[Community Composition and Assessment of the Aquatic Ecosystem of Periphytic Algae in the Yangtze River Basin].

To explore the periphytic algae community structure in the Yangtze River basin, samples were collected from 130 sampling sites, including the source to the estuary along the mainstream of the Yangtze River, eight primary tributaries, and the tributary of the Three Gorges area. The periphytic algae densities of different areas in the mainstream of the Yangtze River ranked from high to low were the upstream area, source area, middle and lower area, and the Jinsha River. The high periphytic algae density in the upstream area was associated with the shift in nutrition level, and the high periphytic algae density in the source area was associated with human activity. The spatial pattern of the periphytic algae community in the whole main stream from west to east presented the alternating dominance of Bacillariophyta and Cyanophyta; the Bacillariophyta () had a competitive advantage in the main stream, and the distribution of the periphytic algae community was driven by total nitrogen, total phosphorus, and pH. For the tributary of the Yangtze River, the periphytic algae density in the Three Gorges tributary area was far higher than those in the eight primary tributaries; the periphytic algae community was dominated by Cyanophyta (), which had a competitive advantage in the tributaries of the Yangtze River. The distribution of the periphytic community was driven by dissolved oxygen and pH. According to the diversity analysis and assessment, the periphytic algae community in the source area showed lower species richness and higher evenness, thus leading to a high -diversity and good assessment result (mesosaprobic zone). The middle and lower reaches of the Yangtze River also showed the same assessment result, the mesosaprobic zone. However, the community evenness of the middle and lower reaches was significantly lower than that of the source area, thus making the middle and lower reaches of the Yangtze River have a significantly lower -diversity than that of the source area. All areas of the Yangtze River showed good water quality assessment; however, different areas had different WQI index numbers, and the assessment results of the WQI index were inconsistent with the results of the aquatic assessment. Therefore, a comprehensive assessment of aquatic ecosystem health should use both aquatic assessments and water quality assessments.