In-situ responses of phytoplankton to graphene photocatalysis in the eutrophic lake Xingyun, southwestern China

Graphene photocatalysis is receiving increased attention for its potential to be used as a novel green technology for mitigating harmful algae in highly eutrophic waters. However, graphene is seldom applied to in situ aquatic ecosystems for environmental applications. Here, the impacts of graphene photocatalysis on phytoplankton and environmental conditions were evaluated through an in situ macrocosm experiment in the eutrophic Lake Xingyun, southwestern China. The graphene photocatalysis treated area had significantly reduced conductivity, total nitrogen (TN), total phosphorus (TP) and dissolved phosphorus concentrations, as well as increased dissolved oxygen (DO) concentrations. The abundances of all species of the genus Microcystis were significantly reduced in the graphene photocatalysis-treated area; in contrast, the abundances of all species of the diazotrophic genera, including Anabaena and Aphanizomenon, greatly increased after treatment with graphene photocatalysis. Eukaryotic algae, especially Chlorophyta, Euglenophyta and Pyrrophyta, as well as Cryptophyta, had significantly higher abundances in the graphene photocatalysis-treated area, whereas most of the eutrophic diatom species had lower abundances in the treated area. These observed differences in eukaryotic algae between the two groups might be related to their sensitivity to graphene photocatalysis and their tolerance of nutrients. Generally, graphene photocatalysis can make a great contribution to the improvement of eutrophic water, as evidenced by the reduction in cyanobacteria abundance and phosphorus concentration, as well as the increase in species richness and the dissolved oxygen concentration in the treated area. However, the mechanisms underlying these differences in phytoplankton community structure and environmental conditions require further study.