FIGURE 2 Environmental conditions along the salinity gradient. The distribution of (a) temperature (T), (b) dissolved inorganic nitrogen (DIN) and (c) orthophosphate (PO43¯) in surface water in the Krka River Estuary (triangles) and in the Wenchange River Estuary (squares).
Phytoplankton blooms developed in both estuaries. Much higher Chla concentrations were detected in the Wenchang River Estuary than in the Krka River Estuary (Figures 3a-b and Table S2). The specific pigments roughly identified phytoplankton groups (Figures 3c-d and Table S2). The dominance of fucoxanthin indicates that diatoms were the main blooming group in both estuaries. The decrease inviolaxanthin and lutein pigments with decreasing salinity suggests that riverine chlorophytes and prasinophytes were acclimated to less saline waters in the estuaries. In the Krka River Estuary, the significant contribution of 19’–hexanoyloxyfucoxanthin at intermediate salinities indicates an important involvement of prymnesiophytes, while lower salinities support the development of nanoflagellates. The pigment contribution in the Wenchang River Estuary suggests that different phytoplankton groups have evolved compared to the Krka River Estuary. In addition to diatoms, the largest contributions to the phytoplankton community in the Wenchang River Estuary were cyanobacteria (zeaxanthin ), as well as chlorophytes, which are related to chlorophyll b .