Nutrient-rich submarine groundwater discharge fuels the largest green tide in the world

Shibin Zhao; Bochao Xu; Qinzhen Yao; W C Burnett; M A Charette; Rongguo Su; Ergang Lian; Zhigang Yu

doi:10.1016/j.scitotenv.2020.144845

Nutrient-rich submarine groundwater discharge fuels the largest green tide in the world

Sci Total Environ. 2021 May 20:770:144845. doi: 10.1016/j.scitotenv.2020.144845. Epub 2021 Jan 21.

Authors

Shibin Zhao¹, Bochao Xu², Qinzhen Yao³, W C Burnett⁴, M A Charette⁵, Rongguo Su⁶, Ergang Lian⁷, Zhigang Yu³

Affiliations

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

PMID: 33736390
DOI: 10.1016/j.scitotenv.2020.144845

Abstract

One of the largest "green tide" (Ulva prolifera) outbreaks in the world has occurred every year from 2007 to present in the Southern Yellow Sea, China. Currently, the coastal area around Jiangsu Province (Subei Shoal region) is thought to be the origination point of these giant green tide blooms. The combination of high nutrient demand but low river discharge and other inputs suggests that there is a significant flux of submarine groundwater discharge (SGD) in this area. By using a radium mass balance model, we estimated the SGD flux in the area to be (0.7-1.4) × 10⁹ m³ d^-1 (6.1-12 cm d^-1), at the high end of SGD fluxes worldwide. Geographically, Subei Shoal is less than 5% of the entire Southern Yellow Sea area, while our calculated SGD flux just for the shoal area is ~3 times larger than previously documented for the whole Southern Yellow Sea. Therefore, Subei Shoal may be considered a SGD hotspot that plays an important role in SGD associated material fluxes. Compared to inputs from local rivers, atmospheric deposition, and anthropogenic activities, SGD-derived nutrients are the main source term that can support the growth of macroalgae. We specifically highlight that this type of areas that are shallow, intensively mixed, anthropogenically polluted, sandy or muddy with heavy bio-irrigation, may have a higher risk of suffering harmful ecological problems, even with limited terrestrial runoff.

Keywords: Green tide; Radium; Southern Yellow Sea; Subei shoal; Submarine groundwater discharge.

MeSH terms

China
Environmental Monitoring*
Groundwater*
Nutrients
Rivers