MODELING THE EFFECTS OF CONSERVATION TILLAGE ON SEDIMENT AND NUTRIENT LOADING IN THE MAUMEE RIVER

A hydrologic model of the Maumee River basin in NW Ohio was constructed to determine the relative effects of different drivers (weather, tillage practices, crop planting) on sediment and nutrient flow in the river.

The Maumee River watershed is the largest in the Great Lakes region, draining an area over 16,000km². Though it only contributes a small percentage of the water into the Western Basin of Lake Erie, it contributes by far the largest volume of sediment. The area, previously known as the Great Black Swamp, was drained and clear cut for agricultural development in the 19^th century. Today around 80% of the watershed is agricultural land usage. The rich organic soil contributes excessive sediment /nutrient loading within the western basin of Lake Erie, contributing to excessive algal blooms.

Conservation tillage was introduced in the 1980’s as a means of reducing these sediment/nutrient loads. Recent years have seen reduced sediment yields within the Maumee River, however phosphate concentrations have risen after over the same time period. In addition, phosphate peaks are occurring during the late summer months where there were none before. These later summer inputs of phosphate may contribute to increased blooms of a potentially harmful algae, Microcystis.

Hydrological modeling was performed using ArcSWAT. A calibrated model was developed using 1992 land use practices, hydrograph sediment and nutrient data from the Waterville, OH USGS gauging station. This model was the used to test the hypothesis that the implementation of conservation tillage could explain both the overall reduction in sediment and increase phosphate peaks in the later summer months. Scenarios were run for 1980-2009 using historical weather data, varying tillage, crop percentages and fertilizer application. It was found that historical weather patterns alone were sufficient to explain the increase in late summer phosphate peaks; weather and conservation tillage explained the overall reduction in sediment load; the area of corn row crops best explained the increase in phosphate. The finding that late summer storms are an important factor in late season phosphate delivery has implications for how the western basin responds to predicted climate change.