Research On The Ecohydrology And Model Of Eutrophication Reservoirs

Based on the investigation and assessment of large reservoirs in Yangtze Basin, this paper analyzed the causes and characteristics of the eutrophication occurred in these reservoirs. The relationships between ecohydrological pattern and eutrophication were researched in the view of ecohydrological processes of watershed and hydrological regime; stochastic model of eutrophication was also studied, which provided the theoretical basis for ecohydrology.Based on the methods such as clustering analysis and principal component analysis, this paper studies the relationship between the ecohydrological pattern of watershed and eutrophication. The results manifests that status of land usage, population denity and hydraulic retention time are the main factors influencing the eutrophication of reservoirs. Owning to the different location and function of reservoirs, significant differences exsist in eutrophic states. Water quality of the reservoir inflow was decided by soil types of watershed,status of land usage and vegetation coverage. The results showed that the eutrophic state is obviously related with the type and function of the reservoirs. The eutrophication level of lake-type reservoirs is higher than that of rive-type reservoirs; the eutrophication level of the reservoirs primarily for irrigation is higher than that of reservoirs for power generation. Among the 14 rive-type reservoirs and 13 lake-type reservoirs that have been investigated, 21.4% of the rive-type reservoirs and 69.2% of the lake-type reservoirs have been eutrophicated; 30% of the reservoirs for power generation have been eutrophicated, while the the ratio is 53.8% for reservoirs used to irrigate.The ecohydrological pattern of watershed decided both the type(types) of reservoirs and the hydrodynamics. The plankton communities in the reservoirs showed remarkable differences, which are closely associated with the hydrodynamics and nutrient levels in the reservoirs. Hill-reservoir has a short retention time; its phytoplankton community was characterized by low abundance and no obviously dominant species. The zooplankton was predominated numerically by rotifer and nauplii. Located at the downstream of the river continuous system, Plain-reservoir had higher number phytoplankton species and mediate cell density. The dominant species of phytoplankton were Chlorophyte and Bacillariophyta, and composed of both lacustrine and potamo phytoplankton. The zooplankton was predominated numerically by nauplii.It indicated that the level of eutrophication has high correlativity with the hydrological regime. Through regulating water level or hydraulic retention time, the composition of nutrition and standing crop of algae can be adjusted, therefore effecting eutrophication process. Delaying the retention time of water and reducing the flow speed are helpful for the sedimentation of nutrient, thus preventing the dilution of it, which is profitable for the growth of algae. Based on the Vollenweider model, a stochastic eutrophication model was built. The changing process of total phosphorus concentration was regarded as a random process in the model. Therefore, the model provides the random properties of total phosphorus concentration.Based on the relationship between eutrophication and ecohydrological processes, this paper put forwards the Hydrological conceptual model for eutrophication, which gives the new direction to the study of the hydrological model.