| Danjiangkou Reservoir is the largest artificial freshwater lake in Asia, also the water source of China North Water Transfer Project, engaged a special strategic position. The reservoir take a complex landform with sufficient rainfall and light period, but the topography and the monsoon led to its ununiform spatial and temporal distribution of precipitation. The abundant rainfall and strong self-purification capacity of has ensure a good water quality of Danjiangkou Reservoir. Danjiangkou Reservoir is harmed by more and more excessive human factors in recent years, the impact of changes also laid on aquatic ecological communities.Take concerns of its key position in the water diversion project, the biological community structure and its relationship with environmental factors in Danjiangkou Reservoir were studied in this research. The main contents are basic water quality, community structure of phytoplankton plankton crustaceans and macrobenthic, and their relationship with environmental factors. Planktonic crustaceans including cladocerans and copepods had been sampled, both of which are water pollution indicator organisms and also have a variety of aquatic economic importance in fisheries development and ecological protection has. Phytoplankton is the most important aquatic community organic producers, also the main producer of dissolved oxygen to support the normal operation of the aquatic ecosystem. Phytoplankton community can indirectly reflect the degree of freshwater eutrophication, too much excess algal toxins of some phytoplankton also affect water quality and safety. Macrobenthos also is an important part of aquatic ecosystems, play a key role in construction of sediment and has an important position in the ecological environment. In this research the planktonic crustacean, phytoplankton and macrobenthos species composition in Danjiangkou Reservoir during four quarters from December 2013 to October 2014 has been studied, analyzed seasonal and spatial variation of the community structure. Index of Shannon-wiener, Margalef richness index and Pielou index of planktonic crustaceans and phytoplankton were calculated and planktonic crustaceans and phytoplankton relationship with environmental factors were analyzed using classical correspondence analysis (CCA). This study was designed to reflect the biomes situation of Danjiangkou Reservoir. The results of resent study are as follows:I.Water quality:1.The upstream of Danjiangkou Reservoir is an important supplementary source of ammonia. Ammonia take a high content in the upper reaches to Hanjiang River.2.The nitrate content has a large seasonal change, reached the highest point in summer. Nitrite content is more stable in all season.3.The total phosphorus content take a great seasonal variation, and the content in the remaining three quarters are generally higher than autumn. Total nitrogen content is in stable.4.The transparency, conductivity, pH of this reservoir is under inconsistent trends, transparency take an obvious seasonal changes, the water fall led to the less transparent in two points of Han area, Small Three Gorges estuary and Taocha has another low transparency, and the water level is related. The conductivity of the spatial distribution change less than seasonal, which ranks autumn<Winter<Summer <spring.The pH of Danjiangkou Reservoir rages between 7.45-8.92, belongs to weak alkaline water, of which the seasonal trends is winter<autumn<spring<summer. Ⅱ.Plankton crustacean1.20 genera and 28 species of crustacean zooplankton has been detected in this four quarterly surveys. In which dominant species are Daphia hyaline, Daphina cucullata, Sinocalanus dorrii, Cyclops vivinus, Mesocyclops leuckarti and Thermocyclops hyalinus.2. The density of the reservoir planktonic crustaceans were 5.91ind./L,10.80ind./L. 60.53ind./L and 169.68ind./L since winter 2013 to autumn 2014 showing a rising trend.3. Annual planktonic crustacean density concentrated mainly in Han area, the dam area also has a high density of crustacean zooplankton.4. Planktonic crustacean suffer variety of influence of different environmental factors in different seasons, including conductivity, temperature, transparency, ammonia in have become one of the major environmental factors during the whole year. Temperature showed the greatest impact in Danjiangkou planktonic crustacean community.Ⅲ.Phytoplankton1.76 genera 101 species of phytoplankton were collected during the whole year including Cyanophyta 17 genera and 26 species, accounting for 25.7% of the total number of species and 17 genera and 20 species of Bacillariophyta, accounting for 19.8%. The Chlorophyta, up to 32 genera,45 species accounted for more than 44.6% take the most amount of phytoplankton in Danjiangkou Reservoir.2. The dominant species of phytoplankton changed greatly during the year. Microcystis aeruginosa as well as Melosira granulat, Cyclotella, Anabaena Oscillatoria, Glenodinium, Chlamydomonas microsphaera, Chlamydomonas monadina had become the dominant species during whole year.3.Phytoplankton biomass of Danjiangkou reservoir increased quarter by quarter,displayed an increasing order of winter, spring, summer and autumn for 3.08μg/L,6.49μg/L,128.92μg/L and 481.07μg/L.4. The spatial distribution of phytoplankton in the four seasons change is not in coherence with the evenly distributed in spring and summer, nearly half of the winter biomass concentrated in the Han area, while the phytoplankton biomass account for 39% in area of small Pacific is the highest for all area.5. Phytoplankton community suffered combined effects of temperature, ammonia, nitrate, total nitrogen, total phosphorus content, transparency, conductivity and dissolved oxygen. Different degree of impact of there factors was detected in four quarters separately.Among which ammonia showed great impact in all quarters expect summer, and transparency play a larger role in spring and autumn. TP displayed to be a high impact factor in spring and summer.6. The relative relationship between of the planktonic crustacean community and phytoplankton community in Danjiangkou Reservoir didn’t show significant correlation. Phytoplankton density is 100-1000 times of planktonic crustacean in reservoir.7.Danjiangkou Reservoir appeared to be Moderately polluted by the evaluation method of Shannon-wiener diversity index. But Margalef index reflects the reservoir as clean water in spring and summer. Pielou evenness index showed that Danjiangkou Reservoir are unpolluted in addition to be Moderately polluted in summer. In accordance with phytoplankton density criteria to evaluate water quality, Danjiangkou reservoir can be labeled as clean water. IV.Macrobenthos1. Macrobenthos distributed more focused on the upstream area Langhekou in Danjiangkou Reservoir, with the smaller macrobenthos density showed in Danjiang area. And the spatial distribution change more obviously with the seasons.2.Macrobenthos density showed an obvious seasonal change, with a increasing trends for winter, spring, autumn, summer. Biological density in winter is only 1/30 of the summer.3. Macrobenthos of Danjiangkou Reservoir mainly consists of several groups of Annelida, namely Monopylephorus, Branchiura, Aulodrilus, Limnodrilus and Nais., which take 95% percentage of total biological density. Aulodrilus and Limnodrilus are two most abundant benthic genus in Danjiangkou Reservoir. |
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