| Over a century of intensive agricultural development and wetland drainage have altered the Minnesota River Basin (MRB), resulting in hydrologically unstable streams and polluted water bodies. This study focused on two aspects of streamflow regimes related to land use changes in the MRB: (1) the historical impacts of drainage and associated agricultural practices on the hydrologic regime of two tributary watersheds (Lesueur and Cottonwood) having different drainage densities, and (2) the response to conversions from corn to perennial vegetation and wetland restoration on portions of the Cottonwood watershed as simulated using the Hydrologic Simulation Program-FORTRAN (HSPF) model. Long term trend analysis of stormflow runoff, baseflow, and 7-day low flow indicates an overall increase over the period 1939-2002. Double-mass curve analysis suggests that baseflow and 7-day low flow were higher in the Lesueur than in the Cottonwood. HSPF simulations indicated that conversions from annual corn crops to hybrid poplar and restored wetlands on wet soils reduced annual water yield, peak flows for small storm events, baseflows, and 7-day low flows. The results of this study suggest that converting wet soil areas to perennial woody crops and wetlands in the MRB can potentially improve hydrologic conditions, stream channel stability and water quality. |
