Cascade Damming Of The River And Its Phytoplankton Evolution Carbon Isotope Compositions

Reservoir is one of the major projects with which human beings control and make use of water resource.Damming over the rivers will affect the biogeochemical behaviors of biogenic elements in the rivers. However,at present,in our country a lot of large and medium-sized reservoirs are in the in the medium eutrophic level.So the protection of reservoirs as a special ecosystem unit has become particularly important. The systematical researches of reservoir ecology and its basics,and their applications are still very weak.Obviously,the reports of the researches which are seen as a special ecosystem of reservoir's development and its evolution are rare.And the accumulated research results are quite limited.Through the researches of the plankton compositions,water chemical compositions,and all kinds of carbon and its isotopes in one hydrological year in the typical cascade reservoirs on the Mao Tiao River, this paper deeply discusses the ecosystem evolution of river-reservoir system.The formation of reservoir is after the formation of dam to intercept the river.After the formation of reservoir,the aquatic ecosystem gradually evolves from "river-type" heterotrophic system,rich in attached benthic biology,to "lake-type" self-support system,rich in plankton.This paper aims to provide reasonable and scientific reasons for environment impact assessment of the exploration of the cascade hydropower on the river water environment.This paper draws several conclusions,as following:1 The cascade reservoir hydrochemical characters:the balance of pH, DO and carbon in the reservoir guarantee the virtuous circulation of the lake ecosystem.The main water body of the study area is carbonate water. After the river has been intercepted by the dam,the water level in the reservoir area has risen,and the nature of the hydrochemistry in the reservoir appears to change as the season changes.In spring the five reservoirs where samples were collected by the vertical profiles began to emerge hierarchy structure of water temperature,which continues in summer and autumn and efficiently limit vertical exchange of water.The reservoir affects the fiver water body.The water temperature,DO has decreased,and the pH has increased,and therefore the hydrochemistry compositions show obviously seasonal difference.2 The cascade reservoir phytoplankton characters:The phytoplankton communities in one hydrometeorologist year in 2007-2008. phytoplankton 144 species were identified.They belong to 37 genera,24 families,14orders,8classes and 6divisions respectively in Summer.phytoplankton 236 species were identified.They belong to 44 genera,29 families,18 orders,8 classes and 6 divisions respectively in Autumn.phytoplankton 196 species were identified.They belong to 45 genera,29 families,14 orders,8 classes and 5 divisions respectively in Winter.phytoplankton 178 species were identified.They belong to 36 genera,24 families,15 orders,8 classes and 6 divisions respectively in Spring.Ecosystem evolutive process,from variational equal of annual that: biomass of phytoplankton,cell density,Chlorophyll-a content and C/N moore proportion of phytoplankton were variated in different season. Most of aquatic biomass in summer and Autumn.Diversity index and the water quality were investigated in one hydrometeorologist year in 2007-2008.To estimate the water quality of reservoir by taking use of phytoplankton cell density and Margalef diversity indices that Hongfeng Reservoir is eutrophic,Baihua Reservoir is mesotrophic to light eutrophic.Hongyan Reservoir and Hongjiadu Reservoir are mesotrophic.Light mesotrophic demonstrated in Xiuwen Reservoir,Zaixiangkou Reservoir.In season viritional,except major algae is bacillariophyta in intake of Wujiang River. Cyanophyta-chlorophyta genre demonstrated in Summer. Cyanophyta-chlorophyta-bacillariophyta genre demonstrated in Autumn and Winter.Chlorophyta-Bacillariophyta genre demonstrated in Spring.3 Characteristics of geochemistry of carbon of the cascade reservoir: In the drainage area spatial scale,because of the reservoir the DIC has increased in the water venting from the reservoir,which leads to hierarchy effect of DIC concentration in the spatial scale,the concentration of DOC has decreased,and the concentration of POC didn't show obvious change in the drainage area spatial scale.In the vertical profiles of the water body,the concentration of DIC increased with increasing water depth,while the concentrations of DOC,POC increased with water depth insignificantly.Due to the re-suspension of the bottom sediment,the concentrations DOC and POC of the down part of the vertical profiles sometimes even increase.In time scale,the concentration of DIC appears like this:winter＞spring＞autumn＞summer. Since the water from the reservoir of the upper reaches supplies directly into the reservoir of the lower reaches,cascade reservoir are accumulated many effects.From the upper reaches to the lower reaches,the DIC in the upper water in all reservoirs appears to increase gradually,and the most significant situation in summer.In the study areas the POC in the surface water is the highest in summer,and is the lowest in winter,which is the same as DIC and DOC.The changes of the values of all kinds of carbonic isotopes:in spatial scale,the values ofδ¹³C_DIC in Maotiao River areas show regularly and gradually wave-type decrease,and the values in the surface water is more positive than that of discharge water.In the reservoir vertical profiles,the values ofδ¹³C_DIC basically becomes more negative with the water depth,which is the most significantly in summer,and the values ofδ¹³C_DIC change little in winter.The value ofδ¹³C_DIC responds well to the evolution of the reservoir ecosystem.In time scale,the highest value ofδ¹³C_DIC of emerges in spring,which reflects the evolution of the drainage areas ecosystem indirectly.The values of carbonic isotopes in the planktonic algae appear to be: summer＞spring＞autumn＞winter.But in the spatial scale,because the eutrophication of different degrees occurs to reservoirs on the Maotiao River areas,there is no apparent hierarchy effect on the values of carbonic isotopes in the planktonic algae.