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Cross‐Shelf Transport of Submarine Groundwater Discharge Tracers: A Sensitivity Analysis
Author(s) -
Lamontagne S.,
Webster I. T.
Publication year - 2019
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
eISSN - 2169-9291
pISSN - 2169-9275
DOI - 10.1029/2018jc014473
Subject(s) - submarine groundwater discharge , advection , tracer , environmental science , seawater , storm , groundwater , submarine pipeline , radionuclide , hydrology (agriculture) , dispersion (optics) , range (aeronautics) , oceanography , geology , aquifer , physics , geotechnical engineering , materials science , optics , quantum mechanics , nuclear physics , composite material , thermodynamics
The coastal mass balance for environmental tracers can be used to evaluate submarine groundwater discharge (SGD) and is often estimated using advective‐dispersive cross‐shelf transport models. Here we evaluate the sensitivity of different types of SGD tracers to key variables in this transport model under a wide range of environmental conditions. Salinity and long‐lived radionuclides (here represented by 226 Ra; half‐life = 1,600 years) were transported by a combination of advection and dispersion under the scenarios considered, but short‐lived radionuclides (here represented by 224 Ra; half‐life = 3.66 days) were mostly dispersed unless the offshore coefficient of solute dispersivity ( K x ) was very low (<1 m 2 /s). Sensitivity to variations in key transport variables was further evaluated by reinterpreting the cross‐shelf trends in Ra activity in the semiarid Gulf St Vincent of South Australia (GSV). In GSV, the trends in most Ra isotopes ( 223 Ra, 228 Ra, and 226 Ra) in seawater could be explained similarly by a large number of parameter combinations, implying these tracers would provide highly uncertain SGD estimates in this environment. However, the range of possible parameter combinations was relatively smaller for 224 Ra, suggesting that SGD estimates derived from this tracer would be most reliable for GSV. In both the sensitivity analysis and the reevaluation of the GSV data, K x was the most sensitive parameter in the transport equation. Because K x is an empirical parameter potentially encompassing different dispersion processes in time and space (tidal currents, storms, etc.), it is likely to be tracer, time, and site specific.