Abstract
Surface water-groundwater interactions were studied in a coastal lagoon performing 180 seepage meter measurements and using heat as a tracer in 30 locations along a lagoon inlet. The direct seepage meter measurements were compared with the results from analytical solutions for the 1D heat transport equation in three different scenarios: (1) Homogeneous bulk thermal conductivity (Ke); (2) horizontal heterogeneity in Ke; and (3) horizontal and vertical heterogeneity in Ke. The proportion of fresh groundwater and saline recirculated lagoon water collected from the seepage experiment was used to infer the location of the saline wedge and its effect on both the seepage meter results and the thermal regime in the lagoon bed, conditioning the use of the thermal methods. The different scenarios provided the basis for a better understanding of the underlying processes in a coastal groundwater-discharging area, a key factor to apply the best-suited method to characterize such processes. The thermal methods were more reliable in areas with high fresh groundwater discharge than in areas with high recirculation of saline lagoon water. The seepage meter experiments highlighted the importance of geochemical water sampling to estimate the origin of the exchanged water through the lagoon bed.
Highlights
Exchange fluxes between groundwater (GW) and surface water (SW) bodies are important due to the hydrological [1] and ecological [2,3] consequences for aquatic plants and animals
Water 2019, 11, 1648 important than temporal heterogeneity and highlighted the impact of a correct characterization of the spatial heterogeneity on the discharge estimations, so this study focuses on capturing submarine groundwater discharge (SGD) as a snapshot in time
The results show the existence of an exchange of water between the subsurface and the lagoon
Summary
Exchange fluxes between groundwater (GW) and surface water (SW) bodies are important due to the hydrological [1] and ecological [2,3] consequences for aquatic plants and animals. Understanding the temporal and spatial heterogeneity of exchange fluxes is important as it can affect water resource management plans. Lewandowski et al [6] discussed the historical evolution of studies investigating Lacustrine groundwater discharge (LGD), i.e., exchange fluxes between lakes and groundwater versus that of submarine groundwater discharge (SGD), i.e., exchange fluxes between sea/lagoons and groundwater. The current study is interested in evaluating the methods for quantifying SGD and its inherent spatial heterogeneity. Duque et al [7] recently showed that spatial heterogeneity in exchange fluxes was more
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