Measuring Estuarine Total Exchange Flow From Discrete Observations

Area of Science:

• Estuarine and coastal oceanography
• Hydrodynamic modeling
• Water resource management

Background:

• Estuarine-coastal ocean exchange is vital for nutrient cycling, phytoplankton dynamics, and regulating estuarine conditions like residence time, hypoxia, and acidification.
• Accurate monitoring of estuarine exchange flows is challenging due to complex velocity shear and property gradients, necessitating high-resolution measurements.
• The Total Exchange Flow (TEF) method offers detailed salinity structure insights but demands data resolving the spatio-temporal variability of salinity and currents.

Purpose of the Study:

• To recommend the most efficient spatial sampling resolution for measuring Total Exchange Flow (TEF).
• To determine optimal mooring strategies for capturing estuarine exchange dynamics.

Main Methods:

• Investigated results from three realistic hydrodynamic models of diverse estuary types: a bay, a salt-wedge, and a fjord.
• Employed three mooring strategies with varying lateral (number of moorings) and vertical (sample depths) resolutions.
• Analyzed the sensitivity of exchange volume transport and salinity to sampling resolution.

Main Results:

• Exchange volume transport was more sensitive to sampling resolution than salinity.
• Three to four moorings, evenly distributed across the estuarine channel, captured over 90% of the exchange flow magnitude.
• A minimum of 1-5 sample depths per mooring was sufficient, varying with vertical stratification.

Conclusions:

• Optimized sampling strategies can significantly improve the efficiency of estuarine exchange flow monitoring.
• Recommendations provide a framework for resource-efficient observation and monitoring of water mass exchange in estuaries.
• Findings support better management of coastal resources by enhancing understanding of estuarine dynamics.