|Other Abstract||1. Benthic algae of eleven sites in Xiangxi River and its two major tributaries (Gaolan River and Jiuchong River) was investigated from September 2004 to June 2007. The diatom Achnanthes linearis was the most predominant species, with relative abundance of 42.28%.
Temporally, Shannon-Wiener index, algal richness, density and chlorophyll a concentration tended to be higher in winter and spring than in summer and autumn. Though there was significant seasonal variation of chlorophyll a concentration, ACF indicated that chlorophyll a concentration had high temporal stability in each river. So did PSC similarity. Spatially, benthic algae had highly heterogeneity in Xiangxi River. Shannon-Wiener index, algal richness, density and chlorophyll a concentration were the highest in Gaolan River, then in Xiangxi River, and the lowest occurred in Jiuchong River.
2. The benthic algae and its relationship with landscape characteristics of the watershed was investigated in June 2004 (there were 76 sites used for analyzing in this thesis).
Based on the landscape characteristics of the watershed, all the 76 sites were divided into 4 groups. There were significant differences of physicochemical variables, main dominant species, algal density and chlorophyll a concentration among groups. Land use was the main factor influencing the heterogeneity of benthic algae in the watershed. According to siltation index and TDI, the siltation and trophic status of the watershed were not very high, normally in the mesotrophic or eutrophic status, which was best in Jiuchong River, then in Gufu and Xiangxi River, and relatively poorer in Gaolan River.
3. In order to explore the impact of the large hydropower stations on the benthic algae, GF04 (which was impacted by Gudongkou Rservoir 1 in Gufu River) and GL03 (which was not impacted by reservoir in Gaolan River) were carried out monthly sampling from September 2004 to June 2007.
There were no significant differences of physicochemical variables such as nutrients, temperature and velocity between GF04 and GL03 during the sampling time, which meant that the impacts of resource stress were consistent between GF04 and GL03. Froude number showed hydrodynamics were different between these two sites.The variation of hydrodynamics and habitats were the main factors influencing benthic algae. Results indicated that there were significant differences on PSC similarity, unattached assemblages, erect assemblages and stalked assemblage and their representative species between GF04 and GL03. Evidently a large hydropower station had severe effect on aquatic habitats and benthic algae.
4. In order to evaluate the potential impact of acid mine drainage on the benthic algal communities in Gaolan River, we chose three sites in pyrite area as impaired group (I), four uninfluenced sites were taken as control group (C) and five sites as recovery group (R).
We compared the characteristics of benthic algae among July 2001, June 2004 and July 2007. The results indicated that Margalef index, Simpson index, algal richness, density and chlorophyll a concentration increased obviously, the dominant species changed from tolerant acidic species to other species, and the community also changed greatly, which meant that the impacted area had been restoring. While according to CCA and correlation analysis, Al, Cu, Zn and Mn were the most important factors influencing benthic algae. Benthic algal density, chlorophyll a concentration, AFDM and AI could better indicate the impacts of acid mine drainage.|