Submarine Groundwater Discharge helps making nearshore waters heterotrophic

Submarine groundwater discharge (SGD) is the submarine seepage of all fluids from coastal sediments into the overlying coastal seas. It has been well documented that the SGD may contribute a great deal of allochthonous nutrients to the coastlines. It is, however, less known how much carbon enters the ocean via the SGD. Nutrients (NO₃, NO₂, NH₄, PO₄, SiO₂), alkalinity and dissolved inorganic carbon (DIC) in the submarine groundwater were measured at 20 locations around Taiwan for the first time. The total N/P/Si yields from the SGD in Taiwan are respectively 3.28 ± 2.3 × 10⁴, 2.6 ± 1.8 × 10² and 1.89 ± 1.33 × 10⁴ mol/km²/a, compared with 9.5 ± 6.7 × 10⁵ mol/km²/a for alkalinity and 8.8 ± 6.2 × 10⁵ mol/km²/a for DIC. To compare with literature data, yields for the major estuary across the Taiwan Strait (Jiulong River) are comparable except for P which is extremely low. Primary production supported by these nutrient outflows is insufficient to compensate the DIC supplied by the SGD. As a result, the SGD helps making the coastal waters in Taiwan and Jiulong River heterotrophic.