Unravelling Nutrients and Carbon Interactions in an Urban Coastal Water during Algal Bloom Period in Zhanjiang Bay, China

Nutrients and carbon play important roles in algal bloom and development. However, nutrients and carbon interactions in the period of the spring algal bloom are not well understood. The aim of this study is to explore the nutrients and carbon interactions in the period of the spring algal bloom covering an urban Jinsha Bay (JSB) coastal water in Zhanjiang Bay (South China Sea) using in situ multidiscipline observation. The results showed that the average concentration of total nitrogen (TN), total phosphorus (TP), and dissolved silicon (DSi) was 97.79 +/- 26.31 mu mol/L, 12.84 +/- 4.48 mu mol/L, and 16.29 +/- 4.00 mu mol/L in coastal water, respectively. Moreover, the average concentration of total dissolved carbon (TDC), dissolved inorganic carbon (DIC) and organic carbon (DOC) in JSB was 2187.43 +/- 195.92 mu mol/L, 1516.25 +/- 133.24 mu mol/L, and 671.13 +/- 150.81 mu mol/L, respectively. Furthermore, the main dominant species were Phaeocystis globosa and Nitzschia closterium during the spring algal bloom. Additionally, the correlation analysis showed salinity (S) was significantly negatively correlated with nutrients, indicating that nutrients derived from land-based sources sustained spring algal bloom development. However, as the major fraction of TDC, DIC was significantly positively correlated with S, which was mainly derived from marine sources. Besides, the algal density showed a significant positive correlation with temperature (T) (p < 0.001) and dissolved oxygen (DO) (p < 0.001), but a significant negative correlation with DIC (p < 0.05), suggesting that spring algal blooms may be simulated by water T increase, and then large amounts of DIC and nutrients were adsorbed, accompanying DO release through photosynthesis in coastal water. This study revealed nutrients and carbon interactions in the spring algal bloom of urban eutrophic coastal water, which has implications for understanding the nutrients and carbon biogeochemical cycle and algal bloom mitigation under climate change and anthropogenic pressures in the future.

Automated summary

This study aimed to explore the nutrients and carbon interactions in the spring algal bloom of urban Jinsha Bay (JSB) coastal water. The results showed that the average concentration of total nitrogen, total phosphorus, and dissolved silicon in coastal water was high, indicating the presence of nutrient sources from land. The average concentration of total dissolved carbon, dissolved inorganic carbon, and organic carbon in JSB was also high, mainly derived from marine sources. The dominant species during the spring algal bloom were Phaeocystis globosa and Nitzschia closterium. The study revealed the interactions between nutrients and carbon in the development of spring algal bloom, which has implications for understanding the biogeochemical cycle and mitigation of algal blooms in the future.