不同降水年型黄土高原半干旱撂荒草地水分收支特征

Water Budget of Abandoned Steppe in Semiarid Area on the Loess Plateau in Different Rainfall Pattern Years

以黄土高原六道沟流域半干旱撂荒草地为研究对象,根据2014—2017年连续观测得到的降水量(P)、蒸散量(ET)、土壤贮水量(S)和植被组成等数据,研究了不同降水年型下撂荒草地的水分收支特征。结果显示:(1)观测前期平水年下0—50cm土层土壤贮水量呈现缓慢下降趋势,以第三年的一场暴雨(109.60mm/d)为分界,后期土壤贮水量总体增加,但波动幅度大增,受蒸散量增加的影响,土壤水分消耗明显;(2)年总蒸散量呈逐年升高的趋势,在平水年下,地表蒸散年际变化主要受气候条件影响,丰水年下,地上生物量的作用明显;(3)水分收支呈现季节性,2—6月为撂荒草地的缺水期,7月—次年1月为丰水期,四年观测结果显示草地处于总体水分亏缺状态(总亏缺165.60mm),存在对深层土壤水(50cm以下)的大量消耗。研究结果表明:撂荒草地水分的持续损失是导致撂荒草地发生演替的重要原因,演替过程中植物深层土壤水的大量消耗可能会导致形成的次生草地土壤水分条件更差,需要加强人为干预措施,防止草地再次退化。

Taking abandoned steppe in succession of Liudaogou watershed in the semi-arid area on the Loess Plateau as the research site,we studied the characteristics of the water budget of the successive steppe during the years with different rainfall patterns by using the data of precipitation(P),evapotranspiration(ET),soil moisture(S),vegetation structure during 2014-2017.The results indicated that:(1)in the early stage of observation,the soil water content in 0-50 cm soil layer showed a slowly decreasing trend during years with normal annual rainfall;after the rainstorm(109.60 mm/d)in the third year,the soil water content in the later stage increased generally,but fluctuated greatly,and the soil water consumption was obvious with the increase of ET;(2)the annual total ET increased year by year,and the interannual variations of ET were mainly influenced by climatic conditions during years with normal annual rainfall,but affected by biomass during rainy years;(3)the water budget showed seasonal characteristics,and the dry period for steppe was from February to June,while the period from July to next year′s January was the rainy season;the four-year observation showed that the steppe was in a state of water deficit(165.60 mm in all),and there was a large amount of consumption of deep soil water(below the depth of 50 cm).The results showed that the continuous loss of soil water in steppe was the important cause of steppe succession,and the huge consumption of deep soil water during the successive process may lead to the worse soil water condition for the secondary steppe.Therefore,anthropogenic intervention needs to be reinforced in case of further steppe degradation.