How are the phosphorus levels
in Lake Champlain changing?
Phosphorus concentrations have not decreased significantly in any areas of Lake Champlain, despite reductions in the amount of phosphorus entering the Lake from several of its tributaries. Long-term trends since 1990 indicate that phosphorus concentrations in several segments continue to increase.
Phosphorus is a nutrient that, when overabundant, has a significant impact on a lake ecosystem. This has become a problem for lakes large and small around the world, and Lake Champlain is no exception. Warmer waters are often more productive than cooler waters, supporting more plant and algae growth, including the blue-green algae that thrive on phosphorus. Consequently, shallow, warm bays in Lake Champlain are especially susceptible to problems with excess phosphorus compared to the Main Lake area, which is cold and deep, and has a relatively moderate concentration of phosphorus.
Long-term phosphorus concentrations continue to increase in the Port Henry area of the Main Lake as well as the Inland Sea (Northeast Arm), and in several bays, including Missisquoi Bay, St. Albans Bay, Shelburne Bay, and Malletts Bay (Figure 3). Phosphorus concentrations are more stable, though slightly increasing, in the Main Lake. There are no statistically significant trends in the South Lake, Otter Creek segment, Burlington Bay, or Cumberland Bay. Phosphorus concentrations are lowest in the Main Lake and in Malletts Bay, which together comprise nearly 68% of the total volume of the Lake. Concentrations are greatest at the extreme ends of the Lake, in Missisquoi Bay and South Lake, comprising, respectively, 0.8% and 0.6% of the total volume of the Lake.
Most lake management efforts are focused on phosphorus, but other nutrients, such as nitrogen, also affect water quality in Lake Champlain. Recent research, both in the Lake Champlain region and globally, has investigated the connections among phosphorus, nitrogen, and climate change impacts, such as warming surface waters, on water quality. These changes in water chemistry and temperature affect the biological integrity of the Lake, the number of species of fish, plants, and other organisms, and also can trigger harmful algae blooms (see the Human Health and Toxins section for additional information). Although excess phosphorus is a driver of blue-green algae blooms, nitrogen may affect which blooms become toxic.
The Total Maximum Daily Load (TMDL) is an important management tool that can help resource agencies determine where to focus their management efforts. TMDL is a calculation of the loading capacity—or the maximum amount of a pollutant that a body of water can be expected to handle each day, while safely meeting established water quality standards. The US Environmental Protection Agency (US EPA) is required by the Clean Water Act to use this tool for many different pollutants. In the Lake Champlain Basin, TMDLs have been developed most frequently for pathogens such as the bacteria E. coli or for nutrient pollution, and also for mercury, temperature, and sediments.
The US EPA is currently developing a new phosphorus TMDL for the Vermont portion of Lake Champlain. This will update Vermont’s responsibilities under the original 2002 bi-state Lake Champlain phosphorus TMDL. The New York portion of that earlier TMDL remains in effect. The new phosphorus TMDL for Vermont will be far more comprehensive, accounting for both historic and future climate patterns in the region to project how changes in temperature and precipitation will affect the amount of phosphorus entering Lake Champlain. The new TMDL implementation plan will produce and enforce new Required Management Practices (RMPs) and other tools that farms, other businesses, residents, and communities must use to reduce pollution to the Lake.