Submitted to: Chesapeake Research Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: October 15, 2002
Publication Date: N/A
Technical Abstract: Construction and maintenance of effectively functioning riparian wetlands depend upon knowledge of processes within naturally occurring riparian zones. This study evaluated the impact of a riparian wetland on the export of agricultural contaminants. Three years of continuous stream and groundwater data have been collected, including real-time stream flows for five points along a first-order stream and information gathered from 170 piezometers located in the riparian zone. Stream flow is highly variable (both spatially and temporally) in this watershed, and a positive correlation between stream flows and stream nitrate-N concentrations has been established. Higher hydraulic heads within the subsurface yield higher concentrations of agricultural contaminants (NO3- and pesticides) in the emerging groundwater. Rapid groundwater exfiltration (primarily through subsurface preferential flowpaths) is responsible for most of the agrochemicals that appear in the surface water. One area of the floodplain, comprising 3.5% of the total riparian land area, contributes about 30% of total stream flow and about 40% of average stream nitrate load. The rates and extent of groundwater exfiltration to the surface increase under high moisture (and resultant high stream flow) conditions, leading to higher stream contaminant concentrations and fluxes. Although the biogeochemical characteristics of the surface soils in these areas are favorable for contaminant removal, their effectiveness is limited by hydrological conditions. The system as a whole removes more than 75% of the groundwater contaminants. A detailed understanding of groundwater-to-stream contaminant delivery mechanisms will help in establishing regulations for designing riparian buffers with better contaminant removal capabilities.