How the American Beaver Mitigates Drought Impact

By: Sarah Barker

As we near the end of what is shaping up to be the hottest year in documented history, one of nature’s most impactful (and adorable) engineers is working hard to keep our ecosystems green. The American beaver (Castor canadensis) may be our saving grace as drought and wildfires become more frequent due to the growing climate crisis. Research conducted over the past few decades reveals the profound positive influence beavers have on their habitats across the country, even in extreme conditions. Whether they are meandering through Pennsylvania temperate forests (Margolis et al., 2001), arid landscapes in Nevada (Fairfax & Small, 2018), or habitats west of the Rockies (Fairfax & Whittle, 2020), the importance of beaver activity in building environmental resilience cannot be ignored.

Beavers are herbivorous and semiaquatic mammals, they eat woody vegetation, fruits, and herbaceous plants like skunk cabbage or sedges, and they live both on land and in the water. Beavers are renowned in the animal kingdom for their impressive constructions made from chewed trees, shrubs, and miscellaneous found materials. While large dams may be their calling card, they also build homes called lodges into the banks of water bodies, food caches to sustain them through the winter, and trails and canals for transporting food and building materials.

By building successive dams in the same stretch of a river or stream, beavers can sustain or create wetlands even during intense drought; a behavior we have observed at WCT’s Ashbridge Preserve! Beavers are slow and clumsy on land but are graceful swimmers. Therefore, higher water levels provide easier access to food and less risk of predation. Beavers are also fantastic stewards! They chew down local invasive plants like privet and grapevine for their dams while selectively foraging twigs from natives like black willow or red osier dogwood so that they may produce many more shoots in the following growing seasons. This behavior helps maintain native plant populations as invasive species become increasingly common.

These benefits increase ecosystem biodiversity, organism abundance, and water quality with the impact being so significant that it can be observed by NASA satellites! Green can be seen spreading outward from beaver dams into the surrounding floodplains while other areas without beaver activity wilt under extreme conditions. A study based in Nevada found that in areas where beaver dams had been established, the rate of water evaporation was significantly lower compared to environments lacking beaver activity (Fairfax & Small, 2018). This means that water stays in the ecosystem for longer, and during drought this is critical. Increased water retention supports environmental resilience, with hydrated soils and vegetation being more resistant to wildfires, storms, and erosion, and providing more favorable conditions for wildlife. Depending on the region, increased water level and retention can also allow for the dilution of concentrated salts and nutrients, providing more time for them to be absorbed and broken down, lessening their impact on the environment as a result.

As temperatures continue to rise with each passing year and the weather becomes increasingly unpredictable, these friendly rodents provide fortification and solace for wildlife and humans alike. While they may have a historical reputation as a nuisance, their beneficial environmental impacts are undeniable. Beavers are our allies in the fight to protect and remediate our environment and they sure do look cute doing it!

References:

Dewey, C., Fox, P. M., Bouskill, N. J., Dwivedi, D., Nico, P., & Fendorf, S. (2022). Beaver dams 

overshadow climate extremes in controlling riparian hydrology and water quality. Nature 

Communications, 13(1). https://doi.org/10.1038/s41467-022-34022-0 

Fairfax, E., & Small, E. E. (2018). Using remote sensing to assess the impact of beaver damming 

on riparian evapotranspiration in an arid landscape. Ecohydrology, 11(7). 

https://doi.org/10.1002/eco.1993

Fairfax, E., & Whittle, A. (2020). Smokey the Beaver: Beaver‐dammed riparian corridors stay 

green during wildfire throughout the Western United States. Ecological 

Applications, 30(8). https://doi.org/10.1002/eap.2225 

Hood, G. A., & Bayley, S. E. (2008). Beaver (Castor canadensis) mitigate the effects of climate 

on the area of open water in boreal wetlands in Western Canada. Biological 

Conservation, 141(2), 556–567. https://doi.org/10.1016/j.biocon.2007.12.003 

Margolis, B. E., Castro, M. S., & Raesly, R. L. (2001). The impact of Beaver Impoundments on 

the Water Chemistry of two Appalachian streams. Canadian Journal of Fisheries and 

Aquatic Sciences, 58(11), 2271–2283. https://doi.org/10.1139/f01-166 

NASA. (n.d.). NASA data helps Beavers build back streams. NASA. 

https://spinoff.nasa.gov/Beavers_Build_Back_Streams

Rosell, F., & Campbell-Palmer, R. (2022). Beavers: Ecology, behaviour, conservation, and 

Management. Oxford University Press. 

By: Lauren McGrath, Director of Watershed Protection Program

For the Watershed Program, it has felt like the September that never ends. A warm, dry autumn has made for great foliage, but there are growing concerns about the impact of a fall with no rain. Fall of 2024 has been notably dry, with Philadelphia having the longest dry period since weather record-keeping began 153 years ago – an unbelievable 42 days with no rain. For the first time in the region, there was no rain in October, and temperatures were unseasonably warm, which can cause more water to leave the soil. While the dry period ended with rain on November 8, Chester County is still facing drought conditions expected to persist throughout the month of November. 

With this record-breaking dry spell, what is the impact on local streams?

Unsurprisingly, the lack of rain has a significant impact on the health of local waterways. As rain continues to be elusive in the region, the amount of flowing water in many waterways continues to drop causing physical changes to stream habitat. Low flow conditions can cause dramatic changes to resource availability. The resulting changes to the flow patterns and currents can cause sections of normally flowing streams to become isolated and turn into pools, trapping wildlife in stagnant water. Decreased water levels also means that there is just less space for wildlife in the stream, causing crowding and more competition for fewer resources. In some cases, small streams can dry up entirely. This dramatic loss of habitat has been documented at one site in the Darby Creek Watershed already during this historic drought. 

Droughts also cause changes in water chemistry. With flow patterns changing, the availability of oxygen can be reduced, with slow-moving water failing to distribute dissolved oxygen at levels to support sensitive stream life. This can create life threatening conditions for sensitive stream life. Changes in flow also influence chloride levels. While some chloride is present in the geology of Chester and Delaware Counties, the majority of chloride is introduced into local watersheds through the application of road salts (usually sodium chloride, NaCl) to melt snow and ice in the winter. As the snow and ice melt, the salt flushes into local waterways. In areas where salt is applied frequently and in abundance, the chloride can build up in the soils, leading to salty groundwater and high levels of chloride year round – instead of just after winter storms.  Chloride, including that from road salt, is known to be harmful to sensitive fish and invertebrates in freshwater systems.When salt buildup in soils meets drought conditions, it leads to salty streams. Less rainfall, (or in the case of October 2024 no rainfall), leads to little to no dilution of groundwater entering the stream, increasing the concentration of chloride in local waterways. When these dry conditions are paired with unseasonably warm temperatures (Fig. 1), it is a recipe for rapid evaporation of surface waters (Fig. 2). Evaporation leaves chloride behind, causing even higher concentrations of chloride ions.  During a severe drought, stream systems are almost entirely fed by groundwater, which means the potential for higher concentrations of chloride ions.

Salty streams become extremely dangerous for sensitive aquatic life as temperatures rise, with both chloride and warm streams causing stressful conditions for stream residents. With unseasonably warm days still to come in November and no rain in the forecast, there is likely to be a long-term impact on the health of local streams. Warm air temperatures also mean less oxygen available in the water, increasing the risk factor for aquatic life.

While the drought is not necessarily caused exclusively by climate change, it is being made more severe by the warm temperatures, especially in the fall months of September and October. Models predict that these months will continue to warm at a faster rate than the rest of the year and rainfall events will be extreme, with more rain falling in shorter periods of time. The Watershed Team monitors water temperature, conductivity, and chloride levels at ten sites across Ridley, Crum, and Darby Creeks as well as an additional 34 sites throughout the Darby and Cobbs watershed through the Darby & Cobbs Creek Community Science Monitoring Program on a monthly basis. As data analysis takes place, we will share updates on what we are learning and how you can help stream health.

By: Lauren McGrath, Director of Watershed Protection Program

From October 17 through October 20, 400 trees were planted in the Darby Creek watershed. This project is possible through a generous grant from the Pennsylvania Department of Conservation and Natural Resources (DCNR). The funding, provided through DCNR’s Community Conservation Partnerships Program, enabled the installation of 400 trees and shrubs at Inveraray HOA in Villanova (Radnor Township) over four days. Over 50 volunteers joined Watershed and Stewardship staff to plant 39 species of native trees and shrubs across two acres of land along Abrahams Run, a tributary to the Darby Creek.

This planting effort engaged with new volunteers and a new community – who were all interested in learning more about the importance of healthy waterways and the impact of the restoration of the riparian area. It was a very exciting opportunity to share more about the vibrant life that calls Darby Creek home and to celebrate the newly documented population of freshwater mussels that live nearby!

The impact of these native trees and shrubs on the watershed will be multifaceted. The diverse array of species will provide an immediate visual interest in the landscape, with new colors and textures arriving with each season. For many of these plants, the flowers will turn to fruit in the fall, providing critical food for migratory birds and the falling leaves will provide shelter and nourishment for the life in the stream over the winter months. Each plant will also provide wildlife habitat from the canopy to the roots, giving the banks of Abrahams Run structure and stability against future storms.

By: CJ Chen, Spring 2024 Watershed Team High School Intern

From going out to nature preserves and injecting trees with pesticide, to wading through creeks knee-deep and flipping over rocks to find macroinvertebrates, each week at Willistown brought something new. As a high school intern on the Watershed Protection Program team this spring, I saw how a non-profit conservation group functions and what it’s like to be a real-life scientist. I got to experience field work during monthly sampling days, lab work to process those samples, and the many meetings that facilitate collaboration with the community. I learned that watershed science involves a lot more than just water, it encompasses the many overlapping pieces of environmental studies. 

Through real-world experience, I’ve learned much more than I would have in a traditional classroom setting, preparing me well for my future endeavors as I continue my studies at Haverford College in the fall. Moreover, I was able to apply what I learned at Willistown to an independent project at a local park, in which I completed a study, summarized below. 

The project assesses the water quality of Little Crum Creek that passes through Little Crum Creek Park (est. 1970) in Swarthmore Borough, PA. Little Crum Creek is a small stream beginning in Swarthmore, flowing 3.68 miles¹ before joining  Crum Creek and entering the Delaware River (Map 1a and 1b).

Upstream waterways like Little Crum Creek carry contamination and affect the quality of downstream waters. Thus, Little Crum Creek impacts the health of the Delaware River, a crucial drinking water source for 17 million people across five states. 

Land usage affects the health of the waterways; stream pollution increases as open space diminishes due to land development. The area surrounding Little Crum Creek is heavily developed for retail and residential purposes. Because water cannot soak into the impervious surfaces found in these developed areas–e.g. roadways, parking lots, sidewalks, and rooftops–large volumes of stormwater runoff are channeled through drains, which then end up in streams like Little Crum Creek.

Since 1971, Little Crum Creek has been designated as an impaired stream, meaning it does not fulfill federal water quality standards. Understanding the current health of the creek will allow for further improvements in the stream quality to be made by Friends of Little Crum Creek Park and Swarthmore Borough.

Three complete water tests were conducted from March to May using low-cost Lamotte brand kits. While many parameters were assessed, the most important findings are listed below.

Water temperature influences the ability of salts and oxygen to dissolve in the stream, and many organisms require consistent water temperatures to survive. As rain falls on impervious surfaces like pavement, the water heats up under the sun and channels through drains and sewers into the creek. High temperatures usually reflect that the surrounding landscape has a high percentage of impervious surfaces. In Swarthmore, most of the landscape is heavily developed which is reflected at Little Crum Creek with its elevated water temperatures that exceed acceptable levels established by the state across all three samplings in the park.

Chloride and specific conductivity (SPC) together assess the salt concentration. High concentrations of salts harm aquatic organisms, causing deformities in fish and amphibians and killing sensitive keystone organisms like mussels. Salt most often originates from human activity such as excessive road salting. It was found that Little Crum Creek has a salt issue originating from the unnamed tributary. Further continual study of the elevated salts is needed to determine the exact source in the unnamed tributary.

The high salt levels of Little Crum Creek follow the rising national trend of oversalting roadways. This is seen when the chloride levels found in this study are compared to the water quality data from a 1971 United States Geological Survey (Fig. 1).

These issues may be lessened by planting native streamside vegetation, which will address elevated stream temperature and provide a buffer between the stormwater runoff and the creek. Additionally, reducing road salting in the winter and fertilizing lawns at least 48 hours before rain (if at all), are easy community-led steps to reduce the contamination in Little Crum Creek.

Interested in learning more about Little Crum Creek? Click here to read the full report!

¹McGarity, Arthur. Watershed Assessment of the Lower Crum Creek: Decision Support for a Community-Based Partnership. Swarthmore College, 2001. Web. <https://www.swarthmore.edu/NatSci/watershed/319_Project/Full_319_Report.pdf>.

Calvin Keeys

For hundreds of years, people have been moving to the United States and bringing parts of their culture with them. One effect of this is that wildlife is brought over accidentally or purposely and becomes invasive. Invasive species are non-native organisms that cause damage to a new environment by competing against native species for resources and habitat. Even though it is natural for organisms to enter another environment, this is happening more often now than it has in the past due to human actions such as trade, travel, and climate change.  

Freshwater ecosystems have a greater biodiversity per surface area than marine and terrestrial ecosystems (Havel et al. 2015). Unfortunately, these environments, especially lakes and streams, have been some of the most affected by invasive species and species loss. Most aquatic species cannot move from one body of water to another and have instead been moved by people for reasons such as accidental releases, aquarium releases, and fishermen dumping bait. As people continue to change the environment and weather, many non-native aquatic species are expected to increase their populations because they can survive in different environmental conditions while many native species cannot. Invasive species are also better at handling increased land use from people such as habitat destruction and pollution. Invasive species in aquatic ecosystems and the control of them have cost the United States approximately $7.7 billion USD.

Invasive fish can wipe out native species and cause irreversible damage to their environments, and some of the most notable examples are specific carp species. 

Common carp (Missouri Department of Conservation)

The common carp (Cyprinus carpio) was introduced into the Midwest in the late 1800s primarily as a food fish for growing migrant populations. The popularity of the fish and its ability to live in different water conditions led to the US Commission of Fish and Wildlife stocking carp throughout the country to make up for the declining native fish species that were overfished at the time. Common carp eventually spread to other waters outside of the commission’s control and is now established in rivers and lakes in every state except Alaska. It is an active feeder, disturbing sediments and uprooting plants as it forages. High carp populations can cause a deterioration of water quality and habitat for native fish species under certain conditions, such as smaller water bodies with silty bottoms.

Asian carp species (Tennessee Wildlife Federation)

Asian carp refers to several species of carp: silver (Hypophthalmichthys molitrix), bighead (Hypophthalmichthys nobilis), black (Mylopharyngodon piceus) and grass (Ctenopharyngodon idella) that were introduced in the 1970s to aquaculture ponds and wastewater treatment places in the Southeast to clear weeds and parasites. Asian carp have escaped into the Mississippi River basin by jumping over barriers, intentional release, and through flood events. Asian carp can dominate native fisheries in both abundance and biomass, consuming 5-20 percent of their body weight daily. Their high level of feeding on plankton can outcompete native fish and eliminate the main food source for larval and native planktivorous fish. 

They are continuing to make their way up the Mississippi River and its tributaries, the Missouri River and the Illinois River since they are all connected. The Illinois River is connected to the Great Lakes by the Chicago Sanitary and Ship Canal, a manmade connection. The Great Lakes provide a wide range of habitat types that Asian carp can use for spawning, recruitment and maturation. When not feeding on plankton, Asian carp will eat detritus and root in the bottom of protected embayments and wetlands, which could threaten aquatic vegetation that provides spawning habitat for native fish and breeding areas for native waterfowl. Experts are worried that if these fish get into the Great Lakes, they may negatively affect the area’s $7 billion/year fishing industry. 

There are a few ways that you can prevent the spread of invasive fish. Learn to identify juveniles and adults. If you catch one while fishing, do not release it and instead contact your nearest fish and game agency or the US Fish and Wildlife Service (703-358-2148) as soon as possible. Only use wild-caught bait fish in waters where they came from. With your help, we can stop this problem from getting worse. 

References

“Asian Carp Control | U.S. Department of the Interior.” Doi.gov, Aug. 2018, www.doi.gov/ocl/asian-carp-control-0.

‌“Asian Carp – New York Invasive Species Information.” Nyis.info, 2024, nyis.info/invasive_species/asian-carp/. 

Brown, Kubie. “The American Dream: How Invasive Species Have Created New Fisheries | MeatEater Fishing.” Themeateater.com, MeatEater, 18 Jan. 2023, www.themeateater.com/fish/general/the-american-dream-how-invasive-species-have-created-new-fisheries. 

“Common Carp – Mississippi National River & Recreation Area (U.S. National Park Service).” Nps.gov, 2017, www.nps.gov/miss/learn/nature/ascarp_common.htm. 

Couch, Claire, et al. “Evaluating the Institutional and Ecological Effects of Invasive Species Prevention Policy: A Case Study from the U.S. Fish and Wildlife Service.” Management of Biological Invasions, vol. 14, no. 2, 2023, pp. 269–88, https://doi.org/10.3391/mbi.2023.14.2.06.

Havel, John E., et al. “Aquatic Invasive Species: Challenges for the Future.” Hydrobiologia, vol. 750, no. 1, 2015, pp. 147–70, https://doi.org/10.1007/s10750-014-2166-0.

“History of Common Carp in North America – Mississippi National River & Recreation Area (U.S. National Park Service).” Nps.gov, 2023, www.nps.gov/miss/learn/nature/carphist.htm. 

“Invasive Carp Overview – Mississippi National River & Recreation Area (U.S. National Park Service).” Nps.gov, 2023, www.nps.gov/miss/learn/nature/ascarpover.htm.

‌ Klein, Zachary B., et al. “Suppression of Invasive Fish in the West: Synthesis and Suggestions for Improvement.” North American Journal of Fisheries Management, vol. 43, no. 2, 2023, pp. 369–83, https://doi.org/10.1002/nafm.10827.
Varble, Sarah, and Silvia Secchi. “Human Consumption as an Invasive Species Management Strategy. A Preliminary Assessment of the Marketing Potential of Invasive Asian Carp in the US.” Appetite, vol. 65, 2013, pp. 58–67, https://doi.org/10.1016/j.appet.2013.01.022.