By: Sarah Barker

Rivers and streams are very dynamic, changing physically and chemically with every passing minute. Erosion, the process of sediment wearing away over time, plays an essential role in this endless shaping and reshaping. The movement of sediment in freshwater systems is incredibly important for water quality and habitat health. Soil binds to nutrients and salts, trapping them and preventing them from washing into streams. When severe weather events or abnormal conditions carry away large amounts of sediment these pollutants are freed into the water column, impacting wildlife and drinking water. The rate of erosion is also heavily influenced by the amount of development in the surrounding watershed. As land around a stream is developed, runoff increases and erosion worsens.

Often, erosion is considered as a consequence of storms. However, in humid, temperate climate regions like Southeastern Pennsylvania, the most influential form of erosion actually occurs in the winter, called freeze-thaw erosion. This type of erosion happens in natural cycles when extreme differences in temperature, from below freezing to above freezing, occur over a short period of time. As water freezes in the soil it expands, loosening soil particles, when it warms up suddenly after a cold spell this ice melts, creating space between particles and causing them to wear away more quickly. The impact of freeze-thaw erosion worsens after winter rain as the flow of water over already weakened banks accelerates soil loss. Development near water only makes the issue worse, providing hardened surfaces for runoff to speed into flowing water like a race track, bringing more and more loosened soil down with it. It is projected that these freeze-thaw cycles will only increase as climate change continues to modify normal weather patterns towards extremes.

Erosion on the side of a stream bank in Darby Creek.

There are other factors that can contribute to the severity and frequency of freeze-thaw cycles as well. One of the most important is the presence of vegetation along stream banks. Roots hold soil together, slowing erosion in general, however, the density of plants matter too! A 2006 study found that dense plant cover insulates banks from extreme temperature shifts over the course of a day, protecting soil from more frequent freeze-thaw cycles. Stretches of bank without dense canopy or understory were much more vulnerable to daily changes in temperature and experienced as many as four times the number of freeze-thaw cycles as densely planted sections (Wynn & Mostaghimi, 2006).

The local geology and predominant soil type of a region also significantly influence the impact of freeze-thaw erosion. Fine sediment types like clay, silt, or loam tend to be much more susceptible to this process than coarser varieties. In addition, the Piedmont region of Southeastern Pennsylvania is more heavily impacted compared to other kinds of regional geology, like the Atlantic Plain (Inamdar et al., 2018). At Rushton Woods Preserve, an ongoing erosion study documenting the progressive changes within an erosion feature called a headcut may show just how severe freeze-thaw cycles can be when these factors combine. 

Starting in June 2024, 40 pieces of  rebar, called erosion pins, were hammered into the sides of a headcut at Rushton Woods Preserve to measure the rate of soil movement due to erosion. The study area is mostly fine sediment under a canopy of beech trees, but there is sparse understory to help secure soil. Several recent freeze-thaw erosion events were documented this winter where freezing nights were followed by winter rainfall, leading to rapid movement of soil. Some erosion pins were completely buried in frozen sediment, so that they could not be measured until the next warm day. Data is still being collected, but these winter freeze-thaw measurements are already significant to the study!

Erosion is a complicated natural process, and scientists are still untangling the many mechanisms that may play a role in its impacts. However, there are some things that are very clear. Planting dense vegetation along stream banks combats severe and frequent freeze-thaw cycles. In addition, proper stormwater runoff management is vital for keeping soils stable as winter rainfalls increase in frequency. Freeze-thaw cycles themselves are normal for this area, but it is important to make sure that the rate of erosion doesn’t outpace what local streams can handle. Protecting the land around waterways is essential for healthy habitat and clean water!

References:

Inamdar, S., Johnson, E., Rowland, R., Warner, D., Walter, R., & Merritts, D. (2017). Freeze–thaw processes and intense rainfall: The one-two punch for high sediment and nutrient loads from mid-atlantic watersheds. Biogeochemistry, 141(3), 333–349. https://doi.org/10.1007/s10533-017-0417-7 

Luffman, I., & Nandi, A. (2019). Freeze-thaw induced gully erosion: A long-term high-resolution analysis. Agronomy, 9(9), 549. https://doi.org/10.3390/agronomy9090549 

Wynn, T. M., & Mostaghimi, S. (2006). Effects of riparian vegetation on stream bank subaerial processes in southwestern Virginia, USA. Earth Surface Processes and Landforms, 31(4), 399–413. https://doi.org/10.1002/esp.1252 

By Watershed Protection Program Co-op Sarah Barker

Deep in the sleepy haze of a deciduous forest dawn, between bowing black willows and proud sycamores, a lovely little creature works his way back home. Charlie Woodscomb, known to his family and friends as “Chompy” — although he much preferred his given name (even if he wouldn’t admit it to his loved ones) — pattered through the brush towards his warm lodge, ready for a long day’s rest after patrolling his territory throughout the moonlit night. It had been an average night’s work, collecting alder shoots and a bit of aspen for his cache. Along his meandering route, he paused for a moment to smell the air for any signs of unwelcome guests in his modest kingdom. Beavers may be the proud engineers of this landscape, but even Charlie could admit that vision wasn’t their strongest asset. However, his mighty clan made up for this shortcoming with many other wonderous capabilities.

Once he had confirmed with both his powerful nose and sensitive ears that no trouble seemed to stand in between him and his cozy den, he resumed his leisurely promenade, admiring the sounds of water crashing over the many riffles as it danced down to his stately abode. The lodge was something to behold alright! As he stopped to reflect on how lucky he was, he began to reminisce. He had poured countless dark and rainy nights into the lodge’s construction with his beautiful wife, Sandy. For several lonely months before meeting Sandy, he had scouted and prepared this particular stretch of the meandering stream they now called home. 

Charlie had left his parents’ den shortly after his second harvest moon, having decided that it was time to set off and establish a home of his own. He had grown up in a wonderfully large and boisterous family, he had enjoyed playing with his younger siblings, taking turns grooming their thick fur, and contributing to the nightly patrol as he got older and could take on more serious responsibilities. Eventually, he began to long for a home he built himself, a warm shelter where he could protect and take care of his future mate and litters of kits from the harsh winters and raging storms. So, he set off to face the great beyond, taking his first pioneering steps from the valleys of the ancient mountains he called home, onward towards meadows and wetlands just as his father had done many ripe moons ago.

After traveling for several long nights, he found his new home in these gorgeous woodlands, full of dense swaying canopies. The sheer amount of foliage and freshly sprouted woody shoots made his mouth water immediately! He knew that this hidden oasis would be perfect for his future family, and he wasted no time in skittering down the stream bank to find a nice bend on which to begin his very first dam. However, he faced many obstacles in these abundant lands. Just as he had discovered this cornucopia of lush greenery, other creatures of the forest soon began to wander through the area in search of nourishment. Most were not threatening to him, and included friendly songbirds picking at the juicy serviceberries and a couple of muskrats hoping for a tasty cattail snack. These friends he greeted with a kind hum. He had enjoyed socializing with his fellow beavers back at his parents’ den, and so he relished these brief encounters, however fleeting; that was, until he first spotted the red fox. 

Charlie had seen first-hand the devastation these cunning predators could unleash upon a family, and so he made sure to scent-mark his territory vigilantly, hissing and slapping his tail against the water whenever that cursed creature came too close. Thankfully, he was pretty large for his age, and in wonderful shape due to his tireless construction efforts and incessant swimming. The fox carefully backed away upon hearing the powerful sharp snap of his tail, realizing his strength, and recognizing that he would be much more trouble than a quick meal was worth.

Every so often, Charlie would catch a glimpse of crimson fur between the box elders and red maples, but soon enough, the fox gave up on his territory, moving on to find a more vulnerable source of calories. Charlie breathed a great sigh of relief once he noticed this departure, as he had begun to worry that he would have to find another meander to call home. 

His peace was only short lived however, as but a few weeks after the fox had left, the rain began. Normally, he loved a good bit of rain; it expanded his swimming range and allowed him access to new, temporary tributaries or ephemeral pools for even more delicious treats, but this rain was ferocious and unrelenting. He tried his best to prevent the downpours from washing away all his hard work, but mother nature could not be bested, not even by a mighty beaver such as himself. After two long weeks of brutal battering, the great progress he had made on his new dam disappeared downstream, along with the cache of twigs he had begun to stock up for the winter.

Heartbroken and downtrodden, Charlie wondered if he should give up and look for another stretch of river to build his home, but the cold was creeping ever closer and there was no guarantee that there would be suitable foraging grounds further downstream. He had found himself in a great big pickle indeed. After several debates with himself which led to nowhere, he decided to put a pause on his pity party and go for a nice moonlit swim to clear his head; he found that he always had his best ideas when he was diving for submerged morsels. As he started the trek toward his usual mud slip, he began to pick up the scent of someone new. He paused for a moment to focus on the unfamiliar perfume, hesitant at first, for fear that another tricksy fox had happened upon his territory and was now lying in wait for him.

However, he was surprised and intrigued when he realized that he was smelling another beaver, one with whom he was not previously acquainted! Charlie, now full of excitement and anxiety at the thought of finally meeting another fellow beaver, sped down the small trail he had gradually carved out over the past few weeks, and headed toward the stream bank. But once he saw the gorgeous, shiny dark fur in front of him, his heart skipped a beat. The mysterious visitor turned to greet him, and he fell in love all at once. She introduced herself to him with a hum. Her name was Sandy, and he thought that she had lovely teeth and beautiful paws.

Now after two blissful Beaver moons together, they were finally expecting their first litter of kits, much to Sandy’s and his delight! They had enjoyed their time together as a couple, but they were quite eager to welcome the fun and happiness that little ones would certainly bring to their newly expanded accommodations. Sandy and Charlie had worked tirelessly on their pristine dam, homey lodge, overflowing food cache, and sprawling trails that weaved throughout their foraging territory. Charlie, stuck in his nostalgic musings, startled a bit when Sandy herself got his attention with a whine. She had just returned from her night’s foraging and patrolling as well, and was eager to settle down into the warmth of their den for a good day’s rest. Charlie easily obliged, following her into the small pool in front of their comfortable home. As the sun began to rise, he thought about how he was oh so grateful that he didn’t abandon this flourishing land and all the surprising richness it had to offer.

Glossary: terms listed in order of appearance

Cache | Caches are collections of various branches, twigs, and other woody debris which are stashed in a submerged location near the resident Beaver’s lodge as a method of long-term food storage in case of storm events preventing active foraging and as a stockpile for the winter months when Beavers rarely leave their dens to conserve heat and energy.

Harvest Moon | Each full moon corresponding to a calendar month has a traditional name which denotes what is happening in the environment during that season. This system was developed centuries ago by Native American tribes and while some names differ depending on the tribe, there is a general twelve-moon, twelve-month list which is still in use today in the Northern hemisphere! The Harvest moon represents September due to the abundance of crops ready for harvest during early fall.

Smelling Another Beaver | Beavers can tell from scent alone the age, sex, and relative social class (dominant vs. subordinate) of another beaver from its scent. Castoreum which is the substance produced by beavers to scent-mark is unique to the individual beaver and plays an essential role in both territorial defense and communication. There is evidence to suggest that this high level of recognition can help to prevent inbreeding or mating outside of the established mating pair. These processes can help beavers to avoid the negative effects of inbreeding on genetic diversity or prevent hostile or apathetic behavior from a mate in response to unrelated kits in the family lodge. However, these mating traits can change depending on the range of dispersal of beaver pairs and obstacles preventing ideal mating such as heavy snowfall.

Beaver Moon | The Beaver moon coincides with November as an indicator of the intense preparation and increased activity level of beaver families preparing for winter at this time of year.

References:

Coolman, Aaron (2023). [A beaver swimming in a shallow stream] [Photograph]. Willistown Conservation Trust.

Rosell, F. N., & Campbell-Palmer, R. (2022). Beavers: Ecology, behaviour, conservation, and Management. Oxford Academic. Oxford University Press. Retrieved June 1, 2023, from https://academic.oup.com/book/38841/chapter-abstract/337749534?redirectedFrom=fulltext. 

By Watershed Protection Program Co-op Sally Ehlers

The northern snakehead (Channa argus) is a type of fish that is originally from Asia which has made its way to Pennsylvania and is causing problems in local streams. In 2004, an angler found a northern snakehead in Meadow Lake in FDR Park in Philadelphia County. This was the first confirmed sighting of this type of fish in Pennsylvania. 

About a year later, there was a recorded catch in the Delaware River. They have since spread through canals, reservoirs, lakes, and rivers along the East Coast and as far west as the Mississippi River. The presence of the northern snakehead is worrisome because it can be harmful to other fish and their homes. The northern snakehead is a voracious predator and eats other fish. This aggressive behavior can reduce the number of other fish in a waterway. Northern snakeheads will compete with other fish for food and habitat.

One thing that makes the northern snakehead unique is its ability to survive in water with many different levels of dissolved oxygen. Even if there is not a lot of dissolved oxygen in the water, the northern snakehead can still survive. This is because it has a special organ called a suprabranchial organ, or primitive lung. This organ allows the northern snakehead to breathe air directly from the atmosphere. They can even survive out of water for up to four days if they stay moist. This adaptation, in combination with its ability to move across land for short distances by wriggling on its fins, allows it to easily travel from one body of water to another.

To stop the northern snakehead from spreading, the Pennsylvania Fish and Boat Commission has made some rules: 

1. Do not keep or sell northern snakeheads. 
2. Do not release them into other bodies of water. 

This ensures the northern snakehead does not continue to spread.

The Pennsylvania Fish and Boat Commission is also working hard to teach people how to identify the northern snakehead. If people know what to look for, they can help make sure it doesn’t spread to other areas. The northern snakehead has some distinctive features, such as a long body with a single fin running along the length of the back, a somewhat flattened head, and a brown body with dark blotches.

The northern snakehead can be confused with the native North American Bowfin (Amia calva). In the western part of Pennsylvania, northern snakeheads may also be confused with burbot (Lota lota). These species have similar body shapes and coloration, however, there are some key differences. As the name implies, the northern snakehead has enlarged snake-like scales on its head. The Northern American Bowfin does not have scales on its head, rather it has bony plates between its lower jaw bones. The burbot has a scaly head, but unlike the northern snakehead, it has two fins on its back. 

If you catch a northern snakehead, it is essential to report it to the Pennsylvania Fish and Boat Commission by calling 815-359-5163 or visiting their website. You are also encouraged to kill it, freeze it, and record the location where you found it. This information is useful for figuring out the geographic range of the northern snakehead and possibly finding ways to control its spread.

References:

“California’s Invaders: Snakehead,” California Department of Fish and Wildlife,

https://wildlife.ca.gov/Conservation/Invasives/Species/Snakehead#:~:text=Snakeheads%20have%20small%20heads%20with,days%2C%20if%20they%20stay%20moist

“Northern Snakehead,” Chesapeake Bay Program,

https://www.chesapeakebay.net/discover/field-guide/entry/northern-snakehead

“Northern Snakehead,” Pennsylvania Fish and Boat Commission,

https://www.fishandboat.com/Fishing/All-About-Fish/Catch-PA-Fish/Pages/Snakehead.aspx

“Northern Snakehead,” Pennsylvania Sea Grant, https://seagrant.psu.edu/sites/default/files/snakehead2013_reduced_0.pdf

“Northern Snakehead Fish,” Smithsonian’s National Zoo and Conservation Biology Institute, https://nationalzoo.si.edu/animals/northern-snakehead-fish