Nitrogen, Copper from Choptank River Pollute Chesapeake Bay

WASHINGTON, DC, August 20, 2010 (ENS) – An in-depth study of pollutants in a large river that flows into Chesapeake Bay has revealed “troublesome” levels of nitrogen and copper, says a team headed by U.S. Department of Agriculture scientists.

Scientists with the USDA’s Agricultural Research Service conducted the study in the watershed of Maryland’s Choptank River, a major tributary of the Chesapeake Bay on the Delmarva Peninsula.

Greg McCarty, a soil scientist with the ARS Hydrology and Remote Sensing Laboratory and Laura McConnell, a chemist at the ARS Environmental Management and Byproducts Utilization Laboratory, led the Choptank project from their base in Beltsville, Maryland.

The Choptank River at Denton, Maryland (Photo by AMK1211)

Sampling the water every two months for three years, the scientists found that nitrate concentrations often exceeded levels that can cause algal blooms.

Nitrate concentrations were highest at the headwaters where farming is concentrated, suggesting that agricultural fertilizers, including manure and poultry litter, are primary sources.

After studying nutrient and herbicide flows from 15 subwatersheds, McCarty says, “We have discovered that watersheds with more forests or wetlands export less nitrate to the river.”

Forests and wetlands naturally slow the movement of water on the land, allowing nature to process nitrates.

“This area of the bay has historically been drained by ditches, which short-circuit these natural filters within the landscape,” McCarty says. “Farmers can use drainage-control strategies to slow the movement of water from their fields, thereby restoring some of the filtering capacity of the land. A combination of riparian buffers, wetlands, and controlled drainage management are needed to mitigate nutrient pollution.”

Phosphorus concentrations were similar throughout the river, suggesting multiple sources for this polluting nutrient, the researchers found. While some evidence points to wastewater treatment plants as a likely primary source, agriculture is also a major contributor to the phosphorus pollution.

Nitrates are a concern, because in high quantities they cause human health problems. Both nitrates and phosphorus contribute to the growth of harmful algae blooms.

High copper concentrations were found in almost all samples at the lower reaches of the Choptank, but not in the upstream areas.

“This suggests that copper loss from antifouling boat paint is the primary source of the copper, rather than agriculture,” says Dean Hively, a visiting physical scientist from the USGS Eastern Geographic Science Center. “The levels were high enough to be toxic to clams and other aquatic invertebrates that help feed and filter the bay.”

Herbicides and their byproducts were present year-round. Concentrations did not approach established levels of concern for aquatic organisms. Still, the scientists say, this research shows the importance of agricultural practices that reduce herbicide losses, particularly from springtime applications.

McCarty says the overall goal of the Choptank research is to “develop a set of measurement and modeling tools for assessing the effectiveness of commonly used conservation practices at a watershed scale. “We use remote-sensing techniques to broaden measurements of the effectiveness of practices from one field to the entire watershed.”

The results of this study were published in the journal “Science of the Total Environment.”

The study was done as part of the Conservation Effects Assessment Project, CEAP. Since it started in 2004, CEAP has investigated the effects of conservation practices and Farm Bill conservation programs on 37 watersheds nationwide.

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