NSFC - Environmental Hydraulics and Water Quality

Poster Abstract

Investigations of Ecological Successions of Oxbow Lakes in the Upper Yellow River Basin

Wednesday, January 4
10:00 AM - 5:00 PM
Location: ChuLv Hall

The well-developed meandering rivers created numerous oxbow lakes in the upper region of the Yellow River Basin. The hydro dynamics, water quality and substrate conditions change gradually as the oxbow lakes evolving, resulting in successional variations in aquatic ecology. In this study, we investigated the environmental conditions, vegetation and macroinvertebrate assemblages of the oxbow lakes at different evolutional stages in a typical meandering river in the upper Yellow River Basin. Hydro dynamics, water quality and substrate conditions of the oxbow lake and the main river were statistically compared using the analysis of variance (ANOVA). In addition, the compositional differences of macroinvertebrate assemblages in the oxbow lakes and the main river channel were analyzed using the permutational multivariate analysis of variance (perMANOVA). Detrended correspondence analysis (DCA) was conducted to reveal the general patterns of macroinvertebrate distribution along the environmental gradients, and to establish a prediction model of macroinvertebrate assemblage variation as the oxbow lake evolving. The results indicate significant differences of hydro dynamics, water quality and substrate conditions in the oxbow lakes and the main river channel. The significance of environmental differences was affected by the hydrological connectivity between the lakes and the river. Taxa richness of macroinvertebrates was found low in the main channel owing to the sand riverbed. The formation of oxbow lakes resulted in a dramatic increase in the aquatic habitat diversity, and, subsequently, improving the taxa richness and abundance to different extents. High daily fluctuation in water quality was detected in the oxbow lakes, leading to the complicated and variable physicochemical aquatic environment. The evolution of oxbow lakes was divided into four general stages based on the hydrological connectivity levels: (1) the connecting stage, (2) the semi-connecting stage, (3) the closed stage, and (4) the extinction stage. Ecological conditions of the connecting oxbow lakes were generally similar to that of the main channel. The oxbow lakes in the semi-connecting stage were dominantly affected by hydrological conditions: in low water periods without hydro connectivity, typical lacustrine ecological characteristics were found in the oxbow lakes, while in periods with adequate water supply, the oxbow lakes connected with the main channel and the original lacustrine system transformed to a fluvial system. The closed oxbow lakes were metastable lacustrine ecosystems, and gradually evolved into the semi-aquatic and then terrestrial ecosystems as water evaporated. The ammonia-nitrogen concentration in the oxbow lake water was significantly higher than that in the main channel, leading to a strong basicity in the oxbow lake environment, which was probably associated with the frequent grazing activities in this region.

Xiongdong Zhou

Tsinghua University

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Mengzhen Xu

Tsinghua University

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