Date of Award

1996

Degree Type

Thesis

Degree Name

Master of Arts in Marine Affairs

Abstract

Calculations and measurements of nitrogen in groundwater, stream flow and atmospheric deposition were used to see if the cumulative impacts of management decisions over a fifteen year period of time resulted in measurable changes in nitrogen loading to six of the salt ponds on the south shore of Rhode Island. The changes in the source and transmission of nitrogen were tested by comparing calculated and measured nitrogen data from 1980 and 1995. The calculated method included a nitrogen budget based on land-use and literature values for nitrogen loss to groundwater. The second method compared concentrations of nitrogen in groundwater taken from 111 private homeowner wells in 1980 and 1994. The Paired Student test was used to test for statistically significant differences. Stream flux from 1980 was compared to data collected in 1994-95 from three streams and the Saugatucket River. Atmospheric deposition of nitrogen is based on 1980 measurements from the University of Rhode Island, Graduate School of Oceanography and Fraher (1991). National averages of nitrogen concentrations in overland runoff were compared to 1980 measurements of runoff in the salt pond region to see if they could be used to estimate nitrogen loading in 1995. Nitrogen loading increases are evident in the calculated budget, measured groundwater concentrations, stream flux, and atmospheric deposition. Septic systems were the major groundwater source of nitrogen to each of the salt ponds in 1992 and are projected to be a major source when the watersheds are fully developed. Calculations of nitrogen loading at buildout from residential land-use may be underestimated because building variances and grandfathering of substandard lots which are not currently accounted for in the loading budgets. There were no significant differences between the 1980 and 1994 groundwater concentrations of nitrogen. Atmospheric deposition of nitrogen has increased between 1980 and 1990 for wet deposition of nitrogen. A comparison of different methods of calculating or measuring over-land runoff indicates that national concentrations are considerably higher than measured concentrations in southern Rhode Island.