Study And Simulation On The Response Of Vegetation Succession To Drainage Water And Salt In Ditch Wetland In Arid Area

As an important part of the ditch wetland ecosystem in arid areas,vegetation plays an irreplaceable role in maintaining the ecological balance of irrigation areas,improving the ecological environment of irrigation areas,purifying the water quality of farmland drainage,and reducing non-point source pollution.However,while farmland drainage in arid areas outputs excess water,it often also outputs a large amount of salt,which will inevitably have a significant effect on the succession of species,community structure,spatial pattern,and other aspects of wetland vegetation in ditches.To make sure that the drainage ditch wetland ecosystem in arid areas works well,this paper takes the farmland-ditch wetland system in the saline-alkali improvement area of Lubotan in Fuping,Shanxi Province as the research object,and adopts the combination of indoor and outdoor experiments,theoretical analysis and model simulation.The comprehensive observation and experiment with farmland drainage-soil water and salt-wetland vegetation as the core were carried out to study the soil water and salt transport and vegetation succession of ditch wetland under the current situation and controlled drainage mode,so as to reveal the response mechanism of vegetation evolution of ditch wetland in arid areas to drainage water and salt,and put forward the suitable drainage control scheme of drainage ditch in arid areas.The main research results are as follows:(1)Based on the improved Green-Ampt slope rainfall infiltration model,the Aver’yanov’s phreatic evaporation equations under crop growing and the principle of water and salt balance,a theoretical model of soil water and salt transport in the drainage ditch slope was established,and the soil water and salt dynamics in different zones of the drainage ditch slope during the monitoring period were calculated and simulated.The HYDRUS-2D numerical model was used to simulate the soil water and salt transport dynamics of the drainage ditch slope.The results shnwed that the simulation results of the drainage ditch slope soil water and salt transport theoretical model and the HYDRUS-2D numerical model were in good agreement with the measured values,and the error was within an acceptable range.It can be used to predict the soil water and salt dynamics of the drainage ditch slope of the ditch wetland in the arid area under the influence of farmland drainage.(2)The vegetation community of ditch wetland in the study area has obvious zoning phenomenon.The vegetation community was divided into two areas:reed area and symbiotic area,and the vegetation community was divided into three areas:reed area,transition area and symbiotic area.The vegetation species in the dry ditch community were more than those in the ditch,and the dominance of single species was less than that in the ditch.The vegetation niche in the study area is similar,and the adaptability to soil salinity is similar.Phragmites australis,Suaeda salsa,Artemisia annua and Chrysanthemum indicum can better utilize the environmental resources of ditch wetlands in arid areas;pearson correlation analysis,canonical correlation analysis and redundancy analysis showed that the key soil factors determining the species richness of drainage ditch wetlands in arid areas were soil moisture content and electrical conductivity.(3)Different water and salt environments in ditch wetland soil have different effects on seed germination and plant growth of typical vegetation.The soil salt content of reed seed germination should not exceed 10 g/kg,low salt(<5 g/kg)and medium water(35%)are more conducive to reed seed germination;the soil salt content of Suaeda salsa seed germination should not exceed 25 g/kg.Low salt(<10 g/kg)and high moisture(moisture content 35%,45%)are beneficial to the germination of Suaeda salsa seeds.The plant height of Chenopodium album was mainly affected by soil moisture.The plant number and basal stem of Setaria viridis were affected by soil moisture,soil salinity and soil water-salt interaction.The plant height and leaf area of Suaeda salsa were affected by water level and salinity.(4)Based on the Levins model,the evolution model of typical plant quantity change rate and biomass change rate in ditch wetland was established,and the changes of reed quantity and Suaeda biomass in the study area were simulated.The simulated values of reed area and transition area were highly fitted with the measured values,and the simulation results of symbiotic area were relatively poor due to the complex resource competition between vegetation.The growth and evolution of Phragmites australis and Suaeda salsa under different soil water and salt changes were simulated.The results showed that the water level had a great influence on the growth of Phragmites australis.The salt in the germination period of Suaeda salsa should not be too high,and the appropriate increase of soil salt in the growth period could increase the biomass accumulation of Suaeda salsa.(5)Compared with the current drainage mode,the controlled drainage depth of 1.5 m is beneficial to the growth of typical plant Phragmites australis in the ditch wetland of the study area.When the controlled drainage depth is 1.2 m,the growth of Suaeda glauca in the transition zone is better.Considering the agricultural production,the water and salt environment of the ditch wetland,the vegetation growth status and the ecological environment effect of the ditch wetland,the controlled drainage depth of 1.5 m is a more suitable drainage control scheme in the study area.In addition,for the drainage ditches with poor ecology or new construction,the prefabricated vegetation blanket technology can be used to speed up the rapid ecological restoration and reconstruction of drainage ditch wetlands in arid areas according to the coupling relationship of farmland drainage-soil water and salt-vegetation succession.In summary,the study revealed the response mechanism of vegetation evolution to drainage water and salt in arid area ditch wetlands,constructed an evolution model of typical plant quantity change rate and biomass change rate in ditch wetlands,and proposed suitable drainage regulation schemes for arid area drainage ditches.The research results have important theoretical and practical significance for enriching and improving agricultural water resource management,and can provide scientific basis for the construction of similar ecological irrigation areas,saline alkali land management,and environmental protection.