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Nitrogen Inputs to Seventy-four Southern New England Estuaries: Application of a Watershed Nitrogen Loading Model
Citation:
LATIMER, J. S. AND M. Charpentier. Nitrogen Inputs to Seventy-four Southern New England Estuaries: Application of a Watershed Nitrogen Loading Model. ESTUARINE, COASTAL AND SHELF SCIENCE. Elsevier Science Ltd, New York, NY, 89(2):125-136, (2010).
Impact/Purpose:
Excess nitrogen input to coastal aquatic resources of the United States is a problem of broad national significance. National, regional and local environmental managers are in the process of developing methods and models that will aid in the determination of how much nitrogen is too much for estuaries. This study provides a method for these managers to estimate nitrogen loading rates for estuaries. The paper describes the application of a validated watershed nitrogen loading model to small-to-medium size estuaries in New England. Results show that nitrogen loading rates vary considerably for estuaries along the New England coastline. The loading model, together with the results of its application, can be used to construct empirical stressor-response models useful in determining critical nitrogen loading limits to protect estuaries from the effects of cultural eutrophication.
Description:
Excess nitrogen inputs to estuaries have been linked to deteriorating water quality and habitat conditions which in turn have direct and indirect impacts on both commercial and recreational fish and shellfish. This paper is the first of a two-part series that applies a previously published watershed nitrogen loading model to estimate the nitrogen loading rate to small-to-medium sized, shallow, embayment-type estuaries in southern New England. The companion paper will illustrate how eelgrass spatial extent changes with nitrogen inputs for a subset of estuaries. The study estuaries exhibited a significant gradient in nitrogen inputs. Loading rates were estimated from <50 to 3.7x10^5 kgN yr-1 which is a gradient range of a factor of over 7,000. On a volume normalized basis, loading rates were from <1 to 140 gN m-3 yr-1, and on an areal basis, from 24 to 3,300 kgN ha-1 yr-1. These represent a gradient of approximately a factor of 140. Therefore, all other factors being equal, the study design is sufficient to evaluate ecological effects, conceptually tied to excess nitrogen, along a pollution gradient. In addition to providing total dissolved nitrogen loading inputs rates to the study estuaries, the model provides an estimate of the relative magnitudes of the nitrogen sources to each estuary. Cumulative results of this analysis reveal the following source ranking: atmospheric deposition (combined, 53%), wastewater (36%) and fertilizer (12%). For any particular estuary the relative magnitudes of the source types vary dramatically.