In coastal inlets such as bays and fjords, the mixing of salt and fresh water regulates many aspects of the local environment, from nutrient concentrations to oxygen levels and the composition of phytoplankton communities. Studying these areas is critical to our understanding of niche ecosystems and ocean-land exchanges, but knowing how to best deploy monitoring instruments to capture a complete picture of these dynamic environments is challenging.
In 2011, scientists began refining a framework called total exchange flux (TEF) for analyzing how water mixes in estuaries. Until recently, TEF was mainly used to model very specific situations. But in a recent study published in Journal of Geophysical Research: OceansLemagie et al investigated realistic hydrodynamic models to predict how best to use moored instruments to measure TEF in three large natural estuaries: San Diego Bay in Southern California, the Salish Sea, and the Strait of Juan de Fuca between British Columbia and Washington State and the outlet of the Columbia River off Oregon and Washington.
The three sites represent very different types and shapes of estuaries. San Diego Bay is a shallow estuary that receives little rainfall. The Strait of Juan de Fuca is a relatively deep fjord. and the Columbia River outlet is a salt wedge, where fresh water flows outward over incoming salt water.
In each model, the researchers varied the lateral and vertical distribution of instruments to identify the best configurations. Their results suggested that in all three cases, an even distribution of three to four monitoring devices in the estuarine channel, with each measurement at one to five depths, could capture more than 90% of the water exchange.
The findings are encouraging, the authors say, because they suggest that monitoring with a limited number of instruments is a feasible way to measure TEF in estuaries and better understand the water exchanges that regulate these complex ecosystems.
EP Lemagie et al, Measuring Estuarine Total Exchange Flow From Discrete Observations, Journal of Geophysical Research: Oceans (2022). DOI: 10.1029/2022JC018960
Provided by the American Geophysical Union
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Reference: Estuary Inflows and Outflows Measurement (2022, November 8) Retrieved November 8, 2022 from https://phys.org/news/2022-11-ins-outflows-estuaries.html
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