Effects of ecological restoration on water quality and benthic macroinvertebrates in rural rivers of cold regions: A case study of the Huaide River, Northeast China

Abstract

Various human activities can damage the structure of rural rivers ecosystems and reduce their self-purification capacity. In Northeast China, the cold climate also poses serious challenges to river restoration. What types of restoration technology should be adopted and what impacts the restoration project will bring, in terms of river ecological function improvements, should be further discussed. To investigate the effects of ecological restoration projects and different restoration measures on water quality and benthic macroinvertebrates of rural rivers in cold regions in Northeast China, benthic macroinvertebrates and 10 indicators of water quality including ammonium (NH4+-N), nitrate (NO3–-N), total nitrogen (TN), total phosphorus (TP), chemical oxygen demand (COD), dissolved oxygen (DO), water temperature (Tem), pH (pH), electrical conductivity (EC) and chlorophyll-a (Chla) were monitored. We analyzed the temporal and spatial changes of benthic macroinvertebrates and 6 typical water quality indicators including NH4+-N, NO3–-N, TN, TP, COD and DO, which were collected in 4 seasons at 7 typical river sections. The Water Quality Index (WQI) was used to evaluate the seasonal and spatial variation of water quality during monitoring period, and a new WQImin model consisting of six crucial parameters, i.e., pH, DO, NH4+-N, TN, TP and COD, was established by principal component analysis. The results showed that the ecological restoration project enhanced the self-purification capacity of the river, and increased diversity of benthic macroinvertebrates. The maximum removal rates of the main pollution indicators NH4+-N, NO3–-N, TN, TP and COD were 96.49 %, 43.92 %, 49.69 %, 8.3 % and 25.95 %, respectively. The maximum increase rates of DO and benthic macroinvertebrates diversity were 77.96 % and 310.9 %, respectively. The operation effect of the restoration project had an obvious seasonal effect, with the best effect during the spring and summer. The project still has good repair effect in winter. In terms of water purification, the effect of the overflow weir combined with aquatic organisms was better than that of the single overflow weir in the river channel. There was the best effect of the engineering measures in summer. The ecological restoration project can improve the river water quality and the benthic macroinvertebrates conditions. Compared to before the restoration, WQImin values increased 168.81 % and 44.21 % in winter and summer, respectively, and Shannon index increased 6.57 % and 41.67 % in summer and autumn, respectively.