Estimation of submarine groundwater discharge and nutrient loading using radium isotopes quartet in Kuwait

Abstract

The water resources in the arid region like Kuwait are a scarce commodity. With the increasing population, industry and urbanization have lead to the demand of water resources with respect to both in quantity and quality. Therefore, quantification of submarine groundwater discharge is essential for sustainable groundwater management. Moreover, submarine groundwater discharge plays a vital role in delivering nutrients, dissolved carbon, and trace elements to the sea. This study used the naturally occurring radioactive isotopes to identify and estimate the SGD in the coastal strip of Kuwait along the Arabian Gulf. The study gains its significance in determining the loss of brackish groundwater from inland, in the arid region. The groundwater samples were collected from wells along the coast. Seawater samples were collected from Kuwait bay and open sea in transects. Samples were analyzed for major ions, nutrients, and 223Ra, 224Ra, 226Ra, and 228Ra. Box model and offshore gradient model approaches were used to estimate the SGD. The variation of 223Ra, 224Ra, 226Ra, and 228Ra concentrations was studied in different transects, and it was inferred to be influenced by the Kuwait coastal jet in the territorial waters. The water mass residence time calculated for the Kuwait Bay and the open sea ranged from 10 to 58 and 12 to 64 days, respectively. The 223Ra-based horizontal eddy diffusion coefficients for the Kuwait Bay and the south Arabian Gulf were 205.1 and 827.5 m2/s, respectively. The estimation of SGD fluxes in the Kuwait Bay using box model approach based on the spatial distribution of 226Ra and 228Ra were 3.05 × 106 and 5.46 × 106 m3/day, respectively. Similarly, the estimated SGD fluxes for the south Arabian Gulf by offshore gradient model using 226Ra and 228Ra concentrations were 2.92 × 108 and 3.0 × 107 m3/day, respectively. The nutrient fluxes from groundwater to Kuwait Bay and open sea were estimated for PO43−-P, SiO2-Si, and NO3−-N using box model and offshore gradient model approach.