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Title: Refinement of a comprehensive watershed water quality model with application to the Chesapeake Bay Watershed
Authors: United States. Environmental Protection Agency. Chesapeake Bay Program Office
AQUA TERRA Consultants
Donigian, Anthony S.
Bicknell, B. R.
Chinnaswamy, Radha V.
Deliman, Patrick N.
Keywords: Modeling
Water quality
Chesapeake Bay (Md. and Va.)
Publisher: U. S. Army Engineer Waterways Experiment Station, Environmental Laboratory
Engineer Research and Development Center (U.S.)
Series/Report no.: Technical report (U.S. Army Engineer Waterways Experiment Station) ; EL-98-6.
Description: Technical report
Abstract: The focus of this research work was to improve the overall utility of the Chesapeake Bay Watershed Model, based on the U.S. Environmental Protection Agency Hydrologic Simulation Program - Fortran (HSPF) model, as a planning tool for comprehensive watershed planning and assessment. The specific improvements recommended and tasks performed in this effort included refinement of the agricultural (AGCHEM) module simulation to better represent plant uptake impacts of agricultural practices and nutrient management scenarios, testing the AGCHEM refinements, applying the refined AGCHEM to selected subbasins of the Chesapeake Bay drainage, and recalibrating the refined Watershed Model to the selected subbasins. The addition of a yield-based plant uptake option in the AGCHEM module of HSPF, derived from Nitrate Leaching and Economic Analysis Package uptake formulation, provides an improved algorithm for representing the plant uptake component of nutrient balances for agricultural croplands. The new algorithm allows for direct consideration of expected plant yields for both N and P, seasonal distribution of uptake rates and multiple cropping periods, N fixation by leguminous plants, and stress conditions related to available nutrient levels and moisture conditions. Testing of the algorithms shows that it is sensitive to the available plant nutrients in the soil layers and to the target levels defined by the user corresponding to expected crop yields. Furthermore, decreased application rates will allow uptake levels to remain unchanged only if the plant-available nutrients are sufficient to meet crop needs. This has important implications for agricultural Best Management Practices that include nutrient reduction components. The overall Watershed Model recalibration results show a significant improvement from earlier efforts with improved seasonal variation and tracking of observed nutrient concentration values. However, problems still remain for selected constituents and subbasin sites, and further "fine tuning" of the calibration is recommended along with more detailed investigations into the instream algal and benthic simulation. Demonstration simulations of alternative nutrient reduction scenarios have shown that the Watershed Model with the refined AGCHEM plant uptake routines provides a reasonable representation of nutrient balances at the watershed scale for evaluation of management options for nutrient reduction objectives.
Rights: Approved for public release; distribution is unlimited.
Appears in Collections:Technical Report

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