Water Quality Assessment for Detecting Submarine Groundwater Discharge (SGD) Pollution in the Coastal Area of Krakas Beach, North Lombok District, Indonesia

One of the water resources in the coastal area is a submarine groundwater discharge (SGD) found in Krakas Beach, Lombok Utara, Indonesia. This spring discharge plays a role in providing high nutrient intake and balancing the nitrogen and other dissolved organic compounds within a coastal ecosystem. On the other hand, the SGD could be a freshwater resource for the local community and support marine tourism. The sustainable groundwater intake in the coastal area could cause coastal pollutions through eutrophication, temperature degradation and salinity shock to coral reefs. Thus, assessing water quality in the surrounding SGD area is crucial to determine the pollution level induced by freshwater contamination. The groundwater samples from the source of SGD and wells in the surrounding coastal area were collected and analyzed geochemically in the laboratory. We employed Alpha radioactivity analysis to detect the emergence of groundwater pollution. The 222Rn of groundwater ranged from 339.3843.44 Bq/m3, SGD 242.6–1626.15 Bq/m3, and non-SGD area 39.93–89.42 Bq/m3, respectively. We found that the nitrate concentration predominated the nutrient content of groundwater in the study area (approximately 23.93 mg/L). The high nitrate concentration in the groundwater was in line with the increasing nutrient evoked by the SGD (ranging from 1 to 3.3 mg/L), whereby the nitrate concentration exceeded the quality standard for marine biota. The N:P ratio was  > 16 in the study area showing the imbalanced condition due to SGD. Additionally, the emergence of SGD tremendously declined the salinity, resulting in the low coral cover in the surrounding SGD area.