Research ProjectRiparian Buffers

Nutrient and sediment trapping by stream side forests and wetlands

aerial view of streams with and without riparian buffers

Well-developed riparian forests (green arrows) outline streams and help protect stream water quality. More pollution from cropland reaches streams where riparian buffers are missing (white arrows).

Project Goal

We study the ability of stream side forests and wetlands (“riparian buffers”) to remove pollutants in the water draining from farms and developed land. We want to understand where riparian buffers are present, which buffers actually trap pollutants, and how much of different pollutants they remove.


Field studies at SERC were among the first to demonstrate that stream side or riparian forests can trap sediments and nutrients draining from farm fields and keep them from entering streams, rivers, and estuaries like Chesapeake Bay.  Those studies sampled water as it left farm fields and moved through riparian buffers toward streams.  The amounts of nitrogen, phosphorus, and sediment all went down as the water moved downhill through a riparian buffer, so much of the pollutants that left the farm were gone when the water reached a stream.  That’s important because excess amounts of nutrients can cause ecological problems. For example, too much nitrogen leads to an overabundance of microscopic plant growth in the water. When those plants die and decay, they consume the oxygen that other organisms need to thrive.  Knowledge of these potential benefits of riparian forests has led to widespread efforts to restore riparian buffers throughout the United States.  Adding more riparian buffers is the solution most frequently proposed by land managers working to drop pollutant inputs to Chesapeake Bay below the levels needed to restore the bay.

Now we’re studying the effects of riparian buffers over much larger areas.  We use digital maps of land cover, topography, and streams together with measurements of nutrient levels in hundreds of streams.  We account for the placement of riparian buffers along the flow paths leading from croplands to streams, and then build statistical models that estimate nutrient loss from source areas, nutrient removal in riparian buffers, and nutrient delivery to streams.  We recently completed such an analysis for the nitrogen lost from croplands across the entire Chesapeake Bay watershed.  Now we’re working to test if better land cover maps and better information on the underground environment can improve our understanding of nutrient removal in riparian buffers.

Scientific Papers--Spatial Analysis and Modeling

Xia, Yongqiu, Weller, Donald E., Williams, Meghan N., Jordan, Thomas E. and Yan, Xiaoyuan. 2016. Using Bayesian hierarchical models to better understand nitrate sources and sinks in agricultural watershedsWater research, 105: 527-539. doi:10.1016/j.watres.2016.09.033

Weller, Donald E. and Baker, Matthew E. 2014. Cropland riparian buffers throughout Chesapeake Bay Watershed: Spatial patterns and effects on nitrate loads delivered to streams. JAWRA Journal of the American Water Resources Association, 50(3): 696-712. doi:10.1111/jawr.12207 

Weller, Donald E., Baker, Matthew and Jordan, Thomas E. 2011. Effects of riparian buffers on nitrate concentrations in watershed discharges: new models and management implications. Ecological Applications, 21: 1679-1695. doi:10.1890/10-0789.1

Baker, M. E., Weller, Donald E. and Jordan, Thomas E. 2007. Effects of stream map resolution on measures of riparian buffer distribution and nutrient retention potential. Landscape Ecology, 22: 973-992. doi:10.1007/s10980-007-9080-z

Baker, M. E., Weller, Donald E. and Jordan, Thomas E. 2006. Improved methods for quantifying potential nutrient interception by riparian buffers. Landscape Ecology, 21: 1327-1345. doi:10.1007/s10980-006-0020-0

Weller, Donald E., Jordan, Thomas E. and Correll, David L. 1998. Heuristic models for material discharge from landscapes with riparian buffers. Ecological Applications, 8(4): 1156-1169.

Scientific Papers--Field Studies and Syntheses

Jordan, Thomas E., Weller, Donald E. and Correll, David L. 1998. Denitrification in surface soils of a riparian forest: effects of water, nitrate and sucrose additions. Soil Biology and Biochemistry, 30(7): 833-843.

Correll, David L., Jordan, Thomas E. and Weller, Donald E. 1997. Failure of agricultural riparian buffers to protect surface waters from groundwater nitrate contamination. In: Gibert, J., Mathieu, J. and Fournier, F., Groundwater/surface water ecotones: Biological and hydrological interactions and management options. Cambridge, UK: Cambridge University Press,(International Hydrology Series) pp.162-165.

Lowrance, Richard, Altier, Lee S., Newbold, J. Denis, Schnabel, Ronald R., Groffman, Peter M., Denver, Judith M., Correll, David L., Gilliam, J. Wendell and Robinson, James L. 1997. Water quality functions of riparian forest buffers in Chesapeake Bay watersheds. Environmental management, 21(5): 687-712.

Lowrance, Richard, Altier, Lee S., Newbold, J. Denis, Schnabel, Ronald R., Groffman, Peter M., Denver, Judith M., Correll, David L., Gilliam, J. Wendell, Robinson, James L., Brinsfield, Russell B., Staver, Kenneth W., Lucas, William and Todd, Albert H. 1995. Water quality functions of riparian forest buffer systems in the Chesapeake Bay Watershed: a report of the Nutrient Subcommittee of the Chesapeake Bay Program. EPA 903-R-95-004, CBP/TRS 134/95. Annapolis, MD: U. S. Environmental Protection Agency,

Correll, David L., Jordan, Thomas E. and Weller, Donald E. 1994. Coastal plain riparian forests: Their role in filtering agricultural drainage. In: Kuster, J. A. and Lassonde, C., Altered, artificial, and managed wetlands. Focus: agriculture and forestry. Berne, NY: Association of State Wetland Managers, pp.67-72.

Weller, Donald E., Correll, David L. and Jordan, Thomas E. 1994. Denitrification in riparian forests receiving agricultural discharges. In: Mitsch, W. J., Global Wetlands: Old World and New. New York: Elsevier Press, pp.117-131.

Jordan, Thomas E., Correll, David L. and Weller, Donald E. 1993. Nutrient interception by a riparian forest receiving inputs from adjacent cropland. Journal of Environmental Quality, 22(3): 467-473.

Correll, David L. and Weller, Donald E. 1989. Factors limiting processes in freshwater wetlands: An agricultural primary stream riparian forest. In: Sharitz, R. R. and Gibbons, J. W., Freshwater Wetlands and Wildlife. Oak Ridge, TN: U.S. Department of Energy, Office of Scientific and Technical Information, pp.9-23.

Peterjohn, William T. and Correll, David L. 1986. Effect of riparian forest on the volume and chemical composition of baseflow in an agricultural watershed. In: Correll, David L., Watershed Research Perspectives. Washington, DC: Smithsonian Institution Press, pp.244-262.

Peterjohn, William T. and Correll, David L. 1984. Nutrient dynamics in an agricultural watershed: Observations on the role of a riparian forest. Ecology, 65(5): 1466-1475.