Effects Of Biological Soil Crusts On Eco-hydrological Processes And Water Balance In Sand Land

Biological soil crusts widely distributed in desert ecosystems,which play an important ecological role and affect many ecological processes.Soil moisture is the main abiotic limiting factor in desert areas,it is important to study the effects of biological soil crusts on ecohydrological processes and water balance for vegetation restoration and reconstruction in this area.Based on long-time observation and simulation experiments,this study,the redistribution process of precipitation infiltration,leakage,and evaporation of bare sand and different biological soil crusts of fixed dunes in Mu Us sand land was observed.The soil moisture income and expenditure of different biological soil crusts covered soil were analyzed,and the annual difference of soil water balance was determined.The mainly conclusions are as follows:(1)The biological soil crusts of fixed dunes is well-developed,with coverage of 65.40%(algae crusts: 23.10 ± 3.20%,moss crusts 42.30 ± 4.60%).The development of the biological soil crusts changed the physical and chemical properties of soil which affected the hydrological process: the clay content,organic matter content,soil porosity and soil water holding capacity were increased;in order to determine the soil depth of this study,the root of Artemisia ordosica was investigated by excavation.The results showed that the roots of Artemisia ordosica in fixed dunes were mainly distributed in 0-40 cm,0-40 cm could be regarded as the representative soil depth of the study on the influence of biological soil crusts on the hydrological processes of sand land.(2)In this study,the precipitation simulation method was used to determine the impact of biological soil crusts covered soil on precipitaion infiltration under different levels.The results showed that compared with bare sand,biological soil crusts hinders precipitation infiltration under the same precipitaion.The water leakage at 40 cm is reduced,and the maximum infiltration depth and infiltration rate of precipitation are affected,as follows: bare sand > algae crusts >moss crusts.(3)The influence of different types of biological soil crusts covered soil and bare sand on soil evaporation was measured under natural conditions.The results showed that the 0-10 cm soil will form dry sand layer after precipitation,which hinders the water migration in the lower soil pores,reduces the evaporation rate of bare sand,which leads to the evaporation of the soil covered by biological soil crusts is higher than that of bare sand.Based on the evaporation rate of different types of soil crust and bare sand rainfall,the evaporation process can be divided into three stages: the stable stage,the rapid decline stage and the vapor diffusion stage.The evaporation of different types of soil crusts was mainly reflected in the duration of the first stage:moss crusts > algae crusts > bare sand.(4)Based on the long-term fixed-point observation of soil water dynamics of different types of biological soil crusts and bare sand,it was found that compared with bare sand,under different rainfall conditions(dry year,wet year and normal year),the coverage of biological soil crusts on the surface of soil was beneficial to increase the water content of shallow soil(0-10 cm),but its existence reduced the soil water content of 10-40 cm.The shallow layer of soil water is beneficial to the occurrence of soil evaporation,which increases the water branching in the water balance of sandy ecosystem,and even leads to the deficit of soil water.In conclusion,the biological soil crusts changed the soil physical and chemical properties that affect the hydrological process after the shifting dunes are fixed in Mu Us sand land,resulted in the shallow infiltration depth and large evaporation of the soil covered by biological soil crusts,which reduces the available water of plants,and even leads to water deficit in relatively dry years,It increases the possibility of vegetation degradation and even death.Therefore,in the process of vegetation restoration and reconstruction in Mu Us sand land,the influence of widely distributed biological soil crusts on soil water balance should be fully considered.