以植被生物完整性评价梁子湖湖滨湿地生态系统健康

湖滨湿地植被是湖滨带生态系统的主要特征,以湖滨湿地植被为对象可评价湖滨带生态系统健康状况。通过对梁子湖湖滨湿地植被的详细调查,共鉴定出植物182种,隶属于52科128属,其中湿生植物147种,水生植物35种。水生植物中有20种挺水植物,6种浮叶植物和9种沉水植物。采用植被生物完整性(VIBI)方法评价梁子湖湖滨湿地生态系统健康,对21个备选指标进行筛选分析,建立了以挺水植物物种数、多年生植物物种数、外来物种百分比、香农多样性指数、植物区系质量指数FQAI、耐受性物种百分比、敏感性物种百分比为核心指标的评价体系,三分法对指标进行赋值,将梁子湖湖滨湿地划分为健康、良好、一般和较差4个等级。评价结果表明,梁子湖湖滨湿地22个调查位点中,处于健康状态的有3个位点,良好6个,共占总位点数的41%,一般和较差分别为7个和6个,共占59%。总体上看,东梁子湖和牛山湖湖滨湿地位点健康状况较好,而西梁子湖湖滨湿地差异性较大,山坡湖南部湖湾和前江大湖北部位点健康状况良好,张桥湖湖滨湿地健康状况一般,评价较差的6个位点集中在宁港湖周围和前江大湖南部沿岸。底质和人类活动如水位调控、围网养殖、放牧等是影响梁子湖湖滨湿地植被生物完整性的主要原因。

HEALTH ASSESSMENT OF RIPARIAN WETLAND ECOSYSTEM OF LAKE LIANGZIHU BY VEGETATION INDEX OF 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. Vegetation with the advantages including ease of identification and immobility is the key feature of wetland ecosystem and can be used to assess the health status of the wetland ecosystem. Lake Liangzihu, as the Wetland Nature Reserve of Hubei Province, plays an important role in biodiversity protection by offering habitat for waterbirds, macrophytes and fish. 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. 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. 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, andthe 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 were 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 of vegetation survey showed that there were 182 plant species belonging to 52 families and 128 genera in Lake Liangzihu, including 147 hygrophytes, 20 emergent macrophytes, 6 floating-leaved plants, 9 submerged macrophytes, respectively. 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. The results indicated that in the 22 sampling sites we have investigated, only 3 and 6 were in 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. The main factors affecting the biological integrity of vegetation were sediments and human activities such as water level regulation, enclosure aquaculture and grazing.