Ecological Effects Analysis Of Several Small Wetlands Ecological Restoration Projects

Small rivers and lakes,as the links between land and water,are the main channels through which nutrients,pollutants and suspended solids from terrestrial ecosystems entering large rivers and lakes.The ecological restoration of small rivers and lakes can effectively reduce the nutrient load into rivers and lakes.It is an important measure to restore wetland ecosystems from the source and control non-point source pollution.It is of great significance for eutrophication control.The small river wetlands in Tongli National Wetland Park of Wujiang in Jiangsu Province sustained serious eutrophication due to the concentration of birds and the agitation of ships.In order to improve the water quality,the parallel crossing water system was designed in the wetland park with management of ships.By controlling the ship route,the crossing and parallel connection of the shipping and non-shipping river sections was formed,which promoted the redistribution of nutrients in the shipping and non-shipping river sections through the flow of water bodies.At the same time,the removal of sediment was carried out in both rivers.For reservoir-pond wetland,the park forms different micro-habitats such as shoal,shallow and deep water areas through partial deep excavation,which can increase biodiversity,promote redistribution of nutrients among different micro-habitats and improve water quality.In this study,water samples were collected from dredging and non-dredging sections from boating and non-boating rivers.Water quality effects of shipping control and dredging measures were compared and analyzed.For the restored reservoir wetlands,surface water samples and sediment samples were collected from shoal,shallow and deep waters areas respectively to study the distribution characteristics of nutrients such as C,N and P in different water depths.The results showed that:(1)In the parallel river system,total phosphorus(TP)concentration in boating rivers was higher than that in the parallel rivers in winter and spring.However,total nitrogen(TN)concentration in winter was slightly lower in boating rivers than that in parallel rivers,but slightly higher than that in spring.The design of parallel river system can increase the heterogeneity of water body between main rivers and parallel rivers,and promote the transfer and redistribution of nutrient elements among the parallel river system.(2)Concentrations of ammonia nitrogen(NH4+-N)and nitrate nitrogen(N03-=N)in the water of the dredging section decreased in both winter and spring.In addition to the no-boating rivers in winter,the TN concentration in other rivers decreased after dredging.In winter,the concentration of TP in the dredging sections was higher than that in the non-dredging sections.In spring,the concentration of TP in the dredging sections of the boating river was lower than that in the non-dredging section.In the dredging section of the non-boating rivers,the concentration of TP was higher than that in the non-dredging section.Dredging can effectively reduce the concentration of N in water.In order to control the TP in the water body,no sediment removal should be taken in the non-boating rivers.The TP in the water body can be kept at a low level,and the sediment could not be cleared if it is not necessary.(3)The contents of organic carbon(TOC)and total nitrogen(TN)in the sediments of deep water area of reservoir pond wetland were significantly higher than those of shallow water area and shoal area,while the contents of TP,average particle size and separation coefficient in deep water area were significantly lower than those.The heterogeneity of surface water was very small among different water depth gradients,and there were significant differences in nutrient content and grain size structure in sediments.With the increase of water depth,the contents of TOC and TN in sediments increased,while the contents of TP decreased.Limited excavation is conducive to the enrichment of TOC and TN in deep water sediments,and the micro-topography of deep pools and shallows is conducive to the spatial redistribution of C,N and P nutrients.