Date of Completion

5-10-2020

Embargo Period

5-6-2020

Advisors

Julie Granger, Craig Tobias, Claudia Koerting, Jamie Vaudrey

Field of Study

Oceanography

Degree

Master of Science

Open Access

Open Access

Abstract

Little Narraganset Bay has seen an increase in filamentous algae, colloquially known as cladophora, over the past twenty years. The Pawcatuck River is the dominant input of freshwater to Little Narraganset bay, delineating the Connecticut and Rhode Island border. There are three point sources of nitrogen on the river system: two waste water treatment facilities (WWTF) in the estuary and one fabric processing plant within the upper-watershed in Kenyon, RI. Non-point sources include a myriad of farms specializing in turf and animal husbandry, as well as septic systems for the majority of the watershed that are not serviced by the WWTFs. Prior research has produced yearly flux estimates of nitrogen (N) yet point to different anthropogenic sources including sewage for estuarine WWTF and fertilizer from upriver as predominant nutrient sources of N algal growth. Samplings, conducted weekly for an annual cycle, at the Westerly and Stillman Bridges at the mouth of the Pawcatuck River – upstream of seawater intrusion, and seasonal down-river transects from Wakefield, RI to Westerly, RI were collected in order to track seasonal changes and determine sources of N along the river. Nutrients of N (nitrate, nitrite, and ammonium), phosphate, and nitrate isotopes were measured at each sampling point. Nitrate isotopes provided additional power for analysis to help differentiate various input sources into the river as well as to determine cycling of N on the river. Results indicate that there were significant seasonal variations in nutrient input of nitrate and ammonia linked to seasonal discharge rates where high discharge occurs in the winter and low flow occurs in the summer. With seasonal discharge rates, the WWTFs contribute negligible amounts of N to the river in winter and up to 15% of the loading in the summer. Results also signify that the overall annual flux of the Pawcatuck river into Little Narraganset Bay are consistent with prior estimates, where DIN, DON, and TN export is equal to 18 x 106, 15 x 106, and 32 x 106 moles of N per year respectively indicating there have been no major changes N flux in the upper river.

Major Advisor

Dr. Julie Granger

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