Impacts Of Changing Flow And Sediment On Fish And Habitat Modeling Of The Yangtze River

Dam construction on rivers and other human activities impact the environment and ecology while they provide flood safety, power generation, irrigation and water resources. This paper studies the environmental and ecological responses of the middle and lower Yangtze River stressed by dams, pollution and other human activities through field investigation, analysis, and numerical modeling. The main results are as follows:1) Fish community and fishery harvest are impacted by dam construction and habitats fragmentation. Statistical analysis shows that most fish species like habitats with low velocity. The river training and management should aim at reduce flow velocity.2) The concentration of heavy metals (Cr, Cd, Hg, Cu, Fe, Zn, Pb and As) in water, sediment, and fish/invertebrate were investigated in the middle and lower reaches of the Yangtze River during 2006-2007. The concentrations of heavy metals were 100-10,000 times higher in the sediment than in the water. Benthic invertebrates had relatively high concentrations of heavy metals in their tissues due to their proximity to contaminated sediments. The pollutants were accumulated in the food chain. Benthic invertivore fish had moderately high concentrations of heavy metals whereas phytoplanktivore fish, such as the silver carp, accumulated the lowest concentration of heavy metals.3) Analysing the life cycle and habitat conditions of Chinese sturgeon, habitat suitability equations are developed and suitability distribution curves are obtained. Twelve groups of survival rate of juvenile Chinese sturgeon under various conditions in 1982 to 1993 are used to test the equation. The calculate result agree well with these data. A two-dimensional sediment mathematical model is developed, which is coupled with a Chinese sturgeon habitat model. The model is used to simulate the Chinese sturgeon spawning sites in the reach from the Gezhouba dam to Yichang in 1999 and 2003. The results show that simulated result coincide with measured data. The model is used to calculate the habitat suitability index for different scenarios, the habitat suitability index value is high for the discharge falls within the range of 10000～30000 m~3/s for Chinese sturgeon to spawn, higher and lower discharges are not so suitable for the Chinese sturgeon to spawn.4) This paper also develops a one-dimension habitat suitability model for the four major Chinese carps. They are the black carp (Mylopharyngodon piceus), the grass carp (Ctenop haryngodon idellus), the silver carp (Hypoph thal michthys molitrix) and the big-head carp (Aristichyths nobilis), which are the major fishery species in the Yangtze River. The model is used to simulate the habitat suitability for the four carps in the reach from Yichang to Chenlingji. The simulated results agree with measured data. The modeling results indicate that the four carps will find the reach the best habitat for spawning if the daily-average discharge is in the range 8000～15000m~3/s with an increment of discharge higher than 800m~3/s per day.