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UNDERSTANDING EUTROPHICATION AND HYPOXIA IN THE PAWCATUCK RIVER ESTUARY: A MONITORING AND MODELING STUDY
Citation:
Cashel, F. AND Chris Knightes. UNDERSTANDING EUTROPHICATION AND HYPOXIA IN THE PAWCATUCK RIVER ESTUARY: A MONITORING AND MODELING STUDY. New England Estuarine Research Society Fall Meeting 2022, Providence, RI, November 17 - 19, 2022.
Impact/Purpose:
Waste water treatment plants release nutrients, such as carbon, nitrogen, and phosphorous, into rivers. When these nutrients are added to rivers, they result in a decrease in oxygen and growth of algae. A system of interest is the Pawcatuck River estuary, which has two waste water treatment plants that release into the river. This system is shallow and is influenced by the upstream flow draining the Wood-Pawcatuck watershed and the downstream tidal boundary (Fishers Island Sound). In this work, we have developed a series of mathematical models to represent the processes governing the flow of water in the river, including the influence of the upstream freshwater and downstream saline water, and governing the concentrations of nutrients, algae, and dissolved oxygen. Combining analysis of our modeling and observed data, this work has improved our understanding of this system. Results suggest the importance of carbon decreasing dissolved oxygen in the surface waters, and the long term sediment oxygen demands on the deeper waters. Our work identifies the importance of phytoplankton and macroalgae on influencing dissolved oxygen concentrations in different locations with the estuarine system.
Description:
Human disturbances (e.g., habitat degradation, increased nutrient inputs) contribute to eutrophication of coastal ecosystems, harming seagrass and macrofauna. The Pawcatuck River Estuary (CT/RI) is a shallow, urban estuary with zones of hypoxia. Here, we assess eutrophication dynamics and hypoxia using observed data and a multimedia modeling approach. Sensitivity analyses assessed relative importance of phytoplankton growth, carbonaceous biological oxygen demand (CBOD) decay, and diagenesis of organic carbon on dissolved oxygen concentrations ([DO]). Results suggest the importance of different processes governing [DO] over time and space. CBOD lowers [DO] near the river surface, and stratification and sediment oxygen demand (SOD) lowers [DO] in bottom waters. Phytoplankton growth and respiration caused large daily swings in [DO]. Macroalgae limited growth of phytoplankton via shading and nutrient depletion. Our conclusions will be used to inform a total maximum daily load to improve water quality and encourage the return of seagrass.
