An estimation of nutrient fluxes via submarine groundwater discharge into the Sanggou Bay-A typical multi-species culture ecosystem in China

Submarine groundwater discharge (SGD) is now recognized as an important process of land/ocean interactions in coastal zones (LOICZ). In this study, the initial results of the SGD-derived nutrient fluxes into Sanggou Bay, Shandong, China, in June 2012 are reported. This bay is a typical multi-species culture ecosystem with aquaculture species, such as kelp, scallops, shrimp, and oysters. Using a Ra-224/Ra-228 activity ratio (AR) apparent age model, the average residence time of water in the bay was estimated to be 5.12 days, which was comparable with a flushing time of 6.08 days. Based on the non-conservative inventory of Ra-226 and Ra-228 in the water column, the average SGD fluxes into the bay were evaluated to be between 2.59 x 10(7) and 3.07 x 10(7) m(3) d(-1), and the SGD-derived nutrient fluxes (mol/month) had DIN (dissolved inorganic nitrogen) value between 1.16 x 10(8) and 1.38 x 10(8), DIP (dissolved inorganic phosphorus) value between 4.17 x 10(5) and 4.92 x 10(5), and DSi (dissolved silicon) value between 633 x 10(6) and 7.50 x 10(6). Additionally, the riverine nutrient inputs to the bay were an order of magnitude lower than the SGD-derived inputs for the DIN and DIP. To balance the nutrient budget, a fertilizer input of N (approximately 4.76 x 10(7) mol/month) and P (approximately 5.58 x 10(6) mol/month) is required for aquaculture activities. The fertilizer is a major fraction of the DIP input compared to the SGD. SGD-driven nutrient fluxes may play an important role for nutrient recycling and are required to support the high density of aquaculture activities in the Sanggou Bay. (C) 2014 Elsevier B.V. All rights reserved.