The Macrobenthos Community Structure and Its Relationships with Water Quality Factors in the Liujiang River Basin

In order to study the influence of water quality factors (DO, COD_Mn, NH₃-N, As, Hg, Cd, Pb) on macrobenthos community structure in different hydrological seasons in the Liujiang River basin, investigations were conducted in the Liujiang River basin and 4 phyla, 7 classes, 16 orders, 54 families and 68 genera (species) of macrobenthos were identified. The Czekanowsiki is 83.76% and the species richness is slightly higher in the dry season than in the wet season. There were 4 and 2 dominant species of macrobenthos in dry and wet seasons respectively, showing obvious seasonal succession. The results of TWINSPAN and DCA analysis show that there are certain differences in the temporal and spatial distribution of the macrobenthos community structure in the Liujiang River basin. In both the dry and the wet season, there are 3 different macrobenthos communities distributed respectively around the source, the upper and middle reaches and the lower reaches of the main stream and tributaries of the river. The indicator species in the community show a gradual transition from clean species to pollution-tolerant species. The results of indicator species analysis shows that, in the dry season, there are a total of 8 macrobenthos species that can be used as indicator species for the communities at the source of the Liujiang River and the upper reaches of the Dahuan River, namely Baetis sp., Serratella sp., Zaitzevia sp., Cheumatopsyche sp., Dugesia sp., Antocha, Chironomus sp. and Caenis sp., and the other communities have no significant indicator species. In the wet season, there are 5 macrobenthos species that can be used as indicator species for community division, among which Semisulcospira cancellata and Oncomelania sp. are indicator species in the middle and upper reaches of the Liujiang River and Amphigomphus hansoni, Corbicula fluminea and Gyraulus compressus are indicator species in the lower reaches of the Liujiang River. The CCA analysis results show that COD_Mn and DO are the water quality factors that have important effects on the macrobenthos community structure in the Liujiang River basin in the dry and wet seasons, the heavy metal factors (Cd, Pb, Hg) have a greater impact on the distribution of macrobenthos in the dry season, and NH₃-N has a greater impact on the distribution of macrobenthos in the wet season.