Does submarine groundwater discharge contribute to summer hypoxia in the Changjiang (Yangtze) River Estuary?

Xiaoyi Guo; Bochao Xu; William C Burnett; Qinsheng Wei; Haiming Nan; Shibin Zhao; Matthew A Charette; Ergang Lian; Guangquan Chen; Zhigang Yu

doi:10.1016/j.scitotenv.2020.137450

Does submarine groundwater discharge contribute to summer hypoxia in the Changjiang (Yangtze) River Estuary?

Sci Total Environ. 2020 Jun 1:719:137450. doi: 10.1016/j.scitotenv.2020.137450. Epub 2020 Feb 22.

Authors

Affiliations

¹ Frontiers Science Center for Deep Ocean Multispheres and Earth System, and Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, Ocean University of China, Qingdao 266100, China; Laboratory for Marine Ecology and Environmental Science, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266237, China; College of Chemistry and Chemical Engineering, Ocean University of China, Qingdao 266100, China.
² Frontiers Science Center for Deep Ocean Multispheres and Earth System, and Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, Ocean University of China, Qingdao 266100, China; Laboratory for Marine Ecology and Environmental Science, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266237, China; Marine Isotope and Geochronology Facility, Qingdao National Laboratory for Marine Science and Technology, Qingdao, 266071, China. Electronic address: xubc@ouc.edu.cn.
³ Department of Earth, Ocean and Atmospheric Science, Florida State University, Tallahassee, FL 32306, USA.
⁴ Laboratory for Marine Ecology and Environmental Science, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266237, China; First Institute of Oceanography, Ministry of Natural Resources, Qingdao, 266061, China.
⁵ Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA, USA.
⁶ State Key Laboratory of Marine Geology, Tongji University, Shanghai, 200092, China.
⁷ First Institute of Oceanography, Ministry of Natural Resources, Qingdao, 266061, China.
⁸ Frontiers Science Center for Deep Ocean Multispheres and Earth System, and Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, Ocean University of China, Qingdao 266100, China; Laboratory for Marine Ecology and Environmental Science, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266237, China.

PMID: 32120100
DOI: 10.1016/j.scitotenv.2020.137450

Abstract

The Changjiang (Yangtze) River Estuary (CJE) is one of the largest and most intense seasonal hypoxic zones in the world. Here we examine the possibility that submarine groundwater discharge (SGD) may contribute to the summer hypoxia. Spatial distributions of bottom water ²²²Rn suggest a hotspot discharge area in the northern section of the CJE. SGD fluxes were estimated based on a ²²²Rn mass balance model and were found to range from 0.002 ± 0.004 to 0.022 ± 0.011 m³/m²/day. Higher SGD fluxes were observed during summer hypoxia period. The well-developed overlap of the distribution patterns for SGD flux and dissolved oxygen (DO) implies that SGD could be an important contributor to summer hypoxia in the region off the CJE. We suggest that SGD contributes to the seasonal hypoxia either: (1) directly via discharge of anoxic groundwaters together with reducing substances; and/or (2) indirectly by delivering excess nutrients that stimulate primary productivity with consequent consumption of DO during organic matter decomposition.

Keywords: (222)Rn; Changjiang River Estuary; Hypoxia; Submarine groundwater discharge.