Wetlands are valuable resources for sustaining biological diversity, but unfortunately they have historically diminished in both quantity and quality. However, little is known about the degree to which the biology of wetlands changes in response to human disturbances. Recently, wetland condition has been assessed using functional assessment methods. Although functional assessment methods include a function for support of wildlife habitat, they usually do not directly measure the biological communities in wetlands and therefore cannot substitute for a biological assessment method.
Indexes of biological integrity (IBIs) are one of the most commonly used methods by federal and state agencies in the United States to assess the health condition of wetlands. The IBI approach provides a direct measure of aquatic life that is represented by diverse natural flora and faunal communities. Many groups of organisms have been used as indicators to estimate environmental quality. IBIs have rarely been applied in China; they have been reported only in a small number of studies that evaluated the health of stream ecosystems by means of Benthic-IBI and Fish-IBI. Vascular plants are quickly emerging as one of the best indicators of human-mediated disturbances in the environment, and yet no plant-IBI approach has been used to assess wetland health in China.
In this study, we developed a plant-based IBI (P-IBI) to evaluate the condition of the Baiyangdian wetland in response to anthropogenic disturbances. Soil, water, and plant samples were collected from 23 sites in the Baiyangdian wetland during field surveys in 2009 and 2010. Thirty vegetation community composition metrics were evaluated, and nine were eventually selected based on the strength of their correlation with the human disturbance gradient. These metrics included:Percentage of native species; Percentage of perennial species; Number of genera of native perennial plant species; Percentage of monocotyledon species; Number of aquatic guild species; Number of sensitive species; Percentage of tolerant species; and Percentage of annual, biennial and introduced species, and so on. The composite scores summed in the IBI score should also show a strong response to the degree of disturbance of the wetland. We delineated plant data into metrics of the data set and analyzed these metrics using principal components (PCs) and cluster analyses. Each of nine metrics that constituted the P-IBI was scored and included in the total IBI score. After analysis, four quality classes (Good, Fair, Poor, and Very Poor) were determined based on the calculated IBI value:35-45, Good; 27-34, Fair; 19-26, Poor and <18, Very poor. Six of the 23 sites in the Baiyangdian wetland were characterized as Good, five as Fair, seven as Poor, and five as Very Poor. Pearson's correlation analysis between P-IBI and water chemical-physical variables showed that P-IBI corresponded strongly with conductivity (-0.571, P<0.01), Fe (-0.64, P<0.01), Cu (-0.59, P<0.01) and Zn (-0.52, P<0.01). The results suggested that the P-IBI approach was feasible for assessing the health of the Baiyangdian wetland. Insufficient water supply and deteriorating water quality that could be attributed to human disturbances primarily contributed to the degradation of the Baiyangdian wetland.