Effects of fluvial processes and human activities on stream macro-invertebrates

Benthic macro-invertebrates are vital components of river ecosystems. The effects of fluvial processes and human activities on the distribution of macro-invertebrates were studied through field investigations and experiment. Sixty-one sampling sites on 31 rivers in China were selected to investigate the structures of macro-invertebrate assemblages. The rivers, according to their fluvial conditions, are classified as streams with a stable channel bed, degrading channel bed, aggrading channel bed, and intensive bed load motion. The structures of macro-invertebrate fauna for the four types of rivers are very different. Stable rivers have a large number of individuals, abundant fauna, and high biodiversity; while the density and taxa richness for degrading rivers are small, and those for aggrading rivers are much less; whereas the ecology of rivers with intensive bed load motion are the worst. This paper proposes that streambed stability is the primary influential factor shaping the structure of benthic macro-invertebrate communities. Organic pollution can obviously result in the decrease of biodiversity, in the simplification of macro-invertebrate structures, and in the distortion of functional feeding group composition. In a river with high total nitrogen content, the relative abundance of collector-gatherers is high, and that of collector-filterers, scrapers, shredders, and predators are low. Scrapers, shredders, and predators disappear in severely polluted rivers. The isolation of aquatic habitat results in a distinct decrease of individual numbers and taxa richness. This result demonstrates that the connectivity of aquatic habitat significantly affects macro-invertebrate assemblages. A practical method to calculate a Habitat Suitability Index (HSI) is proposed, integrating the effects of the primary physical (including biotic and abiotic) and chemical factors. The biodiversity and taxa richness increase non-linearly with HSI.