelled to stain snowy meadows brown, attention shifted to the icy river.
On the Susquehanna, rising waters started moving ice into accumulating piles of car-sized chunks behind dams and at choke points along the river’s course. During warmer weather, stream gauges provide a depth of water reference known as a stage (measured in feet) that corresponds to a rate of flow passing the gauge site (measured in cubic feet per second). On occasions when ice and debris block river channels during winter, these readings can fluctuate wildly and the relationship between stage and flow can become dubious. When the water is running ice-free at Harrisburg for example, a gauge reading of about 11.1 feet is indicated when the river flow rate is approximately 162,000 cubic feet per second. But due to its impact on the capability of the river channels to pass water, the presence of slow-moving and jammed ice can cause rapid and sometimes unpredictable variations in gauge readings, even when the flow rate remains steady. Impaired by an ice jam at the gauging station or just downriver, a flow of 162,000 cubic feet per second could lead to a stage measurement significantly higher than 11.1 feet, and the area of adjacent floodplain inundated by rising waters will increase to a corresponding degree. Conversely, a jam upstream of the gauging station could cause the reading to drop below 11.1 feet—at least temporarily—then look out, a dangerous surge could be forthcoming!
At Harrisburg, the ice jam behind the Dock Street Dam in January, 1996, caused devastating flooding in the city’s Shipoke neighborhood, on City Island, and in low-lying areas along the river’s west shore.
Just upriver from the Dock Street Dam at Harrisburg, the Susquehanna at the United States Geological Survey gauging station on the east side of City Island crested at 25.08 feet on January 20, 1996. As the rising waters finally began heaving the jammed ice up and over the dam, the scouring energy of the departing glacier-like mounds would carry away two spans of the truss-construction Walnut Street Bridge on the west side of the island, and eventually collapse a third. After receding during the remainder of the day and through the night, yet another aggregation of chunked ice would cause the river to crest again on January 21st, this time at 24.66 feet. Under free-flowing conditions, these readings would correspond to a river flow of just under 600,000 cubic feet per second; that’s more than 250 million gallons per minute!
Downriver at Conewago Falls, ice jams behind the York Haven Dam and at several choke points within the riverine archipelago that extends from Haldeman Island to Haldeman Riffles in Lancaster County would be relieved as the river crested there during the afternoon of January 21st. The following photograph accurately relates the scene, minus the stench of mammalian feces and petroleum emanating from the polluted water of course.
Our friends (L to R) Rick Morton, Bob Zeager, Dan Seitz and his daughter Sierra witness the ice-choked Susquehanna River cresting below Conewago Falls on January 21, 1996. Bob awoke the previous morning inside his mobile home (left rear) to discover he was rapidly being surrounded by fast-rising water. With the ice-covered road now submerged in over three feet of river, he had no hope of getting out with his van, so he started removing clothing and a few other essentials by canoe. Dan soon arrived to move a few of his things to higher ground and de-energize both properties. We did our best to lend a hand, then we all got out of the floodplain. A short time after we had departed, Rick arrived and became concerned when he saw Bob’s van, now in almost four feet of water alongside his home. Rick parked his conveyance, also a van, on a rise in the lowland terrain, then made his way back the old Pennsylvania Canal towpath to make sure Bob wasn’t stranded. After concluding that he had already evacuated, Rick returned via the towpath to his van. He then discovered that yet another surge of quickly rising water had inundated the ice-covered section of access road by which he had arrived, so he was forced to wade out, leaving his vehicle behind. A short time later, he reached us by telephone proclaiming, “I’m out!”, and filled us in on the details. As the flood receded, Rick was able to retrieve his van on January 22nd. Bob’s van was totally destroyed and both his and Dan’s mobile homes were left uninhabitable. Though by no means their first experience with river flooding, this event proved particularly costly and stressful for Bob and Dan…the effects life-altering. The moral of the story: floodplains are for flooding, not filling, not building, and certainly not dwelling. Floodplains happen to make outstanding wildlife preserves, and that’s what this water-purifying alluvial terrace wetland is today. (Vintage 35 mm image)
Today’s NOAA/GOES satellite image serves as a little reminder of the big three. That’s right, it’s the three big “natural” disasters—wildfires, inland flooding, and coastal flooding (lucky for us, our region is at present millions of years removed from severe threats posed by the tectonic disasters—earthquakes, volcanoes, and tsunamis—and is not particularly prone to frequent tornadoes). Each continues to cause an increasing volume of property damage and threaten a greater number of lives because of where and how we choose to make our homes and erect our structures.
Earlier today, smoke from forest fires in central Canada sweeps through the skies of the Great Lakes, New England, and the Mid-Atlantic States north of the Mason-Dixon Line. Meanwhile off North Carolina, Tropical Storm Dexter is seen developing over warm ocean waters east of the Gulf Stream. (NOAA/GOES satellite image)
For all of human existence, the dynamics of the atmosphere have been shaping the topography and the ecosystems of the planet. In recent times, we’ve had the advantage of satellite technologies to show us spectacular images of atmospheric events as they happen. And through the various branches of science, we’ve come to understand the impact these events have upon the landscape and the people who live and/or work there.
Forestry sciences have helped us to understand how natural fuels, humidity, temperature, rainfall, soil moisture, wind, and human encroachment influence the frequency and severity of wildfires. These discoveries have led to changes in forest management and implementation of practices such as prescribed burns to reduce accumulated fuel loads. Because human development typically lowers soil moisture and brings along with it additional sources of ignition, many land managers and fire departments have warned of the ever increasing dangers of wildland-urban interface fires. These warnings have gone largely unheeded for more than four decades as millions of homes and other combustible structures have been erected within areas prone to fires capable of uncontrollable growth into disastrous conflagrations. The tinderbox wildlands—they’re a nice place to visit, but we ought not to live there!
Tropical storms and other sources of heavy precipitation bring about quite the hubbub over flooding. Meteorologists spend a lot of time explaining it all, but it’s almost as if no one pays any mind. For a people who check the weather forecast several times a day, every day of our adult life, just to get a leg up on how that weather is going to change day by day and hour by hour, you would think we would better anticipate the climatic events that happen over the long term. In particular, you would think we would have an awareness of our own individual susceptibility to flooding— a grasp of how, where, and why floods occur. You would think that repeated episodes of flooding would compel society to embrace an ethic that treated water as the valuable commodity it is. Yet, we all seem to follow the same patterns of behavior. First, we drain, dump, pipe, curb, channel, ditch, grade, pave, and pump to get the rain that falls upon our property off of our property. Then, the chump downstream gets really mad that we sent our water his way and flooded him out, so he takes the same measures to send even more water to the next poor slob down the line until finally the now polluted slurry of runoff floods the street, a cellar, a house, a business, or a stream—a stream that has been channelized so it no longer has a floodplain to absorb, hold, purify, and infiltrate the stormwater. Why was the stream channelized? So we could fill in the floodplain and build upon it of course. Two things come to mind here. First, if we’re going to be selfish enough to flood out our neighbors, then why shouldn’t we be totally selfish and keep for ourselves all the water that falls upon our place. After all, we’re going to need that water some day. And second, the floodplain is a nice place to visit, but we ought not to build there. Floodplains are for flooding; thousands of years of erosion have shaped them that way—it’s a gravity thing!
Next, we look at the lessons from geology, more specifically coastal geomorphology. Through these disciplines we know that the coastal plain—the flat land that spent most of the last 35.5 million years (the time since the meteor strike at the present-day mouth of Chesapeake Bay) as a beach or a tidal marsh—today stands mostly less than three dozen feet above sea level. We know that the sands forming barrier islands along the Atlantic seaboard, which are only several feet above sea level, shift their shape and position with the tides. Over the decades and centuries, these islands migrate and compensate for changes in climate and tidal patterns as well as sea levels. Behind their shifting dunes, vast tidal marshes are protected from seasonal storms including the periodic nor’easter or hurricane. Despite the importance of barrier island dynamics to the integrity of the bays and estuaries they protect, and despite their vulnerability to coastal storm surges, winds, and flooding, we choose to build there. In fact, the greatest population densities in the United States, and in many other countries of the world, are on the beach. It’s not because these hundreds of millions of people are fishing or loading/unloading ships for a living—it’s mostly for the view. Despite their importance to fisheries and other coastal life, we continue to alter and destroy the near-tidal areas of the the barrier islands and bays. We go to great expense to “save” for our uses the lands that should be getting inundated by rising sea levels to create new shallow tidewater zones. We waste spectacular amounts of money pumping sand back onto beaches to keep naturally migrating sediments from changing their shape and position in response to the tides. We keep putting more people and more capital at risk by urbanizing these low-lying areas. Building on the beach is absolute madness. It’s an ecological catastrophe from day one and a human catastrophe soon after.
All of the lands impacted by these natural events have two things in common. Each becomes a potential disaster area if people choose to construct their homes or businesses there. And each, if left in its wild state and given a buffer space from human activity, reacts with natural time-derived mechanisms in response to the same events. These mechanisms are often essential for provision of the unique ecosystems required by many of our most threatened wildlife species. Human encroachment into floodplains, wetlands, tidal marshes, beaches, and xeric uplands is a double-edged sword. It first decimates populations of these uncommon species by destroying and fragmenting their specialized habitats. Then, it sets the stage for the fires, floods, and other disasters that endanger the lives and property of the people living there. Considering the ramifications of building in these fire and flood susceptible areas, we can and should live somewhere else, especially when the wildlife requiring these places often can’t.
This evening’s smoky sunset over the Susquehanna at Chiques Rock was courtesy of Canadian wildfires.
Soon after their arrival during the late 1600s, the earliest trans-Atlantic human migrants to settle the Lower Susquehanna River Watershed began the process of eliminating many of our largest native fish species. They started by extirpating nature’s steward of lowland streams and wetlands, the North American Beaver. The beaver’s meticulously maintained dams and fisheries-friendly ponds were promptly replaced by man-made impoundments designed to permanently divert water for powering lumber and grain mills. Behind these structures, silt deposits accumulated as the forests were clear cut and the land subjected to highly erosive farming methods. Mill dams would eventually be located on nearly every mile of suitable low-gradient stream in the basin. Populations of native coldwater fishes including Brook Trout were quickly lost or left isolated in scattered headwaters.
With their navigation of creeks blocked by nearly impenetrable mill dams, seasonally migratory freshwater and anadromous fish were denied access to their traditional spawning waters. The latter then had their populations seriously depleted, and in some cases extirpated, following construction of hydroelectric dams on the lower Susquehanna during the first half of the twentieth century. The loss these latter species, including the herrings, Striped Bass, and sturgeons, all of which attain great size only because of their ability to make a sea run to access the year-round food energy available in the Atlantic, constitute a tremendous reduction in the numbers, variety, and mass of fish occurring in the river and its tributaries.
Add to these events the various sources of pollution entering the lower Susquehanna’s waterways during the intervening years including acid mine drainage, agricultural nutrients and sediments, stormwater runoff, untreated domestic and industrial sewage, illegal dumping, pesticides, etc., and one can easily understand how the watershed’s native fishery was lost as a commercial, food, and recreational resource.
Presently, the effort to restore populations of self-sustaining anadromous fishes to the lower Susquehanna is stalled due to the presence of introduced invasive species, particularly Northern Snakeheads, in the river’s waters below Conowingo Dam. Lifts that carry migrating fishes over the lower river’s hydroelectric dams during the spring run are shut down to avoid extending the range of the hoards of non-native snakeheads to waters upstream of their present location. Any translocation of anadromous fish must now be completed by manually separating desired species from among the invaders and loading them into a tank truck for transport to waters upstream of the dams. But Northern Snakeheads are currently so prevalent at Conowingo that they are overwhelming the lift used for collecting and sorting fish as well.
Any slight hope that had existed for a return of harvestable stocks of American Shad or other sea-run native species to the Susquehanna and its tributaries seems to be fading. And widespread improvements to water quality that would promote reestablishment of sustained populations of native coldwater fishes like Brook Trout are strictly a long-range goal.
Recreational anglers, however, still remain in the game—but their reward is a bit of a booby prize. To compensate fisherman for the loss of their quarry on the river and in streams, and to promote an interest in the fishing pastime and conserving waterways, the stocking of various species of “game fish” has been a continuous undertaking, particular since the middle decades of the twentieth century. Some of these introductions are planned, others, like the release of Northern Snakeheads, are unsanctioned and outright illegal. The one thing most introductions have in common is that they consist of hardy, aggressive, predatory fishes that are non-native species (or native transplants from watersheds such as the Mississippi). Their presence, especially in large concentrations and particularly during the time immediately following introduction, can have a deleterious impact on native stream inhabitants. Some introduced fish, the Flathead Catfish for example, are upon discovery deemed invasive species; others, like the Smallmouth Bass, escape such a label not because they lack negative impacts on stream communities and ecosystems, but because they have been present for extended periods of time and have thus been accepted as part of the local fishing culture.
Hatchery-raised Rainbow Trout stocked by the hundreds in a lower Susquehanna valley creek for angling. The Rainbow Trout is native to the streams and rivers of the Pacific coast of North America. An anadromous form is known as the “Steelhead”. These sea-run trout with access to marine food sources during their growth years attain more than twice the size of freshwater forms and acquire oversized hooked jaws before ascending waterways to spawn.
The creation of recreational fisheries comprised of introduced species has certainly helped maintain an interest in the fishing hobby and in the conservation of waterways. It has even been a driving force for spectacular restorations of streams that otherwise would have languished in an impaired condition with little in the way of diversity of species—native or non-native. As anglers, we are especially indebted to those who’ve devoted their time, energies, and, in some cases, a lot of money to projects that specifically seek to reestablish native waterways within the challenging landscape of the Lower Susquehanna River Watershed. With an eye on the future, perhaps now is a good time to join them and focus our passion for freshwater angling on steering fisheries management more toward the native ecosystems approach. Quality instead of quantity.
In that spirit, here are three items we can add to our tackle boxes this season to be better fisheries conservationists, instead of our own worst enemies.
Lead-free Weights- Replace the lead in your tackle box with tungsten or other lead-free alternatives to eliminate the potential impact this poisonous metal can have on you and wildlife like waterfowl and Bald Eagles. Make a special effort to rid your inventory of small pieces of shot that can easily be ingested by animals as they feed. Realistic Lures- Add sport to your fishing by using artificial lures. Today’s selections include very realistic versions of native fishes, crayfish, frogs, and other aquatic creatures. Use these life-like imitations and you won’t need to harvest native minnows and other wildlife from populations that are already being subjected to negative impacts from stocked legions of predatory “game fish”. You’ll also eliminate the risk of introducing non-native bait species into your favorite fishing waters!Trash Bag- Always bring a trash bag and carry out your litter. Be especially vigilant about monofilament fishing line.Fishermen are their own worst enemies, so you’ll need to pick up after the other guy too. Show the landowners and land managers who are our hosts a little consideration.
Best of luck this fishing season. We hope your time outdoors will motivate you to get involved with efforts to keep your local waterways clean. You might even be inspired to assist with projects that are planned or currently underway in the Lower Susquehanna River Watershed to restore stream segments, wetlands, and floodplains. Many of these projects are grassroots efforts and they’d love to have your participation. Your local county conservation district can steer you towards an active restoration group near you. Give them a ring.
Hatchery-raised Rainbow Trout and a “Golden Rainbow Trout” stocked for anglers in a restored segment of a stream in Lebanon County, Pennsylvania. The “Golden Rainbow Trout”, also known as the “Banana Trout”, is a Rainbow Trout color variant developed through multi-generational selective breeding of offspring produced by crossing a typical male with a yellow-mottled female mutant discovered in a hatchery in West Virginia in 1955. Today, “Golden Rainbow Trout” breed true, golden males crossed with golden females yielding golden young. The less colorful “Palomino Rainbow Trout” is produced by crossing a “Golden Rainbow Trout” with a typical Rainbow Trout.
Our wildlife has been having a tough winter. The local species not only contend with cold and stormy weather, but they also need to find food and shelter in a landscape that we’ve rendered sterile of these essentials throughout much of the lower Susquehanna valley’s farmlands, suburbs, and cities.
Planting trees, shrubs, flowers, and grasses that benefit our animals can go a long way, often turning a ho-hum parcel of property into a privately owned oasis. Providing places for wildlife to feed, rest, and raise their young can help assure the survival of many of our indigenous species. With a little dedication, you can be liberated from the chore of manicuring a lawn and instead spend your time enjoying the birds, mammals, insects, and other creatures that will visit your custom-made habitat.
What makes some neighborhoods so appealing? It’s the foresight property owners had a half a century or more ago when they planted their lawns and gardens with a variety of sturdy, long-lived trees and shrubs. They’ve not only minimized the need for mowing grass, they’ve provided the present-day residents of their home with added thermal stability during both the blazing heat of summer and the chilling cold of winter.
Fortunately for us, our local county conservation districts are again conducting springtime tree sales offering a variety of native and beneficial cultivated plants at discount prices. Listed here are links to information on how to pre-order your plants for pickup in April. Click away to check out the species each county is offering in 2025!
Pickup on: Thursday, April 24, 2025 or Friday, April 25, 2025
During its 2025 tree seedling sale, the Cumberland County Conservation District is offering Northeast Native Wildflower seed mix for four dollars per ounce. One ounce plants approximately 200 square feet of bare soil. This is a Zebra Swallowtail visiting nectar-rich flowers during July of the first year after sowing this mix at a site along the Susquehanna.
Pickup on: Thursday, April 24, 2025 or Friday, April 25, 2025
Able to thrive in wet soils, Red-osier and Silky Dogwood shrubs are ideal plants for intercepting and polishing stormwater in swales, detention/retention basins, and rain gardens. With their crimson twigs in winter, they look great along borders among clusters of cedars, pines, spruces, and other evergreens. They make an excellent choice for soil stabilization along the shorelines of streams, ponds, and other bodies of water too. Buy a dozen or more to create a showy mass planting in your soggy spot.
The Franklin County Conservation District is offering American Elm seedlings in bundles of 25 for 36 dollars. Start them in pots for a couple of years to really get ’em going, then find places with damp soil and plenty of room to give ’em a try. During autumn, they look great in the company of spruces, white pines, and other large evergreens.
We purchased these Eastern White Pine, Norway Spruce, and Common Winterberry plants from the Lancaster County Conservation District Tree Sale about four years ago. They’re filling in as understory growth in the margins beneath some thirty-year-old Eastern Hemlocks to create dense cover for resident and visiting fauna at susquehannawildlife.net headquarters.
For 2025, the Lebanon County Conservation District is offering Dawn Redwood (Metasequoia glyptostroboides) trees in packs of ten for twelve dollars. Though native to Asia, these adaptable trees present little threat of naturalizing and have many positive attributes in a conservation planting. Given ample space, the Dawn Redwood, a relative of the sequoias, will rapidly grow to a towering giant. They create a particularly dramatic landscape feature when planted in clumps of three to five trees or more. With age, the trunks become stout and very sturdy. Don’t like raking? The finely divided deciduous foliage can be left where it falls in autumn. It usually disintegrates by spring to enrich the soil and promote more growth.The genus Metasequoia was first described in 1941 based upon fossils collected in Jurassic and earlier strata from widespread locations in the northern hemisphere. Metasequoia were believed extinct until just a few years later when a small number of living Dawn Redwoods were first discovered in southern China. Now distributed around the world for cultivation, direct descendants of this wild population of Metasequoia glyptostroboides are available for nearly anyone in a temperate climate to plant and grow to exceptional size. (National Park Service image)The Lebanon County Conservation District is also selling Bald Cypress trees. They’re offered in bundles of ten for ten dollars. These long-lived trees resemble the Dawn Redwood. Both are tolerant of damp ground, but the native Bald Cypress is the species to choose for placement along streams, in wetlands, and on other sites with standing water or saturated soil.Wildlife rich Bald Cypress swamps currently occur on the Atlantic Coastal Plain as far north as Sussex County, Delaware. Just to the south, they’re also found along Chesapeake Bay in areas that, during the last glacial maximum when sea level was 300 to 400 feet below today’s tide lines, were the Lower Susquehanna River Watershed in portions of present-day Maryland and Virginia. The northward post-glacial range extension of Bald Cypresses is now blocked by centuries of human intervention that has eliminated, isolated, or fragmented the wetland habitats where they could potentially become established. Why not lend them a hand? Plant a cypress swamp in your flood-prone bottomland. (National Park Service image by Andrew Bennett)
A privacy planting of sturdy, native Eastern White Pines and Northern Red Oaks thriving around the border of a parking area where they also provide shade from the sun and help infiltrate a share of the stormwater that would otherwise become runoff.This year, the York County Conservation District is offering a Showy Northeast Native Wildflower and Grass seed mix for $19.99 per quarter pound. Sure beats mowing!
If you live in Adams County, Pennsylvania, you may be eligible to receive free trees and shrubs for your property from the Adams County Planting Partnership (Adams County Conservation District and the Watershed Alliance of Adams County). These trees are provided by the Chesapeake Bay Foundation’s Keystone 10-Million Trees Partnership which aims to close a seven-year project in 2025 by realizing the goal of planting 10 million trees to protect streams by stabilizing soils, taking up nutrients, reducing stormwater runoff, and providing shade. If you own property located outside of Adams County, but still within the Chesapeake Bay Watershed (which includes all of the Susquehanna, Juniata, and Potomac River drainages), you still may have an opportunity to get involved. Contact your local county conservation district office or watershed organization for information.
As they mature, tree and shrub plantings along streams return pollution-controlling functions to floodplains and provide critical habitat for wildlife. These riparian buffers not only improve water quality for fisheries, they also create travel corridors that prevent terrestrial animal populations from becoming isolated.Do you own a parcel of streamside or wetland acreage that you’d like to set aside and plant for the benefit of wildlife and water quality? Contact your local county conservation district office and ask them to tell you about CREP (Conservation Reserve Enhancement Program) and other programs that may offer incentives including payment of all or a portion of the costs of plantings and other habitat improvements.
We hope you’re already shopping. Need help making your selections? Click on the “Trees, Shrubs, and Woody Vines” tab at the top of this page to check out Uncle Tyler Dyer’s leaf collection. He has most of the species labelled with their National Wetland Plant List Indicator Rating. You can consult these ratings to help find species suited to the soil moisture on your planting site(s). For example: if your site has sloped upland ground and/or the soils sometimes dry out in summer, select plants with a rating such as UPL or FACU. If your planting in soils that remain moist or wet, select plants with the OBL or FACW rating. Plants rated FAC are generally adaptable and can usually go either way, but may not thrive or survive under stressful conditions in extremely wet or dry soils.
NATIONAL WETLAND PLANT LIST INDICATOR RATING DEFINITIONS
OBL (Obligate Wetland Plants)—Almost always occur in wetlands.
FACW (Facultative Wetland Plants)—Usually occur in wetlands, but may occur in non-wetlands.
FAC (Facultative Wetland Plants)—Occur in wetlands and non-wetlands.
FACU (Facultative Upland Plants)—Usually occur in non-wetlands, but may occur in wetlands.
UPL (Upland Plants)—Almost never occur in wetlands.
Using these ratings, you might choose to plant Pin Oaks (FACW) and Swamp White Oaks (FACW) in your riparian buffer along a stream; Northern Red Oaks (FACU) and White Oaks (FACU) in the lawn or along the street, driveway, or parking area; and Chestnut Oaks (UPL) on your really dry hillside with shallow soil. Give it a try.
The deluge of rain that soaked the lower Susquehanna watershed during last week is now just a memory. Streams to the west of the river, where the flooding courtesy of the remnants of Hurricane Debby was most severe, have reached their crest and receded. Sliding away toward the Chesapeake and Atlantic is all that runoff, laden with a brew of pollutants including but not limited to: agricultural nutrients, sediment, petroleum products, sewage, lawn chemicals, tires, dog poop, and all that litter—paper, plastics, glass, Styrofoam, and more. For aquatic organisms including our freshwater fish, these floods, particularly when they occur in summer, can compound the effects of the numerous stressors that already limit their ability to live, thrive, and reproduce.
(Environmental Protection Agency image)
One of those preexisting stressors, high water temperature, can be either intensified or relieved by summertime precipitation. Runoff from forested or other densely vegetated ground normally has little impact on stream temperature. But segments of waterways receiving significant volumes of runoff from areas of sun-exposed impervious ground will usually see increases during at least the early stages of a rain event. Fortunately, projects implemented to address the negative impacts of stormwater flow and stream impairment can often have the additional benefit of helping to attenuate sudden rises in stream temperature.
While a row of trees along a creek can help provide protection from the thermal impact of the sun, a vegetative riparian buffer must be much wider to be effective for absorbing, cooling, and treating runoff from fields, lawns, and paved surfaces. This buffer is too narrow to prevent surface runoff from polluting the water.
Of the fishes inhabiting the Lower Susquehanna River Watershed’s temperate streams, the least tolerant of summer warming are the trouts and sculpins—species often described as “coldwater fishes”. Coldwater fishes require water temperatures below 70° Fahrenheit to thrive and reproduce. The optimal temperature range is 50° to 65° F. In the lower Susquehanna valley, few streams are able to sustain trouts and sculpins through the summer months—largely due to the effects of warm stormwater runoff and other forms of impairment.
Sculpins, including the Blue Ridge Sculpin (Cottus caeruleomentum) seen here, are native coldwater fishes which, during the 11,000 years since the last glacial maximum, have had the availability of their favored habitat sharply reduced by warming water temperatures and a rising Atlantic. During this interval, seawater has inundated the path of the “Late” Pleistocene lower Susquehanna which passed through the section of flooded river watershed we now call Chesapeake Bay and continued across the continental shelf to what was, during the glacial maximum, the river’s mouth at Norfolk Canyon. Today, cut off from neighboring drainage basins, sculpins survive exclusively in cold headwaters, and only in those where human alterations including pollution, dams, channelization, and reduced base flow haven’t yet eliminated their isolated populations. Formerly believed to be composed of two widespread North American species, the Slimy Sculpin (Cottus cognatus) and the Mottled Sculpin (Cottus bairdii), study in recent decades is discovering that sculpin populations in the present-day lower Susquehanna and neighboring Potomac headwaters consist of at least three newly delineated species: Blue Ridge Sculpin, Potomac Sculpin (Cottus gerardi), and Checkered Sculpin (Cottus sp.), the latter an as yet undescribed species found only in the refugium of limestone springs in the Potomac drainage in West Virginia; Frederick and Washington Counties, Maryland; and Franklin County, Pennsylvania. (United States Geological Survey image)Stare at this for a little while, you’ll figure it out…………More than 11,000 years ago, during the last glacial maximum, when sea level was about 275 feet lower than it is today, there was no Chesapeake Bay, just a great Susquehanna River that flowed to the edge of the continental shelf and its mouth at Norfolk Canyon. It was a river draining taiga forests of pine, spruce , and fir, and it carried along the waters of all the present-day bay’s tributaries and more. The section of the river’s watershed we presently call the lower Susquehanna was, at the time, the upper Susquehanna watershed. Brook Trout and sculpins had the run of the river and its tributaries back then. And the entire watershed was a coldwater fishery, with limestone and other groundwater springs providing not refuge from summer heat, but a place to escape freezing water. (United States Geological Survey base image)Norfolk Canyon, the mouth of the Susquehanna River during the most recent glacial maximum, now lies more than 275 feet below the surface of the ocean and plunges to more than a mile in depth along the finger of out wash from the gorge. (United States Geological Survey image)Tens of thousands of trout are raised in state-operated and cooperative nurseries for stocking throughout the lower Susquehanna valley. These rearing facilities are located on spring-fed headwaters with sufficient flow to assure cold temperatures year round. While the Rainbow Trout and Brown Trout (Salmo trutta) are the most commonly stocked species, the Brook Trout (Salvelinus fontinalis) is the only one native to American waters. It is the least tolerant of stream warming and still reproduces in the wild only in a few pristine headwaters streams in the region. During spring, all three of these species have been observed on rare occasions entering the fish lift facilities at the hydroelectric dams on the river, presumably returning to the Susquehanna as sea-run trout.
Coldwater fishes are generally found in small spring-fed creeks and headwaters runs. Where stream gradient, substrate, dissolved oxygen, and other parameters are favorable, some species may be tolerant of water warmer than the optimal values. In other words, these temperature classifications are not set in stone and nobody ever explained ichthyology to a fish, so there are exceptions. The Brown Trout for example is sometimes listed as a “coldwater transition fish”, able to survive and reproduce in waters where stream quality is exceptionally good but the temperature may periodically reach the mid-seventies.
The Eastern Blacknose Dace is sometimes classified as a “coldwater transition fish”. It can be found in headwaters runs as well as in creeks with good water quality.The Longnose Dace is another “coldwater transition fish” known only from clear, clean, flowing waters.
More tolerant of summer heat than the trouts, sculpins, and daces are the “coolwater fishes”—species able to feed, grow, and reproduce in streams with a temperature of less than 80° F, but higher than 60° F. Coolwater fishes thrive in creeks and rivers that hover in the 65° to 70° F range during summer.
The Creek Chub is a familiar species of “coolwater fish” seldom found remaining in waters exceeding 80 degrees Fahrenheit.The Yellow Perch (Perca flavescens) was perhaps the most frequently targeted coolwater “gamefish” in the Lower Susquehanna River Watershed prior to the introduction of the Northern Pike (Esox lucius) and Muskellunge (Esox masquinongy). Today’s prevalence of warmwater streams and the dozens of species of non-native predatory fishes now naturalized within them have left the Yellow Perch populations greatly reduced and all but forgotten by anglers. Out of sight, out of mind. (National Park Service image)
What are the causes of modern-day reductions in coldwater and coolwater fish habitats in the lower Susquehanna River and its hundreds of miles of tributaries? To answer that, let’s take a look at the atmospheric, cosmic, and hydrologic processes that impact water temperature. Technically, these processes could be measured as heat flux—the rate of heat energy transfer per unit area per unit time, frequently expressed as watts per meter squared (W/m²). Without getting too technical, we’ll just take a look at the practical impact these processes have on stream temperatures.
HEAT FLUX PROCESSES IN A SEGMENT OF STREAM
Heat Flux Processes on Stream and River Segments. These processes could be measured as heat flux—the rate of heat energy transfer per unit area per unit time. (Environmental Protection Agency image)
INCOMING TEMPERATURE AND FLOW—The baseline temperature of stream water entering a given segment of waterway is obviously the chief factor determining its temperature when exiting that segment. Incoming temperature and flow also determine the water’s susceptibility to heat absorption or loss while transiting the segment. Lower flows may subject the given volume of water to a greater loss or gain of heat energy during the time needed to pass through the segment than the same volume at a higher flow. Lower flows may also reduce stream velocity and extend a given volume of water’s exposure time to the exchange of heat energy while moving through the segment. Generally speaking…
…the higher the stream flow, the less a given volume of that stream’s water may be impacted by the effects of the heat flux processes within the segment.
…the lower the stream flow, the more a given volume of that stream’s water may be impacted by the effects of the heat flux processes within that segment.
…the temperature and flow rate of precipitation entering the segment are factors that determine the impact of its heat energy transfer to or from a given volume of the stream’s waters.
…the temperature and flow rate of runoff and point-source discharges entering the segment are factors that determine the impact of their heat energy transfer to or from a given volume of the stream’s waters.
Stormwater from impervious surfaces including roads, parking lots, roofs, and lawns quickly impacts temperatures in small creeks. Channelized streams are availed few of the positive attributes provided by many of the heat flux processes we’re about to see. They therefore suffer from severe impairment and are exposed to temperature extremes that few aquatic organisms can survive. Runoff from sun-heated pavement during a summer thunderstorm can often exceed 100 degrees Fahrenheit and can, at sufficient flow rate, quickly raise the temperature of a small stream to well over 90 degrees.Stormwater runoff not only poses a thermal threat to waterways, its a significant source of a wide variety of pollutants.
GROUNDWATER INPUT—In streams connected to the aquifer, the temperature in a flowing segment can be impacted by the influx of cold groundwater. With temperatures ranging from about 52° to 60° Fahrenheit, groundwater will absorb heat from the stream in summer, and warm it in the winter. In warmwater streams, coldwater and coolwater fishes will often seek areas of the substrate where groundwater is entering for use as refugium from the summer heat. Yellow Perch in the lower Susquehanna are known to exhibit this behavior.
Creeks and rivers connected to the aquifer and receiving supplemental flow from it are known as “gaining streams”. These streams frequently feed water into the aquifer as well. (United States Geological Survey image)When flowing through an area experiencing drought or an excessive removal of groundwater (lots of wells, etc.), a waterway can become a “losing stream”, one that surrenders a portion of its flow to recharge the aquifer. Further downstream, the reduced flow can make such a creek or river more susceptible to the effects of heat flux processes. (United States Geological Survey image)Seriously depleted aquifers can lead to a “disconnected stream”. Smaller waterways subjected to these conditions will sometimes lose all their flow to the ground, often causing a catastrophic failure of the aquatic ecosystem supported therein. (United States Geological Survey image)Urban runoff overwhelms this small stream with polluted water than can reach temperatures of 100 degrees or more (left), then lets it high and dry with no baseflow during periods of dry weather (right) as the waterway becomes disconnected from the much-depleted aquifer.Well-designed and properly constructed stormwater retention basins not only recharge groundwater supplies for wells and streams, they can also help prevent thermal pollution in waterways. Planted with native wetland species and allowed to thrive, they can become treasured wildlife islands in otherwise inhospitable environs. The benefits don’t stop there; plants also help sequester nutrients contained in the runoff.
HYPORHEIC EXCHANGE—Related to groundwater input, hyporheic exchange is the slow movement of water through the rock, sand, gravel, and soils composing the streambed, saturated shoreline, shallow aquifer, and connected floodplain of a creek or river. As a heat flux process, hyporheic exchange helps moderate extremes in seasonal water temperatures by conducting energy between the solid materials in the zone and the flowing water. Hyporheic zones are important habitats for many species of aquatic invertebrates and spawning fish. Natural chemical processes within these zones convert ammonia-producing wastes into nitrite, then nitrate, allowing it to be absorbed as food by plants growing in the stream or in the alluvium within the zone. Vegetation removal, channelization, legacy sediments, silt deposits, and man-made walls and dams can negate the benefits of hyporheic exchange.
Exchange of surface and ground water within the hyporheic zone is most directly associated with high-gradient (left) and meandering (right) segments of streams. (United States Geological Survey image)Very common on streams in the lower Susquehanna valley are these accumulations of legacy sediments at the sites of former mill ponds. After the dams were removed, the creeks began eroding their way down through the mire as they tried to reestablish their floodplains and find their native substrate. These trapped waterways are not only cut off from their hyporheic zones, they’re now a major source of nutrient and sediment pollution. Misguided landowners like this one frequently dump fill into these sites to “save their land” and “control flooding”. The fill and materials added to “shore up the banks” do nothing to fix what ails the creek, but instead displace more water to make the impact of flooding even more widespread.Rehabilitation projects that remove legacy sediments help restore hyporheic exchange by reconnecting the stream to its underlying geology, its floodplain, and its wetlands. Rising waters remain in the floodplain where they get a good bio-scrubbing and help replenish the creek and groundwater supply. As the experts say, “floodplains are for flooding.”
ATMOSPHERIC EXCHANGE (CONVECTION, EVAPORATION)—Primarily a process by which a stream loses heat energy and cools its waters, atmospheric exchange is also a means by which a warm air mass can relinquish heat to cooler waters and thus increase their temperature. This phenomenon can be dramatically enhanced when a stream passes through a so-called urban heat island where air temperatures remain warm through the night. Convection, the movement of heat energy through a fluid (liquid or gas), causes warmer, less-dense water to rise to the surface of a stream, particularly where there is minimal turbulence. When the air above is cooler than the water’s surface layer, the stream will conduct heat energy across the water/atmosphere interface causing the warmed air molecules to rise in a convection column. If the atmospheric relative humidity is less than 100%, some surface water will vaporize—a process that expends more of the stream’s heat energy. The rate of convective and evaporative cooling in a given stream segment is directly related to the degree of difference between the water temperature and air temperature, and to the relative humidity in the air mass above the lake, creek, or river. The mechanical action of stream turbulence including rapids, riffles, and falls increases the contact area between air and water to maximize the atmospheric exchange of heat energy. The convective air current we call surface wind has a turbulent wave-producing effect on water that can also maximize atmospheric exchange; think of a cold autumn wind robbing heat energy from a warm lake or river or a hot summer wind imparting its heat to a cooler creek. These exchanges are both conductive in nature (air-to-water/water-to-air) and evaporative, the latter being expedited by the movement of dry air over warm water.
Usually classified as one of the coolwater fishes, the bottom-dwelling Tessellated Darter can thrive in the warmer creeks and in the main stem of the Susquehanna by inhabiting riffles where atmospheric exchange in the form of increased evaporation helps reduce temperatures and convective currents carry the cooler, well-oxygenated water to the streambed.Humans utilize the concept of atmospheric exchange, adopting the phenomena of evaporation and convection to cool the hot waters produced during electric generation and other industrial processes before discharge into a lake or river.
STREAMBED CONDUCTIVE EXCHANGE—In the lower Susquehanna watershed, there may be no better natural example of streambed conductive exchange than the Triassic-Jurassic diabase pothole bedrocks of Conewago Falls on the river at the south end of Three Mile Island.
During sunny days, the massive diabase pothole rocks at Conewago Falls absorb solar (shortwave) radiation, then conduct that heat energy into the flowing water, often continuing to pass the accumulated warmth into the river during the night. On cloudy days, the riverbed collects longwave atmospheric radiation, a heat flux process that yields significantly less energy for conduction into the rapids, riffles, and pools of the falls. During periods of low river flow, the heating effect of streambed conductive exchange can become magnified. Compared to conditions that prevail when torrents of turbid water are rushing through the falls, partially exposed bedrock surrounded by clear water collects radiated energy much more efficiently, then conducts the heat to a greatly reduced volume of passing water. During summer and autumn, this process can create a mix of temperature zones within the falls with warmer water lingering in slow-moving pools and cooler water flowing in the deeper fast-moving channels. Along the falls’ mile-long course, a haven is created for aquatic organisms including warmwater and some coolwater fishes, oft times attracting anglers and a variety of hungry migrating birds as well.Classified as one of our coolwater fishes, the Fallfish finds favorable conditions for feeding, growing, and spawning in the well-oxygenated waters of Conewago Falls.Though the lower Susquehanna River is classified as a warmwater fishery, the Northern Hog Sucker (Hypentelium nigricans), another of our native coolwater fishes, finds the fast-moving waters of Conewago Falls to its liking. Northern Hog Suckers are known to inhabit streams cold enough to host trout. They exhibit remarkable home range fidelity, sometimes spending their entire lives occupying the same several hundred feet of waterway. Northern Hog Suckers are often designated an indicator of good water quality, intolerant of many stream impairment parameters. Their presence in Conewago Falls provides testament to the quality of the warmwater fishery there.An unnatural example. The reduced base flow in this channelized and severely impaired creek has been rendered vulnerable to the negative impacts of several heat flux processes including streambed conductive exchange. Urban stormwater/surfacewater inflow, solar (shortwave) radiation, and heat conducted into the stream from the masonry walls, curbs, and raceway can all conspire to cook aquatic organisms with life-quenching summer water temperatures exceeding 90 degrees Fahrenheit.
SOLAR (SHORTWAVE) RADIATION—The sun provides the energy that fuels the earth’s complex climate. The primary heat flux process that heats our planet is the absorption of solar radiation in the shortwave spectrum, which includes ultraviolet, visible, and infrared frequencies at the upper end of the longwave spectrum. Streams and other bodies of water absorb the greatest amounts of solar (shortwave) radiation during the weeks around summer solstice when the sun at mid-day is closer to zenith than at any other time of the year. However, the heating impact of the radiation may be greatest when the volume of water in the creek, river, or lake is at its minimum for the year—often during early fall.
The rate, measured in watts per square meter, at which solar (shortwave) energy is directly radiated to a given area on the earth’s surface (including streams and other waters) is determined by: solar activity, the angle of the sun in the sky, aspect (slope) of the receiving surface, the opacity of the overlying atmosphere, and the distance of the earth from the sun. The former varies with the year’s seasons, the time of day, and the latitude of a given area. The latter is currently at its annual minimum when earth is at perihelion during the early days of January, thus providing the northern hemisphere with a little bump in radiation during the shortest days of the year when the sun is at its lowest angle in the sky. (NASA image)A varying portion of the solar (shortwave) radiation reaching the earth is reflected back into space by clouds. A smaller share is absorbed by the atmosphere, thus heating it. An even lesser quantity is reflected back into space by water and land. The remainder of the energy is absorbed by the planet’s surfaces, its water and land. (NASA image)
INCIDENT SHORTWAVE RADIATION—Also known as insolation (incoming solar radiation), incident shortwave radiation is the sum total energy of both the direct solar radiation that travels to the earth’s surface unaffected by the atmosphere and the diffuse radiation, waves that have been weakened and scattered by constituents of the atmosphere before reaching the planet’s surface. On a cloudy day, the warming of terrestrial surfaces including streams and other bodies of water is the result of diffuse radiation. On days with any amount of sunshine at all, both direct and diffuse radiation heat our waters and lands.
Warmwater fishes such as the native Pumpkinseed (Lepomis gibbosus) thrive in sun-drenched 70-to-85-degree waters as long as other heat flux processes prevent sudden temperature increases and oxygen depletion.Mowed stream banks offer a waterway no protection from incoming solar (shortwave) radiation, nor terrestrial forms of impairment including nutrient-rich stormwater runoff and silt.
REFLECTED SHORTWAVE RADIATION—known as albedo, reflected solar (shortwave) radiation is energy directed away from the earth’s surface before being absorbed. A surface’s albedo value is basically determined by its color, black having little reflective value, white and silvery surfaces reflecting nearly all solar (shortwave) radiation away. A surface with no reflective properties has an albedo value of 0, while a totally reflective surface has a value of 1. Clean snow with a value of about 0.85 to 0.9 (85% to 90%) is a highly reflective surface; yellow snow isn’t as good. A stream, river, or lake blanketed with ice and snow will absorb very little solar energy and will rely upon other heat flux processes to trigger a melt and thaw. The surface of open water has a varying albedo value determined mostly by the angle of the sun. Solar radiation striking the water’s surface at a low angle is mostly reflected away, while that originating at an angle closer to zenith is more readily absorbed.
To avoid the heating effects of solar (shortwave) and atmospheric longwave radiation, coldwater and coolwater fishes require streams offering protection from full exposure to direct sunlight and cloud cover. Runs and creeks flowing beneath a closed canopy of forest trees are shielded from 25% or more of incoming radiation and are thus able to better maintain thermal stability during the most vulnerable period of the year for temperature-sensitive fishes, May through October.
LONGWAVE RADIATION—Radiation in the longwave spectrum is composed of infrared waves at frequencies lower than those of the shortwave spectrum. Longwave radiation, sometimes just called infrared radiation, is produced by the earth and its atmosphere and is propagated in all directions, day and night. It warms mostly the lower atmosphere which in turn warms the earth’s surface including its waters. Some longwave energy can even be radiated into the waterway from its own streambed—and the stream can return the favor. Other forms of mass surrounding a stream such as a rocky shoreline or a man-made structure such as bridge pier can trade longwave radiation with a waterway. The effect of these latter exchanges is largely trivial and never rivals the heat flux transfer of warm to cold provided by conduction.
Longwave radiation emissions slow as the temperature of the emitting mass decreases, just as they also increase with temperature of the mass. Longwave radiation emissions therefore decrease with altitude along with the temperature of the water vapor, carbon dioxide, methane, and other gases that produce them. As such, the highest reaches of the atmosphere have a greatly reduced capability of shedding longwave radiation into space. At ground level, lakes, creeks, and streams receive their greatest dose of longwave radiation while beneath the cover of low-lying clouds or fog. (NASA image)
CANOPY RADIATION—Trees emit longwave radiation that may have a limited heat flux impact on waterway temperature. This radiation is diffuse, of scattered effect, and scarcely detectable, particularly beneath multilayered dense canopies. Some of the infrared energy transmitted by the tree canopy is radiated skyward as well.
WATER RADIATION—Water, like all earthly matter composed of vibrating molecules, emits longwave radiation. This heat flux process provides an ongoing cooling effect to streams, rivers, lakes, and oceans—warmer ones shedding infrared energy at a faster rate than those that are cold.
Now that we have a basic understanding of the heat flux processes responsible for determining the water temperatures of our creeks and rivers, let’s venture a look at a few graphics from gauge stations on some of the lower Susquehanna’s tributaries equipped with appropriate United States Geological Survey monitoring devices. While the data from each of these stations is clearly noted to be provisional, it can still be used to generate comparative graphics showing basic trends in easy-to-monitor parameters like temperature and stream flow.
Each image is self-labeled and plots stream temperature in degrees Fahrenheit (bold blue) and stream discharge in cubic feet per second (thin blue).
The West Conewago Creek drains much of the Gettysburg Basin’s Triassic redbeds in Adams and northern York Counties in Pennsylvania and includes a small headwaters area in northern Maryland. The gauge station is located just a over a mile upstream from the waterway’s mouth on the Susquehanna just below Conewago Falls. Right through the summer heatwave, this 90-day graph shows a consistent daily pattern of daytime rises in temperature and nighttime cooling. To the right, a rapid cool down can be seen coinciding with two periods of high water, the first from a series of heavy thundershowers, the second from flooding caused by the remnants of Hurricane Debby. Notice that the early August downpours were so heavy that they cooled the hot surface runoff and waterway quickly, without creating a rise in stream temperature at the gauging station. Had this monitoring device been located on a small tributary in an area with an abundance of impervious surfaces, there would probably have been a brief rise in stream temperature prior to the cooldown. (United States Geological Survey image)
The daily oscillations in temperature reflect the influence of several heat flux processes. During the day, solar (shortwave) radiation and convection from summer air, especially those hot south winds, are largely responsible for the daily rises of about 5° F. Longwave radiation has a round-the-clock influence—adding heat to the stream during the day and mostly shedding it at night. Atmospheric exchange including evaporative cooling may help moderate the rise in stream temperatures during the day, and certainly plays a role in bringing them back down after sunset. Along its course this summer, the West Conewago Creek absorbed enough heat to render it a warmwater fishery in the area of the gauging station. The West Conewago is a shallow, low gradient stream over almost its entire course. Its waters move very slowly, thus extending their exposure time to radiated heat flux and reducing the benefit of cooling by atmospheric exchange. Fortunately for bass, catfish, and sunfish, these temperatures are in the ideal range for warmwater fishes to feed, grow, and reproduce—generally over 80° F, and ideally in the 70° to 85° F range. Coolwater fishes though, would not find this stream segment favorable. It was consistently above the 80° F maximum and the 60° to 70° F range preferred by these species. And coldwater fishes, well, they wouldn’t be caught dead in this stream segment. Wait, scratch that—the only way they would be caught in this segment is dead. No trouts or sculpins here.
The Codorus Creek drains primarily the carbonate valleys of York County to the south of the West Conewago watershed. This gauge station is located about a mile upstream from the creek’s mouth on the Susquehanna just below Haldeman Riffles. The graphic pattern is very similar to that of the West Conewago’s: daily heating and cooling cycles and a noticeable drop in stream temperature in early August caused by a day of thundershowers followed by the remnants of Hurricane Debby. (United States Geological Survey image)
Look closely and you’ll notice that although the temperature pattern on this chart closely resembles that of the West Conewago’s, the readings average about 5 degrees cooler. This may seem surprising when one realizes that the Codorus follows a channelized path through the heart of York City and its urbanized suburbs—a heat island of significance to a stream this size. Before that it passes through numerous impoundments where its waters are exposed to the full energy of the sun. The tempering factor for the Codorus is its baseflow. Despite draining a smaller watershed than its neighbor to the north, the Codorus’s baseflow (low flow between periods of rain) was 96 cubic feet per second on August 5th, nearly twice that of the West Conewago (51.1 cubic feet per second on August 5th). Thus, the incoming heat energy was distributed over a greater mass in the Codorus and had a reduced impact on its temperature. Though the Codorus is certainly a warmwater fishery in its lower reaches, coolwater and transitional fishes could probably inhabit its tributaries in segments located closer to groundwater sources without stress. Several streams in its upper reaches are in fact classified as trout-stocked fisheries.
This is a zoomed-in look at the previous graph showing the impact of a rainfall event on the water temperatures in Codorus Creek. Unlike the sharp declines accompanying the deluge of flood waters during the two events in early August, these lesser storms in late June generated just enough runoff to capture heat energy from impervious surfaces and warm the creek, temporarily breaking the daily heating/cooling cycle. Upstream in the immediate area of the runoff, the impact on the stream and/or its tributaries was probably much more dramatic, certainly raising temperatures into the nineties or above. (United States Geological Survey image)Kreutz Creek drains a carbonate bedrock area of York County and flows parallel to the Lincoln Highway (US 30) to enter the Susquehanna at Wrightsville. The gauging station is about one mile upstream from the creek’s mouth. (United States Geological Survey image)
The Kreutz Creek gauge shows temperature patterns similar to those in the West Conewago and Codorus data sets, but notice the lower overall temperature trend and the flow. Kreutz Creek is a much smaller stream than the other two, with a flow averaging less than one tenth that of the West Conewago and about one twentieth of that in the Codorus. And most of the watershed is cropland or urban/suburban space. Yet, the stream remains below 80° F through most of the summer. The saving graces in Kreutz Creek are reduced exposure time and gradient. The waters of Kreutz Creek tumble their way through a small watershed to enter the Susquehanna within twenty-four hours, barely time to go through a single daily heating and cooling cycle. As a result, their is no chance for water to accumulate radiant and convective heat over multiple summer days. The daily oscillations in temperature are less amplified than we find in the previous streams—a swing of about three degrees compared to five. This indicates a better balance between heat flux processes that raise temperature and those that reduce it. Atmospheric exchange in the stream’s riffles, forest cover, and good hyporheic exchange along its course could all be tempering factors in Kreutz Creek. From a temperature perspective, Kreutz Creek provides suitable waters for coolwater fishes.
Muddy Creek drains portions of southern York County through rolling farmland and woodlots. There are no large impoundments or widespread urban impacts in the watershed, which may help explain its slightly lower temperature trends. (United States Geological Survey image)
Muddy Creek is a trout-stocked fishery, but it cannot sustain coldwater species through the summer heat. Though temperatures in Muddy Creek may be suitable for coolwater fishes, silt, nutrients, low dissolved oxygen, and other factors could easily render it strictly a warmwater fishery, inhabited by species tolerant of significant stream impairment.
Chiques Creek drains mostly limestone farmland in northwestern Lancaster County. The gauging station is located near the stream’s mouth on the Susquehanna at Chiques (Chickies) Rock. Oscillations in temperature again resemble the other waterways, but daily highs remain almost entirely below 80 degrees. (United States Geological Survey image)
A significant number of stream segments in the Chiques watershed have been rehabilitated to eliminate intrusion by grazing livestock, cropland runoff, and other sources of impairment. Through partnerships between a local group of watershed volunteers and landowners, one tributary, Donegal Creek, has seen riparian buffers, exclusion fencing, and other water quality and habitat improvements installed along nearly ever inch of its run from Donegal Springs through high-intensity farmland to its mouth on the main stem of the Chiques just above its confluence with the Susquehanna. The improved water quality parameters in the Donegal support native coldwater sculpins and an introduced population of reproducing Brown Trout. While coldwater habitat is limited to the Donegal, the main stem of the Chiques and its largest tributary, the Little Chiques Creek, both provide suitable temperatures for coolwater fishes.
Streams in the Chiques Creek and similar limestone watersheds often pass through areas with significant bedrock formations. Heat flux processes including groundwater input, hyporheic exchange, and streambed conductive exchange can have a greater influence on water temperature along these segments.A breeding condition Eastern Balcknose Dace, one of the coldwater transition fishes found in the Chiques and its tributaries.The Common Shiner (Luxilus cornutus), a fish tolerant of warmwater streams, prefers cool, clear waters for spawning. For protection from late-spring and summer heat, breeding males may seek a section of creek with a streambed inflow of limestone groundwater to defend as their nesting territory.A closeup of the Chiques Creek graph showing what appears to be a little bump in temperature caused by surface runoff during a couple of late-May showers. Stream rehabilitation is an ongoing process and the pressures of land disturbances both old and new present challenges to those who make it their passion to fix the wrongs that have been inflicted upon our local waters. Even the exemplary Donegal Creek faces new threats from urbanization in one of its headwater areas several miles to the northwest of the historic springs. (United States Geological Survey image)Conewago Creek (East) drains primarily Triassic redbed farmlands in Dauphin, Lancaster, and Lebanon Counties. Much of the headwaters area is forested but is experiencing an increasing rate of encroachment by housing and some commercial development. Conewago Creek (East) enters the Susquehanna on the east side of Conewago Falls at Three Mile Island. The watershed is equipped with three U.S.G.S. gauge stations capable of providing temperature data. This first one is located just over a mile upstream of the creek’s mouth. (United States Geological Survey image)
Despite its meander through and receipt of water from high-intensity farmland, the temperature of the lower Conewago (East) maxes out at about 85° F, making it ideal for warmwater fishes and even those species that are often considered coolwater transition fishes like introduced Smallmouth Bass, Rock Bass, Walleye, and native Margined Madtom. This survivable temperature is a testament to the naturally occurring and planted forest buffers along much of the stream’s course, particularly on its main stem. But the Conewago suffers serious baseflow problems compared to other streams we’ve looked at so far. Just prior to the early August storms, flow was well below 10 cubic feet per second for a drainage area of more than fifty square miles. While some of this reduced flow is the result of evaporation, much of it is anthropogenic in origin as the rate of groundwater removal continues to increase and a recent surge in stream withdraws for irrigation reaches its peak during the hottest days of summer.
A juvenile Rock Bass.A juvenile Margined Madtom.A closer look at the Conewago Creek (East) graphic shows the temperature drop associated with a series of thundershowers and the remnants of Hurricane Debby in early August. Despite the baseflow being below five cubic feet per second, the cooling effect of the downpours as measured in the area of the gauge was significant enough to overwhelm any heating of runoff that may have occurred as precipitation drained across hardened soils or man-made impervious surfaces. (United States Geological Survey image)
A little side note—the flow rate on the Conewago at the Falmouth gauge climbed to about 160 cubic feet per second as a result of the remnants of Hurricane Debby while the gauge on the West Conewago at Manchester skyrocketed to about 20,000 cubic feet per second. Although the West Conewago’s watershed (drainage area) is larger than that of the Conewago on the east shore, it’s larger only by a multiple of two or three, not 125. That’s a dramatic difference in rainfall!
The Bellaire monitoring station on Conewago Creek (East) is located on the stream’s main stem just downstream from the mouth of Little Conewago Creek, a tributary with its origins in farmland and woodlots. (United States Geological Survey image)
The temperatures at the Bellaire monitoring station, which is located upstream of the Conewago’s halfway point between its headwaters in Mount Gretna and its mouth, are quite comparable to those at the Falmouth gauge. Although a comparison between these two sets of data indicate a low net increase in heat absorption along the stream’s course between the two points, it also suggests sources of significant warming upstream in the areas between the Bellaire gauge and the headwaters.
Data from the gauge site on the Little Conewago Creek shows a temperature averaging about five degrees cooler than the gauge several miles downstream on the main stem of the Conewago at Bellaire. (United States Geological Survey image)
The waters of the Little Conewago are protected within planted riparian buffers and mature woodland along much of their course to the confluence with the Conewago’s main stem just upstream of Bellaire. This tributary certainly isn’t responsible for raising the temperature of the creek, but is instead probably helping to cool it with what little flow it has.
A stream like the Little Conewago Creek with daily temperatures that remain mostly below 80 degrees and retreat to 75 degrees or less during the night can be suitable for coldwater transition fishes like these juvenile Eastern Blacknose Dace (top) and Longnose Dace.
Though mostly passing through natural and planted forest buffers above its confluence with the Little Conewago, the main stem’s critically low baseflow makes it particularly susceptible to heat flux processes that raise stream temperatures in segments within the two or three large agricultural properties where owners have opted not to participate in partnerships to rehabilitate the waterway. The headwaters area, while largely within Pennsylvania State Game Lands, is interspersed with growing residential communities where potable water is sourced from hundreds of private and community wells—every one of them removing groundwater and contributing to the diminishing baseflow of the creek. Some of that water is discharged into the stream after treatment at the two municipal sewer plants in the upper Conewago. This effluent can become quite warm during processing and may have significant thermal impact when the stream is at a reduced rate of flow. A sizeable headwaters lake is seasonally flooded for recreation in Mount Gretna. Such lakes can function as effective mid-day collectors of solar (shortwave) radiation that both warms the water and expedites atmospheric exchange.
The Conewago Creek (East) Watershed from the Bellaire U.S.G.S. Gauging Station (lower left) upstream to the headwaters in Mount Gretna. (United States Geological Survey image)
Though Conewago Creek (East) is classified as a trout-stocked fishery in its upper reaches in Lebanon County, its low baseflow and susceptibility to warming render it inhospitable to these coldwater fishes by late-spring/early summer.
Despite being considered a warmwater fish, the River Chub (Nocomis micropogon) will ascend streams like the Conewago to seek cooler, gravel-bottomed waters for spawning. Reduced baseflow has probably rendered the stream currently too small for this species on Pennsylvania State Game Lands in Colebrook where this specimen was photographed in 2018.The Golden Shiner, another warmwater fish, often ascends streams to enter cooler water. Juvenile Golden Shiners like this one will move into shallower headwaters not only to seek reduced temperatures, but to escape large predatory fishes as well.Irrigation of agricultural fields using a large portion of the already diminished baseflow in the Conewago Creek (East) just downstream of the Bellaire gauging station. Despite millions of dollars in investment to rehabilitate this Susquehanna valley stream, the riparian buffers and other practices can have little effect when the creek gets sucked down to just a trickle. Low baseflow is a hard nut to crack. It’s best prevented, not corrected.Hammer Creek, a trout-stocked fishery, originates, in part, within Triassic conglomerate in the Furnace Hills of Lebanon County, then flows north into the limestone Lebanon Valley where it picks up significant flow from other tributaries before working its way south back through the Furnace Hills into the limestone farmlands of Lancaster County. From there the stream merges with the Cocalico Creek, then the Conestoga River, and at last the Susquehanna. Note the tremendous daily temperature oscillations on this headwaters stream as it surges about 15 degrees each day before recovering back close to groundwater temperature by sunrise the next day. (United States Geological Survey image)Headwaters of Hammer Creek including Buffalo Springs, a significant source of cold groundwater feeding the western leg of the stream. The large dams on this section that created the Lebanon and Rexmont Reservoirs have been removed. (United States Geological Survey base image)
The removal of two water supply dams on the headwaters of Hammer Creek at Rexmont eliminated a large source of temperature fluctuation on the waterway, but did little to address the stream’s exposure to radiant and convective heat flux processes as it meanders largely unprotected out of the forest cover of Pennsylvania State Game Lands and through high-intensity farmlands in the Lebanon Valley. Moderating the temperature to a large degree is the influx of karst water from Buffalo Springs, located about two miles upstream from this gauging station, and other limestone springs that feed tributaries which enter the Hammer from the east and north. Despite the cold water, the impact of the stream’s nearly total exposure to radiative and other warming heat flux processes can readily be seen in the graphic. Though still a coldwater fishery by temperature standards, it is rather obvious that rapid heating and other forms of impairment await these waters as they continue flowing through segments with few best management practices in place for mitigating pollutants. By the time Hammer Creek passes back through the Furnace Hills and Pennsylvania State Game Lands, it is leaning toward classification as a coolwater fishery with significant accumulations of sediment and nutrients. But this creek has a lot going for it—mainly, sources of cold water. A core group of enthusiastic landowners could begin implementing the best management practices and undertaking the necessary water quality improvement projects that could turn this stream around and make it a coldwater treasure. An organized effort is currently underway to do just that. Visit Trout Unlimited’s Don Fritchey Chapter and Donegal Chapter to learn more. Better yet, join them as a volunteer or cooperating landowner!
The male Creek Chub, one of our coolwater fishes, develops head tubercles and becomes flushed with color during spawning season. Hammer Creek not only provides a home for the Creek Chub, its cold headwaters provide refuge for a population of native Brook Trout too.Like no other example we’ve looked at so far, this closeup of the Hammer Creek graphic shows temperature bumps correlating with the stormwater runoff from early August’s rains. Because the stream flow is small and the precipitation rate was not as great at this location, the effect of heat flux from runoff is more readily apparent. (United States Geological Survey image)Brook Trout adult and juvenile. (United States Fish and Wildlife Service image by Ryan Hagerty)
For coldwater fishes, the thousands of years since the most recent glacial maximum have seen their range slowly contract from nearly the entirety of the once much larger Susquehanna watershed to the headwaters of only our most pristine streams. Through no fault of their own, they had the misfortune of bad timing—humans arrived and found coldwater streams and the groundwater that feeds them to their liking. Some of the later arrivals even built their houses right on top of the best-flowing springs. Today, populations of these fishes in the region we presently call the Lower Susquehanna River Watershed are seriously disconnected and the prospect for survival of these species here is not good. Stream rehabilitation, groundwater management, and better civil planning and land/water stewardship are the only way coldwater fishes, and very possibly coolwater fishes as well, will survive. For some streams like Hammer Creek, it’s not too late to make spectacular things happen. It mostly requires a cadre of citizens, local government, project specialists, and especially stakeholders to step up and be willing to remain focused upon project goals so that the many years of work required to turn a failing stream around can lead to success.
Riparian buffers with fences to exclude livestock can immediately begin improving water quality. With establishment of such vegetative buffers, the effects of stressors that otherwise eliminate coldwater and coolwater fishes from these segments will begin to diminish.Within five to ten years, a riparian buffer planted with native trees is not only helping to reduce nutrient and sediment loads in the stream, it is also shielding the waters from heat flux processes including the solar (shortwave) radiation that raises water temperatures to levels not tolerated by coldwater and coolwater fishes.A well-established riparian buffer.A forested stream.
You’re probably glad this look at heat flux processes in streams has at last come to an end. That’s good, because we’ve got a lot of work to do.
Add one more benefit to the wildflower meadow, it infiltrates stormwater to recharge the aquifer much better than mowed grass. And another related plus, it reduces runoff and its thermal pollution. Besides, you don’t have time to mow grass, because we have work to do!Our native coldwater fishes including the Potomac Sculpin will survive only if we protect and expand the scattered few habitats where they have taken refuge. They have no choice but to live in these seriously threatened places, but we do. So let’s give ’em some space. How ’bout it? (United States Fish and Wildlife Service image by Ryan Hagerty)
Check out these glistening gems—mating damselflies on a late spring afternoon.
It’s two pairs of Powdered Dancers, males clasping ovipositing females, a striped blue form female on the left and a brown form female on the right.A male Stream Bluet (Enallagma exsulans) perched on a grass stem in a vegetated buffer along a rehabilitated creek.A pair of Stream Bluets, male clasping female.A male Ebony Jewelwing (Calopteryx maculata) looking for a mate.There she is, the shy female Ebony Jewelwing among the shelter of some streamside foliage.A male Variable Dancer (Argia fumipennis).A mating pair of Variable Dancers, male clasping female.Two mating pairs of Variable Dancers, males clasping ovipositing females.Two pairs of mating damselflies, Powdered Dancers (left) and Variable Dancers (right), with both females ovipositing.A male Double-striped Bluet (Enallagma basidens) showing his stuff.A female Fragile Forktail.Mating Powdered Dancers, male clasping female, and an ovipositing female Fragile Forktail.A pair of mating Orange Bluets (Enallagma signatum) in wheel position, male above and female below.
Aren’t they precious? You bet they are.
To see these and other damselflies, as well as their larger cousins the dragonflies, be certain to visit your favorite vegetated lake, pond, stream, or wetland on a sunny afternoon. You might be surprised by the variety of colorful species you can find.
And to help identify your sightings, don’t forget to visit our “Damselflies and Dragonflies” page by clicking the tab bearing that name at the top of this page.
Imagine a network of brooks and rivulets meandering through a mosaic of shrubby, sometimes boggy, marshland, purifying water and absorbing high volumes of flow during storm events. This was a typical low-gradient stream in the valleys of the Lower Susquehanna River Watershed in the days prior to the arrival of the waves of trans-Atlantic human migrants that started to inundate the area during the seventeenth century. Then, a frenzy of trapping, tree chopping, mill building, and stream channelization accompanied the east to west surge of settlement across the region. The first casualty: the indispensable lowlands manager, the North American Beaver (Castor canadensis).
Nineteenth-century beaver traps on display in the collection of the State Museum of Pennsylvania in Harrisburg. Soon after their arrival, trans-Atlantic migrants (Europeans) established trade ties to the “trans-Beringia”/”Pacific-rim” migrants (“Indians”) already living in the lower Susquehanna valley and recruited them to cull the then-abundant North American Beavers. By the early 1700s, beaver populations (as well as numbers of other “game” animals) were seriously depleted, prompting the Conoy, the last of the Indian peoples to reside on the lower Susquehanna, to disperse to the north. The traps pictured here are samples of the types which were subsequently used by the European settlers to eventually extirpate the North American Beaver from the Lower Susquehanna River Watershed during the 1800s.
Without the widespread presence of beavers, stream ecology quickly collapsed. Pristine waterways were all at once gone, as were many of their floral and faunal inhabitants. It was a streams-to-sewers saga completed in just one generation. So, if we really want to restore our creeks and rivers, maybe we need to give the North American Beaver some space and respect. After all, we as a species have yet to build an environmentally friendly dam and have yet to fully restore a wetland to its natural state. The beaver is nature’s irreplaceable silt deposition engineer and could be called the 007 of wetland construction—doomed upon discovery, it must do its work without being noticed, but nobody does it better.
North American Beaver diorama on display in the State Museum of Pennsylvania in Harrisburg. Beavers were reintroduced to the Susquehanna watershed during the second half of the twentieth century.A beaver dam and pond on a small stream in the Lower Susquehanna River Watershed.Beaver dams not only create ponds, they also maintain shallow water levels in adjacent areas of the floodplain creating highly-functional wetlands that grow the native plants used by the beaver for food. These ecosystems absorb nutrients and sediments. Prior to the arrival of humans, they created some of the only openings in the vast forests and maintained essential habitat for hundreds of species of plants as well as animals including fish, amphibians, reptiles, and birds. Without the beaver, many of these species could not, and in their absence did not, exist here.Their newly constructed lodge provides shelter from the elements and from predators for a family of North American Beavers.Floodplains managed by North American Beavers can provide opportunities for the recovery of the uncommon, rare, and extirpated species that once inhabited the network of streamside wetlands that stretched for hundreds of miles along the waterways of the Lower Susquehanna River Watershed.A wintering Great Blue Heron is attracted to a beaver pond by the abundance of fish in the rivulets that meander through its attached wetlands.Beaver Ponds and their attached wetlands provide nesting habitat for uncommon birds like this Sora rail.Lesser Duckweed grows in abundance in beaver ponds and Wood Ducks are particularly fond of it during their nesting cycle.Beaver dams maintain areas of wet soil along the margins of the pond where plants like Woolgrass sequester nutrients and contain runoff while providing habitat for animals ranging in size from tiny insects to these rare visitors, a pair of Sandhill Cranes (Antigone canadensis).Sandhill Cranes feeding among Woolgrass in a floodplain maintained by North American Beavers.
Few landowners are receptive to the arrival of North American Beavers as guests or neighbors. This is indeed unfortunate. Upon discovery, beavers, like wolves, coyotes, sharks, spiders, snakes, and so many other animals, evoke an irrational negative response from the majority of people. This too is quite unfortunate, and foolish.
North American Beavers spend their lives and construct their dams, ponds, and lodges exclusively within floodplains—lands that are going to flood. Their existence should create no conflict with the day to day business of human beings. But humans can’t resist encroachment into beaver territory. Because they lack any basic understanding of floodplain function, people look at these indispensable lowlands as something that must be eliminated in the name of progress. They’ll fill them with soil, stone, rock, asphalt, concrete, and all kinds of debris. You name it, they’ll dump it. It’s an ill-fated effort to eliminate these vital areas and the high waters that occasionally inundate them. Having the audacity to believe that the threat of flooding has been mitigated, buildings and poorly engineered roads and bridges are constructed in these “reclaimed lands”. Much of the Lower Susquehanna River Watershed has now been subjected to over three hundred years-worth of these “improvements” within spaces that are and will remain—floodplains. Face it folks, they’re going to flood, no matter what we do to try to stop it. And as a matter of fact, the more junk we put into them, the more we displace flood waters into areas that otherwise would not have been impacted! It’s absolute madness.
By now we should know that floodplains are going to flood. And by now we should know that the impacts of flooding are costly where poor municipal planning and negligent civil engineering have been the norm for decades and decades. So aren’t we tired of hearing the endless squawking that goes on every time we get more than an inch of rain? Imagine the difference it would make if we backed out and turned over just one quarter or, better yet, one half of the mileage along streams in the Lower Susquehanna River Watershed to North American Beavers. No more mowing, plowing, grazing, dumping, paving, spraying, or building—just leave it to the beavers. Think of the improvements they would make to floodplain function, water quality, and much-needed wildlife habitat. Could you do it? Could you overcome the typical emotional response to beavers arriving on your property and instead of issuing a death warrant, welcome them as the talented engineers they are? I’ll bet you could.
Here’s something to look forward to in the new year. The good citizens of East Donegal Township in Lancaster County have partnered with Alliance for the Chesapeake Bay to establish an extensive wildflower meadow on what had been a mowed field of turf grass at Riverside Park in the Susquehanna floodplain near Marietta. As the photo shows, the lawn plants have been eliminated in preparation for seeding with a diverse assortment of native grasses and wildflowers to provide habitat for birds and pollinators including butterflies, bees, and other insects. Once established, the meadow’s extensive vegetative growth will help reduce stormwater runoff by better infiltrating rainfall to recharge the aquifer. During flood events, the plantings will provide soil stabilization and increase the ability of the acreage to uptake nutrients, thus reducing the negative impact of major storms on the quality of water in the river and in Chesapeake Bay. Check the project’s progress by stopping by from time to time in 2024!
Are you worried about your well running dry this summer? Are you wondering if your public water supply is going to implement use restrictions in coming months? If we do suddenly enter a wet spell again, are you concerned about losing valuable rainfall to flooding? A sensible person should be curious about these issues, but here in the Lower Susquehanna River Watershed, we tend to take for granted the water we use on a daily basis.
This Wednesday, June 7, you can learn more about the numerous measures we can take, both individually and as a community, to recharge our aquifers while at the same time improving water quality and wildlife habitat in and around our streams and rivers. From 5:30 to 8:00 P.M., the Chiques Creek Watershed Alliance will be hosting its annual Watershed Expo at the Manheim Farm Show grounds adjacent to the Manheim Central High School in Lancaster County. According to the organization’s web page, more than twenty organizations will be there with displays featuring conservation, aquatic wildlife, stream restoration, Honey Bees, and much more. There will be games and custom-made fish-print t-shirts for the youngsters, plus music to relax by for those a little older. Look for rain barrel painting and a rain barrel giveaway. And you’ll like this—admission and ice cream are free. Vendors including food trucks will be onsite preparing fare for sale.
And there’s much more.
To help recharge groundwater supplies, you can learn how to infiltrate stormwater from your downspouts, parking area, or driveway…
Does your local stream flood every time there’s a downpour, then sometimes dry up during the heat of summer? Has this problem gotten worse over the years? If so, you may be in big trouble during a drought. Loss of base flow in a stream or river is a sure sign of depleted groundwater levels in at least a portion of its drainage basin. Landowners, both public and private, in such a watershed need to start infiltrating stormwater into the ground instead of allowing it to become surface runoff.You can direct the stormwater from your downspout, parking area, or driveway into a rain garden to help recharge the aquifer that supplies your private or public well and nearby natural springs. Displays including this model provided by Rapho Township show you how.
…there will be a tour of a comprehensive stream and floodplain rehabilitation project in Manheim Memorial Park adjacent to the fair grounds…
Have you seen banks like these on your local stream? On waterways throughout the Lower Susquehanna River Watershed, mill dams have trapped accumulations of sediments that eroded from farm fields prior to the implementation of soil conservation practices. These legacy sediments channelize creeks and disconnect them from their now buried floodplains. During storms, water that would have been absorbed by the floodplain is now displaced into areas of higher ground not historically inundated by a similar event.Adjacent to the Manheim Farm Show grounds, the Chiques Creek Stream Restoration Project in Manheim Memorial Park has reconnected the waterway to its historic floodplain by removing a dam and the legacy sediments that accumulated behind it.Chiques Creek in Manheim following removal of hundreds of truck loads of legacy sediments. High water can again be absorbed by the wetlands and riparian forest of the floodplain surrounding this segment of stream. There are no incised banks creating an unnatural channel or crumbling away to pollute downstream waters with nutrients and sediment. Projects similar to this are critical to improving water quality in both the Susquehanna River and Chesapeake Bay. Closer to home, they can help municipalities meet their stormwater management (MS4) requirements.Mark Metzler of Rettew Associates guides a tour of the Chiques Creek rehabilitation. Here, cross vanes, stone structures that provide grade control along the stream’s course, were installed to gently steer the center of the channel away from existing structures. Cross vanes manipulate the velocity of the creek’s flow across its breadth to dissipate potentially erosive energy and more precisely direct the deposition of gravel and sediment.
…and a highlight of the evening will be using an electrofishing apparatus to collect a sample of the fish now populating the rehabilitated segment of stream…
Matt Kofroth, Lancaster County Conservation District Watershed Specialist, operates a backpack electrofishing apparatus while the netting crew prepares to capture the temporarily stunned specimens. The catch is then brought to shore for identification and counting.
…so don’t miss it. We can hardly wait to see you there!
This stream restoration project is currently underway along a one-mile-long segment of Lancaster Conservancy lands along Conewago Creek. The mountain of dirt is one of several stockpiles of legacy sediments removed to reestablish the floodplain’s historic geomorphology. After eroding from cropland during the years prior to soil conservation, legacy sediments accumulated behind mill dams on waterways throughout the lower Susquehanna watershed. After removal of the dams, creeks were left trapped within the sediment-choked bottomlands, incising steep muddy banks as they cut a new path through the former mill ponds. Excavating legacy sediments from these sites eliminates creek banks and allows floodwaters to again spill directly into wetlands along the stream course. With floodplain and wetland functions restored, nutrients are sequestered, high water is infiltrated to recharge aquifers, sediment loads from collapsing banks are eliminated, and much-needed habitat is created for native plants and animals.
To learn more about this project and others, you’ll want to check out the Landstudies website.
