| A study on spatiotemporal distribution of soil moisture in small watershed of the LoessPlateau is important for arrangements of soil and water measures. The Wangdonggouwatershed, located in the gully region of the Loess Plateau, was selected as a study area. Thedynamic monitoring and field observation under different land use types and landforms ofsoil water content were used to quantify the temporal variation and spatial distribution of soilmoisture in the watershed and to assess applicability of topographic wetness index in theresearch area. The main conclusions are as follows：(1) The seasonal dynamic variation characteristics of soil moisture was analyzed. Soilmoisture in the soil profiles not only had a hierarchical characteristic with season change, butalso was closely related with land use types. As affected by climate conditions, soil watercontent in the50cm soil layer changed rapidly with seasons; soil water content in the150cmsoil layer had the lowest soil moisture in June; and soil water contents for farmland, orchardland, locust forest, sea buckthorn and alfalfa fluctuated at14%,12%,11%,11%and9%,respectively. Cropland and grassland did not have a dried soil layer resulted from biologicaluse in the6m soil moisture profile. But orchard, forest, alfalfa and woodland had dried soillayers resulted from biological use at the same soil depths. Soil moisture deficit underperennial vegetation was greater than annual vegetation. In contrast to June,the depth of soilmoisture compensated after rainy season was400cm for farmland, while the depths were200cm for forestland, orchard land and alfalfa. As for the annual change of soil moisture,characteristics of soil moisture at the same sample point in the watershed between2003and2011were distinct. Soil water content in the3-6m soil layer decreased in forestland andorchard, but increased in cropland and grassland.(2) The spatial distribution features of soil moisture in the watershed was studied, Resultfrom soil moisture measurements in the Wangdonggou watershed shows that its upper andmiddle reaches were drier and its lower reaches were wetter. In the whole watershed, soil water content in the3m profile was the lowest on ridge slope and the highest on gully slope,Soil water contents on tableland and ridge top were between ridge slope and gully slope. soilwater content in the3m profile was the lowest in locust forest and highest in winter wheat,whenever in dry season or in rainy season. Soil water contents among different land use typeswere in the order of cropland＞grassland＞orchard＞forestland. Soil water content in the6msoil layer for orchard was more deficit with tree age increasing, Moreover, dried soil layerswere serious for orchard land, locust forest and alfalfa. soil water storage within the6m werein the order of tableland＞ridge top＞ridge slope. Soil water content was the lowest in arange of5to10m far from forestland belt. soil water storage within the4m profile indifferent landforms were in the order of lower slope＞middle slope＞upslope, Shady slopehad more soil water storage in the240cm soil layer than sunny slope, soil water content inthe1-6m profile was22%for loessal soil and was only9%for red soil.(3) The applicability of topographic wetness index in the study area was evaluated. Ingeneral, the relationship between topographic wetness index and soil water content was weak;However, the relationship between topographic wetness index and soil water content underthe same land use type was close, the topographic wetness index was suitable for expressingthe distribution characters of soil moisture, But under the condition of the same landform anddifferent land use types, the topographic wetness index is not well to express characters ofsoil water content. Therefore, it is necessary to revise and improve the definition of currenttopographic wetness index and its calculation. |
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