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Improved Simulation of DO and Water Clarity with Increased Ecological Complexity in a 3D Water Quality Model
Citation:
Cashel, F. AND C. Knightes. Improved Simulation of DO and Water Clarity with Increased Ecological Complexity in a 3D Water Quality Model. New England Estuarine Research Society (NEERS) Spring Meeting, Freeport, ME, April 18 - 20, 2024.
Impact/Purpose:
Rhode Island and Connecticut have Waste Water Treatment Plants that discharge into the Pawcatuck River, which forms the border between Rhode Island and Connecticut. The Pawcatuck River is a shallow, small estuary that empties into the Little Narragansett Bay before emptying into the Atlantic Ocean. Discharge into the River results in growth of algae, which decreases the amount of light that penetrates through the water column. The reduction in light impacts the growth of seagrass. Additionally, the discharge results in decreased levels of oxygen in the water, which impacts fish and wildlife. This research serves to develop a three-dimensional mathematical model to allow us to simulate the discharge into the estuary and incorporate the physics governing water movement, tidal influences, and salinity as well as the processes governing nutrient affecting oxygen concentrations. Developing this model will allow us to investigate the different levels of impact of the treatment plants, upstream natural sources, and possible impacts of climate change, land use change, and feasible management strategies for the treatment plants.
Description:
Anthropogenic disturbances have increased the frequency, area, and intensity of eutrophic events in coastal ecosystems, harming seagrass and macrofauna. The Pawcatuck River and Little Narragansett Bay (CT/RI) is a small, shallow estuary with zones of hypoxia due to algal growth. Here, we study the governing mechanisms of dissolved oxygen (DO), water clarity, phytoplankton, and macroalgae blooms using observed data and a mechanistic modeling approach. We developed a three-dimensional hydrodynamic-water quality model with macroalgae and multiple size classes of phytoplankton. The high spatial resolution and ecological complexity of the model captured the spatiotemporal variation of DO, with depth, stratification and sediment oxygen demand, as well as phytoplankton growth dynamics in the mid-river, and macroalgal-driven light and nutrient limitation in the Bay. This work provides a greater understanding of the factors impacting DO and water clarity, which may increase the capacity of management to recover coastal seagrass populations.
