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 .