Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
8884812 | Estuarine, Coastal and Shelf Science | 2018 | 47 Pages |
Abstract
To evaluate the role that submarine groundwater discharge (SGD) plays in the carbon and nutrient budgets in subtropical Sansha Bay, southeastern China, radium isotopes were used as SGD tracers and investigated in the bay and surrounding groundwater. In general, the activity of radium isotopes (223,224,226,228Ra) decreased from the bay head to the outlet that connects with the East China Sea. Based on the ratio of 224Ra and 228Ra, the water age was estimated to be 5.49â¯Â±â¯3.64 and 1.50â¯Â±â¯0.83 days in winter and summer, respectively. A three end-member mixing model and a box model were set up based on the mass balance of 226Ra and salinity to quantify SGD. The flux of SGD was calculated to be 9.33â¯Â±â¯8.17â¯Ãâ¯105â¯m3â¯dâ1 (3.8â¯Â±â¯3.4â¯Ãâ¯10â3â¯m3â¯mâ2 dâ1) in winter and 4.89â¯Â±â¯3.35â¯Ãâ¯106â¯m3â¯dâ1 (2.0â¯Â±â¯1.4â¯Ãâ¯10â2â¯m3â¯mâ2 dâ1) in summer, which were at least a few times less than the concomitant river discharge into the bay. In groundwater, an enrichment of dissolved inorganic nitrogen, phosphorus, and organic carbon was associated with relatively high activities of 226Ra. The SGD-associated nutrient flux was 1.99â¯Â±â¯1.74-95.0â¯Â±â¯83.2â¯Î¼molâ¯mâ2 dâ1 in winter and 0-0.89â¯Â±â¯0.55â¯mmolâ¯mâ2 dâ1 in summer of phosphate, 6.76â¯Â±â¯5.92-7.21â¯Â±â¯6.32â¯mmolâ¯mâ2 dâ1 in winter and 66.2â¯Â±â¯40.8-93.6â¯Â±â¯57.7â¯mmolâ¯mâ2 dâ1 in summer of dissolved inorganic nitrogen, and 1.20â¯Â±â¯1.05-1.74â¯Â±â¯1.52â¯mmolâ¯mâ2 dâ1 in winter and 5.93â¯Â±â¯4.06-8.22â¯Â±â¯5.63â¯mmolâ¯mâ2 dâ1 in summer of silicate. The flux of dissolved organic carbon via SGD was 0.17â¯Â±â¯0.15-0.33â¯Â±â¯0.29â¯mmolâ¯mâ2 dâ1 in winter and 1.31â¯Â±â¯0.81-2.94â¯Â±â¯1.81â¯mmolâ¯mâ2 dâ1 in summer. The flux of N carried by SGD into Sansha Bay was comparable to the estuarine flux in winter, while was an order of magnitude greater than the estuarine flux in summer. The minimum flux of silicate via SGD was about half as much as the estuarine flux in summer, while was an order of magnitude smaller than the estuarine flux in winter. The minimum SGD-associated P flux was at least two orders of magnitude smaller than the estuarine flux in both seasons. Therefore, SGD on embayment scale is an important pathway for nitrogen from land to sea. These great SGD-associated nutrient fluxes may contribute to eutrophication and hypoxia in such stratified embayment.
Related Topics
Physical Sciences and Engineering
Earth and Planetary Sciences
Geology
Authors
Guizhi Wang, Aiqin Han, Liwen Chen, Ehui Tan, Hui Lin,