Abstract

Coastal aquifers are characterized by a mixing zone with freshwater–saltwater interactions, which have a strong relationship with hydrological forcings such as astronomical and storm tides, aquifer recharge and pumping effects. These forcings govern the aquifer hydraulic head, the spatial distribution of groundwater salinity and the saline interface position. This work is an empirical evaluation through time-series analysis between aquifer head and groundwater salinity associated with the sea-level dynamics and the aquifer recharge. Groundwater pressure, temperature and salinity were measured in a confined aquifer in the northwest coast of Yucatan (México) during May 2017–May 2018, along with precipitation. Cross-correlation and linear Pearson correlation (r) analyses were performed with the data time series, separating astronomical and meteorological tides and vertical recharge effects. The results show that the astronomical and meteorological tides are directly correlated with the aquifer head response (0.71 < r < 0.99). Salinity has a direct and strong relationship with the astronomical tide (0.76 < r < 0.98), while the meteorological tide does not (r < 0.5). The vertical recharge showed a moderate correlation with the aquifer head (0.5 < r < 0.7) and a nonsignificant correlation with the groundwater salinity (r < 0.5). In this study, the sea level (r > 0.7) is a more important forcing than the vertical recharge (with 0.5 < r < 0.7). Empirical relationships through time-series analysis and the separation of individual hydrological forcings in the analysis are powerful tools to study, define and validate the conceptual model of the aquifer.

Highlights

  • Coastal aquifers, characterized by freshwater–saltwater interactions, are crucial for maintaining regional biodiversity in various ecosystems, supporting socio-economic development, and providing a reliable source of water supply in coastal zones

  • Empirical relationships through time-series analysis and linear and cross-correlation methods were used as a useful tool to understand the dynamics of coastal aquifers and to assess the aquifer response due to regional hydrologic forcings

  • The astronomical tide is the most correlated (Pearson r-value) hydrological forcing to the aquifer head, followed by the meteorological tides, and the precipitation

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Summary

Introduction

Coastal aquifers, characterized by freshwater–saltwater interactions, are crucial for maintaining regional biodiversity in various ecosystems, supporting socio-economic development, and providing a reliable source of water supply in coastal zones. Time series analysis has been applied in aquifer head data to study the change in the regime of the aquifer, to obtain hydraulic characteristics such as storage and hydraulic conductivity, and to understand multiple interactions between hydrological forcings and the water table (Trglavcnik et al 2018; Bakker and Schaars 2019; Fernández-Ayuso et al 2019) These studies have focused on the effects of hydrologic forcings on the aquifer head, but not on the groundwater salinity or on the dynamic of the saline interface. This gap is explored in the research reported in this paper

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