Author(s): Hongru Liang; Ruihua Nie; Lu Wang; Yunqi Fu
Linked Author(s): Lu Wang
Keywords: Bed degradation; Stream habitats; Macroinvertebrates; Mountain rivers; Ecological health
Abstract: Influenced by climate change and human activities, since the mid-20th century, the sediment flux of 47% of the world's rivers has significantly decreased, and the sediment flux of rivers in the Northern Hemisphere has decreased by 50% since 1984 (Dethier et al., 2022). The reduction in sediment flux has led to widespread bed degradation, such as in the Rhine River in Europe, the Mississippi River in the USA, the Nile River in Africa, and the Yangtze River in China (Ylla et al., 2022). Bed degradation causes a decrease in river habitat stability and heterogeneity and a decline in water quality, severely damaging river biological communities. For instance, there has been an increase in the concentration of water quality nutrients (Shields et al., 2010), a decline in habitat heterogeneity and stability (Bravard et al., 1997), a decrease in the richness of aquatic macrophytes, and a reduction in fish size, abundance, richness, and diversity (Shields et al., 1994). However, some scholars have shown that bed degradation does not significantly affect grain size, channel slope, and fish habitat (Duncan et al., 2011). Therefore, this article evaluates the ecological health of degraded mountain rivers from three aspects: water quality, habitat quality, and benthic index of biotic integrity based on field inspections and data analysis, and reveals the impact mechanisms of bed degradation on river ecology (stream habitats, macroinvertebrates community). The study found that in the typical mountain incised river region (rivers in front of the Longmen Mountains), the water quality index (WQI) ranged from very poor to sub-healthy, with Qingbai River having the best water quality, followed by Mianyuan River; the habitat quality of the morphological quality index (MQI) ranged from poor to sub-healthy, with Mianyuan River having the best habitat quality; and the benthic index of biotic integrity (BIBI) ranged from very poor to healthy, with Mianyuan River having the highest benthic index of biotic integrity. Overall, the Mianyuan River has the healthiest river ecology. The study indicates that bed degradation causes a decline in the morphological quality index, but to some extent, it is beneficial for the benthic index of biotic integrity and has no significant impact on water quality. In degraded rivers, flow velocity is the physical environmental variable with the highest impact on the spatial distribution of benthic animals, followed by the longitudinal gradient and degradation depth, while the water quality variable with the highest impact is total nitrogen. In degraded rivers, degradation depth is the physical environmental variable with the highest impact on the community structure of benthic animals, followed by the longitudinal gradient and flow velocity, while the water quality variable with the highest impact is dissolved oxygen.
Year: 2024