Nutrient changes in the Bohai Sea over the past two decades

Wen Liang; Yan Wang; Jinglong Mu; Nian Wu; Juying Wang; Sumei Liu

doi:10.1016/j.scitotenv.2023.166696

Nutrient changes in the Bohai Sea over the past two decades

Sci Total Environ. 2023 Dec 10:903:166696. doi: 10.1016/j.scitotenv.2023.166696. Epub 2023 Sep 1.

Authors

Wen Liang¹, Yan Wang², Jinglong Mu¹, Nian Wu³, Juying Wang⁴, Sumei Liu⁵

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, China.
² National Marine Environmental Monitoring Center, Dalian, China.
³ 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, China; Laboratory for Marine Ecology and Environmental Science, Qingdao National Laboratory for Marine Science and Technology, Qingdao, China.
⁴ National Marine Environmental Monitoring Center, Dalian, China. Electronic address: jywang@nmemc.org.cn.
⁵ 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, China; Laboratory for Marine Ecology and Environmental Science, Qingdao National Laboratory for Marine Science and Technology, Qingdao, China. Electronic address: sumeiliu@ouc.edu.cn.

PMID: 37660818
DOI: 10.1016/j.scitotenv.2023.166696

Abstract

With the growing problem of eutrophication in the Bohai Sea, actions have been taken to reduce nutrient inputs, but it remains to be seen whether nutrient levels and structure have been ameliorated. In this study, the nutrient trends in the Bohai Sea are re-examined based on observations from 2000 to 2019. The results suggest that dissolved inorganic nitrogen (DIN) concentrations and DIN/DIP (dissolved inorganic phosphate) ratios gradually increased from 2000 to 2013 but dramatically decreased from 2013 to 2019. The increase and decrease rates of DIN concentrations decreased with increasing water depth, indicating that DIN concentrations in nearshore waters responded more rapidly to changes in human activities. However, DIP concentrations responded weakly to nutrient inputs, with their trends uncoupled. The DIN/DIP ratios have declined close to and in some seasons even below the canonical Redfield ratio in areas with water depths >20 m recently, implying that relative nutrient limitation in these areas may be shifting from relative phosphorus (P) limitation to absence of relative nutrient limitation or relative nitrogen (N) limitation. Atmospheric deposition, wastewater discharge, and riverine input were responsible for 66 %, 21 %, and 13 % of the variance in the decline of DIN concentration, respectively. Several environmental indicators responded positively to the decrease in DIN concentrations and DIN/DIP ratios, with varying degrees of recovery recently. Our study proves the phased success of various nutrient reduction measures taken by the Chinese government to improve the environment of the Bohai Sea over the past decade.

Keywords: Bohai Sea; Environmental recovery; Nutrients; Policy control; Regime transfer.