The impact of nutrient enrichment on the phytoplankton and bacterioplankton community during a mesocosm experiment in Nan'ao of Daya Bay

The increase of nutrient input into coastal seawaters has caused severe eutrophication and changed the phytoplankton and bacterioplankton community in different ways. A 10-day mesocosm experiment was carried out in Nan'ao with nine mesocosms (M0-M8) by adding different combinations of N, P and Si, either on the first day only or in a daily enrichment during the experiment, in order to assess the response of phytoplankton and the bacterioplankton community. The results showed that phytoplankton abundance increased with nutrient enrichment and over 95% of total identified phytoplankton species was dominated by diatoms and dinoflagellates. Algal blooms were observed in M6 and M7 on day 7 and day 10, with a peak value of phytoplankton cell density in M6 and M7 of 9.92x10(6) cells/l and 4.59x10(7) cells/l, respectively. A-proteobacteria and -proteobacteria dominated the bacterioplankton community in all experimental mesocosms. Lower N:P ratio in the mesocosm seawater led to higher biodiversity of bacterioplankton. The results also indicated that bacterioplankton and phytoplankton had an opposite nutrient uptake strategy. Bacterioplankton is introduced in the analysis of nutrient enrichment of the plankton community, and this study would benefit from further research on food webs and biogeochemical cycles and will help to resolve the existing eutrophication problems in Nan'ao.