The Use Of Chironomid Pupal Exuvial Technique(cpet) In River Biomonitoring

The chironomid is a species-rich family of aquatic flies that are typically the most abundant and widely distributed macroinvertebrate taxon in the freshwater, which plays a significant role in the biomonitoring and assessment of ecosystem health. Chiromomid pupal exuviaes, a cast skin after adult emergence, has been selected as an effective tool to dectect the community structure and degeneration of water qulity. In order to determine the relation of chironomid community and spatial water quality variations, also to develop a local chironomid-based assessment framework, pupal exuviae was collected monthly at 11 sites in Liuxi River catchment during June 2014 to May 2015.The major result are as follows:1.A total of 96 species, belonging to 4 subfamilies, were identified. Among 4 subfamilies, the Tanypodinae representing by 11 species which belong to 9 genera, and Diamesinae by 2 species belonging to 2 genera, Orthocladiinae 40 species(24 genera) and Chironomidae 43 species(27 genera). The top three dominant species in the total commnity are Corynoneura ecphora,Orthocladiinae sp. and Stempellinella tamaseptima.2.Based on the community analysis, generally, the species diversity before monsoon(dry months: 2014.11- 2015.03) is higher than that after monsoon(rainy months: 2015.06- 2015.10). The spatial variation of species richnes was also corresponded to the river gradient, with higest value in the middle section, following by the upstreams and downstreams.3. The total abundance of pupal exuviae reflected a distinct bimodal emergence patterns, with two peaks occuring in spring-early summer and autumn seasons, respectively. For the species emergence patterns, it can be sumerized into unimodal, bimodal or multimodal models. The high diverse Chironominae and Orthocladiinae spcecies include various emergence patterns. Some tolerant species occurred in the whole year, while some sensitive species only occurred in the certain month.4.Species tolerance value was weighted by the species frequency and abundance. River assessment system based on chironomid biotic index(Chiro-BI) was tentatively created in this study. The result was compared with the criteria of traditional Shannon-winner and B-BI of benthic maroinvertebratres. The result showd that the water quality of upstream sites was good(S1 clean, S5 slightly polluted), middle and upper reaches suffer moderate polluted levels(S2, S3, S6, S7), and the downstream sites suffer moderate pollution.