Submarine groundwater discharge (SGD) as a main nutrient source for benthic and water-column primary production in a large intertidal environment of the Yellow Sea |
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| Authors: | Hannelore Waska Guebuem Kim |
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| Institution: | 1. Centre for Coastal Biogeochemistry, School of Environment, Science and Engineering, Southern Cross University, PO Box 157, Lismore, NSW 2480, Australia;2. GNS Sciences, PO Box 30368, Lower Hutt 5040, New Zealand;1. Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA;2. State Key Lab of Marine Environmental Science, Xiamen University, Xiamen 361005, China;1. National Marine Science Centre, School of Environment, Science and Engineering, Southern Cross University, Coffs Harbour, NSW, Australia;2. School of Environment, Science and Engineering, Southern Cross University, Lismore, NSW, Australia |
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| Abstract: | The biogeochemistry and magnitude of submarine groundwater discharge (SGD) was investigated in one of the largest tidal flat ecosystems worldwide, along the Yellow Sea coast. A representative semi-enclosed embayment located in the south eastern Yellow Sea, Hampyeong Bay, was chosen for this purpose. Groundwater and seawater samples were collected in three seasons (May, July, and September) and analyzed for Ra isotopes, nutrients, and photosynthetic pigments. The biogeochemistry of SGD was strongly influenced by tidal oscillations and seasonal precipitation changes and switched from a brackish, nutrient-enriched regime in May and July to an exclusively saline regime, with lower nutrient concentrations, in September. SGD magnitudes, calculated by using a 226Ra mass balance model, were 0.14 m3 m? 2 d? 1 in May and 0.35 m3 m? 2 d? 1 in September. A nutrient mass balance was established for the two campaigns, which suggests that SGD causes the flushing of substantial amounts of pore water nutrients into this embayment; because of SGD, the embayment acts as a source of dissolved inorganic silicates (DSi) that are transported to the open ocean. Potential C fixation rates derived from this nutrient mass balance were compared with two different models for water-column phytoplankton productivity based on water-column Chl a and local irradiation levels. The Chl a-based models generally showed lower C fixation rates than the nutrient-based mass balance, indicating removal of up to 70% of the nutrients by other primary producers, such as benthic algae. During monsoon season, when benthic algal biomass is high and nutrient fluxes are substantial due to a terrestrial component, SGD — driven benthic primary production could play a significant role in this large tidal flat ecosystem. |
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