Land use and climate impact on sediment and nutrient loads into Lake Ashtabula, North Dakota, USA

Lake Ashtabula continues to be listed as impaired water body by the USEPA due to excessive nutrients. A Soil and Water Assessment Tool (SWAT) model was developed for the Lake Ashtabula watershed to estimate the sediment and nutrient loads entering the lake under different land use and climate scenarios. Impacts of flows from the Devils Lake outlets flowing into the lake Ashtabula via Sheyenne River were also included. The study showed that biofuel cropland expansion and increases in precipitation would generate higher streamflow, sediment, and nutrient loads into Lake Ashtabula. However, decreases in precipitation would decrease sediment and total phosphorus loads, but not necessarily total nitrogen loads. Flow from Devils Lake had the most significant impacts on both streamflow and nutrient loads. This well-calibrated and validated watershed model can be used for developing nutrients and sediment Total Maximum Daily Load (TMDL) program for the Lake Ashtabula.