CLIMATE AND CULTURAL IMPACTS ON WATER FLOW IN THE MAUMEE RIVER, OH

The Maumee River watershed, the largest in the Great Lakes region, drains an area over 16,000 km², and discharges to the Western Basin (WB) of Lake Erie. Current land use is approximately 70% agricultural, runoff from which has led to excess sediment/nutrient loading in the WB. The timing and concentration of nutrients, particularly phosphates is linked to harmful cyanobacterial algal blooms (HABs), which can produce harmful toxins. As in many Great Lakes watersheds, climatic and anthropogenic drivers have modified discharge volume and nutrient loads over the past century which causes changes in water, sediment, and nutrient flux and impacts the water quality of the WB, which supplies drinking water for Toledo, OH.

To differentiate climate (temperature, precipitation) changes from anthropogenic drivers (land use change, tillage/fertilizing practices), a SWAT hydrological model of the Maumee River watershed was used to test the effects of varying these parameters. A 20-year model was calibrated using data from the Waterville, OH USGS gauging station. The model tested the effects of tillage practices and climate variation on sediment concentrations. Sediment concentration was used as a proxy for key nutrient delivery as it correlates highly with phosphates.

One notable trend in discharge in the past century (1920-2011) is the increase of high flow events in summer (Jul-Aug), which deliver nutrient pulses to the WB during preferred growing conditions of HABs. Trends in precipitation, not land use change, drives the shift to increased late summer peak flows.

Climate scenarios from the downscaled projections derived from the World Climate Research Programme's (WCRP's) Coupled Model Intercomparison Project phase 3 (CMIP3) multi-model dataset were used as inputs to the model. Simulation results from 1975-2009 were validated against the USGS gauging station at Waterville, OH. Model results for A1B, A2 and B1 climate scenarios show an increase in annual flow in the river, consistent with trends for the past century, but a decrease in total summer flow during the next half century. Increased high flow events coupled with decreased total flow in the same months would indicate that these peak flow events will be significant late summer sources for nutrient delivery and will influence the prevalence of HABs in the WB of Lake Erie.