Linghui Kong

Phytoplankton development and ecological status during a cyanobacterial bloom in a tributary bay of the Three Gorges Reservoir, China.

Reservoirs can provide suitable conditions for cyanobacterial bloom development, which may impact on water quality and biological communities. Weekly surveys in a cyanobacterial bloom process were carried out in the mainstream and Xiangxi Bay of the Three Gorges Reservoir (China), from June 6 to July 18 in 2008. By application of the phytoplankton functional group approach, the spatiotemporal pattern, impact factors, and the ecological status based on Q index (assemblage index) were analyzed. The depth of euphotic layer was apparently the key factor driving the phytoplankton functional group variations. Longitudinal patterns of phytoplankton distribution were detected during this bloom: in the beginning phase, groups D (mainly Stephanodiscus hantzschii) and B (Cyclotella stelligera) dominated in the mainstream of the Three Gorges Reservoir and the mouth area of Xiangxi Bay, group Y (Cryptomonas species) dominated in the upper area, while groups J (mainly Pediastrum duplex), F (mainly Sphaerocystis schroeteri) and G (Pandorina morum and Eudorina elegans) were important in other areas; in the mid phase, group M became absolutely dominant in the whole region; and in the ending phase, besides groups M and Y, groups X2 (Chroomonas acuta, Pyramimonas nanella, etc.) and Lo (Ceratium hirundinella) became more important in the lower and upper area respectively. Generally the ecological status was bad, temporally varied with the bloom process. No spatial difference of ecological status was found in the mainstream, while longitudinal patterns in Xiangxi Bay were detected for different phases: firstly a few sites had relatively better status than the others, then nearly all the sites were in the bad condition, and at last the status in the downstream was better than that in the upstream. The longitudinal patterns of ecological status were related to phytoplankton distribution, disturbed by jacking from the downstream and flood from the upstream of Xiangxi Bay.

Comprehensive Assessment of Danjiangkou Reservoir Ecosystem Health

Seasonal investigations on water environment and plankton were carried out from July 2007 to May 2008 in the four selected regions of Danjiangkou Reservoir(Regions Danjiang,Hanjiang,Qushuikou and Wuqing).Ecosystem health index(EHI) and trophic state index(TSI) were used to assess the ecosystem health state of the reservoir.The results showed that,the health state of the whole reservoir was at medium eutrophication level during the study periods and displayed a decreasing trend spatially as follows: Danjiang,Qushuikou,Hanjiang and Wuqing regions.Besides,the health state of some regions displayed seasonal varitations: It was at medium eutrophication level in the regions of Danjiang and Qushuikou in the whole year;it became worse in Hanjiang region in summer,but medium in other seasons;the state of the Wuqing region was worst or worse in the whole year.Moreover,the comparison of assessment results from the two methods concluded that Danjiangkou Reservoir belonged to response ecosystems,and EHI method was suitable for the assessment of its ecosystem health state.