Bay Watch

Biologists have an ambitious goal for the Chesapeake Bay: adding 10,000 miles of forest buffers to keep the waters clean

You can tell the health of a body of water by the quality of the vegetation on its banks. If it’s lush, green, and plentiful, you can bet you have a healthy bay, pond, or river. Aside from serving as a home to wildlife—and a place to take a break on that canoe trip—these vegetative areas, called riparian forest buffers, are one of nature’s tools for cleaning water. These buffers slow storm water runoff from adjacent land, which means less nutrients, especially phosphorus and nitrogen from nearby farms, and less silt enter the waterways.

Located within the Chesapeake Bay watershed, George Mason University has long been home to a number of research studies aimed at improving the health of the bay and its tributaries. One of the latest efforts by Mason’s Environmental Science and Policy (ESP) Department is directly focused on a crucial goal of the Chesapeake Bay Program’s restoration effort: to significantly increase riparian forest buffers by 10,000 miles by 2010.

“Less nutrient load helps reduce the chance of algal blooms, which can negatively affect the level of dissolved oxygen in the water needed to maintain a rich and diverse population of aquatic organisms,” says John Wilder, MS Biology ’93 and PhD Environmental Science and Public Policy ’02, with the Engineer Research and Development Center, Topographic Engineering Center of the U.S. Army Corps of Engineers. “Slowing the overland storm water runoff also helps reduce the amount of sediment entering the waterways. Other pollutants are trapped by the buffer, helping to preserve the water quality of streams, rivers, and eventually the bay itself.”

“The reason why this project is important is that it provides actual baseline information on the extent and change in riparian buffer land use,” says Mason freshwater ecologist Chris Jones, principal investigator for the study. “Nobody really knew the extent of the current riparian forest, nor could they effectively track changes. Some people have tried to use satellite imagery for this purpose, but the resolution was too coarse to pick up the narrow bands of land adjoining streams.”

Wilder, an affiliate professor in ESP, came up with an approach that uses aerial photography and geographic information systems (GIS) to overcome this shortcoming. The use of aerial photography results in a higher-resolution image because the sensor is closer to the ground. “Because the buffer being analyzed is only 100 feet wide, the satellite imagery gives no margin of positional error,” says Wilder.

According to Wilder, if a pixel—and satellite pixels show 30 meters by 30 meters—shifts just a tiny amount from its true location, which happens throughout an image that has been stretched to a map projection, the cover of that spot is mischaracterized. Even more error is then introduced when change detection is attempted because it is impossible to perfectly align two images taken at different times. “By using high-resolution imagery and direct photo interpretation, we were able to substantially increase the accuracy of the analysis,” says Wilder.

The aerial photography approach was tested on selected watersheds in Maryland and Pennsylvania. Because of the success at these sites, the U.S. Forest Service commissioned the research team, which includes Mason graduate students trained by Wilder, to repeat the technique in several other locations.

The team recently finished work in Henrico, James City, and Spotsylvania counties in Virginia; Prince George’s County, Maryland; and Dauphin County, Pennsylvania, examining the effect of population growth on riparian forest cover. Aerial photo mosaics of these locations from 1993 to 1994 and 2002 to 2003 were analyzed to determine the change in areal coverage throughout a 100-foot-wide digital buffer zone.

Overall, during this period, riparian zone development increased in the five study sites by 8.5 percent, while the forest cover declined by 2.5 percent. The findings were presented at a Chesapeake Bay Program Forestry Workshop held in Annapolis.

“Quantifying the nature, magnitude, and spatial location of land use and land cover change in the forested riparian buffer zone is the first step in developing management strategies that can help to mitigate water quality problems,” says Wilder.