The Community Structure And Dynamics Of Plankton In Siminghu Reservoir

In order to understand the evolution rule of plankton and realize the relationship between plankton withfisheries, the physicochemical properties of water quality and plankton assemblages were investigated monthlyfrom August,2012to July,2013in Siminghu reservoir. The comprehensive trophic status index and PrincipalComponent Analysis (PCA) were used to analysis water quality characteristics and the correlations between them;Correspondence Analysis (CA) was used to analysis the main environmental factors that affect planktoncommunities structure; At the same time plankton data was compared with the data from24years ago to analysisecological evolution in Siminghu reservoir; Correlation analysis was used to explore the impact of top-downeffect on plankton communities, and a fishery countermeasure were proposed based on it. The main results aresummarized as follows:1. The main factors affecting the water level of Siminghu reservoir were surface runoff and human control.Water temperature had obvious seasonal changes, it was high in summer and was low in winter, no thermoclineappeared in summer. pH value of water was between7.28~9.67, greater than7, which indicate Siminghureservoir belongs to the weak alkalinity. Phytoplankton biomass was the major factor that determine transparencyand dissolved oxygen, and it also was the major component of organics in Siminghu reservoir. Nitrogen contentwas positively correlated with water level changes indicated that surface runoff input was one of the importantfactors affect the nitrogen concentration in the reservoir. Phosphorus mainly existed in the dissolved forms andtotal phosphorus mainly came from reservoir endogenous release caused by water body mixing. The mainparameters method and comprehensive trophic state index analysis indicated that water quality in Siminghureservoir is in the middle-eutrophic levels currently and developing to eutrophication level.2.211species of phytoplankton were identified in Siminghu reservoir, and the ranges of cell abundance andbiomass were3.70×103~1.04×108cells/L and8.65×10-4~14.09mg/L, respectively. The abundance andbiomass of phytoplankton keeped high from August to October while reached the low level from March to Aprilin the next year, which showed significant seasonal variation but no spatial difference. Phytoplankton assemblagesin Siminghu reservoir was dominanted by cyanophyta, bacillariophyta and chlorophyta. Pseudoanabaena sp.,Aphanocapsa delicatissima, Planktolyngbya subtilis were the primary abundance dominant species, Synedra nana,Melosira sp., Chlamydomonas globosa were the primary biomass dominant species. Correspondence analysisshowed that water temperature was the most dominant factor affecting phytoplankton community structure, andthe dominant factors were different in different sample sites indicated that the ecosystem of Siminghu reservoirexisted spatial heterogeneity certainly. An increasement in the number and miniaturization in the size ofphytoplankton were found by comparing with the date from24years ago which probably resulting from theincreasement of fish standing stock. According to the evolution of the dominant species, we inferred thatSiminghu reservoir became eutrophic type24years ago while now nitrogen content increased further,transparency reduced and light conditions worsen.3.150species of zooplankton were identified in Siminghu reservoirs, and the ranges of cell abundance andbiomass were198.0~7258.0/L-1and0.28mg/L~5.64mg/L, respectively. The abundance of zooplankton reacheda peak in February and June while falled to minimum in April, the biomass reached maximum in March while reached minimum in December. Both abundance and biomass of zooplankton showed significant seasonalvariation but no spatial difference. Tintinnopsis wangi, Tintinnidium fluviatile, Polyarthra trigla, Keratellacochlearis, Anuraeopsis fissa were the primary abundance dominant species, Daphnia hyalina, Bosmina coregoni,Diaphanosoma leuchtenbergianum, Thermocyclops, Polyarthra trigla, Epiphanes senla were the primary biomassdominant species. Correspondence analysis showed that water temperature, chlorophyll a, total phosphorus,euphotic layer, ammonia nitrogen and water level were the dominant factors affecting zooplankton communitystructure. Spatial differences existed in the dominant factors between the sample points. A decrease in theabundance and biomass and miniaturization in the size of zooplankton were found by comparing with the datefrom24years ago, which possibly resulting from top-down effect by fish predation and zooplankton fertilitydecline caused by the increasement of cyanobacteria density and microcystin.4. Dynamic changes of plankton in Siminghu reservoir had the specificities of lakes in temperate zone.Correlation analysis showed that herbivorous zooplankton had certain top-down effect on phytoplankton, but ithad a limit. The top-down effect—predation pressure on plankton from silver carps and bighead carps increasedcomparing with24years ago, which was one of reasons leading to plankton miniaturization. The stocking ofsilver carps should be increased and bighead carps decreased in Siminghu reservoir as the fisherycountermeasures to control the algae overgrowth and prevent the blooms.