The Influence Of Megahbrama Amblycephala To The Competitive Landscape Of Vallisneria Natans And Hydrilla Verticillata

Submerged macrophytes, herbivorous fishes and filter-feeding benthonic animals are important components of shallow lake ecosystems. With interactive effects, they influence on water quality. Submerged macrophytes can keep the water being clear by absorbing nutrients such as nitrogen and phosphorus, inhibiting the release of nitrogen and phosphorus from the sediment, promoting the settlement of suspended particles, inhibiting the growth of phytoplankton, improving the transparency of the water body. Different submerged macrophytes with different pattern have different ability of purification: Meadow-forming submerged macrophytes, such as Vallisneria natans, which biomass concentrated on the surface of sediments, have a stronger purification capacity; however canopy-forming submerged macrophytes, such as Hydrilla verticillata, can’t effectively reduce the sediment nutrient release and have a feeblish purification capacity, because the most biomass near the surface. But canopy-forming submerged macrophytes have a faster growth rate than meadow-forming submerged macrophytes, and reduce the growth of meadow-forming submerged macrophytes by occupying the top of spout and covering the light. So we can maintain water quality by controlling the canopy-forming submerged macrophytes and promoting the meadow-forming submerged macrophytes. Herbivorous fishes prefer to feeding canopy-forming submerged macrophytes which have finely-divided leaves and lower C: N: P, thus this is helpful to the growth of meadow-forming submerged macrophytes. But when excess herbivorous fishes eat up the canopy-forming submerged macrophytes, they will start to feed the meadow-forming submerged macrophytes. Therefore, researching the influence of herbivorous fishes to the competitive relation between meadow-forming submerged macrophytes and canopy-forming submerged macrophytes will help to know the regulative ability of herbivorous fishes to the canopy-forming submerged macrophytes, and then provide scientific basis for increasing water quality and restoration of lakes. On this basis, we have studied the competitive relation between V. natans and H. verticillata, and the effects of Megalobrama amblycephala on the competition. And then we can put effort into providing theoretical basis and support for lake ecological restoration.We settled three treatment groups to study the competitive relation between V. natans and H. verticillata, they were group of V. natans, group of H. verticillata and intercropping group, respectively, each group with 8 replicates. A month later, we took 4 of these replicates. The results showed that:(1) V. natans and H. verticillata significantly reduced the TN, TDN, TSS concentrations, and V. natans have a better ability to reduce various forms of nitrogen;(2) Except for the group of V. natans, the TP and TDP concentration rose in other groups. But the TDP concentrations in group of V. natans were< intercropping group< group of H. verticillata. This indicates that V. natans have higher removal efficiency of TP than H. verticillata;(3) The group of H. verticillata increased DO concentrations at the starting of this experiment, but at last the intercropping group exceeded the group of H. verticillata;(4) The biomass and growth rate of the plants in group of V. natans and group of H. verticillata were higher than intercropping group. This shows that there is a competitive relation between them;(5) The growth parameter, leaf parameter, root morphological parameter, biomass allocation parameter of intercropping group’s V. natans were all lower than the group of V. natans, but there wasn’t significant difference between the group of H. verticillata and the intercropping group’s H. verticillata.It shows that V. natans was inhibited, but not for H. verticillata.To study the effects of M. amblycephala on the relationship of V. natans and H. verticillata, we added 4 M. amblycephala which is about 100 g into the remaining 4 replicates of each group. The results showed that:(1) DO in each group changed after M. amblycephala were added, but the group of V. natans had the smallest change, and also the percentage of illumination rose in the group of V. natans;(2) The group of H. verticillata had maximal biomass reduction, followed by the intercropping group’s H. verticillata, and the biomass of the group of V. natans rose slightly.(3) The growth parameter including leaf parameter, root morphological parameter, biomass allocation parameter among all groups had small variability, but no significant differences among them.Besides, as classic filter-feeding benthonic animals, freshwater bivalves can filter-feeding the phytoplankton and suspended particles, improve the transparency of the water body and reduce the degree of eutrophication of aquatic ecosystems. To study the efficiency of filter-feeding of filter feeders, our study aimed to reveal the influence of A. woodiana on the TSS, Chla and water nutrients via setting different levels of A. woodiana biomass. The results showed that:(1) A. woodiana can lower the concentrations of TSS and Chla in the water quickly;(2) The concentrations of TSS and Chla decreased faster in the treatments of high biomass of A. woodiana;(3) A. woodiana decreased the concentrations of TN, TP, TDP and boosted the TDN in the second day, while there is no significant difference between the blank treatments and the A. woodiana treatments at the end of this experiment.The above results show that, V. natans and H. verticillata can effectively reduce the eutrophication of water bodies, but V. natans is better than H. verticillata. When two submerged macrophytes exist, H. verticillata have obvious inhibition on V. natans. Between these two submerged macrophytes, M. amblycephala prefer to feeding H. verticillata, affecting the competition between them, making V. natans grow faster, but it may cause the deterioration of water quality again. A. woodiana can reduce the TSS concentrations and phytoplankton biomass obviously in eutrophic water quickly, but on a long view, it can’t improve the water qualities. We can use A. woodiana to improve the transparency of the water body and provide growing conditions for submerged macrophytes.