Quantifying the Effects of Land Use On Water Quality At the Watershed Level Using N-SPECT.

Land use and water quality are linked in that poorly managed land can negatively impact receiving waters. Water quality sampling is one method to evaluate watershed condition but can be cost-prohibitive based on area or parameters being tested. The use of computer models allows for the assessment of environmental conditions from the field level to the regional scale for pollutants such as nitrogen (N), phosphorus (P), and total suspended solids (TSS). Having the ability to input site specific conditions allows for a more accurate simulation of existing and possible future conditions. The objective of the research was to use the Nonpoint Source Pollution and Erosion Comparison Tool (N-SPECT), developed by the National Oceanographic and Atmospheric Administration (NOAA) to quantify N, P and TSS  dynamics for the Sassafras River watershed.  N-SPECT requires readily-available digital data from certain internet websites that encompass land use, soils, elevation, and rainfall to be used in the simulations. The digital data requirements for analysis of the Sassafras River watershed in northeastern Maryland included land use/land cover from the NOAA’s Coastal Change Analysis Program, soils from the U.S. Department of Agriculture’s Soil Survey Geographic database (SSURGO), a precipitation grid file from Oregon State University, and a digital elevation model (DEM) from the U.S. Geological Survey. Outputs were GIS layers that provided both a graphical representation and quantitative evaluation of runoff and pollutants and included both accumulated and localized estimates of N, P, and TSS. Utilizing N-SPECT’s Management Scenario tool, land use changes were developed for both accumulated and localized runoff and N in a Sassafras River subwatershed. N-SPECT’s simulated values were consistent with expectations based on soil type, elevation, slope, and local land use conditions.