Study On Eco-hydrology And Ecosystem Health Diagnosis Of Peatland In Northeast China

The world's peatland covers an area of more than 4 million square kilometers,with a carbon storage of 480 Gt,accounting for more than one third of the world's soil carbon pool,and more than half of the atmospheric carbon content.It plays an important role in mitigating global climate change and contributes to global atmospheric carbon.The regulatory effect of serotonin also has a profound impact.Hydrological dynamics affect the changes in carbon storage and flux of peatlands,which can aggravate or slow the release of carbon on land,while climate change and human disturbance can change the ecological and hydrological processes of peatlands.Existing studies have shown that the global peatland has now been transformed from a net carbon sink to a net carbon source.In high latitudes,northern peatland is more sensitive to the disturbance of environmental changes.This paper takes typical peatlands in Northeast China as the research object.Based on the wetland water level dynamic observations at 11 monitoring points,8 consecutive years and 427 rainfall processes,as well as the natural attribute data of watersheds and peatlands obtained from multiple field surveys,MIKE SHE is used.Constructed a peatland ecological hydrological model coupling surfacegroundwater and including boundary hydrological environment;calculated the water flux between the watershed subsystems and hydraulic connections between the subsystems according to the simulation results,revealing the influence of boundary hydrological environment on the hydrological dynamics of peatlands;On the basis of analyzing the hydrological characteristics of peatlands,a "water level profit and loss index" was established to diagnose the health status of peatlands and reveal the causes of health damage.The main results of this research are as follows:1.Characteristics of peatland hydrological regime in the study area: The interannual variation of peatland water level is positively correlated with annual rainfall,and has a certain time lag.The hydrological regime is significantly affected by the rainfall of the previous year;continuous low-water years have increased water level fluctuations.The fluctuation range has been significantly narrowed after the occurrence of continuous rich and normal water years,indicating that sufficient rainfall plays a very important role in maintaining the water level and stability of "rain-fed" peatlands;the water level is difficult to maintain in the wet years after continuous dry years.The level of the water level in the year was restored to the level of a normal year;the fluctuation range of the water level during the year was significantly affected by the length of the rainless period and the intensity of rainfall.The water level in different areas of the peatland was significantly heterogeneous due to the micro-topography and other environmental differences;the peak water level during the year appeared in the highest rainfall In January,the wetland water level rises with the increase of monthly rainfall,and decreases with the decrease of rainfall,but the different periods of "rain and heat" will aggravate the hydrological situation of wetland drought.Studies have shown that water level dynamics are closely related to factors such as peatland vegetation,micro-topography,and soil structure.Human disturbance and boundary environmental conditions are also important factors that cannot be ignored.The combined effect of the above-mentioned multiple factors leads to the appearance of patches of different health conditions in the peatland,and affects the succession trend of the community.2.This research uses MIKE SHE to construct a hydrological model of a peatland ecosystem that couples surface-groundwater and includes boundary hydrological environments.Through the peatland-watershed two-scale simulation research method,it solves the problem of isolated research on non-closed hydrological units and actual conditions.Difficulties with big differences.The watershed model with a 90-meter grid is used to determine the hydrological boundary conditions for the peatlands,and the hydrology within the peatlands is simulated with a 30-meter grid,which effectively reflects the heterogeneity between patches in the peatlands,and gives the model parameters clear ecology Learn meaning.The fitting degree of simulation results of multi-point water level in peatland all reached more than 0.75,and the results were highly reliable,which more accurately and objectively expressed the continuity of surface-groundwater movement and the temporal and spatial heterogeneity of hydrological dynamics in the study area.The simulation results provide detailed hydrological process data.The calculation results of the boundary water flux show that the agricultural activities in the study area have caused obvious negative impacts on the hydrological environment of the peatland watershed,seriously disturbing the natural ecosystems such as forests,rivers,and peat.The hydrological connection between the land,most of the hydraulic connection between the peatland and the catchment area has been artificially blocked;due to the artificial river bed,the water level of the river has been lower than the surface for a long time,and the river water cannot flow over the river embankment to supply water to the peat land;Water is exported unidirectionally to the river in the form of surface slope flow and lateral flow in the underground saturation zone.Catchment water in the non-glacial period(May to October)accounts for 1/3 of the total recharge of peatlands,and less than 1/5 in the rainy season(July to September).The main source of water during rainfall,according to this hydrological process The quantitative results can draw the conclusion that the current peatland is "rain-fed".The study also showed that the evapotranspiration in the study area during the ice-free period(May to October)was 2.4mm/d,and the water consumption exceeded 1/2 of the total recharge.The summer evapotranspiration was 3.3mm/d,accounting for approximately 2/3,the amount of water delivered to the atmosphere exceeds the amount of water exported from the land boundary.The deterioration of the boundary environment has greatly reduced the source of water supply for peatlands,the activity of surface hydrological processes has decreased,and the function of regulating and storing water resources has weakened;in addition,the continuous "release of water" during the rainless period has aggravated the drought stress in the peatlands adjacent to the river.3.The hydrological prediction results of the drought of peatland show that the decomposition of peat results in extremely significant changes in the hydrological process,which is the fundamental reason for the decline of hydrological ecological services.Studies have shown that when the bulk density of peat increases to 0.5 g/cm3,the peat land flow will change from full-storage flow to super-permeable flow,and the surface slope flow(discharged into rivers + land boundary overflow)will increase by more than 50%,The water storage capacity of peatlands is reduced by about 40%.The decline in available water not only leads to the weakening of the peatland's ability to allocate water in space and time,and the decline in regulation and storage,but also the deterioration of the wet environment and changes in the biological community due to the reduction of the phreatic level,which in turn promotes the decomposition of peat,resulting in a "water level drop-" The positive feedback regulation mechanism of "peat decomposition" accelerates peatland drought.The dryness of peatlands will not only lead to the decline of hydrological service functions,but the positive feedback effect of the drop in water level and the decomposition of peat will also promote the transformation of peatlands from carbon sinks to carbon sources.This process is usually irreversible.Preventing the decomposition of peatlands will help maintain the structure and structure of peatlands.The integrity of function is extremely important,and it is an important goal of peatland ecosystem management and maintenance.4.Based on the spatio-temporal variation characteristics of peatland water level,this study constructed a peatland ecosystem health diagnosis method with water level break-even time(TBEP)and water level break-even index(TBEindex)as the main parameters,and used negative feedback adjustment based on drought stress.The response ability to judge the health status.This method has the characteristics of good consistency,strong objectivity,and clear results.It is suitable for long-term monitoring of the health status of peatlands.It can also be used to judge the trend of peatlands from carbon sinks to carbon sources based on the results of health diagnosis.In addition,this method is not only It is suitable for the same climate area and also for the health comparison between peatlands in different climate areas.TBEindex reflects the degree of drought stress.A positive value indicates a strong ability to maintain the wet environment and good health;on the contrary,a negative value,the greater the absolute value,the longer the water level deficit will be,and the worse the water level maintenance ability will be,indicating that the system is under drought stress.The more serious the severity,the worse the health status;using this method in conjunction with factors such as climate,landforms,vegetation,soil and human interference,the results of health diagnosis on peatlands show that the health status of different patches in the peatlands in the study area is significantly different,Showing four types of degradation,damage,sub-health and health.Among them,the eastern patch(TBEindex =-0.325)and the southern patch(TBEindex =-0.182)are in a degraded state,the northern patch(TBEindex =-0.150)is in a state of impaired health,and the central-northern patch(TBEindex =-0.059? 0.017)is in a sub-healthy state,and the southwestern patch(TBEindex =-0.196)is in a healthy state.5.Maintaining a wet environment is vital to the survival of peatlands.It is the key to preventing peat decomposition,maintaining the integrity of the organizational structure,improving the resilience of the ecosystem,and maintaining the health of the ecosystem.The mechanism mainly depends on the suppression of peat.Two negative feedback adjustment functions for decomposition and suppression of evapotranspiration.The health diagnosis results show that(1)the peatland with damaged patches has the characteristics of high peat soil bulk density,high biomass and canopy closure,and large impact on lateral flow drainage,and the system has the negative feedback regulation function of inhibiting peat decomposition and evapotranspiration.Decline or failure is an important reason for the decline of the stability of the peatland ecosystem and the weakening of its resilience;(2)The drastically changing wet environment,coordinated to destroy the positive feedback adjustment mechanism of peat properties,will cause the peatland to continue to develop in the direction of aridification;(3)The negative feedback regulation mechanism of the degraded patches has basically failed and is developing towards a trend of continuous deterioration;(4)The shrubs with damaged patches of health have an obvious tendency to invade the center of the peatland,and the area is gradually expanding;(5)Peat in the study area Most areas of the land are still in a healthy or sub-healthy state,but future climate change may cause sub-healthy plaques to turn into health-impaired plaques.Active human interference can enhance the negative feedback regulation mechanism and system of sub-healthy plaques.Resilience helps combat the negative effects of climate change.Therefore,the future development trend of such climate changesensitive patches mainly depends on the implementation of ecosystem management strategies and protection measures.The deteriorating health status of the peatland in the study area shows that the current “fence management and protection” approach is not enough to protect or restore the health of the peatland ecosystem.Instead,the watershed hydrology should be used to restore different ecology in the catchment area.The hydraulic connection of the system reduces the intensity of agricultural production's utilization of wetland water demand.Maintaining the normal fluctuation range of the wetland water level,maintaining a normal wet environment,reconstructing the negative feedback adjustment mechanism of the system,enhancing elasticity and resilience against disturbances are the key measures to be implemented in the management of the peatland ecosystem.