Potential use of 15N to assess nitrogen sources and fate in Narragansett Bay
Anthropogenic N inputs have been identified as the main source of N to Narragansett Bay, a relatively well-mixed estuary in the northeast coast of the United States. Despite a well constrained N budget high levels of primary production during the summer months, mostly in the form of sporadic “blooms”, cannot be explained in terms of current budget estimates. Inputs from the adjacent Rhode Island Sound have been invoked as a potential source of N to account for the Bay's summer production. ^ The dissolved inorganic nitrogen (DIN) from the Rhode Island Sound and the anthropogenic N entering the estuary through the upper reaches of the bay are isotopically distinct in terms of their 14N, 15N ratios. Measurements of the N isotopic ratios of near-surface water <153 >μm particulate organic matter (POM)—as a proxy for phytoplankton—suggest that the isotopic signals of these two sources of N mix conservatively along the Bay's estuarine gradient, signifying that their relative contribution to the Bay's primary production is potentially traceable. Using this approach, the estimated input of N from the Rhode Island Sound entering the Bay during one summer season was not different from previous estimates and still did not supply adequate N to support the average levels of summer primary production in the Bay. ^ The N isotopic ratios in intertidal mussels collected throughout the Bay seem to confirm the general distribution pattern of N isotopic ratios in the Bay revealed by the POM measurements. However, towards the Providence-Seekonk River estuary in the upper part of the Bay, isotopic ratios decline. This last finding is in disagreement with the conservative mixing of isotopic ratios suggested by earlier measurements and may be caused by particulate matter with very low N isotopic ratios discharged from sewage treatment plants into this region of the Bay. ^
Biology, Oceanography|Biogeochemistry|Environmental Sciences
Joaquin E Chaves,
"Potential use of 15N to assess nitrogen sources and fate in Narragansett Bay"
Dissertations and Master's Theses (Campus Access).