Research Of Basement Structural Forms Restoration Of Wetland In Lake Buffer Zone

Wetland basement, as the basis of plants, is also the activity places for microorganisms and benthic fauna. Improving the conditions of the basement is the foundation of wetland ecological restoration, and the morphological optimization of basement is an important measure to improve conditions of the basement.Firstly, the impacts of basement structural form on the distribution of nutrients in water and sediments were studied by example of a typical concave basal wetland in the study. It showed that the nutrients distribution was uneven regardless in water or sediments, which was related with the depth of overlying water. As the increases of overlying water depth (decreases of basal elevation), total nitrogen and total phosphorus concentration in water decreased firstly and then increased, and reached the lowest value with a water depth from 30cm to 50cm. nitrogen and phosphorus concentration in sediment increased with the increases of water depth, reached the highest value with a water depth from 70cm to 80cm. It concluded that the nutrient distribution of wetlands was greatly influenced by the water flow regime, and water flow regime was affected by the structural formof concave basement through analysis by software F1UENT.Then,the impacts of basement structural form on purification characteristics of nutrients in the overlying water were studied in the typical concave basal wetland. As results showed that the nutrient concentration of water would be rapid increase with stormwater runoff into the wetlands,at the beginning of the Storm ended, wetland system for water nutrients reductions was given priority to physical settlement, after a period of time, wetland system for water nutrients reductions was mainly biodegradable. Both of these two processes were subject to the effect of physical and chemical conditions of basement, which were caused by the basement structural form. In wetland system, there were "efficient purification zone" and "inefficient purification zone". The ups and downs of the substrate caused a change in the depth of the overlying water in wetland, which leaded to the differences of physical and chemical indicators of basement, futher affecting the level of nutrients removal efficiency.Finally, the nutrients removal efficiencies of various basement structural forms on the "water and sediment" system were studied in typical condition of water depth(40cm) through constructing five kinds of different basements(the beveled substrate, the planar substrate, the concave substrate, the convex substrate and the more natural-type substrate) under simulated condition in laboratory. The study found total nitrogen removal rates of the five different basements above were, in order,28.84%,25.22%,27.07%,31.23%,35.23%; and total phosphorus removal rates were basically the same with only a slight difference caused by ingestion of aquatic plants. Different wetland basement structural form, resulted in the difference of the specific surface area of.sediment-water interface, consequently affecting the attachment space of basal biofilm and exchange degreeof sediment and water, eventually affecting purification efficiency and effectiveness about nutrients of wetland system. In addition, the substrate morphology also affects the strength of the light distribution of the substrate, thereby affecting the development and growth of aquatic plants, thus making the nutrients removal efficiencies of wetland system quite different.