This paper presents some new data on the spatial distribution and temporal variations of microalgae communities: nanophytoplankton (referred to as nano), picophytoplankton (Pico) and cyanobacteria (cyano). in the Bach Dang Estuary and their potential relationships with environmental factors. Distribution of microalgae density in the study area varied according to season and algal groups. During the rainy season, the cyanobacteria density increased seaward
whereas no significant trend was observed for the nano and pico. In the dry season, the nano and pico densities decreased gradually seaward whereas. in contrast, the cyanobacteria increased seaward. Temporal variations of microalgal densities varied depending on algal group, station and season. Algal density was not correlated with water temperature. Nano (in dry season) and cyanobacteria (at both seasons) were correlated with salinity at stations sampled to examine spatial distribution. During temporal surveys, cyanohacteria and pico correlated well with salinity depending on the station. Nano was the only group correlated with turbidity. in Bach Dang rivermouth in the dry season: Chlorophyll a (chi a) concentrations correlated with the nano and pico densities inthe-surface layer at all stations sampled during the spatial survey (in rainy season). In the dry season, Chi-a concentration at the stations investigated for temporal variations correlated with pico (at Pha Rung and Bach Dang rivermouth stations), nano (Cam river station) and cyanobacteria (Bach Dang rivermouth station). Algal density showed no significant correlation with either nitrate, nitrite, ammonium and phosphate concentrations at the spatial stations, whereas cyanobacteria were correlated with silicate in rainy season, like nano in the dry season. The (emporal mriations of algal density at Bach Dang rivermouth in dry season matched those of some nutrients. such as cyanobacteria with nitrite, phosphate and silicate
pico with nitrite, phosphate, silicate and dissolved inorganic nitrogen.. nano with nitrate. Microalgae did not correlate with neither heavy fnetals (Hg, Cd, As, Cu. Pb, and 2n) nor total pesticides.