Assessment of Submarine Groundwater Discharge (SGD) Zones Along the Coastal Tract of Odisha

Abstract

Submarine Groundwater Discharge (SGD) is the continuous flow of groundwater under favourable hydrogeological and hydrological settings, which carries nutrients, traces metals and other contaminants to the sea coast and influences the coastal ecosystem. Therefore, integrated site-specific field investigations are necessary for identifying the SGD zones and its magnitude assessment for sustainable development of the coastal ecosystem. An attempt has been made to identify the potential SGD zones along the 485 km long coastline of Odisha using the groundwater level data and physico-chemical analysis of groundwater, pore water and sea water samples. The areas having an occurrence of groundwater level above mean sea level (more than tidal amplitude) together with the absence of any significant seasonal/diurnal variation in groundwater levels were identified as probable SGD zones. In situ measurement of basic water quality parameters (temperature, pH, salinity, EC, DO, etc.) was carried out at every 3–5 km intervals along the coastline for sea water (44), pore water (43) and groundwater (36) samples using portable multiparameter water quality kit during the field investigation. The pore water samples, indicating low salinity (<25 ppt) and low EC values (<35 mS/cm), were considered to be suspected SGD. A total number of seven such suspected zones were identified along the coastal tract of Odisha. The pore water salinity in these seven locations is found to be 14.6 ppm (Chaumukh–Balasore), 3.05 ppt (Chandipur–Balasore), 3.71 ppt (Madanpur–Balasore), 19.79 ppt (Pentha–Kendrapara), 18.9 ppt (Beleshwar–Puri), 12.59 ppt (Golden Beach, Puri) and 0.46 ppt (Nolia Nuagaon, Ganjam) in the proximity of sea coast between low tide and high tide. The nutrients (Nitrate, Phosphate and Silica) analysed in the pore water samples also have shown elevated signatures for the identified zones, thus support possible SGD and need further conformation using stable isotopes, sea surface temperature and radon measurements.