Chlorophyll-a concentration variations in Bohai sea: Impacts of environmental complexity and human activities based on remote sensing technologies

Abstract

This study extensively explores the intricate dynamics of the Bohai Sea ecosystem, a semi-closed marginal sea in China, influenced by both environmental complexity and human activities. By utilizing chlorophyll-a as an indicator, we closely examine how phytoplankton responds to coastal environmental conditions and stressors. The temporal analysis conducted over the 23-year period from 1998 to 2020 reveals a distinctive "bell-shaped" variation in chlorophyll-a concentration. Spatially, a declining trend is observed from coastal to central regions, characterized by widespread low-value areas. Employing M-K and slope trend analyses, we observe a 42.13 % decline in the northern Bohai Sea, contrasting with a significant 57.87 % increase in the central and southern regions. The innovative aspects of this research lie in identifying the complex interplay between chlorophyll-a concentration, human pollution controls, and nutrient inputs. Factors contributing to chlorophyll-a concentration, ranked by significance, include sea surface temperature, photosynthetically available radiation (PAR), and wind speed. Remarkably, the negligible impact of the "2015 Tianjin explosion" underscores the robustness of the Bohai Sea's chlorophyll-a dynamics. Furthermore, the positive correlation between phosphorus input and chlorophyll classifies Bohai Bay as a phosphorus-limited aquatic ecosystem. In conclusion, this study provides crucial insights for the preservation of the Bohai Sea ecosystem, emphasizing the necessity for ongoing monitoring and management strategies in the face of evolving environmental and anthropogenic influences.