Recently increased vegetation in Greenbelt Lake may appear worrisome, but it is a sign of a natural ecosystem, of nature independently creating and sustaining the 23-acre lake’s rich plant and animal life. If the growth continues, it would indicate the lake is evolving toward marshland.
What’s Happening?
Local kayakers and fisherfolk have reported increased growth in coves both near the peninsula and Lakecrest Drive, and along the lake perimeter. Kayakers report enough growth to impede paddling. Fisherfolk note pros and cons; the plants catch lures, but also provide habitat for fish to grow larger, for a more satisfying catch. The growth includes algae, water primrose, smartweed and the water chestnut noticed this summer (see greenbeltnewsreview.com/issues/GNR20220804.pdf). The algae’s green surface foam was visible until early November, though less so with recent cooler temperatures. Aquatic ecologists say that increased plant growth in freshwater lakes varies with nutrient levels and water temperatures.
Source of Plants?
Animals, especially waterfowl, bring plant life to the lake, as do water flow, wind and rain. The lake is rich in phosphorous and nitrogen that encourage plant growth. Draining the lake for the 2020 dam repair probably allowed more plants to take root in the exposed floor. As plants die, they collect on the floor and reduce its depth (20 feet at its deepest), which warms the water and encourages growth. This is particularly true in the shallower coves, where marsh succession would begin. Phosphorous and nitrogen vary throughout the year, encouraging more and less growth.
Man-made and Natural
Although the lake is man-made, it has the natural life cycle of any freshwater lake. Algae is a base of the food chain. It produces oxygen for fish and is eaten by tadpoles, fish and aquatic insects. The plants serve as food for turtles, beavers and waterfowl, as well as providing cover for fish and other animals to develop and hide from predators. Birds use them for nesting materials.
As a result, the lake has a large and diverse animal population including turtles: yellow-eared sliders, red-eared sliders, painted and eastern snapping; American bullfrogs; beavers; brown and rainbow trout stocked by Maryland’s Department of Natural Resources; and birds including cormorants, kingfishers, egrets, herons, geese, mallards, grebes, green-winged teals, mergansers and other waterfowl. The Anacostia Watershed Society (AWS) reported that the 2020 lake draining exposed hundreds of native eastern floater mussels larger than those in the tidal Anacostia River, indicating good nutrition.
Greenbelt’s environmental coordinator Kevin Carpenter-Driscoll said the city cares for the lake by supporting the natural ecosystem without unduly disturbing it. Examples include removing invasive plants (water chestnut) and adding native plants (arrow arum, lizardtail). Greenbelt worked with the Prince George’s County Department of Environment and the Clean Water Partnership to dredge sediment from the two forebays (near Braden Field and Lakecrest Drive), but does not dredge the lake, which would disturb plants and animals and any natural succession toward marshland. Carpenter-Driscoll said the city accepts gradual encroachment of marsh conditions over coming generations, because the alternative is losing the wildlife. He said, “The lake wants to become what it wants to become.”
What Should Be Done?
Carpenter-Driscoll and AWS said that nutrients and plants are neither good nor bad and no mitigations are currently indicated. He said too many nutrients would be concerning because excess phosphorous and nitrogen from yard waste, pet waste and fertilizer can deplete oxygen for fish, encourage overgrowth and kill aquatic animals. But the forebays filter sediment and excess nutrients from stormwater, so cleaner water enters the lake. He doubts excess nutrient sources like sewage or heavy fertilization exist in Greenbelt, adding that Public Works doesn’t fertilize public property, instead believing that soil erosion and sediment have more impact, which the forebays mitigate.
Carpenter-Driscoll is considering water quality tests for 2023, to confirm acceptable water quality or any unexpected findings bearing investigation. Also, Greenbelt Recreation Director Greg Varda said a forthcoming Buddy Attick Park Master Plan will address water quality through minimizing impervious surfaces and landscaping and management practices sensitive to the natural environment, as well as erosion and sediment. Residents can manage yard and pet waste responsibly, minimize fertilizer and learn from recent tips published in the News Review (see Merits of an Untidy Fall Yard, November 17, page 12; Make Like a Tree and Leave, November 24, page 2).
Keep Calm and Carry On
The plants will vary over time and contribute to a diverse ecosystem, because nature organizes itself based on available species and environmental conditions, according to Greenbelter Peter May, assistant research professor in the University of Maryland’s Environmental Science and Technology Department. AWS natural resource specialist Jorge Montero concurred: “While people are annoyed by aquatic plants because of boating, they are great ecologically.”
Greenbelt Lake may become a marsh, like Jug Bay and Kenilworth Park. Impervious surfaces, climate-increased stormwater and lake temperature, soil erosion, pet waste and fertilizer may affect the lake, and woodlands, wetlands, rain gardens and forebays will filter sediment and excess nutrients. Greenbelters can let the lake continue to independently manage itself and take individual and community actions to support it, its plant and animal treasures, helping the Anacostia and Chesapeake Bay watersheds to remain productive and beautiful for wildlife and humans.