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Spatial and temporal controls on nutrient fluxes across a mixed-use watershed in north-central Ohio
  • Ozeas Costa
Ozeas Costa
The Ohio State University

Corresponding Author:[email protected]

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Over the last century, runoff from farms and cities, along with land cover and land use changes, have drastically altered the mass balance of nutrients in aquatic systems, affecting both their ecological functioning and the living communities they support. Here we present the results of a multi-year, long-term study designed to assess the control of land-use and hydrology on nutrient fate and transport within a mixed land-use watershed in north-central Ohio. A total of 64 streams (with a mix of urban, cropland, pasture, and forest catchments) have been sampled periodically since the summer of 2008. Hydrological conditions during the study period exhibited marked seasonality, with usually dry winter seasons (average ppt: 23.5±7.4 cm) and wet spring seasons (average ppt: 34.5±8.1 cm). Runoff generation in response to precipitation events is faster in streams draining developed catchments and slowest in forested streams, where runoff is generated only by events > 10 mm/day. Hydrologic connectivity in the watershed appear to be limited, since only about 25% of precipitation inputs were translated into quick flow. There is a significant, positive correlation between runoff and nutrient concentrations (R2 values are: 0.40 for streams draining urban landscapes, 0.34 for forested streams, 0.30 for cropland, and 0.28 for pastureland). We also observed significant inter-annual and seasonal variations on both DIN (p = 0.02) and PO4 concentrations (p < 0.01). Compared to dry years, nutrient fluxes during wetter years are, on average, 16% higher in urban catchments and 47% higher in forested catchments, but 32% lower in pasture-dominated catchments. Baseflow is responsible for only between 20-30% of the annual nutrient export from the watershed.