The Response Of Phytoplankton Community To Submerged Plant Habitat In Eutrophic Water

Eutrophication refers to a high concentration of nitrogen and phosphorus which is outof self-purification in the water, making an increase in the number of certain algal groupsand individuals, a decline of transparency and a reduction of dissolved oxygen. Waterpollution problems caused by the eutrophication is one of the important issues the worldfacing. For the problem of eutrophication, we studied the effect of purification and theresponse of phytoplankton community to the four submerged plants （such as Vallisnerialongipedunculata（G）、Hydrilla verticillata（H）、Potamgeton malaianus（M）、Vallisneriaspiralis（P）） in eutrophic water through a simulation experiment in an enclosed cement pitby sediment capping technology and phyto-remediation technology in this paper. And alsothe best coverage of Vallisneria longipedunculata in water restoration was explored at thesame time. By exploring the differences of water habitats caused by different submergedplants and coverage from the perspective of phytoplankton, this paper aims at providingtheoretical basis for remediation, to explore a practical treatment measures which has agood ecological effect.The results showed that:By covering the sediments with physical materials only （Without submerged plants）,can slow the release of nutrients, keep the density and biomass of phytoplankton remains ata lower level in a short period of time. The density of phytoplankton keeps at5×105cell·L^-1,but the cell density value increases in magnitude later, the number is more than2.5×106cell·L^-1. The biomass of phytoplankton changes from2.0mg.L^-1to more than8.0mg.L^-1.What’s more, the biodiversity index is lower in the water without submerged plants, atabout1.46in average. There is a significant difference between water with submergedplant and water without it. The water habitats created by submerged plants are veryimportant for maintaining the biodiversity phytoplankton.When planting Vallisneria longipedunculat in the water by a larger proportion（such as100%or80%）, phytoplankton bio-diversity and uniformities are relatively higher, at about2.1and2.0in average. But there is a greater impact on water nutrients and phytoplanktoncaused by the decline of submerged plants. When the proportion of plants is40%, thefluctuations of phytoplankton are least. Therefore, in practical applications to reduce thesecondary pollution of submerged plants and its impact on phytoplankton in, exploring the appropriate proportion of the planting is very important.The species of the phytoplankton community, biomass and community structure aredifferent in the pits with different plants, such as Vallisneria longipedunculata, Hydrillaverticillata, Potamgeton malaianus, Vallisneria spiralis. Between the four plants, the plantof Vallisneria longipedunculata and Vallisneria spiralis can inhibit the growth ofphytoplankton effectively and cause changes in phytoplankton community structure. Andby planting Hydrilla verticillata, it’s better enhancing its community structure complexityand biodiversity. The four submerged plants can purify eutrophic water significantly, theorder of nutrient removal efficiency of the four submerged plants is: Vallisnerialongipedunculata> Potamgeton malaianus> Vallisneria spiralis> Hydrilla verticillata.In different water inhabits formed by the four submerged plant, the quantity ofphytoplankton is significantly positively correlated with the nutrient, and theShannon-Wiener diversity index and Pielou evenness index have a significantly positivelycorrelation with TP, the coefficients is0.398and0.367respectively, a significantlynegatively correlation with TN:TP at-0.418and-0.404respectively.