The Study Of Fishery Resources And Ecopath Model In Jinshahe Reservoir Ecosystem, Hubei Province

Jinshahe reservoir, one of the large reservoirs in middle Yangtze River, is a typical hill-type reservoir and the only one drinking water resource of Hong’an County. It’s a representative reservoir in many aspects such as the characters of catchment areas, the pattern of reservoirs and integrated functions and so on. In this study, we investigated the current status of fisheries resources and assessmented the water nutritional status in the Jinshahe reservoir, moreover, we built a model based on software Ecopath with Ecosim(Ew E) for the reservoir to analysis the compositions and functions of the reservoir ecosystem quatitively and discuss the effect of large range of stocking silver carp and bighead carp on the reservoir system. The main results were as follows:1.In the whole year, the range of water temperature, p H and DO in the Jinshahe reservoir were 5.8~33.2℃, 7.20~8.69 and 7.45~10.28 mg/L, respectively. The value of NH4+-N, NO2--N, NO3--N, TN were 0.0173~0.6763 mg/L, 0~0.0057 mg/L, 0.0421~0.2968 mg/L and 0.2167~0.9543 mg/L, respectively. The PO43--P and TP values were 0.0003~0.0222 mg/L and 0.0040~0.0350 mg/L respectively. The content of COD, Chla and organic detritus were 0.6231~2.0625 mg/L, 0.0035~0.0197 mg/L and 1.488~3.411 mg/L respectively. The physicochemical parameters were within the range of II in the national surface water standard except for total nitrogen. According to TLI index, the nutrition status belongs to mesotrophic waters in spring, summer and autumn, but it belongs to oligotrophic water in winter.2.There were 216 phytoplankton species in the Jinshahe reservoir, which belongs to 8 phyla and 94 genuses. The range of phytoplankton density and biomass were 7.99×105~360.20×105 ind./L and 0.7906~7.5478 mg/L respectively. Redundancy analysis(RDA) was used to analysis the relationship between dominant species and the environment factors, the result showed that PO43--P, TP and DO had mostly affected on phytoplankton community. 95 zooplankton species were identified and most of them were protozoan and rotifera. The density and biomass of zooplankton were 4939.90~27238.10 ind./L and 0.5579~1.4890 mg/L respectively. RDA indicated that NO3--N, TN and TP were the dominant environment factors affected on the community structure of zooplankton. There were 23 macrozoobenthos species were indentified, midges larvae were the dominant species in the Jinshahe reservoir, the density and biomass were 320.00~1750.00 ind./L and 1.0846 ~10.9478 g/m2 respectively. Meanwhile, NH4+-N, PO43--P and TP were the dominant environment factors to macrozoobenthos community. According to the dominant species, density and biomass of community strcture, as well as biotic indexes, the assessment results showed the same tendency in trophic status with TIL index.3.An Ecopath model was built to evaluate the ecosystem of the Jinshahe reservoir. The result showed that there were four effective trophic levels(TLs) in the reservoir ecosystem, the four levels belong to pyramidal type and energy mainly flowed between them. Energy passageway of the system consisted of grazing food chain and detritus food chain. The whole system made an inefficient use of primary productivity. The indices TPP/TR(total primary production/ total respiration), CI(Connectance Index) and FCI(Finn’s cycling index) indicated that the reservoir ecosystem structure was simple, thus it has poor ability of anti-interference to environment. Large stocking with bighead carp was harmful to the reservoir system. On one hand, large density of fish magnified the predator pressure to zooplankton and caused the inefficient use of phytoplankton, on the other hand, bighead carp has negative effect on some carnivorous fishes that may have adverse consequence on the stability of ecosystem.At all, Jinshahe reservoir has higher nitrogen content in contrast with the former researches, and phosphorus is closely correlated to food organism of fish. So measures should be done to control the input of nitrogen and phosphorus elements in case of eutrophication. On the other hand, management should control the stocking of bighead carp and adjust the ratio of bighead carp with silver carp, meanwhile, raise the amount of predatory fishes appropriately, to highlight the stability of the Jinshahe reservoir.