| The Yangtze riverine wetland is an important ecological barrier of the Changshu city. Influenced by the recent rapid population growth, industrialization, urbanization, increasing agricultural non-point source pollution and irrational exploitation of wetland resources, the Yangtze riverine wetland in Changshu is suffering from destruction and influence of hunman activities. In order to investigate the wetland plant community diversity and the influence on it from water quality, this study applied sampling method to imply investigation and observation of the plant communities and water quality in five estuarine areas, Fushantang, Wangyuhe, Haiyangjing, Changhuhe, and Baimaotang, of which the soil soil nutriture of substrate, geological and hydrological conditions are resemble. Applying with community species diversity index method, univariate analysis of variance and correlation analysis, the general condition of wetland vegetation, the main community types and plant species composition, diversity characteristics of the riverine wetland were studied. Single factor index method and the integrated pollution index method were used to evaluate the water quality of wetland status and the correlation analysis was implied to study the influence on plant community diversity from the water quality. On this basis, wetland plant community preservation management strategies and utilization measures were proposed for further research of riverine wetland plant community diversity and wetland plant resources conservation and utilization. The main conclusions are as follows:1. The species compositions of plant communities are quite simple in the study area. The whole wetland is associated with advanced vascular plant species counts to 48 species belong to 42 genera and 21 families in total. The riverine wetland vegetation consists majorly of Form. Phragmites australis and Form. Scirpus validus, whereas Form. Scirpus planiculmis, Form. Sagittaria trifolia and Form. Zizania latifolia are scattered as patches in some observing areas. The communities are generally consists of 2 or 3 layers, with a small number of accompanying species. The main dominant species is Phragmites australis, and Importance Values (IVs) of edificators such as Scirpus validus, Scirpus planiculmis, Sagittaria trifolia and Zizania latifolia are also high, other dominant species are seasonal dominant species. And the dominant species within the same year indicate the presentation trend of non-hygrophytes to hygrophytes. Suffering from the invation of invasive alien species, including Solidago canadensis, Conyza canadensis, and Alternanthera philoxeroides, and xerophytes, the species composition and community structure of wetland plant communities reflects degradation characteristics, such as xerophilization and decreasing IVs of dominant species.2. The wetland plant community diversity index increased. The a-diversity index in yr 2010 is higher than which in yr 2009 generallly, except certain observing areas. The Specis Richnesses (R) of the plant communities increase, whereas the distribution evennesses of species decrease. The a-diversity indexs of plant communities in different observing areas are significantly different from each other. Changhuhe bayou area has the highest a diversitiy indices, while it is the lowest in Baimaotang bayou area. Shannon-Wiener diversity index (H) and the probability of interspecific encounter (PIE) have the same variation trend in two years, the two indices in yr 2010 are higher than that in yr 2009, except the Baimaotang bayou area. Simpson dominance index (D) and Pielou evenness index (J) have the same variation trend in two years, these two indices also showed an upward trend except the Wanyuhe bayou area.3. The results of single factor index evaluation indicate that the water quality varies from calss V to inferior class V. The major exceeding pollution factor which surpasses the standards is TN. And the results of comprehensive pollution indices evaluation indicate that the comprehensive contaminated degree of water quality showes the order of Changhuhe bayou area> Haiyangjing bayou area> Baimaotang bayou area>Wangyuhe bayou area> Fushantang bayou area. The water qualities of both years in Changhuhe bayou area are the worst, the exceeding pollution factors are TN, NH3-N, CODMn and TP. The a-diversity indices of plant communities increases along with the increasing of NH3-N, CODm,,, BOD5, TN, and TP in the water, but has no significant correlation with pH. The variation feature of water quality of each year in different observing areas shows the similar trend of a diversity variation feature. In the context of a certain threshold, the increasing concentration of contaminants, such as nitrogen and phosphorus, can provide the necessary nutrients plants need for growth, which will help to increase the diversity of wetland plant communities. However, high levels of nutrients in the water, may became a potential impact of wetland degradation factors.4. The protection and management strategy of the Yangtze riverine wetland in Changshu are:a. to strengthen management and planning; b. to strengthen monitoring and dynamics studies of wetlands; c. to enhance pollution control and protect the wetland environment. To restore the riverine wetland plant community, preserving and protecting actions should be taken in both habitat improvement and vegetation recovery pertinently, with long period monitoring, management and assessment of the restoration actions. In the aspect of wetland resources utilization, three-dimensional development of wetland vegetation and wetland tourism should be adopted to realize the basic rule of wetland protection should be considered first combing with appropriate development. |
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