Major
Geology and Geological Oceanography
Advisor
Christopher Kincaid
Advisor Department
Oceanography, Graduate School of
Date
4-2020
Keywords
Nitrogen, Flow Model, Narragansett Bay
Creative Commons License
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 4.0 License.
Abstract
Nitrogen is an important nutrient in ecosystems, as it is used in many biological processes, including the creation of DNA and RNA. However, excess nitrogen in an ecosystem can have adverse effects, such as triggering algal blooms, which limit sunlight penetration to bottom growth, and create anoxic zones. Large scale strategies to remove excess nitrogen from wastewater treatment plants have been utilized, but they are expensive and can potentially remove too much, while increasing greenhouse gas emissions. Thus, it is essential that we understand the accurate full nitrogen budget for an estuary.
Narragansett Bay, an important coastal marine ecosystem that supports both natural life and human industry, has been the subject of many studies of nutrient conditions. Sources of nitrogen input from the atmosphere and the land have been studied rather intently. However, input of nitrogen from offshore – specifically, what happens to the nitrogen from the mouth of the Bay on its way to the productive mid-portion – is not well understood. While some past studies have mentioned this source, they do not go into depth, and none use direct measurements to inform their estimation of offshore nitrogen influx as being about 15% of total nitrogen input. Recent data on flow and nutrient concentrations suggest that the nitrogen flux through the mouth of the Bay is now in excess of what comes in from treatment plants; this may also be supported by research in other estuaries, such as Chesapeake Bay.
This project aims to take a deeper look at the flow of nitrogen into Narragansett Bay from offshore sources. To obtain direct nitrogen measurements, 3 samples were taken at different depths, from each of 3 Acoustic Doppler Current Profiler (ADCP) locations, for a total of 9 samples, at the mouth of the East Passage. These samples were then sent to a lab for analysis of concentrations of the main constituents of marine nitrogen content, NO2, NO3, and NH4+. After the nitrogen data were received, they and ADCP current velocities were fitted into a circulation and transport model for the East Passage, using the MATLAB computational platform. The numerical simulations will predict how nitrogen concentrations entering in the bottom water at the mouth of the Bay evolve during transit north to the mid- Bay.