Seasonal and spatial variations of water quality and trophic status in Daya Bay, South China Sea.

Coastal water quality and trophic status are subject to intensive environmental stress induced by human activities and climate change. Quarterly cruises were conducted to identify environmental characteristics in Daya Bay in 2013. Water quality is spatially and temporally dynamic in the bay. Cluster analysis (CA) groups 12 monitoring stations into two clusters. Cluster I consists of stations (S1, S2, S4-S7, S9, and S12) located in the central, eastern, and southern parts of the bay, representing less polluted regions. Cluster II includes stations (S3, S8, S10, and S11) located in the western and northern parts of the bay, indicating the highly polluted regions receiving a high amount of wastewater and freshwater discharge. Principal component analysis (PCA) identified that water quality experience seasonal change (summer, winter, and spring-autumn seasons) because of two monsoons in the study area. Eutrophication in the bay is graded as high by Assessment of Estuarine Trophic Status (ASSETS).