We measured annual discharges of water, sediments, and nutrients from 10 watersheds with differing proportions of agricultural lands in the Piedmont physiographic province of the Chesapeake Bay drainage. Flow-weighted mean concentrations of total N, nitrate, and dissolved silicate in watershed discharges were correlated with the proportion of cropland in the watershed. In contrast, concentrations of P species did not correlate with cropland. Organic P and C correlated with the concentration of suspended particles, which differed among watersheds. Thus, the ratio of N:P:Si in discharges differed greatly among watersheds, potentially affecting N, P or Si limitation of phytoplankton growth in the receiving waters. Simple regression models of N discharge versus the percentage of cropland suggest that croplands discharge 29-42 kg N ha-1 yr1 and other lands discharge 1.2-5.8 kg N ha-1 yr-1. We estimated net anthropogenic input of N to croplands and other lands using county level data on agriculture and N deposition from the atmosphere. For most of the study watersheds, N discharge amounted to less than half of the net anthropogenic N.
CITATION STYLE
Jordan, T. E., Correll, D. L., & Weller, D. E. (1997). Nonpoint source discharges of nutrients from piedmont watersheds of Chesapeake Bay. Journal of the American Water Resources Association, 33(3), 631–645. https://doi.org/10.1111/j.1752-1688.1997.tb03538.x
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