Abstract
Submarine groundwater discharge (SGD) demarcated as a significant component of hydrological cycle found to discharge greater volumes of terrestrial fresh and recirculated seawater to the ocean associated with chemical constituents (nutrients, metals, and organic compounds) aided by downward hydraulic gradient and sediment-water exchange. Delineating SGD is of primal significance due to the transport of nutrients and contaminants due to domestic, industrial, and agricultural practices that influence the coastal water quality, ecosystems, and geochemical cycles. An attempt has been made to demarcate the SGD using thermal infrared images and radon-222 (222Rn) isotope. Thermal infrared images processed from LANDSAT-8 data suggest prominent freshwater fluxes with higher temperature anomalies noted in Cuddalore and Nagapattinam districts, and lower temperature noted along northern and southern parts of the study area suggest saline/recirculated discharge. Groundwater samples were collected along the coastal regions to analyze Radon and Physico-chemical constituents. Radon in groundwater ranges between 127.39 Bq m-3 and 2643.41 Bq m-3 with an average of 767.80 Bq m-3. Calculated SGD fluxes range between -1.0 to 26.5 with an average of 10.32 m day-1. Comparison of the thermal infrared image with physio-chemical parameters and Radon suggest fresh, terrestrial SGD fluxes confined to the central parts of the study area and lower fluxes observed along with the northern and southern parts of the study area advocate impact due to seawater intrusion and recirculated seawater influence.
Highlights
Submarine groundwater discharge (SGD) demarcated as a discharge of terrestrial groundwater influenced by hydraulic gradient from land aquifers to the ocean and recirculated seawater through the aquifer sediments influenced by currents, waves, and tides [1]
Landsat 8 satellite data product for Tamilnadu coast representing January 2019 downloaded from USGS website has been used to acquire the sea surface temperature for the study area (Fig. 2)
QSGD is the terrestrial, fresh SGD flux usually measured as m/d, FSGD being the ascribed Rn 222 flux measured in Bq/m2/h1, and Rn 222 gw is the groundwater attributed Radon usually measured as Bq/m3
Summary
Submarine groundwater discharge (SGD) demarcated as a discharge of terrestrial (fresh) groundwater influenced by hydraulic gradient from land aquifers to the ocean and recirculated seawater through the aquifer sediments influenced by currents, waves, and tides [1]. The impact of the human population influencing coastal aquifers is found to induce groundwater aided by increased supply of chemical constituents (major ions, trace elements) and nutrients resulting in alteration of coastal ecosystems [13]. An attempt has been made in the proposed study to evaluate the use of aerial thermal infrared (TIR) imagery using LANDSAT-8 data sets, along with chemical concentrations like salinity and Radon to quantify SGD fluxes to the Bay of Bengal. Thermal infrared (TIR) images can resolve the spatial variation of groundwater discharge due to contrasting temperature and density varying waters (saline and fresh) [15,16]. TIR and Radon have been used to isolate groundwater discharge sites to the Bay of Bengal
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