Decadal surface water quality trends under variable climate, land use, and hydrogeochemical setting in Iowa, USA

摘要: Understanding how nitrogen fluxes respond to changes in agriculture and climate is important for improving water quality. In the midwestern United States, expansion of corn cropping ethanol production led increasing N application rates 2000s during a period extreme variability annual precipitation. To examine effects these changes, surface quality was analyzed 10 major Iowa Rivers. Several decades concentration flow data were with statistical method that provides internally consistent estimates history reveals flow-normalized trends are independent year-to-year streamflow variations. Flow-normalized concentrations nitrate+nitrite-N decreased from 2000 2012 all basins. evaluate discharge loading on trends, multiple conceptual models developed calibrated flow-weighted concentrations. The recent declining can be attributed both very high low long (e.g., 8 year) subsurface residence times some Dilution depletion stored occurs years discharge. Reduced transport increased storage low-discharge years. Central basins showed greatest reduction concentrations, likely because smaller volumes shorter times. Effects land-use Rivers may not noticeable or peripheral Iowa, obscured central where flows strongly affect trends.