| A health ecosystem can withstand the environmental pressures, and continued to maintain its biological integrity. Biological integrity is the ability of an aquatic ecosystem to support and maintain a balanced, integrated, adaptive assemblage of organisms having a species composition, diversity, and functional organization comparable to that of natural habitats within a region. The ecosystem can be seen health with the high biological integrity. The Index of Biological Integrity(IBI) is one of the common methods to assess the health of ecosystem with many indicators. Vegetation with the advantages including ease of identification and immobility is the key feature of wetland ecosystem, which can be used to assess the health status of the wetland ecosystem, providing a theoretical basis for lakeside wetlands protection and restoration.Lake Liangzihu, as the Wetland Nature Reserve of Hubei province, plays an important role in biodiversity protection by offering habitate for waterbirds, macrophytes and fish. However, with the rapid development of economy and urbanization accelerated of the watershed of Lake Liangzihu, human impacts such as fence farming, tourism attractions construction, construction of dams, and other human activities become more and more, the riparian wetland of Lake Liangzihu suffered damage to some degree, the pressure on the ecosystem is increasing gradually, and the risk of degradation is also increasing.In this paper, to evaluate the health status of the riparian wetland of Lake Liangzihu, a vegetation index of biotic integrity (VIBI) was developed from data collected by vegetation survey. The vegetation survey were carried out in two seasons, summer and winter, respectively.In summer,182 plant species belonging to 52 families and 128 genera in Lake Liangzihu were identified, including 147 hygrophytes,20 emergent macrophytes,6 floating-leaved plants,9 submerged macrophytes, respectively. The Shannon diversity index were between 0.78 and 2.49. The dominant plant species were Conyza Canadensis, Cynodon dactylon, Carex argyi, Echinochloa crusgalli, Juncus effuses, Zizania caduciflora, Typha orientalis and Trapa bispinosa. The dominant association were Trapa bispinosa Ass., Vallisneria natans-Trapa bispinosa-Nymphoides indica Ass., Phragmites australis-Zizania caduciflora Ass. and Vallisneria natans-Najas minor-Hydrilla verticillata Ass.In winter,102 plant species belonging to 39 families and 89 genera in Lake Liangzihu were identified, including 94 hygrophytes,4 emergent macrophytes,1 floating-leaved plants,3 submerged macrophytes, respectively. The Shannon diversity index were between 1.30 and 2.30. The dominant plant species were Cynodon dactylon, Calamagrostis epigejos, Artemisia lavandulaefolia, Galeopsis bifida, Imperata cylindrical and Hydrocotyle sibthorpioides. The dominant association were Cynodon dactylon Ass., Calamagrostis epigejos Ass., Artemisia lavandulaefolia-Cynodon dactylon Ass., Hemarthria altissima -Suaeda glauca-Artemisia lavandulaefolia Ass., Galeopsis bifida-Cynodon dactylon Ass., Hydrocotyle sibthorpioides-Cynodon dactylon Ass., Carex breviculmis Ass. and Phragmites australis Ass.To establish the VIBI calculation,21 candidate vegetation metrics based on species richness and composition, vegetation abundance, ecological affinity, and species tolerance were tested for their ability to discriminate between impaired and least-impaired habitat conditions. In summer, seven discriminatory metrics, Number of emergent species, Number of perennial species, Percent exotic species, Shannon-weaver diversity index, Floristic Quality Assessment Index(FQAI), Percent tolerant plant species and Percent intolerant plant species, were finally selected with a range test, box-and-whisker analysis and Pearson correlation analysis. We then assigned scores for each metric based on the statistical analysis by using three scoring method, the scoring criteria were based on the distribution of the metrics'values across all sites. The total VIBI score was obtained by summing the scores from the 7 metrics, resulting in a maximum score of 35. The criteria of health ranking was finally determined based on the 25% percentile of VIBI value in reference sites. Four quality classes (Good, Fair, Poor, and Very poor) of the health status were defined. The results indicated that in the 22 sampling sites we have investigated, only 3 and 6 were good and fair, respectively, totally covering a percentage of 41%, while 59% of which were not satisfactory. In general, the health status of eastern Liangzi Lake, Niushan Lake, Shanpo Lake and northern part of Qianjiang Lake were good, Zhangqiao Lake were in poor, and the six worse sites were along the coast of Ninggang Lake and southern Qianjiang Lake.In winter, through the same analysis, we get fivet core metrics, they were Number of perennial species, Percent annuals species, Shannon-weaver diversity index, Percent tolerant plant species and Percent intolerant plants species. The results indicated that in the 17 sampling sites, only 6 were good or fair, covering a percentage of 35%, while 65% of which were not so good. The health status of eastern Liangzi Lake were quite good. The three sites of Niushan Lake was good, poor and very poor, respectively. The sites in northern part of Qianjiang Lake were fair, the health status of Zhonghu Lake, especially along the coast of Ninggang Lake and Nanzui, were poor.Overall, the coverage of hygrophytes in the riparian wetland of Lake Liangzihu was wide, the species was rather rich. But the species of aquatic plants were small. The health status of eastern Liangzi Lake, Niushan Lake, Shanpo Lake and northern part of Qianjiang Lake were good, Zhangqiao Lake were in poor, along the coast of Ninggang Lake and Nanzui were very poor.The main factors effecting the biological integrity of vegetation were natural factors such as sediments, meteorological disasters, and human activities such as water level regulation, enclosure aquaculture and graze. |
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