Diversity And Community Succession Of Macrophytes In Jianghan Lake Groups

In recent years, the irrational anthropogenic interferences made aquatic plant resources dried up and the diffusion path of aquatic organisms were blocked by building dykes between rivers and lakes. The action of reclaiming land from bay made a habitat loss of aquatic plants at the coastal zone and water quality gradually deteriorated by discharging a large amount of pollutants into the lakes. At the same time, excessive farming intensified the eutrophication degree of lakes, leading to serious damage of the natural habitat and over-exploitation of resources. Therefore, the work of studying, managing and protecting aquatic biodiversity has become increasingly important and necessary. Based on previous results and data obtained from field investigation in2011, we studied the species diversity and dynamic changes of aquatic plants, the distribution of aquatic vegetation, community construction and succession features of Janghan Lake Groups, such as Liangzi Lake, Chang Lake, Futou Lake and Zhangdu Lake. In order to explore the driving factors of aquatic plant community succession, we used correspondence analysis in this study and then put forward protection suggestion and measures. Main results are as follows:(1) The species number and dominant species changed a lot in Janghan Lake Groups. From1982to2011, the aquatic plant resources of Liangzi Lake had been abundant and the dominant submerged plants hardly changed, including Potamogeton crispus, Vallisneria denseserrulata and P.malaianus. Newly increased dominant species were Zizania latifolia Trapa bispinosa, Alteranthera philoxeroides, Eichhornia crassipes and Elodea nuttallii. During the year of1985and2011, there was an obvious variation on species quantity and dominant species in the lake of Changhu. Aquatic plants of Potamogetonaceae decreased significantly and previous dominant species, such as P.maackianus, nearly disappeared. However, some emergent plants, such as Zizania latifolia and Typha angustifolia, and invasive plants including Alteranthera philoxeroides and Eichhornia crassipes became new dominant species. Between1988and2011, the aquatic plant species and dominant species varied to a certain extent in Futou Lake. Nymphaea tetragona, Najas ancistrocarpa, N. graminea and N. gracillima disappeared during the period. The original dominant species, including P.maackianus, Vallisneria denseserrulata and Hydrilla verticillata, turned into sub-dominant species or companion species. From1992to2011, vegetation types, species quantity and dominant species increased obviously in the lake of Zhangduhu. Trapa bispinosa had always been dominant species in this lake and newly increased dominant species were Echinochloa crusgalli, Polygonum hydropiper, Typha angustifolia, Alteranthera philoxeroides and Eichhornia crassipes.(2) The type and the number of dominant community changed obviously in Janghan Lake Groups. In the lake of Liangzi, P. malaianus association took dominant position before, but now it scatterred in certain waters and didn’t form an association. Newly increased associations were P. hydropiper association, N. nucifera+E. ferox association and so on. The dominant aquatic plant associations in Liangzi Lake gradually varied from submerged macrophytes to the submerged+emergent+floating macrophytes. In the lake of Changhu, the numbers of dominant submerged aquantic plant association decreased and the structure of associations simplified. Newly increased associations were E. crassipes association, Z. latifolia association and N. nucifera association. The dominant aquatic plant associations gradually varied from submerged macrophytes to the emergent+floating macrophytes associations in Changhu lake. In the lake of Futou, emergent plant associations and free-floating plant associations of lagre area newly appeared, and M. spicatum+C. demersum association became a new association. The dominant aquatic plant associations gradually varied from submerged macrophytes to the submerged+emergent+free-floating macrophytes in Futou lake. The number of emergent plant associations increased a lot, T. bispinosa association had always been the dominant floating-leaved association and submerged associations changed unobviously. A large area of Ceratopteris pterioides, invader Eichhornia crassipes and mass propagated Alteranthera philoxeroides made up new associations.(3) The vegetation coverage, the mean biomass per m2and the totle biomass seemed to decrease obviously in Liangzi lake, Chang lake, Futou lake and Zhangdu lake. During30years in the lake of Liangzi, the vegetation coverage reduced to14.42%from100%, the mean biomass per m2decreased to99.52g/m2from4420g/m2and the totle biomass declined by 88.33%. During26years in the lake of Changhu, the vegetation coverage reduced to4.2%from90.8%, the mean biomass per m2decreased to193.5g/m2from1537.5g/m2and the totle biomass declined by87.5%. During23years in the lake of Futou, the vegetation coverage reduced to6.9%from80.5%, the mean biomass per m2decreased to406g/m2from3115g/m2and the totle biomass declined by91.96%.(4) CCA analysis showed that the main environment factors affecting plant distribution in Lake Liangzi, Changhu, Futou and Zhangdu were TN and TP. Our analyses indicated that the human disturbances such as large-scale seine farming activities, dam in enclosures, irrational sewage of industrial and domestic wastewater, excessive use of agricultural fertilizer, water eutrophication and sightseeing were the main reasons for reduction of aqautic plant diversity of the typical lakes in Janghan Lake Groups.