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United States Department of Agriculture

Agricultural Research Service

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Research Project: Conservation Effects Assessment Project (Ceap) 2014 - Agricultural Research Service Benchmark Watershed Assessment Studies (On Croplands)

Location: Hydrology and Remote Sensing Laboratory

Project Number: 1245-13610-028-76
Project Type: Interagency Reimbursable Agreement

Start Date: Apr 01, 2014
End Date: Sep 30, 2016

Objective:
The Hydrology and Remote Sensing Laboratory (HRSL) plans to develop improved monitoring technologies and new adaptive management tools for quantifying the water quality impacts of cover crops using validation data from the Choptank Watershed. In FY13, results were published on the use of an herbicide metabolite (MESA) as a reliable tracer of agricultural nitrate-N fate and transport in the Choptank River Watershed (McCarty et al. 2014). This work aids identification of critical areas in the Choptank River Watershed contributing to high nitrate concentrations in streams and aids the evaluation of BMPs for nitrate mitigation. We have installed two in situ optical sensors that can detect nitrate and dissolved organic carbon at the Greensboro and Tuckahoe State Park (Tuckahoe) USGS gauge stations. HRSL will now investigate the use of the Soil Water Assessment Tool (SWAT) model with different Digital Elevation Model (DEM) resolutions and choice of DEM source, to determine if their impact on sediment load prediction is significant.

Approach:
During FY14, an in situ phosphorus sensor at Tuckahoe will be installed. This sensor will provide detailed flux measurements of dissolved carbon and nutrients from two sub-basins within the Choptank River Watershed. Within the Choptank River estuary there is considerable temporal and spatial variation in nutrient concentrations, with agricultural production and urban water treatment plants as potential sources. A robust set of dissolved trace organics associated with these two potential sources can be used to develop correlations with dissolved nutrient concentrations, helping to identify the sources contributing the nutrient loads delivered to the estuary. ARS has demonstrated a robust agricultural tracer and is working towards developing a robust urban tracer for the Choptank estuary. HRSL is now extending the application of the SWAT model to larger basins within the Choptank watershed. The Choptank River, above the tidal line, is fed by two major tributaries--the Tuckahoe to the west and the Upper Choptank to the east, providing two adjacent sub-watersheds within the larger Choptank Watershed. Although both of these sub-watersheds are similar in size, monitoring data have shown different behavior in terms of nutrient export patterns. The aim of this investigation is to apply the SWAT model to each of the two sub-watersheds defined by the USGS gauge stations at Tuckahoe and Greensboro and then compare the model simulation results with respect to pollution load amounts and patterns. Model simulations under current planting and cover crop conditions a the two sub-watersheds will establish a baseline of nutrient load reduction effectiveness that will be compared to an extensive and long-term USGS monitoring station and the newly installed nutrient sensor at the outlet of exercise will provide a better understanding of the cause of the observed differences in nutrient losses from the two sub-watersheds and the effectiveness of different cover crop scenarios, in terms of implementation of crop cover species, planting dates, and location.

Last Modified: 9/23/2014
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