Study On The Effect Of The Biochar For The Construction And Decontamination Efficiency Of Submerged Plant System

In order to speed up the rapid recovery of water environment after dredging in some seriously polluted areas in Baiyangdian Lake,the rapid construction of submerged plant system is a key link in the improvement of water ecology.Based on the characteristics of sediment distribution in the dredging area of Baiyangdian Lake,this study has systematically investigated the effect of biochar improved sediment on the plant growth and decontamination efficiency of three submerged plant systems?Ceratophyllum demersum,Vallisneria natans,Hydrilla verticillata?through the field simulation experiments,and the strategies for the sediment improvement of Baiyangdian have been put forward;Based on the improvement of sediment quality,the influence of the water depth and water level fluctuation on the growth and water purification effect of Hydrilla verticillata is investigated,and the construction strategy of submerged plants in Baiyangdian dredging area has been proposed.The main achievements obtained are as follows:The sediment quality of Nanliuzhuang dredging area is slightly alkaline,and all the sediment color grade,water content,total nitrogen,total phosphorus and organic matter content show a decreasing trend with the increase of depth.After dredging,the surface sediment?50?60 cm?has a low moisture content,shows a harden state,and is in a barren state with a low content of nutrient elements.The biomass of the three submerged plants shows a trend of decreasing first and then increasing at the different biochar doses,the biomass of the three submerged plants is increased most significantly at 20 mg/g,with the relative growth rates of 0.057,0.068 and 0.051 mg/?g·d?;the MDA value showed a trend of decreasing first and then increasing,and it is the smallest at 20 mg/g,and the plant is the least stressed.Under the dosing of40 mg/g biochar,the plant chlorophyll is the lowest,and the photosynthesis is affected.The addition dose of 20 mg/g biochar can significantly improve the removal of TN,NH₄⁺-N,TP and oxygen enrichment in water.The addition of an appropriate amount of biochar can improve the relative abundance of Acidobacteria in the substrate,and the relative abundance of Firmicutes is reduced to resist the environmental stress.On this basis,it is proposed that after the endogenous dredging,the biochar is added to the mud-water mixing interface with a dry weight mass ratio of 1:50 between the biochar and sediment to improve the sediment,and the strategy for the reasonable control of exogenous pollution input into the industry and agriculture etc.is combined to provide the technical support for the restoration of the aquatic plant growth and water quality purification in Baiyangdian Lake in the future.Under the background of proper amount of biochar addition,water depth can have an important effect on the growth and water purification of Hydrilla verticillata?indigenous species?under the improved substrate of biochar.The relative growth rate of Hydrilla verticillata is increased first and then decreased in the range of water depth from 0.4 to 1.6 m,the relative growth rate of hydrilla reaches 0.090mg/?g·d?at 1.2 m.the Hydrilla verticillata grows the best,which is the optimum water depth of Hydrilla verticillata;the fluctuation rate of low water level with 4 cm/3d can produce a certain promotion improvement for the growth of Hydrilla verticillata;the removal effects of Hydrilla verticillata system on TN,NH₄⁺-N,TP,and COD are better,with the cumulative removal rates reaching 57.02%,92.34%,67.75%,and 71.81%,respectively.The strategy of establishing the submerged plant community at the different blocks is put forward by dividing the dredging areas of Baiyangdian into the shallow water area and deep water area,in the shallow water area,a priority shall be given to the priority cutting and planting of Hydrilla verticillata,Potamogeton pectinatus and Najas minor;in the deep water area,the submerged plant community is restored by means of the separated ecological construction mode,the water level is lowered in the enclosure first,and the water level is restored by means of the Potamogeton wrightii and Ceratophyllum demersum,after the community is stabilized,the enclosure is removed and the water area is connected.