QUALITY MODEL VARIABLES TO ESTIMATE ATRAZINE LOADING IN MORGAN CREEK, MARYLAND

As part of an intensive study of agricultural watersheds being done by the U.S. Geological Survey (USGS) National Water-Quality Assessment (NAWQA) Program, a spatial analysis of landscape data was conducted at the Morgan Creek, Maryland (33 km2) Watershed. A geographic information system (GIS) was used to identify areas within this watershed that would most likely produce saturation-excess and infiltration-excess overland flow. These areas were further analyzed according to their flow-path distance to streams and used to estimate the potential delivery of atrazine to surface-water bodies. In the watershed, the corn fields, on which atrazine is applied, are likely to produce more infiltration-excess overland flow than saturation-excess overland flow. The highest TWI values are located in high clay soils near the stream. This approach will be applied to multiple NAWQA agricultural watersheds throughout the country to estimate in-stream atrazine concentrations