Spatial pattern of phytoplankton and its habitat conditions of Tonle Sap Lake in Cambodia during the low-water and high-water seasons.

The spatial patterns of phytoplankton and their habitat conditions were investigated in Tonle Sap Lake, Cambodia, in 2014. During both the low- and high-water seasons, the stratification of water column was weak, and the euphotic zone depth was only half of the total water depth. The concentrations of dissolved inorganic phosphorus (DIP) and phytoplankton biomass indicated by chlorophyll <italic>a</italic> (Chl <italic>a</italic>) per unit volume during the low-water season was three to four times higher than those during the high-water season, whereas the per unit area weights integrated through the water column did not show any seasonal differences on the whole-lake scale. In the high-water season, the intrusion of river water with a very high nitrogen:phosphorus (N:P) ratio (25–189) appeared to be the predominant nutrient source for the lake water with a low N:P ratio (7–27). In contrast, the N:P ratio of the laker water (2–20) was relatively low during the low-water season, implying the possibility of N-limitation. During the low-water season, Chl <italic>a</italic> concentrations were significantly higher in the north basin, which is far from the connecting point to the Tonle Sap River. Non-metric multidimensional scaling (nMDS) ordination indicated seasonal and horizontal variations in the phytoplankton composition at the surface. The abundance of diatoms (<italic>Aulacoseira</italic> and <italic>Suriella</italic>) that favor mixing conditions tended to be higher in the offshore area and during the high-water season. Blooms of cyanobacteria that favor nutrient-rich and low-water movement conditions tended to occur at north basin stations and during the low-water season. [ABSTRACT FROM AUTHOR]