Modeling 150 years of anthrpogenic nitrogen loading to Narragansett Bay

Decisions about the management of nitrogen entering estuarine systems are best made in the context of a solid understanding of past inputs. The watershed of Narragansett Bay has a long history of intensive human exploitation, with consequences for the amount of nutrient loading to the bay. We present a model of N loading to the bay, based on 150 years of town-level data on population, sewer construction, animal agriculture, the use of commercial fertilizers, and land cover, as well as regional trends in atmospheric deposition. We validate our model results using modern and historic measurements of DIN flux for the three largest sub-watersheds within our study area.

Our model shows rapid increases in N during the late 19^th and early 20^th Centuries, with slower but seady increases throughout the 20^th Century. Total population is the most important driver of N loading watershed-wide, though historical trends in agriculture and the construction of sewers are of great importance in some parts of the watershed.