Research On Relationship Among Submerged, Floating Plant Community Structure And Water Environmental Factors

Higher hydrophyte plays an important role in ecological system, which not only can absorb water and nutrient, secrete allelopathic substance inhibiting the growth of phytoplankton, but also can improve the physical, chemical and biological characteristics of lake ecosystems. At present, reclaiming farmland from lakes and aquaculture make lake hydrophyte in China facing habitat fragmentation, species communication and migration blocked, population near the threshold and other severe challenge. NaSi Lake hydrophyte is facing the same problems. Thus studying on NaSi Lake hydrophyte, especially on pelagic zone submerged plant and floating plant community structure, and analyzing the effect of water environmental factors on the distribution and growth of NaSi Lake hydrophyte will provide the reference for sustainable utilization of lakes resources and higher plants restoration. And the study also will provide theoretical basis and feasible measures for improving lake water quality using aquatic vascular plants and other pure biological methods,In present study, hydrophyte community in NanSi Lake pelagic zone was analyzed. Using sampling method, and determined the water quality at the same time, and then used the method of statistics, mathematical ecology and other data processing and analysis to explore the correlation between the dynamics of hydrophyte community structure and the water quality. The main research content included NaSi Lake hydrophyte species composition, classification of plant communities, important value, biological diversity and biomass analysis, the relationship among species diversity, biomass and water quality.Through research on community structure of submerged plant and floating plant in NanSi Lake and its relationship with environment, the thesis put forward several conclusions:1). The survey results in2011showed that, a total of26species of aquatic plants were identified in NaSi Lake, belonging to16families,19genera and26species, respectively. They included7families,10genera and14species of monocotyledon plants,7families,7genera and10kinds of dicotyledonous plants. There were a total of12species in15points of the sampling area, including9species of submerged plants,2species of floating plant,1species of floating plants. Submerged plant is the main life NaSiHu open water aquatic plants.2) There were11main community types of submerged and floating vegetation in NanSi Lake, including9submerged plant communities,2floating plant communities. Most of them were submerged plant communities:①Potamogeton crispus community②Potamogeton lucens community③Potamogeton pectinatus community④Potamogeton malaianus community⑤Myriophyllum spicatum community⑥Potamogeton crispus and Myriophyllum spicatum community⑦Ceratophyllum demersum community⑧Vallisneria spiralis community⑨ Hydrilla verticillata community; and there were2floating plant communities, including①Epinephelus awoara community②Hydrocharis dubia community.3) The biomass and distribution of submerged and floating plant existed significant difference in different seasons. In April, Potamogeton crispus was the dominant species of NanSi Lake submerged plant, followed by Potamogeton lucens. Ceratophyllum demersum, Potamogeton pectinatus and Myriophyllum spicatum were little, such as low biomass. Epinephelus awoara was the dominant species of floating plant. The order of the important value was Potamogeton crispus> Potamogeton lucens> Epinephelus awoara>Ceratophyllum demersum>Potamogeton pectinatus> Myriophyllum spicatum>Trapabispinosa>Potamogeton malaianus> Hydrilla verticillata. The order of biomass was:Potamogeton crispus> Potamogeton lucens> Epinephelus awoara> Potamogeton pectinatus> Myriophyllum spicatum. In June, Potamogeton crispus was still constructive species of submerged plant, Potamogeton lucens also had a widespread distribution, Ceratophyllum demersum, Potamogeton pectinatus and Myriophyllum spicatum began to grow, and Epinephelus awoara was the dominant species of floating plant. The order of the important value was Potamogeton crispus> Potamogeton lucens> Epinephelus awoara> Ceratophyllum demersum> Myriophyllum spicatum> Potamogeton pectinatus>Trapabispinosa> Hydrilla verticillata> Potamogeton malaianus. The order of biomass was:Potamogeton crispus> Potamogeton lucens> Epinephelus awoara> Potamogeton pectinatus> Myriophyllum spicatum>Trapabispinosa. In September, the important value of Potamogeton crispus reduced to the minimum, Myriophyllum spicatum grew rapidly, and becoming the dominant species of submerged plant. Next was Potamogeton pectinatus, Potamogeton lucens in Weishan lake has large distribution. The order of the important value was Myriophyllum spicatum> Potamogeton pectinatus> Potamogeton lucens> Ceratophyllum demersum> Hydrilla verticillata> Epinephelus awoara> Potamogeton malaianus>Trapabispinosa. The order of biomass was: Potamogeton crispus> Potamogeton lucens> Myriophyllum spicatum> Hydrilla verticillata> Epinephelus awoara> Potamogeton malaianus> Ceratophyllum demersum. From the point of space, the order of four lakes biomass was Weishan lake>Dushan lake> Nanyang lake> Zhaoyang lake.Through biodiversity analysis of the submerged plant and floating plant in NanSi Lake pelagic zone, the main plant community species richness Margalef index was coordinated with Shannon-Wiener index and Simpson index. Part of the community species missed due to human facors, which affect the uniformity of the distribution of vegetation. Species richness, diversity and ecological dominance were interlinked; and their changes were basically synchronous.4) Evaluation on the water quality of NanSi Lake. Looking from the monitoring results of NanSi Lake, Dushan lake water quality was best, and eutrophication degree was the lightest. While Nanyang showed the heaviest degree of eutrophication, even some point appeared severe eutrophication (Nanyang lake relieving estuary showed severe eutrophication in April and September). The water quality was all in the stage of eutrophication, except November was mild eutrophic.5) The analysis results showed that the main factors influencing the hydrophyte biodiversity and biomass were water temperature, transparency, chlorophyll. Water temperature showed strong negative correlation with biomass of hydrophyte in September, which may be resulted from the impact of massive death of Potamogeton crispus on the hydrophyte biomass. In April, NanSi Lake aquatic plant species (S), the diversity index (H), biomass (B) showed significant positive correlation with water transparency SD content (P<0.05); In June, the biomass (B) was significantly associated with water transparency (P<0.05); The diversity index (H) was significantly correlated with transparency (SD) in November (P<0.05). The hydrophyte biodiversity index showed positive correlation with water transparency in2011(P<0.05). The study results showed that transparency was the determinants of hydrophyte biodiversity and biomass in NanSi Lake. In September, the number of species of hydrophyte and biodiversity index showed strong negative correlation with chlorophyll. And the reason was that the chlorophyll content was an important indicator of phytoplankton species and quantity, and it also was the dynamic variation of the physical and chemical properties of water body comprehensive reflection index. In general, the chlorophyll content increased with the the numbers of phytoplankton, which showed positive correlation between them. While aquatic plants was negative correlated with the growth of planktonic algae in lakes. The increase of the amount of phytoplankton resulted in blooms in eutrophication water, which floated in water; causing shortages of underwater light conditions and affecting the growth of hydrophyte. The sensitivity of the plant to light was different, which affected the biodiversity of the aquatic plants.