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Field and Watershed Scale N Modeling to Analyze Lag Time and BMP Effects in a Mid-Atlantic Coastal Plain Watershed

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Pp. 281-286 in Total Maximum Daily Load (TMDL) Environmental Regulations: Proceedings of the March 11-13, 2002 Conference, (Fort Worth, Texas, USA)  701P0102.(doi:10.13031/2013.7570)
Authors:   Sanjay Shukla and Saied Mostaghimi
Keywords:   Nitrogen, Baseflow, Groundwater, Atmospheric N Deposition, Nutrient Management

Long-term watershed and field nitrogen (N) balances were used in this study to quantify the surface (baseflow component only) and ground water lag times and effects of BMPs on N discharge from a Virginia Coastal Plain watershed. The baseflow lag time was equal to the ground water lag time plus the time required for the ground water to travel to the streams. Role of atmospheric N (atm-N) deposition was also investigated. Ten-year monitoring data collected in the watershed were used. Field (Field-N) and watershed (Watershed-N) scale N models were developed to simulate N balances and leaching. BMPs evaluated in this study included no-till corn and split N application (SNA). Atm-N deposition was a major source of N in the watershed, accounting for 23% of the total N input. Variations in atm-N deposition were larger than the fertilizer N. Comparison of Field-N results with observed ground water N revealed that the ground water lag time was 2-8 months. The unusually rapid transport of solute was facilitated by discontinuous clay lenses. Implementation of SNA reduced the post-BMP ground water NO3 concentration and detection frequency (> 9 mg/l) by as much as 12 and 44%, respectively. Watershed-N was able to accurately predict the effects of land use on watershed N balances (WNBAL) and baseflow and ground water N. Baseflow la g time was between 4 and 11 months. Post-BMP WNBAL was less than the WNBAL for the pre-BMP period. However, these reductions were mainly due to the 43% reductions in atm-N deposition and 31% increase in plant uptake due to better rainfall conditions. Reductions in WNBAL and N loading caused by BMPs were 5% and 10%, respectively.

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