冻融条件下生物结皮覆盖对土壤饱和导水率的影响

Effect of biological crust cover on soil saturated hydraulic conductivity under freeze⁃thaw conditions

生物结皮(BSC)是广泛分布的地被物,每逢冬春季节,受冻融交替作用影响,结皮土壤的理化性质和水文学特征明显改变且与裸土差异显著,从而影响该地区土壤可蚀性评估和土壤侵蚀防治。采用室内模拟实验,以蓝藻结皮土壤为对象,研究不同冻融交替次数和初始含水量下,土壤三相对温度变化的响应特征并定量分析结皮覆盖土壤在此条件下饱和导水率(Ks)的变化趋势和突变点。结果表明:初始含水量对Ks无显著影响(P>0.05),冻融交替次数对Ks有极显著影响(P<0.01),冻融条件下裸土的平均Ks为1.941 mm/min,结皮覆盖土壤平均Ks为0.325 mm/min,两者具有极显著差异(P<0.01),且随交替次数增加,Ks差异逐渐增大,并在10次时达到最大值为10.13倍。不同冻融含水量下的结皮土壤的Ks在冻融10—20次时趋近,平均值为0.219mm/min。冻融作用显著改变土壤结构,且在冻融7次时土壤结构变化较明显,冻融过程中<0.1 mm的土壤颗粒显著变化。试验条件下,Ks受因子影响程度大小为:冻融交替次数>土壤结构>结皮厚度>结皮容重>下层土壤容重>冻融初始含水量;冻融次数与结皮厚度、结皮容重、冻融初始含水量的交互效应对Ks有显著影响。

Biological crust is a kind of ground cover which distributes widely.Due to their special physiological mechanisms,algae and moss can thrive and grow under the extreme cold and low light conditions so as form crusts.Biological crust(BSC)exists in various types of climatic region,soil and vegetation,the type of crust reflects the local water conditions and soil nutrient status,meanwhile,the formation of biological crust has an important influence on the occurrence and development of soil,hydrology and erosion processes,affects the physical and chemical properties of the soil,which manifests as the degree of influence of different types of crusts.However,the effect of biological crusts on soil infiltration is still controversial,on the one hand,biological crusts increase the roughness of the soil surface and correspondingly extend the retention time of water on the soil surface,which is not conducive to water infiltration,on the other hand,biological crusts improve soil structure and create water flow channels that are conducive to water infiltration.In this study,we used indoor simulation experiments,took the cyanobacteria crust⁃covered soil as research object to study the response characteristics of three relatives of soil under different freeze⁃thaw cycles and initial water contents,then quantitatively analyzed the trend and change point of the saturated hydraulic conductivity of crust⁃covered soil(Ks).The results show that the initial water content has no significant effect on Ks(P>0.05),and the number of freeze⁃thaw alternation has a very significant effect on Ks(P<0.01).The average Ks of bare soil under freeze⁃thaw conditions is 1.941 mm/min,the average Ks of crust⁃covered soil is 0.325 mm/min,and there is a very significant difference between them(P<0.01).With the increase of the number of alternation,the difference of Ks gradually increase,the Ks of bare soil reaches a maximum of 10.13 times of crust soil at 10 times.The Ks of crust soil under different initial water contents is approaching a similar level after 10-20 freeze⁃thaw alternations,with an average value of 0.219 mm/min.The effects of freezing and thawing significantly change the soil structure,especially after 7 times,and the soil particles lower than 0.1 mm,changing significantly.Under the experiment conditions,the degree of influence of Ks by the factors is as follows:number of freeze⁃thaw cycles>soil structure>crust thickness>crust bulk density>lower soil bulk density>initial freeze⁃thaw water content.The interactive effects of freeze⁃thaw cycles and crust thickness,crust bulk density,and the initial water content have the significant impact on Ks.