Swat modeling of sediment, nutrients and pesticides in the Le-Sueur River watershed, south-central Minnesota.

Abstract

The Le Sueur River Watershed (LRW) of South-Central Minnesota drains 2,850 km² in the Minnesota River Basin. The watershed has an annual discharge of 230 mm and generates significant sediment and chemical pollution. The objective of this study was to quantify the spatial and temporal patterns of sediment, nutrient (nitrate-nitrogen, phosphorus) and pesticide (atrazine, acetochlor and metolachlor) losses from the LRW using the Soil and Water Assessment Tool (SWAT) model. The SWAT model was calibrated and validated from 2000-2006 in the Beauford sub-watershed. The calibrated model was applied to the entire LRW mainly to identify critical pollutant contributing areas and to evaluate effectiveness of alternative best management practices to reduce the loadings. The study has five major parts. The first part deals with hydrologic simulation. The second part identifies the relative contribution of upland and channel sediment sources. The third part deals with water quality impacts of land use and management alternatives on phosphorus and nitrogen losses to the LRW. The fourth part deals with pesticide losses. The fifth part deals with impacts of various biofuel production options on water quality. The LRW has estimated annual loadings of 1.0 kg TP/ha, 18 kg NO3-N/ha and 302,000 t/yr of sediment that contribute to water quality impairments in Lake Pepin and the Mississippi River. Alternative management practices are predicted to reduce upland sediment yield by up to 54%, nitrate-N losses by 22%, and phosphorus loadings by 64%. Overall, the SWAT model was able to accurately simulate the hydrology and transport of chemical pollutants under the land use systems, climate, hydrologic and physiographic settings of South-Central Minnesota.