Citation:

Knightes, Chris, B. Rashleigh, F. Cashel, J. Clough, R. Parmar, K. Wolfe, AND D. Smith. Towards a mechanistic modeling framework for simulating eutrophication in estuaries. Coastal & Estuarine Research Foundation Conference, Portland, OR, November 12 - 16, 2023.

Impact/Purpose:

Estuaries receive nutrients (nitrogen, carbon, and phosphorous) from man-made sources, like waste water treatment plants and agriculture, as well as natural sources, like wetlands and forests. These sources of nutrients impact coastal waters with human and ecological impacts. States and regions are often intereste in improving our understanding on the sources and processes resulting in these impacts, such as low dissolved oxygen concentrations, algal blooms, and reductions in water clarity. One way to investigate these systems is by using mathematical models, which incorporate the processes and phenomenon at these sites. One question that arises is how complex of a model is necessary to capture the important processes, yet not be so complex as to require extensive resources (time and money) to develop and apply. This research looks at different types of model complexity in an effort to better inform how best to choose the level of complexity appropriate to answer the questions being asked about impacts in estuaries.

Description:

Estuaries provide valuable ecosystem services, including biodiversity, flood and storm protection, recreation, tourism, and food. Anthropogenic and natural loadings of nutrients can cause eutrophication, resulting in hypoxic zones; increased algae growth, including hazardous algal blooms; and decreased water clarity and light penetration, resulting in loss of seagrass and associated habitats. Environmental managers may rely on different tools, including the potential application of mechanistic modeling, to investigate and assess a range of  feasible management strategies to address these impacts. One of the challenges in applying mechanistic modeling is matching the model complexity with the system complexity and data availability to sufficiently address the questions and needs. There are a series of different modeling approaches and developments to move towards developing a mechanistic modeling framework to address these needs. Factors for model consideration are the spatial complexity of the system, whether a one-, two-, or three-dimensional modeling domain is necessary to capture the hydrodynamics of the system. Incorporating the necessary state variables and governing processes is also considered as part of the model formulation. The US Environmental Protection Agency (EPA) Office of Research and Development (ORD) has supported the development of different mechanistic models, including EFDC (Environmental Fluid Dynamics Code), WASP (Water Quality Analysis Simulation Program), Hydrologic Simulation Program – Fortran (HSPF), HAWQS/SWAT (Hydrologic and Water Quality System/Soil and Water Assessment Tool), and AQUATOX. This presentation will discuss the application and linkages of these different models to simulate eutrophication in estuaries. Discussion will present different modeling approaches to handle various types of systems, touching on multiple strengths, weaknesses, and challenges in using a range of modeling approaches. Examples will include a 3D EFDC/WASP8 model for Narragansett Bay, Rhode Island and Massachusetts; a 1D HSPF/WASP8 model and a 3D HSPF/EFDC/WASP8 model for the Pawcatuck River and Little Narragansett Bay, Rhode Island and Connecticut, and the development of a new cloud-based tool for linking HAWQS/SWAT to AQUATOX using the National Hydrography Dataset to model estuaries anywhere in the conterminous US.

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