Structure of the phytoplankton community at the Lingshui karst spring and its implications for water environment

The submerged plants in the Lingshui lake has gradually reduced since 2010, and largely disappeared in 2013. In order to explore the causes of degradation of karst water ecosystem at this place, phytoplankton investigation and monitorin to the water environment have been conducted at the Lingshui and Luobotan karst springs in April, July and October of 2016, respectively. The results show dominant phytoplankton of 16 species belonging to 3 phyla at Lingshui and 13 phytoplankton species belonging to 3 phyla at Luobotan. The phytoplankton similarity reached 60% for both places. The basic types of phytoplankton species did not change during the three survey times, and the abundance was characterized by an order of April, July, and October from high to low. Water quality evaluation based on biodiversity indexes and chlorophyll shows that Luobotan was better than Lingshui, indicating that the water environment might degenerate after submerged plants died. RDA and correlation analysis between phytoplankton and environment shows that total nitrogen (TN) was the decisive factor for phytoplankton community. That phytoplankton has stronger absorptive capacity to nitrogen nutrient might be one of the reasons that submerged plants died in the Lingshui lake. The concentrations of HCO3- and Ca2+in the karst water environment can indicate the growth state of phytoplankton.