Submarine groundwater-derived inorganic and organic nutrients vs. mariculture discharge and river contributions in a typical mariculture bay

摘要

Submarine groundwater discharge (SGD) is recognized as one of the most significant pathways for terrestrial nutrient entry into coastal systems. However, SGD-derived nutrient fluxes, particularly organic nutrients, have not yet been considered in the management of mariculture areas. We quantified both saline (12.5 cm day(-1)) and fresh (1.8 cm day(-1)) SGD and related nutrient fluxes using the radium quartet and water mass balance model, respectively, and then reassessed nutrient budgets in a typical mariculture bay. Although fresh SGD accounts for 13 % of the total SGD, it carries 7.4-80.5 % of the total SGD nutrients, suggesting that fresh SGD was an important source of new nutrients with high nitrogen to phosphorus (N/P) ratios (585) into the coastal waters. Based on the rebuilt nutrient budgets, total SGD and mariculture discharge were the two major nutrient sources into the coastal water, providing 2.8-21.2 and 1.9-13.9 times more nutrients than local rivers, respectively. The nutrient speciation results revealed that SGD-derived organic nutrients, which are typically ignored, were dominant (i.e., dissolved inorganic nitrogen and dissolved organic phosphorus through SGD contributed about 22.9 % and 41.5 % of all nutrient resources). Furthermore, China-wide upscaling showed that SGD-derived nutrient fluxes in the mariculture area along the coast of China are comparable those of the rivers in China. Therefore, we suggest that SGD-derived inorganic and organic nutrient fluxes should be incorporated into the ecosystem management of mariculture areas.

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