Mao, X.; Kuang, C.; Gu, J.; Kolditz, O.; Chen, K.; Zhang, J.; Zhang, W., and Zhang, Y., 2017. Analysis of chlorophyll-a correlation to determine nutrient limitations in the coastal waters of the Bohai Sea, China.

The coastal water of Qinhuangdao, a famous resort located in the NW of the Bohai Sea, China, suffered algal bloom for a consecutive 3 years by 2011, causing great economic loss. Based on measurements at 46 sampling points in the study's coastal area in May, August, and October 2011, the seasonal and spatial characteristics of the chemical indicators and chlorophyll-a (Chl-a) were analyzed. The chemical indicators for pH, chemical oxygen demand (COD), and reactive silicate (SiO₃-Si) showed higher concentrations in the summer than in the spring and fall, whereas the nutrients of reactive phosphate (PO₄-P) and dissolved inorganic nitrogen (DIN) presented complex seasonal characteristics under the combined influence of abundant nutrients from rivers and nutrient consumption by large algal bloom in August. Subsequently, two methods—a fuzzy, integrated assessment and an organic pollution index—were used to characterize the organic pollution. The trophic status of most coastal waters were oligotrophic and mesotrophic, and most coastal waters were clean in spring and summer, except in the vicinity of the harbor and estuaries, where the organic pollution index was generally high. Finally, Pearson correlation coefficients of various variables were analyzed, which demonstrated that, commonly, there was a significant positive correlation between COD and Chl-a. Because algal blooms in August changed the nutrients structure of the coastal waters, Chl-a, in a remarkably high concentration, had significant correlation with NO₂-N, the atomic N/P ratio, and the atomic N/Si ratio. The algal bloom aggravated the current P limitation, and the atomic N/P ratio, the PO₄-P concentration, and the COD can be selected as the three most-sensitive indicators of algal bloom in Qinhuangdao coastal water. These findings have provided scientific supports for local authorities who are taking measures to control pollution emissions and to prevent the recurrence of algal blooms.