2-11 A Meta-Analysis to Develop a Salinity-Based Typology for Permeable Nearshore Subterranean Estuaries

Session: Coastal Hydrogeology in an Age of Rising Seas

Presenting Author:

Authors:

Abstract:

The subterranean estuary (STE) plays an important role in controlling the fate of terrestrial and marine chemicals being transported across the groundwater-ocean continuum. Salinity structure, including the extent of seawater-freshwater mixing, is recognized as the key distinguishing feature among STEs and strongly influences the biogeochemical conditions and subsequently the fate of chemicals in the system. Since the concept of the STE was introduced nearly 30 years ago, numerous field studies have characterized groundwater flow, salinity distribution, and mixing conditions within permeable nearshore STEs. The objective of this study was to conduct a meta-analysis to collate available field data and explore the possibility of predicting the salinity distribution and mixing conditions in a STE based on easy-to-measure or determine physical, hydrological, and oceanic parameters. This information is needed to develop a typology for STEs based on salinity structure, analogous to surface estuary typologies. An extensive literature review identified field data from approximately 40 individual field sites worldwide where nearshore STE salinity structure has been measured. Quantitative metrics were used to characterize salinity structure and mixing conditions for each field site, and correlations between these metrics and physical, hydrological and oceanic parameters (e.g., tidal amplitude, wave height, beach slope, fresh submarine groundwater discharge) were statistically evaluated. Overall, it was found that tidal amplitude was the only parameter significantly correlated with salinity structure metrics, but correlations were stronger when physically meaningful combinations of parameters were considered. We propose using the minimum salinity 1 m below the beach face seaward of mean shoreline as a criterion for classifying STEs as stratified, partially mixed, or well-mixed systems. However, this metric showed limited correlations with the evaluated parameters, highlighting the complexity of predicting mixing extent in STEs. The study findings enhance our ability to interpolate and extrapolate information between field sites and advance our understanding of STE functioning at both local and global scales.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-6635

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