Hydrological Dynamics And Numerical Simulation Of A Drained Peatland In Changbai Mountains

Peatland drainage is an important means for humans to interfere with the growth of peatlands,drainage changes the hydrological situation of peatlands,further disturbs the inside biogeochemieal cycle of peatlands,and then leads to the peatlands to be degenerated and the peat accumulation system to be collapsed.To protect the peatland resources and restore the damaged peatland ecosystems,the principle work is to research the hydrological change conditions of peatlands,and restore the natural hydrological situation of peatlands.This paper takes Baijiang River peatland that is degenerated due to drainage as the research area,this peatland is reserving the natural undrained peatlands(undrained area)and the degenerated peatlands caused by drainage(drained area),acquires the peat hydrological characteristics of the original peat sample in undrained area and drained area of scientific determination of the lab,including the important hydrodynamic parameters-saturated conductivity,unit weight,saturated water content,water capacity,porosity,organic matter content and other indexes,it explores drainage has the impact on the peat properties by the contrastive analysis;by the long-term water level and meteorological monitoring,it makes a contrastive analysis for the water level fluctuation characteristics of undrained area and drained area;basing on a large amount of experimental data and the elevation model of the research area,it simulates the groundwater flow movement of the peatlands of Baijiang River by the groundwater simulation software,it carries out a deep analysis for the groundwater movement law and the groundwater balance condition of this area,therefore,it provides the basic guide for restoring the hydrological situation and ecological environment of this peatland.The research obtains the main conclusions as below:(1)The hydrological properties of peat were changed by Peatland drainage,which affected the rate of groundwater migration in peatlands.The degree of influence decreases with decreasing depth,and the critical depth of change in hydrological properties is 60 cm.The average saturated water conductivity,water content and non-capillary porosity of the peat in the drained area are significantly lower than the undrained area,while the soil bulk density,capillary porosity and total porosity in the drainage area are higher than the undrained area.After the peatland is drained,the bulk density is increasing caused by the decomposition of peat,and the water conductivity and water holding capacity are significantly weakened.It indicates that the drainage caused the sedimentation and compaction of the upper peat,which changed the hydrological properties of the peat.The vertical distribution of water properties in the undrained area is more obvious and uniform.With the increase of depth,the saturated water conductivity of peat in the undrained area decreases,the bulk density increases,the saturated water content decreases,and the water holding capacity decreases.The capillary porosity and total porosity increase,and the non-capillary porosity decreases.The vertical distribution of the peat hydraulic properties in the drainage area is more complicated,but still shows uniformity.The limit of the mutation is generally 60cm and 160cm depth.(2)The saturated water conductivity is significantly negatively correlated with the bulk density,and is positively correlated with the saturated water content,positively correlated with the water holding water capacity,and positively correlated with the porosity.The changes of these hydrological properties are positively correlated with the organic matter content.The saturated conductivity on horizontal and vertical direction of this researched area have a height relevance(R~2=0.756,p<0.05),so they can be deduced each other.(3)Water level of the undrained area is higher than the drained area all the year round,the time of the lowest water level in growing season is the first half August,and the water level of the undrained area has the weaker degree of response for rainfall event than the drained area,the water level of the undrained area is more stable,the water level of the drained area is easily affected by weather,and then water level is fluctuated severely.At at the same time the upstream water level is more stable than the downstream water level,and the fluctuation is weaker.The research finds out the difference of the surface peat properties of the undrained area and drained area cause the different water level fluctuation situations,except the impact of surface elevation,the surface peat of the undrained area has the higher water capacity and conductivity than the drained area,so water level is more stable,and not easily interfered by rainfall.(4)The simulation result of groundwater value uncovers the groundwater movement law of Baijiang River peatland,groundwater flow is basically consistent with the surface fluctuation,groundwater mainly flows from the north to the south,groundwater level at the south side of the research area has the larger buried depth,groundwater overall outflows to southeast corner.The hydraulic gradient of the undrained area is more uniform,the hydraulic gradient at the north side of the drained area is larger,but smaller at the south side.(5)The simulated result shows that the groundwater of the research area appears the negative balance,the daily loss of groundwater amount is small,but a whole peatland is always drained out,it is urgently to carry out hydrological restoration.This research tries to carry out hydrological restoration experiment,the result shows that water level rising effect is more obvious through blocking the drains per 40m space.The calculated value of groundwater balance among July~August 2018 is slightly higher than the same period of 2017,from it we can temporarily determine the hydrological restoration experiment is valid,which effectively prevents groundwater from draining out the peatland.