Waquoit Bay Watershed Ecological Risk Assessment: the Effect of Land-Derived Nitrogen Loads on Estuarine Eutrophication
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A nitrogen loading model (NLM) was used to estimate the amount and sources of nitrogen entering the watershed, and an estuarine loading model (ELM) was used to estimate the nitrogen available to producers in shallow estuaries. The NLM indicates that atmospheric deposition is the largest source of nitrogen, but because more atmospheric nitrogen than wastewater nitrogen is intercepted in the watershed, wastewater becomes the largest contributor of nitrogen reaching the bay. By comparing increases in nitrogen loads to losses in the area of eelgrass cover over the last 60 years, it appears that eelgrass disappears once nitrogen loads reach 20 kg/ha/yr. Both the increase in nitrogen load and the decrease in eelgrass can be correlated to decreases in the annual harvest of scallops. The models provide the opportunity for managers to assess a variety of options to reduce nitrogen loads to their estuaries and to achieve the loads that could allow the return of eelgrass to the target area.
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