Empirical relationships of groundwater head\u2013salinity response to variations of sea level and vertical recharge in coastal confined karst aquifers

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.