Interaction between sea surface chlorophyll a and seawater indicators in the sea ranching area: A case study in Haizhou Bay

Abstract

Chlorophyll A (Chla) is a key parameter that reflects phytoplankton biomass and estimates red tide intensity. Studying the distribution characteristics of Chla concentrations and their correlation with various environmental indicators is of great significance. In this study, we analysed environmental monitoring data of Haizhou Bay, Lianyungang, Jiangsu Province, from 2004 to 2021 using a generalized additive model (GAM) to investigate the spatiotemporal variation in sea surface chlorophyll a (Chla) and its correlation with other sea water indicators. The results showed that the concentration of Chla increased gradually over the years but varied within the year, with the highest concentration in summer (July to September). With the passage of years, the fitting results of the model may be more consistent with the actual situation of Chla concentration distribution in this region. Compared with univariate GAM, multivariate GAM could effectively explain the variation in Chla concentration in the region over 20 years. Generally, the variation in Chla concentration is influenced by nutrients, BOD5 and salinity, depth, temperature and DO. BOD5 and depth are significant variables that can explain the variation in Chla concentration, but their interactions should be avoided in the analysis. We believe that the Chla concentration not only is affected by the rapid change in the estuarine environment but also has a potentially positive effect on the time lag effect of sea ranching construction, indicating that the interannual change in sea ranching construction plays a positive role in the potential change in the offshore environment. This study can provide a theoretical basis and an important reference for the further construction and management of sea ranching in the coastal waters of the world.