The linkage between phytoplankton biomass and environment factors: a case study in the Pearl River estuary, China.

With rapid socio-economic development in the Pearl River Delta area, plenty of domestic,industrial, and agricultural effluent is discharged into the Pearl River estuary (PRE), whichresulted in the deterioration of water quality in the region. During two field surveys in March and September 2005 in the PRE, high chlorophyll-aareas were observed. The highest chlorophyll-a concentrations reached 8.34 mg m−3 and6.15 mg m−3 during the two surveys, respectively. Nutrient analysis indicated thatnitrates, phosphates, and silicate concentrations were high. The salinity was near30 psu. Phytoplankton cell density data demonstrated that the high chlorophyll-aconcentrations were related to bloom conditions. In order to find the possible causes of theeutrophication, data for environment factors during and before the observation periods wereobtained, including winds, currents, precipitation, salinity, and sea surface temperature(SST). Between 18 and 20 March 2005, there was a strong northwesterly wind with a speed of 9m s−1 and the surface current flowed southwestward. The salinity rose and the SST droppedduring that time. That suggests the probable occurrence of upwelling, which broughtnutrient-rich bottom cold water up to the sea surface. The precipitation during March 12-15reinforced river runoff, bringing more nutrients into the estuary. With respect to the case inSeptember, a similar situation was observed. 6 days before the event, northwesterly windsprevailed with the highest speed reaching 10 m s−1. The surface current movedsouthwestward. A precipitation rate of 1.3 mm h−1 was observed over the entire study area.Increased salinity was observed during the bloom period. These conditions areupwelling-favorable. It can be concluded that the anomalous high chlorophyll events were very likely related toupwelling during the observation period. The winds favored upwelling. Further, theprecipitation led to the supplement of nutrients from river runoff. The finding from this workis helpful for forecasting algal blooms in productive estuarine waters, like the PRE. Furtherefforts are required to better understand the mechanism of the linkage between highchlorophyll-a and environmental factors. [ABSTRACT FROM AUTHOR]