Submarine groundwater discharge (SGD) is known to transport terrestrial nutrient and other potential pollutants to coastal areas around the world. However, SGD studies in tropical developing regions such as Southeast Asia are scarce even though this area is hypothesized to be an SGD hotspot due to favorable meteorological and hydrological condition. Therefore, this study investigates SGD estimation with nutrient and microbial community composition to analyze the scale of land-based pollutant delivered by SGD to the coastal water in Indonesia.
222Rn was employed as groundwater tracer in the coastal water to estimate SGD rates. Fresh groundwater composed up to 42% of total river discharge and 40% of total SGD at the coastline. Volumetric SGD rates was amounted to 6.6 x 105 m3 d-1, which was comparable with other volcanic SGD studies, and higher than other sub-tropical or temperate regions studies. SGD was confirmed to deliver terrestrial dissolved inorganic nitrogen (DIN) and dissolved silica (DSi) to the coastal system, and also potentially acted as one of the land-ocean delivery pathway for fecal indicator and potentially pathogenic bacteria. Land use analysis suggested that nutrient pool in the coastal hydrological system were originated from human activities, i.e. agriculture, livestock, and municipal wastewater system; the latter was supported by the identification of microbial genera containing fecal indicator and potential human pathogens at the SGD compartments.
Overall, this study shows a notable amount of contaminant discharge in the coastal area via SGD due to a combination of both environmental and anthropogenic factors. Based on the results, the suggested coastal water pollution prevention in this study site will include terrestrial nitrogen containment along the riverbank and estuaries (e.g., a constructed wetland or riparian zones) and development of sewerage system and centralized wastewater treatment plant.