Study On The Resource Of Feed Organisms In Qinghai Lake During Summer

Qianghai Lake is the biggest saline water lake and the biggest lake of China. Naked carp of Qinghai Lake,Gymnocypris przewalskii przewalskii (Kessler),is the unique econimical fish in the lake. The resource the fish has decreased gradurally, and the individual minimization has become obviously since 1957,when the commercial fishing to the fish began。For protecting this species with important value in fishes fauna and in fishery, the gorvement of Qinghai Province has carried out a strictly fishing-ban for ten years in the lake since 2000. and attending to increase the standing crop of the resource of the fish in the lake. In order to understand the variation regularity of the natural fisheires environment,the growth situation and the population structure of the naked carp in the lake during the fishing-ban exactly, we setting up 14 sampling stations with relatively fixed location in lake, have launded a continuous study of 5 years on the feed organisms resource, in each Aug.from 2006 to 2010。1,phytoplankton(1) in summmer of 2006-2010,34 species of phytoplankton, which belonging to 5 divisions 29 genus, were founded in the lake, among them there were 14 genus 18 species of Bacillariaphyta,4 genus 4 species of Cyanophyta,8 genus 8 species of Chlorophyta,2 genus 2 specie of Euglenophyta,1 genus 1 species of Pyrrophyta. Bacillariaphyta was the most important group, and Gyrosigma spenceri was the most important dominant species.The investigation shown that the species number of the phytoplankton has decreased 24 genus compared with the historical data, although diatom has remained dominantly. The genus disappeared included 9 genus of Euglenophyta,9 genus of Chlorophyta.2 genus of Cyanophyta,1 genus of Xanthophyta,1 genus of Pyrrophyta. Cladophora fracta, a species used to plentiful and distribute all over the lake, has alreadly become scarcely.But we also founded two newly genus in the lake, Gymnodinum of Pyrrophyta and Trachelomonas of Euglenophyta. The fauna of the phytoplankton in Qinghai Lake exhibited obviously characteristic of saline water algae.The main reason of the sepcies evolution was the reduce of the environmental quality in the lake.(2) in summmer of 2006-2010, the average densities of the phytoplankton were 61289-117250cells/L, the average biomass were 0.76-1.09mg/L. There was a notable linear relationship between the biomass of the phytoplankton and the Sacchii's depthes.The densities and biomass of the phytoplankton in the areaes of Erlanjian, the mouth of Buha River and the mouth of Wuhalan River were higher than other areaes obviously, for these areaes might get more nitritions from river. The densities and biomass of the phytoplankton in the central area of the lake were also plentiful, due to the location was in the downwind direction of the mouth of Buha River and Shaniu River.2,zooplankton(1) in summmer of 2006-2010,15 species of zooplankton, which belonging to 4 groups 14 genus, were founded in the lake, among them there were 3 genus 3 species of Protozoa.5 genus 6 species of Retifera,3 genus 3 species of Cladocera,3 genus 3 specie of Copepoda.The species number of the zooplankton has decreased obviously compared with the historical data of 1964-1965, and mainly shown as the decrease of the species number of Retifera. The fauna of the zooplankton in Qinghai Lake exhibited obviously characteristic of saline water community.The main reason of the sepcies evolution was also the reduce of the environmental quality in the lake.(2) in summmer of 2006-2010, the average densities of the zooplankton were 217-454ind./L, the average biomass were 0.47-1.14mg/L. Among 4 groups of zooplankton, the density of Protozoa was highest, but the biomass of Copepoda was maximum. Arctodiaptomus salinus was the dominant species of zooplankton, which has taken over 70% of the total biomass of the zooplanktona.(3) In general, the densities and biomass of the zooplankton in the western part and northern part were higher than those of the southern and eastern area. which was similar to the distribution of phytoplsnkton, but there was no notable relativety between the density and the biomass of zooplankton and those of phytoplankton.3,zoobenthos(1)in the summmer of 2006-2008,7 species of zoobenthos, which including 4 genus 5 species of Tendipedidae,1 genus 1 species of Ostracoda,1 genus 1 species of Amphipoda, were founded in the lake. Tendipes gr. Reduetus and Gammarus sp. were the dominant species of zoobenthos.Most of the zoobenthos distributed in the southern and south-western area of the lake. The functional feeding groups of the zoobenthos was dominanted by collectors.The fauna of the zoobenthos in Qinghai Lake also exhibited obviously characteristic of saline water community.(2)in summmer of 2006-2008, the average densities of the zoobenthos were 205-340ind./m2, the average biomass were 0.343-0.492g/m2. The annual variation ranges of the densities and biomass of the zoobenthos were more narow than those of the plankton.(3) compared with the data of 1960s, the species number of zoobenthos was diminution, the reason for that were the difference of invistigating method and the decrease of the environmental quality.(4) in Qinghai Lake, the condition of the bottom was the main factor influcing the distribution of major zoobenthos.4,the evaluation to the water pollution of Qinghai lakeBased on some indexes of phytoplankton, zooplankton, zoobenthos, the water quality of Qinghai Lake was appraised as oligotrophical level and slight pollution.5,the equivalent sphere diameter(ESD) grading of the feed organism and the fish productivity(1) among the feed organisms in Qinghai Lake, the species with the ESD of 200-1000μm were the most important group,which including the dominant species of phytoplankton, zooplankton and zoobenthos.(2) in summer of 2006-2010, the average total biomass of the phytoplankton in Qinghai Lake was about 66712.28t, that of zooplankton was about 66867.07t; in summer of 2006-2008, the average total biomass of the zoobenthos in Qinghai Lake was about 797.31。The plankton, zooplankton especially, were the main foods of the naked carp.(3) it was more reliable to estimate the fish productivity of Gymnocypris przewalskii przewalskii by means of energy transfer rate based on the zooplankton.The fish productivity of Gymnocypris przewalskii przewalskii was evaluated as 41104t per year。(4) this paper took the ESD grading of all feed organism in a lake firtst time, which was valuable to the study of the structure and function of lake ecosystem, and might be an instruction to the fishery management of lake.