Effects of Main Contaminations on the Spatial Distribution of Macroinvertebrates in the Hun River

The relationship between the macroinvertebrate communities and pollutants was evaluated in the Hun River by applying the Canonical Correspondence Analysis (CCA). The results showed that ammonium-nitrogen (NH₃-N) and chemical oxygen demands (COD_Cr) were the two primary pollutants affecting the spatial distribution of macroinvertebrates. The regression analysis revealed that total number of taxa and EPT taxa, which represented the most sensitive taxa, would be lower than the average values in the Hun River when the concentration of NH₃-N and COD_Cr was above 1.0 mg/L and 16.0 mg/L, respectively. The biodiversity was relative higher at the upstream region comparing with downstream regions of Dahuofang Reservoir, which was caused mainly by the NH₃-N and COD_Cr pollution. Both NH₃-N and COD_Cr had significantly negative correlations with Margalef’s diversity index(P<0.05), and NH₃-N also had significantly negative correlations with Shannon-Wiener index, Pielou’s evenness, and Simpson’s diversity index(P<0.05). Several indicators were identified through the biplot of species-environmental ordination of CCA. The Ecdyonurus tobiironis, Rhyacophila nigrocephala and Psychomyia sp. could represent the sensitive indicators of the upstream regions of Dahuofang Reservoir. Meanwhile, the tolerant taxa of Branchiura sowerbyi, Bithynia fuchsianus, and Ephydra sp. represented the main indicators at the tributaries of downstream region of Dahuofang Reservoir. At the same time, the tolerant taxa of Tomocerus sp., Gammarus sp. and Bellamya acruginosa were the main indicators at the main channel of in the downstream region of Dahuofang Reservoir.