Submarine groundwater discharge estimation in an urbanized embayment in Hong Kong via short-lived radium isotopes and its implication of nutrient loadings and primary production

Ra-224 and Ra-223 are adopted as tracers to qualify submarine groundwater discharge (SGD) in Tolo Harbor, a highly urbanized embayment in Hong Kong. Based on the sampling data, a two-layered radium mass balance model is used to estimate lateral SGD and bottom SGD. Total SGD is estimated to be 1.2-3.0 cm d(-1), including lateral SGD of 5.7-7.9 cm el and bottom SGD of 0.3-2.0 cm d(-1). Fresh 5GD is estimated to be (2.1-5.5) x 10(5) m(3) d(-1). Nutrient fluxes (mol d(-1)) from SGD are estimated to be (3-7.4) x 10(4) (dissolved inorganic nitrogen), (2.4-6.2) x 10(2) (dissolved inorganic phosphate) and (6.5-16) x 10(4) (dissolved silicate). Primary productivity is estimated to be (1.5-15) x 10(6) gC d(-1), 2-53% of which is supported by SGD-induced phosphate fluxes. The study indicates that SGD is a significant source of nutrients to coastal waters and may cause an obvious increase of primary production. These findings must be considered in future coastal ecological management. (C) 2014 Elsevier Ltd. All rights reserved.