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MODELING LONG-TERM NITRATE BASE-FLOW LOADING FROM TWO AGRICULTURAL WATERSHEDS
Citation:
Hantush*, M M. AND M. Wang. MODELING LONG-TERM NITRATE BASE-FLOW LOADING FROM TWO AGRICULTURAL WATERSHEDS. In Proceedings, 2003 AWRA Spring Specialty Conference Agricultural Hydrology and Water Quality, Kansas City, MO, May 12 - 14, 2003. American Water Resources Association, Middleburg, VA, CD, (2003).
Impact/Purpose:
information
Description:
Nitrate contamination of ground water from agricultural practices may be contributing to the eutrophication of the Chesapeake Bay, degrading water quality and aquatic habitats. Groundwater flow and nitrate transport and fate are modeled, using MODFLOW and MT3D computer models, in regional aquifers beneath two adjacent agricultural watersheds of the Chester River Basin, Maryland. Field evidence and geochemical analysis indicate the removal of nitrate by denitrification in a thin layer situated at the base of the surficial aquifer. The potential for denitrification in this layer may have impacted nitrate levels in the streams of the two watersheds, and is influenced by groundwater flow patterns, extent of the denitrifying layer below the watersheds, and the regional dip of the underlying strata. The groundwater flow model is calibrated and confirmed successfully. The lack of sufficient nitrate concentration and nitrogen input data, however, precluded a complete confirmation of the transport model. Model simulations predict a significant reduction in long-term nitrate loading from the two watersheds, due to denitrification in aquifer sediments and other riparian-instream nitrate removal processes. The results show the relative contribution of the different loss pathways on the potential reduction of long-term nitrate loading from each watershed. These findings may have an implication on the management of nutrients in the two watersheds.