Response of fish communities to environmental changes in an agriculturally dominated watershed (Liao River Basin) in northeastern China

The aims of this study were to identify the species distribution pattern at local and watershed scales, the response to variation of environmental conditions, and the local factors structuring fish communities in Liao River Basin. A total of 187 sites were sampled during May 2009 to June 2010. Univariate and multivariate methods were conducted to identify the variation of species richness and composition. We identified 56 species in the basin, and the predominant orders were Cypriniformes (33 species) and Perciformes (10 species). Species richness degraded seriously (from 106 to 56 species) compared with the data obtained during the 1980s. Based on the similarity of fish communities, the sampling sites were divided into three groups. Group 1 was distributed in the Hun-Tai River Basin located in the southeast region with less anthropogenic disturbance, and was characterized by high physical habitat quality (high velocity, habitat score, and coarse substrate) and water quality. The other two groups were mainly distributed in the main stem and its tributaries, with more stress (high conductivity, CODMn, NH4+, and sand substrate) caused by agriculture and urban industry. Species richness increased along a longitudinal gradient and reached the maximum in Group 2. The distribution pattern of fish communities was analogue with the scheme of the Grade I aquatic eco-functional zonings and can be used as a good indicator with high verification ability. The indicator species of Group 1 were all small-sized and sensitive to environmental stress, while those species of Groups 2 and 3 were more tolerant. Physical habitat (velocity, habitat score, cobble plus boulder, and dissolved oxygen) and chemical pollutants (NH4+, CODMn, conductivity, and TN) structured the fish communities at the local scale. The degradation of environmental condition reduced physical habitat, water quality, and sensitive taxa in the downstream sections of Liao River Basin.