Anthropogenic Impact On The Eutrophication Process Of The Liuxihe Reservoir Over The Past Fifty Years

Liuxihe Reservoir is a major water source of the Guangzhou City. Along withthe rapid economic development of China, a variety of industries (manufacture,agriculture and tourism) surrounding the reservoir have been rising in recent years.Consequently, there has occurred accelerated degradation in its water quality, which,if further aggravated, would threaten the city’s water security. Through investigationof diatom communities and physicochemical characteristics of cored sediments, thisstudy was designed to reconstruct the eutrophication process in the reservoir over thepast fifty years, based on which the driving factors of eutrophication can be revealed.This study is expected to provide a solid, scientific basis for eutrophication controland water quality management.A total of48sediment samples sectioned at2-cm interval in Core S3(96cm intotal length) drilled at the river entrance in the reservoir were studied for diatoms withrespect to abundance, assemblage composition, and trophic diatom index (TDI).Based on this and combined with modern diatom communities of the reservoir and itscatchment, the historical variation in trophic level of the reservoir was reconstructedfor the past fifty years since the reservoir filling in1958. The major results are asfollows:1. Benthic and planktonic diatoms were studied for48sediment samples and17modern samples, and a total of309species (including variant species) belonging to57genera were identified. The dominant species include Discostella pseudostelligera,Cyclotella radiosa, Achnanthidium minutissimum, Achnanthidium rivulare, andAulacoseira alpigena.2. The sediment core was divided into five consecutive diatom zones based ona cluster analysis (CONISS) of diatom flora. From the bottom upward, the diatomassemblage changed from one dominated by Achnanthidium minutissimum,Achnanthidium rivulare to another one by Discostella pseudostelligera, Cyclotellaradiosa. 3. Community succession was rebuilt over the past fifty years based on diatomabundance and ecological traits of dominant species. The increase in abundance andchange in dominant species suggest an increased trophic level of the reservoir.4. Diatom community data from modern surface samples show that theLiuxihe Reservoir is in a moderate trophic level. Nevertheless, as revealed by diatomabundance and composition from the sediment core, the trophic level of the reservoirhas been escalating, and in particular the eutrophication process has been acceleratedin the most recent years.