Submarine Groundwater Discharge helps making nearshore waters heterotrophic

Shu-Lun Wang,Chen-Tung Arthur Chen,Yi-Jie Lin,Ying Ye,Ting-Hsuan Huang,Xue-Gang Chen,Fu-Wen Kuo,Liyang Yang,Jing Zhang,Xuelu Gao,Hsiao-Chun Tseng,Jiann-Yuh Lou,Tsung-Ren Peng,Hon-Kit Lui,Selvaraj Kandasamy

doi:10.1038/s41598-018-30056-x

Abstract

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.

Highlights

Submarine groundwater discharge (SGD) is the submarine seepage of all fluids from coastal sediments into the overlying coastal areas
The groundwater is isolated from the atmosphere but when the groundwater enters the oceans it is expected that the high pressure of CO2 (pCO2) in the SGD might make the receiving coastal water a CO2 source for the atmosphere
We realize that the SGD sampling sites were not distributed evenly and that seasonal data were not obtained for most sites

Summary

Introduction

Submarine groundwater discharge (SGD) is the submarine seepage of all fluids from coastal sediments into the overlying coastal areas. SGD contains excess carbon[11,12,13,14] It is, less known how nutrients and carbon interact after the SGD enters the oceans. Part of the DOC would decompose, further increase DIC and pCO2. The groundwater is isolated from the atmosphere but when the groundwater enters the oceans it is expected that the high pCO2 in the SGD might make the receiving coastal water a CO2 source for the atmosphere. Whether the SGD would eventually lead to a carbon source or sink into the receiving coastal waters does not have an a priori answer. Only a handful of studies have reported nutrients and carbon in the SGD in China[7,16,17,18,19]. Whether the SGD helps making the coastal waters autotrophic or heterotrophic is evaluated

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Results

Conclusion