Hector Arbuckle, Iowa State University

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Abstract:

Calvert County, Maryland is a peninsula of land bounded by the Patuxent River on one side and by the mainstem of the Chesapeake Bay on the other. Its shores are punctuated by shallow, tidal estuaries referred to locally as tidal creeks. Over the past decade, a monitoring program has studied eleven of these creeks and found symptoms of eutrophication affecting water quality. In the Chesapeake Bay, eutrophication is a complex phenomenon but is associated with increased nitrogen loading caused by land use change and septic system leakage. Our study set out to determine the land use makeup of these eleven watersheds, and to calculate the land use and septic inputs of nitrogen to these watersheds. We used land use raster data from 2013-14 to determine the land use makeup by sector, and downscaled from the CAST model to determine nitrogen inputs. Overall, natural land occupies 65% of the combined area of the watersheds and is responsible for 15% of nitrogen load; the respective figures for developed land are 22% and 35%; for agricultural land, 10% and 27%; and for open water, 3% and 4%. Septics contribute 19% of nitrogen load. Average nitrogen yields are 13.15 lbs/ac/yr from agricultural land, 7.65 lbs/acre/year from developed land, 1.12 lbs/acre/year from natural land, and 6.71 lbs/acre/year from open water. We conclude that nitrogen loads are driven by anthropogenic activities. Reducing atmospheric nitrogen emissions, protecting and restoring natural land, altering dominant patterns of developed land use, reducing yields from agriculture, and upgrading septic systems are all possible steps to decrease nitrogen load and potentially ameliorate eutrophication in these creeks.