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Gassman, Philip W.

The state of Iowa requires developing total maximum daily loads (TMDLs) for over 400 water bodies that are listed on the 303(d) list of the impaired waters. The Raccoon River watershed, which covers approximately 9400 km2 of prime agriculture land and represents a typical Midwestern corn-belt region in west-central Iowa, was found to have three stream segments impaired by nitrate-N. The Soil and Water Assessment Tool (SWAT) was applied to this watershed to facilitate the development of a TMDL. The modeling framework integrates SWAT with supporting software and databases on topography, land use and management, soil, and weather information. Annual and monthly simulated and measured streamflow and nitrate loads were...
Growing demand for corn due to the expansion of ethanol has increased concerns that environmentally sensitive lands retired from agricultural production and enrolled into the Conservation Reserve Program (CRP) will be cropped again. Iowa produces more ethanol than any other state in the United States, and it also produces the most corn. Thus, an examination of the impacts of higher crop prices on CRP land in Iowa can give insight into what we might expect nationally in the years ahead if crop prices remain high. We construct CRP land supply curves for various corn prices and then estimate the environmental impacts of cropping CRP land through the Environmental Policy Integrated Climate (EPIC) model. EPIC provides...
A number of structural and managerial practices were evaluated to determine their environmental and economic effectiveness on animal feeding operations in the upper Maquoketa river watershed in northeast Iowa. Economic and environmental model simulations were performed over a 30-year time horizon for each of these practices using extensive data collected from the study area. Results from model simulations indicate that while most of the practices (including terraces, no till farming, contouring, and in-field contour buffers) would reduce sediment and sediment-bound nutrient losses significantly, they have very little benefit on soluble nitrogen and phosphorus losses. This is primarily because the increased infiltration...
ABSTRACT: The Soil and Water Assessment Tool (SWAT) model was used to assess the effects of potential future climate change on the hydrology of the Upper Mississippi River Basin (UMRB). Calibration and validation of SWAT were performed using monthly stream flows for 1968–1987 and 1988–1997, respectively. The R2 and Nash-Sutcliffe simulation efficiency values computed for the monthly comparisons were 0.74 and 0.69 for the calibration period and 0.82 and 0.81 for the validation period. The effects of nine 30-year (1968 to 1997) sensitivity runs and six climate change scenarios were then analyzed, relative to a scenario baseline. A doubling of atmospheric CO2 to 660 ppmv (while holding other climate variables constant)...
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