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Abstract Estuarine exchange flow controls the salt balance and regulates biogeochemistry in an estuary. The Albemarle‐Pamlico estuarine system (APES) is the largest coastal lagoon in the U.S. and historically susceptible to a series of environmental issues including salt water intrusion and eutrophication, yet its estuarine exchange flow is poorly understood. Here, we investigate the estuarine exchange flow in the APES, its tributary estuaries (Pamlico and Neuse), and sub‐basin Albemarle Sound using the total exchange flow analysis framework based on results from a deterministic numerical model. We find the following: (a) Dynamics controlling estuarine exchange flow in the APES vary spatially and depend on timescales considered. At inlets, estuarine exchange flows respond to both tidal prism and residual water levels at weather‐to‐spring/neap timescales. At a long quasi‐steady timescale represented as annual means, estuarine exchange flow is dominated by barotropic flow. Within the tributary estuaries, estuarine exchange flows at timescales of wind periods are controlled by wind‐induced straining, whereas the quasi‐steady state condition is dominated by gravitational circulation. At Albemarle Sound, exchange flow is dominated by the residual water levels at weather‐to‐spring/neap timescales, while at quasi‐steady state it is controlled by barotropic flow. (b) At the quasi‐steady annual timescale, the salt content decreases with river discharge. At the weather‐to‐spring/neap timescales, salt content is insensitive to variations in estuarine exchange flow, except for within Albemarle Sound. (c) Estuarine exchange flow likely influences the biogeochemistry of the APES by playing a key role in regulating the flushing efficiency and material exchange, a role that has been previously overlooked.
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This content will become publicly available on November 1, 2026
Impact of Estuarine Exchange Flow on Multiple Tracer Budgets in the Salish Sea
Abstract Estuarine exchange flow regulates aspects of estuarine biogeochemical processes; however, other tracer‐specific factors can also play an important role. Here, we analyze realistic simulations from a coupled physical‐biological model to quantify volume‐integrated budgets of heat, total nitrogen (TN), and dissolved oxygen (DO) in the Salish Sea and its sub‐basins. Our goal is to evaluate the role of exchange flow in shaping tracer budgets, extending beyond the traditionally emphasized salt budget in estuaries. The three budgets reveal that exchange flow is a consistently important term with a clear annual cycle, but its relative role differs across tracers. For heat, exchange flow‐driven cooling is primarily offset by atmospheric heating, with the two reaching opposing seasonal extremes in summer. For TN, seasonal variability is dominated by exchange flow, whereas the annual mean is dominated by inputs from rivers and wastewater outfalls, and a loss due to benthic denitrification. The DO budget is the most complex: sinks from exchange flow export and respiration are balanced by sources from photosynthesis and air‐sea transfer. Across all three budgets, the sign of the inflow‐outflow tracer concentration differences determines whether exchange flow imports or exports tracers. These concentration differences, which are strongly influenced by coastal wind conditions, set the distinct seasonality of the exchange flow budget terms, while variations in the exchange flow volume transport play a minor role. Our budget quantification approach, based on archived model output, can be extended to other tracers such as carbon and other estuaries for long‐term budget studies.
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- Award ID(s):
- 2122420
- PAR ID:
- 10657379
- Publisher / Repository:
- Wiley
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Oceans
- Volume:
- 130
- Issue:
- 11
- ISSN:
- 2169-9275
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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