The spatial distribution of environmental factors, chlorophyll a (Chla), phytoplankton abundance, and community structure in the Laizhou Bay were investigated in August 2018 (wet season after pollution control) to clarify the effects of the pollution control of the Xiaoqing River, which is a major source of pollution, on environmental factors and phytoplankton community structure in this area. The results showed that the environmental factors changed significantly after pollution control of the Xiaoqing River. The concentrations of dissolved inorganic nitrogen (DIN), dissolved inorganic silicon (DSi), NO3-, and NO2- decreased significantly, with values only 40.1% to 60.4% of those from the same period of in 2017 (the nearest year before the pollution control), whereas dissolved inorganic phosphorus (DIP) and NH4 increased by 2.5 and 1.4 times that of their concentrations in 2017. The spatial distribution of environmental factors changed significantly, with the nutrient concentrations around the Xiaoqing River estuary noticeably decreasing. The abundance of phytoplankton cells was 21.5×106 cell·m-3, which was close to the results of a previous study, whereas the ρ(Chla) was 2.43 μg·L-1, which decreased obviously. Both microscopic analysis and pigment taxonomy suggested that phytoplankton community structure in the Laizhou Bay changed clearly, with the dominant community shifting from diatoms alone to the co-dominance of diatoms and cyanobacteria. Chaetoceros curvisetus, Skeletonema costatum, and Cerataulina pelagica, which were commonly observed in the Laizhou Bay before pollution control of the Xiaoqing River, decreased in 2018, whereas the abundance of common dominant freshwater species (e.g., Merismopedia sp. and Synedra spp.) increased significantly. Redundancy analysis (RDA) showed that the phytoplankton community was significantly related to nitrogen, phosphate (negative correlation), and salinity (negative correlation) after pollution control of the Xiaoqing River, indicating that the variation in nutrient concentration and the structure of river runoff input may be the main factors affecting phytoplankton community and dominant species structure.
Keywords: Laizhou Bay; Xiaoqing River; environmental factors; phytoplankton; pollution control.