Study On The Succession And Clustering Of Algae And Pollution Status Of Algal Bloom In Representative Water Systems Along The Three-Gorges Valley

Algae bloom reflects the over eutrophication of water. When algal bloom outbreaks, phytoplankton cluster on the surface of water, jeopardizing the surrounding environment and endangering human beings'water consumption and the survival of fish and other aquatic organisms. It brought about serious damages, particularly to water environment of Three Gorges reservoir—the large-scale water in the basin system. After the Three-Gorges reservoir's erection, the flow velocity of Yangtze River and branch rivers becoming slower, the self-clean capacity of the water body decreased, the temperature difference lessened and the light intensity strengthened, the water-level-fluctuating zones formed along both sides of the river and the more gentle backwater area formed in estuary abouchement section—all these will have a direct impact on algae succession, proliferation and clustering behavior, thereby becoming the important factor of algal bloom outbreak in the Three-Gorges reservoir.Based on studying the algae characteristics and seasonal succession laws of Three-Gorges reservoir area typical of the Yangtze River and Jialing River Basin water, the author found that there were 7 planktonic algae, 50 genera and 108 species (including varieties) from November 2006 to October 2007. In the composition of algae community, the Bacillariophyta has the absolute domination (51.8%), then are Cyanophyta and Chlorophyta, and the proportion of others, less. Bacillariophyta cell density percentage was quite high. The Bacillariophyta density of Jialing River water accounted for a higher proportion in spring and a lower proportion in autumn compared with Yangtze River and differences in other seasons were not obvious. The cell density proportion of Cyanophyta in Yangtze and the Jialing River, comparatively low, were not more than 10.12% and 10.71% respectively and the growth peak occurred in spring. Cell density percentage of Chlorophyta in Yangtze River both in spring and winter was the highest, and its proportion in autumn was the lowest (approximately 0%). Chlorophyta in Jialing River in spring and summer occupied the highest proportion.According to planktonic algae's growth characteristics in Yangtze River and Jialing River Typical of Three Gorges reservoir area, the thesis, integrating laboratory simulation method, studied systematically the impact of the major environmental factors (ratio of nitrogen and phosphorus, light intensity and velocity) after the formation of Three Gorges reservoir on the succession of algae community structure and aggregation behavior. Chlorophyta and Cyanophyta are the main algae types in static water, regardless the levels of TN/TP ratio and light intensity, while the dominant algae species is the Microcystis flos-aquae of Chlorophyta. In general, the clustering parameterθof Chlorophyta is bigger than that of Cyanophyta. However, the clustering parameter of both Chlorophyta and Cyanophyta decreases rapidly and the dominancy of the Microcystis flos-aquae starts to disappear when the flow velocity in the dynamic water is over 0.03m·s-1. The ecological assessment of water quality reveals that for all cases the correlation coefficient of (R2) between th biodiversity index (d) and clustering parameter (θ) is greater than 0.81, and water quality is inversely proportional to the clustering ability of the domiant algae species. Since the index d is an assessment critcrion of water quality as well as the nutrient level, and cannot be directly used to evaluate algal bloom, a function (G) is constructed on the basis of the parameterθ. The function G is used to assess the lab data and the actual water pollution in the river. The results indicate that function G can effectively represent the state of algal bloom in a semi-quantitative way.