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Nitrate-nitrogen export from the Raccoon River watershed in west-central Iowa is among the highest in the United State and contributes to impairment of downstream water quality. We examined a rare long-term record of streamflow and nitrate concentration data (1972–2000) to evaluate annual and seasonal patterns of nitrate losses in streamflow and baseflow from the Raccoon River. Combining hydrograph separation with a load estimation program, we estimated that baseflow contributes approximately two-thirds (17.3 kg/ha) of the mean annual nitrate export (26.1 kg/ha). Baseflow transport was greatest in spring and late fall when baseflow contributed more than 80% of the total export. Herein we propose a ‘baseflow enrichment...
Increased irrigation in Kansas and other regions during the last several decades has caused serious water depletion, making the development of comprehensive strategies and tools to resolve such problems increasingly important. This paper makes the case for an intermediate complexity, quasi-distributed, comprehensive, large-watershed model, which falls between the fully distributed, physically based hydrological modeling system of the type of the SHE model and the lumped, conceptual rainfall-runoff modeling system of the type of the Stanford watershed model. This is achieved by integrating the quasi-distributed watershed model SWAT with the fully-distributed ground-water model MODFLOW. The advantage of this approach...
Summary There is convincing evidence that land use/land cover (LULC) change has contributed to increasing discharge in the Upper Mississippi River Basin (UMRB) but key details remain unresolved. In this study, we extend our previous work (Zhang and Schilling, 2006) to quantify how much of the increasing discharge was due to LULC change. We examined daily streamflow for the 1890–2003 period from the US Geological Survey stream gage at Keokuk, Iowa and compiled county agricultural statistics for soybean production in the watershed above the gage to quantify how much of the change in the relation of discharge to precipitation was due to increased soybean cultivation. By allowing the slope of the discharge–precipitation...