Need to Better Understand Phosphorus Concentrations in Lake Champlain Watershed Sparks Study of Winooski River

The U.S. Geological Survey (USGS), in collaboration with the University of Vermont and the U.S. Department of Agriculture, Natural Resources Conservation Service in Vermont, completed a study to understand the distribution of phosphorus in the sediments of the Winooski River, a tributary watershed to Lake Champlain. The results will help evaluate the effectiveness of phosphorus-reduction policies implemented by the State. The Winooski River was selected because it has the largest watershed draining into Lake Champlain, has the largest population, and contributes the second largest amount of phosphorus to the Lake. The results of the study are available in a recently released report.

An estimated four-fold increase in the amount of phosphorus entering Lake Champlain since the early 19th century has resulted in accelerated algal and plant growth in the Lake. Human activities, such as urban and industrial wastewater discharges, and urban and agricultural runoff are responsible for the increase. As the result of the Clean Water Act of 1972, the banning of phosphate detergents, controls on agricultural runoff, and the building of phosphorus-removal capabilities at wastewater treatment plants have helped decrease the amount of phosphorus entering the Lake.

In 1993, however, a Lake Champlain Water-Quality Agreement for higher standards was implemented by the States of Vermont and New York and the province of Quebec, Canada. This agreement required an additional decrease in the amount of phosphorus entering the Lake. “An understanding of the distribution of phosphorus in river-bottom sediment, and the relation between land use, soil type, slope, and stream flow in a contributing watershed, will help policy and planning efforts determine the best way to reduce the amount of phosphorus entering Lake Champlain,” said Ann Chalmers, the principal USGS hydrologist of the project. “Concentrations of phosphorus in river-bottom sediments were 20 percent higher in urban and agricultural areas than in forested areas. Also, the concentrations of phosphorus in river-bottom sediments increased from the headwaters of the Winooski River Basin to the outlet on the shore of Lake Champlain,” said Chalmers.

River-bottom sediments composed of silt and clay contained 60 percent more phosphorus than sandy- bottom deposits. Silt and clay deposits, which are potential sites for the storage of phosphorus, were found in slow-moving or stationary water sites

Copies of the report are available for viewing in public town libraries and the university libraries in Vermont and can be obtained from the USGS at 361 Commerce Way, Pembroke, NH 03275. The report is distributed as Fact Sheet 108-98, titled “Distribution of Phosphorus in Bed Sediments of the Winooski River Watershed, Vermont, 1997.”

General Contact and ordering information: Debra Foster, at (603) 226-7837 or e-mail dhfoster@usgs.gov

Technical questions can be directed to Ann Chalmers at (802) 828-4511 or chalmers@usgs.gov.