Dynamic Steady State in Coastal Aquifers Is Driven by Multi-Scale Cyclical Processes, Controlled by Aquifer Storativity

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Geophysical Research Letters
Coastal aquifers supply freshwater to nearly half the global population, yet they are threatened by salinization. Salinities are typically estimated assuming steady-state, neglecting the effect of cyclical forcings on average salinity distributions. Here, numerical modeling is used to test this assumption. Multi-scale fluctuations in sea level (SL) are simulated, from tides to glacial cycles. Results show that high-frequency fluctuations alter average salinities compared with the steady-state distribution produced by average SL. Low-frequency forcing generates discrepancies between present-day salinities estimated with and without considering the cyclical forcing due to overshoot effects. This implies that salinities in coastal aquifers may be erroneously estimated when assuming steady-state conditions, since present distributions are likely part of a dynamic steady state that includes forcing on multiple timescales. Further, typically neglected aquifer storage characteristics can strongly control average salinity distributions. This has important implications for managing vulnerable coastal groundwater resources and for calibration of hydrogeological models. Key Points: - Average salinities in coastal aquifers are affected by low-frequency cyclical changes in sea level (SL) - High-frequency cyclical forcings generate episodic discrepancies in salinity when modeled with and without considering these processes - Under these multi-scale fluctuations in SL, dynamic steady states of coastal aquifers are affected by aquifer storage properties Plain Language Summary: Coastal communities rely heavily on groundwater for freshwater supply, and the primary risk for this vital resource is salinization. Multiple processes in the ocean-land interface control the salinity of coastal aquifers, and assessments of salinities typically neglect some of these processes. In this work, we show that some of the typically neglected processes may be responsible for large-scale, systematic discrepancies between actual and estimated salinities. This has important implications for the assessment of risks to coastal groundwater reservoirs and for the long-term management of these resources.
© 2022. American Geophysical Union. All Rights Reserved. This article was originally published in Geophysical Research Letters. The version of record is available at: https://doi.org/10.1029/2022GL098599. This article will be embargoed until 11/24/2022.
Paldor, A., Frederiks, R. S., & Michael, H. A. (2022). Dynamic steady state in coastal aquifers is driven by multi-scale cyclical processes, controlled by aquifer storativity. Geophysical Research Letters, 49, e2022GL098599. https://doi.org/10.1029/2022GL098599