Research On The Influence Of Fluvial Processes On Macroinvertebrate Assemblages

Eco-sedimentation is a newly developing inter-discipline, which studies the interaction of substrate, water flow and biotic community. Benthic macroinvertebrates are organisms mainly living in the river bed. Research on the influence of fluvial processes on macroinvertebrate assemblages has positive significance on development of eco-sedimentation. In this thesis, suitable study areas and rivers were selected from different regions of China according to different research purposes. Methodologies of field experiment, sampling and measurement, as well as indoor identification and statistical analysis were applied in the study. The major results were summarized as follows:In summer, the time for macroinvertebrates to colonize stably in new habitats in gravel bed was at least 4-6 weeks. The thickness of hyporheic zone that invertebrates inhabited was larger than 40 cm. The biodiversity and density of macroinvertebrates trended to decrease as the substrate depth increased. In the surface substrate(0-10 cm), the density of macroinvertebrates was influenced by the substrate material. The cobble substrate with median diameter of 2 cm had the highest density, followed by the cobble substrate with median diameter of 10 cm. The gravel-sand substrate had the lowest density.The distribution of macroinvertebrates in the substrateof cobbles with algae biofilm was different from the distribution in the substrateof cobbles without algae biofilm(both substrates had the same median diameter). In the upper layer of the substrates, the biodiversity, density and biomass of macroinvertebrates in the cobbles with algae biofilm were higher than those in the cobbles without biofilm. However, in the lower layer such bio-indices in the cobbles with biofilm were lower than those in the cobbles without biofilm.The streambed stability index is defined as the time needed for unit cross-sectional area change per unit width of the bed due to erosion and sedimentation in ?uvial processes. Streambed stability was the main factor that influenced macroinvertebrate assemblages, counting for 22.7% of the variance. The biodiversity and biomass of macroinvertebrates were highly dependent on the streambed stability. In the situation that other environments were similar, the biodiversity increased with the streambed stability and reached equilibrium when the stability index was over a critical value. If the stability index was lower than 0.6 yr/m, no benthic invertebrates could colonize the streambed, and the biodiversity was zero. The biomass of macroinvertebrates showed an increasing trend with the streambed stability. However, there was no clear relation between the density of macroinvertebrates and the streambed stability.In the Yellow River Source, different river patterns have developed and are developing, among which meandering river is the most common river pattern. The biodiversity of macroinvertebrates in a single sampling site was low. However, the biodiversity of the basin scale was much higher than that of a single sampling site. Meandering rivers usually own very good ecology. Macroinvertebrate assemblages in the different water bodies of meandering river floodplains were different. Hydrological connectivity was the main factor causing the variance of the bio-community. The river channels had the highest biodiversity of macroinvertebrates, followed by the wetlands and the oxbow lakes. The density and biomass of Gastropoda increased from rivers, to the oxbow lakes, and then to the wetlands. The river ecology was special in the Ruoergai Wetland, the Yellow River Source. Compared with the Lanmucuoqu River, which has a similar climate as the Ruoergai Wetland, the β-diversity index of macroinvertebrates inrivers of Ruoergai was higher than that in Lanmucuoqu. However, the α-diversity indicesof macroinvertebrates, the taxa richness, density and biomass of EPT(Ephemeroptera, Plecoptera, Trichoptera) inrivers of Ruoergai were much lower than those in Lanmucuoqu.