Climate and Land Use Changes Impact on Nitrogen Concentrations and Nitrogen Loads in the Minnesota River.

Nitrogen from agricultural lands in the Midwestern United States is ending up in the Gulf of Mexico where it is resulting in hypoxic condition; affecting the fisheries and economy of the region. This study assessed the role of climate and land use changes on streamflow, baseflow (1935-2015), flow weighted N concentrations and N loads (1963-1998) in the Minnesota River at Jordan at the annual and monthly scales. This analysis was done as a step-wise regression using R Statistical package. The land use effects were simulated using the soybean area in the watershed as a surrogate. Annual analysis showed that streamflow, baseflow and N loads are controlled by precipitation of the current and past years and by current year soybean area. Past year precipitation reflects the water storage term of the water balance equation. It shows that the past year’s precipitation contributes to current year baseflow as well as changes in runoff and percolation losses and thus N loads. Monthly analysis showed that besides the current and previous months’ precipitations, previous year’s precipitation and soybean area were also significant variables in explaining monthly stream flow, baseflow, and N loads. There was limited to no effect of these variables in explaining flow weighted N concentrations. 𝑅2 values ranged from 0.32 to 0.89, suggesting that up to 89% of the variability in the dependent variables can be explained by precipitation and soybean area. Regression analysis without soybean area showed that soybean area explained 4 to 20 % of the variability in N loads.