绿洲边缘夹粘沙丘持水特性
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摘要
夹粘沙丘是指剖面中分布有一层红褐色粘化层的沙丘,其夹粘层埋藏深度常在120—500cm左右,厚度在40—100cm之间,粘粉粒含量达到90%以上。夹粘沙丘人工梭梭固沙植被郁闭度在0.5以上,明显高于相同水热条件下的植被生产力,这可能与夹粘层通过改变土壤持水性及水分状况,从而提高了土壤水分承载力有关。以河西走廊绿洲边缘夹粘沙丘为研究对象,在测定0—8.0m剖面土壤物理性质和土壤水分特征曲线的基础上,计算了土壤孔隙分布和持水特性,研究了剖面中土壤持水性的变化规律及其影响因素。结果表明:(1)夹粘层土壤含水量最高,上覆沙土土壤含水量最少且随深度增加而增加,下伏沙土受地下水毛管作用影响水分含量较高;(2)土壤机械组成决定了不同土层的持水特性,土壤中粘粉粒含量越高,田间持水量和饱和含水量就越大,夹粘层的土壤持水性远高于沙土层;(3)夹粘层是沙丘土壤水分暂时贮存的重要土层,可以为植被提供深层土壤水分,这对绿洲边缘人工固沙植被的生存和繁衍有重要影响,而土壤持水性和毛管作用的强弱决定了夹粘层对沙丘水分调节能力的强弱。本研究为深入理解绿洲边缘雨养固沙植被斑块状分布的机理提供了一定的理论依据。
A sandwich dune's profile consists of layers with different soil textures,the upper and lower of which are sandy soil layers,and there is a fine soil pan between the surface and the subsoil. The clay interlayer is composed of silty loam containing over 90% silt and clay. Deposits of this layer occur at depths of 120—500 cm and it ranges in thickness from 40 to 100 cm. In arid areas with precipitation of less than 200 mm,artificial sand-fixing vegetation coverage is approximately10% to 15%; however,the vegetation coverage of the study area with 117 mm mean annual precipitation is approximately65%,which does not meet the zonal water and heat conditions. Water retention is considered to play an important part in affecting the water conditions and soil water carrying capacity of dunes. With regards to water retention,Betti et al. have analyzed the effects of soil texture on water retention,revealing that when the sand content is increased,water retention becomes weaker,and the soil layer has a significant effect on the water-holding capacity,and their studies have focused on analysis of the water-holding capacity of homogeneous soil. In order to study the characteristics and mechanisms of the response of the clay interlayer to water retention,we measured the soil water characteristic curve based on the centrifuge test,particle size measured by Mastersizer-2000,and pore distribution based on the measured soil water characteristic curveand the calculated equivalent porosity at different depths of a sandwich dune. Our results show the following patterns.( 1)The soil moisture content of the clay interlayer was the highest,soil water content increased slightly with depth in the surface soil,and the soil moisture of the subsoil was higher than in the surface,which was affected by the capillary action of groundwater.( 2) Field capacity,wilting coefficient,saturated water content,total porosity,and aeration porosity were significantly correlated with soil physical properties,such as bulk density,sand content,clay content,and particle size.Sandy soil layers were at 0—4.0 m and 4.6—8.0 m. The soil water characteristic curves of these profiles were steep and the soil was loose( aeration porosity,14% —27%) with poor soil water retention. The layer at 4.0—4.6 m was an interbedded layer of silty loam,the soil water characteristic curves of which was smooth and the soil water content was high when the soil water suction was high. This type of soil had less aeration porosity,leading to higher soil water-holding capacity than the upper and lower sandy layers. Furthermore, correlation analysis showed that capillary porosity was not significantly correlated with soil physical properties,but was weakly related to soil water content,and increased significantly only at both the interface between the sandy layer and silty loam layer,and the water table. To a certain extent,the distribution of soil porosity affected the soil moisture content and water conveyance between the clay interlayer and the sand layer. In conclusion,soil textures lead to considerable differences in soil water retention of dunes at the edge of an oasis. The clay interlayer can hold more water compared with all profiles,which improves the water conditions of the dune.( 3) The soil pan is the region where water collects,and provides water resources for plants. It plays an important role in the improvement of sand-fixing vegetation of dunes at the edge of an oasis. Further,the ability of the clay interlayer to regulate the water conditions of dunes depends on soil water retention and soil capillarity. In conclusion,our findings should provide strong support for future understanding of the mechanism of spatial patterns of artificial sand-fixing vegetation.
A sandwich dune's profile consists of layers with different soil textures,the upper and lower of which are sandy soil layers,and there is a fine soil pan between the surface and the subsoil. The clay interlayer is composed of silty loam containing over 90% silt and clay. Deposits of this layer occur at depths of 120—500 cm and it ranges in thickness from 40 to 100 cm. In arid areas with precipitation of less than 200 mm,artificial sand-fixing vegetation coverage is approximately10% to 15%; however,the vegetation coverage of the study area with 117 mm mean annual precipitation is approximately65%,which does not meet the zonal water and heat conditions. Water retention is considered to play an important part in affecting the water conditions and soil water carrying capacity of dunes. With regards to water retention,Betti et al. have analyzed the effects of soil texture on water retention,revealing that when the sand content is increased,water retention becomes weaker,and the soil layer has a significant effect on the water-holding capacity,and their studies have focused on analysis of the water-holding capacity of homogeneous soil. In order to study the characteristics and mechanisms of the response of the clay interlayer to water retention,we measured the soil water characteristic curve based on the centrifuge test,particle size measured by Mastersizer-2000,and pore distribution based on the measured soil water characteristic curveand the calculated equivalent porosity at different depths of a sandwich dune. Our results show the following patterns.( 1)The soil moisture content of the clay interlayer was the highest,soil water content increased slightly with depth in the surface soil,and the soil moisture of the subsoil was higher than in the surface,which was affected by the capillary action of groundwater.( 2) Field capacity,wilting coefficient,saturated water content,total porosity,and aeration porosity were significantly correlated with soil physical properties,such as bulk density,sand content,clay content,and particle size.Sandy soil layers were at 0—4.0 m and 4.6—8.0 m. The soil water characteristic curves of these profiles were steep and the soil was loose( aeration porosity,14% —27%) with poor soil water retention. The layer at 4.0—4.6 m was an interbedded layer of silty loam,the soil water characteristic curves of which was smooth and the soil water content was high when the soil water suction was high. This type of soil had less aeration porosity,leading to higher soil water-holding capacity than the upper and lower sandy layers. Furthermore, correlation analysis showed that capillary porosity was not significantly correlated with soil physical properties,but was weakly related to soil water content,and increased significantly only at both the interface between the sandy layer and silty loam layer,and the water table. To a certain extent,the distribution of soil porosity affected the soil moisture content and water conveyance between the clay interlayer and the sand layer. In conclusion,soil textures lead to considerable differences in soil water retention of dunes at the edge of an oasis. The clay interlayer can hold more water compared with all profiles,which improves the water conditions of the dune.( 3) The soil pan is the region where water collects,and provides water resources for plants. It plays an important role in the improvement of sand-fixing vegetation of dunes at the edge of an oasis. Further,the ability of the clay interlayer to regulate the water conditions of dunes depends on soil water retention and soil capillarity. In conclusion,our findings should provide strong support for future understanding of the mechanism of spatial patterns of artificial sand-fixing vegetation.
引文
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[2]Zheng Y,Zhao W Z,Zhang G F.Spatial analysis of a Haloxylon Ammodendron plantation in an oasis-desert ecotone in the Hexi corridor,Northwestern China.Forests,2017,8(6):200.
[3]Li X R,Tan H J,He M Z,Wang X P,Li X J.Patterns of shrub species richness and abundance in relation to environmental factors on the Alxa Plateau:Prerequisites for conserving shrub diversity in extreme arid desert regions.Science in China Series D:Earth Sciences,2009,52(5):669-680.
[4]李新荣,张志山,谭会娟,高艳红,刘立超,王新平.我国北方风沙危害区生态重建与恢复:腾格里沙漠土壤水分与植被承载力的探讨.中国科学:生命科学,2014,44(3):257-266.
[5]Zhou H,Zhao W Z,Zhang G F.Varying water utilization of Haloxylon ammodendron plantations in a desert-oasis ecotone.Hydrological Processes,2017,31(4):825-835.
[6]孙飞达,陈文业,袁海峰,窦英杰,邴丹珲,冯颖,吴婷.甘肃敦煌西湖荒漠-湿地生态系统土壤水分空间异质性及其影响因子研究.西北植物学报,2016,36(1):165-173.
[7]甄庆,摄晓燕,张应龙,韩凤朋,张兴昌.晋陕蒙能源区不同构型土体水分入渗特性模拟.农业机械学报,2015,46(8):90-96.
[8]李韵珠,胡克林.蒸发条件下粘土层对土壤水和溶质运移影响的模拟.土壤学报,2004,41(4):493-502.
[9]崔浩浩,张冰,冯欣,高业新.不同土体构型土壤的持水性能.干旱地区农业研究,2016,34(4):1-5.
[10]Zhou H,Zhao W Z,Yang Q Y.Root biomass distribution of planted haloxylon ammodendron in a duplex soil in an oasis:desert boundary area.Ecological Research,2016,31(5):673-681.
[11]卢修元,魏新平,邱玥,倪福全.砂土中粘土夹层对入渗过程影响的试验分析.灌溉排水学报,2009,28(6):39-41.
[12]刘思义,魏由庆,梁国庆,邢文刚,王应求.粘土夹层土体构型水盐运动的实验研究.土壤学报,1992,29(1):109-112.
[13]鲍乾,梁建发,王棋,杨瑞.花江喀斯特石漠化区不同经济型植物的土壤蓄水特征.水土保持研究,2017,24(1):18-24.
[14]丁新原,张广宇,周智彬,王永东,鲁晶晶,黎小娟.咸水滴灌条件下塔里木沙漠公路防护林土壤水分物理性质.水土保持学报,2015,29(1):250-256.
[15]孔超,王美艳,史学正,徐胜祥,郭乃嘉,杨培强.基于低场核磁技术研究土壤持水性能与孔隙特征.土壤学报,2016,53(5):1130-1137.
[16]闫永利,魏占民,任秀苹,奇凤.保水剂对土壤持水性影响及在不同土壤中效果比较.节水灌溉,2016,(1):34-38.
[17]王元峰,王辉,马维伟,冯宜明,李俊臻.尕海4种湿地类型土壤水分特性研究.干旱区研究,2012,29(4):598-603.
[18]Xu G Q,Li Y.Rooting depth and leaf hydraulic conductance in the xeric tree Haloxyolon ammodendron growing at sites of contrasting soil texture.Functional Plant Biology,2008,35(12):1234-1242.
[19]吴奇凡,樊军,王继军.晋陕蒙接壤区露天矿不同质地土壤水分运动特征与模拟.煤炭学报,2015,40(5):1134-1142.
[20]李玉山.黄土高原土壤水分循环与农田生产力.西安:陕西人民出版社,2015:28-29.
[21]马昌臣,王飞,穆兴民,康绍忠.小麦根系机械作用对土壤水分特征曲线的影响.水土保持学报,2013,27(2):105-109.
[22]Wang Y Q,Ma J Z,Zhang Y L,Zhao M Z,Edmunds W M.A new theoretical model accounting for film flow in unsaturated porous media.Water Resources Research,2013,49(8):5021-5028.
[23]王俊,黄岁樑.土壤水分特征曲线模型对数值模拟非饱和渗流的影响.水动力学研究与进展,2010,25(1):16-22.
[24]李广文,冯起,张福平,成爱芳.黑河上游草地土壤水分特征曲线研究.干旱区资源与环境,2015,29(10):128-134.
[25]郑健,王燕,蔡焕杰,万吉祥,李志军.植物混掺土壤水分特征曲线及拟合模型分析.农业机械学报,2014,45(5):107-112.
[26]邵明安,王全九,黄明斌.土壤物理学.北京:高等教育出版社,2006:67-70.
[27]郑荣伟,冯绍元,郑艳侠.北京通州区典型农田土壤水分特征曲线测定及影响因素分析.灌溉排水学报,2011,30(3):77-81.
[28]王志超,李仙岳,史海滨,徐鹏程,李河.含残膜土壤水分特征曲线模型构建.农业工程学报,2016,32(14):103-109.
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