【作者】 张北赢；

【导师】 刘文兆； 徐学选；

【作者基本信息】 中国科学院研究生院（教育部水土保持与生态环境研究中心） ， 生态学， 2008， 博士

【摘要】 土壤水是生态系统中植物赖以生存的基础,同时也是流域水循环中最为活跃的部分,影响着植物生长、生态环境建设以及水资源的合理分配与高效利用。黄土高原大部分地区地处半干旱、半湿润地区,加之其特殊成土过程形成的“土壤水库”,使得土壤水在该区生态环境建设中发挥着不可替代的作用。在黄土高原开展的以植被恢复为主的生态环境建设取得一定成绩的同时,土壤水资源储量被认为有减少的趋势。如何在开展生态建设的同时,实现土壤水资源的可持续利用是我们亟待解决的科学问题。本论文对黄土丘陵区延安燕沟流域不同土地利用方式的土壤水分时空变化及亏缺补偿特征进行了研究,并结合稳定性同位素技术,初步探讨了该区水循环中降水、土壤水、河流水和地下水的同位素组成特征,得出了以下结论:1)降水年型对不同植被类型土壤水分的季节变化和剖面垂直变化均有一定影响。旱农坡地平水年土壤水分的季节变化平缓;枯水年雨季前土壤水分缓慢减小,雨季后显著增加;丰水年则整体增加,且雨季后增加明显。刺槐林、沙棘灌丛和白羊草地平水年土壤水分的季节变化表现为整体降低;枯水年沙棘灌丛土壤水分先减后增,刺槐林与白羊草地呈“W”型曲线变化,两个最低值均出现在6月和8月;丰水年沙棘灌丛和刺槐林土壤水分的季节变化呈“V”型,白羊草地土壤水分波动较大,最低值出现在8月。旱农坡地枯水年的土壤水分活跃层和次活跃层深度较平水年下移,丰水年次活跃层消失;丰水年和枯水年,刺槐林和白羊草地土壤水分活跃层深度均较平水年下移,沙棘灌丛则上移。2)梯田各层土壤水分变化态势相似程度较高,即梯田土壤水分的垂直波动较小;不同土地利用方式下均是表层（0-30cm）和中层（30-100cm）土壤水分的灰关联度较大,即土壤水分的变化发展态势较一致,但由于不同利用方式的影响,土壤水分变化态势的相似程度为梯田>白羊草>刺槐>沙棘,除白羊草地外,其他土地利用方式下表层（0-30cm）与深层（100-200cm）的土壤水分灰关联度最小,土壤水分变化差异较大。从各月土壤水分灰关联度来看,沙棘除10月外,其他个月土壤水分变化态势的相似程度较高;白羊草地正好相反,整个生长季土壤水分的变化波动很大;梯田和刺槐林地居中,但各月土壤水分变化态势的相似程度仍存在差异,表现为雨季前各月土壤水分变化较为一致,雨季后的9、10月份与4月份相比差异较大。说明不同的土地利用方式对土壤水分的垂直变化和月动态均产生不同影响。3)不同水土保持措施雨季前后土壤储水均处于亏缺状态。降雨最多的7月份土壤储水亏缺均有不同程度的缓解,退耕坡地和梯田亏缺状态明显减轻;8月份表层土壤储水亏缺加剧;雨季后的10月份土壤储水均得到恢复。退耕坡地土壤储水亏缺度随土层深度的增加而减小,鱼鳞坑则随土层深度的增加土壤储水亏缺程度增大。梯田与水平阶相同,100-200cm土壤储水亏缺度最大,0-50cm次之,50-100cm最小。降雨对退耕坡地和梯田0-200cm土壤水分均有正补偿作用,补偿深度均为160cm。水平阶90cm处和160cm以下均出现负补偿现象。鱼鳞坑仅在30cm处出现负补偿,降雨补偿深度为100cm。在0-200cm土壤剖面上,土壤储水亏缺补偿度CSW依次为退耕坡地>梯田>鱼鳞坑>水平阶。4)黄土丘陵区降水线方程与全球降水线方程以及我国降水线方程相比,斜率与截距均偏小,这与研究区地处内陆,次降雨量小,空气湿度低,降水在降落过程中经过较强的蒸发有关。土壤水同位素组成变化远远小于降水。土壤水的氢氧同位素值均位于当地降水线的右下方,表明降雨在补给土壤水之前经历了强烈的非平衡蒸发,分馏明显。不同土层土壤水的氢氧同位素组成存在差异,表层30cm受降雨的影响较大,深层受土壤蒸发动力影响较大。2007年7月31日和8月10日土壤水氢氧同位素的剖面分布均呈“凹”型,最小值在200cm处,而9月1日土壤水氢氧同位素剖面分布呈“凸”型,最大值在200cm处。地表水氢氧同位素的平均值和标准差均小于降水。地表水氢氧同位素之间的关系为:δD=6.37δ¹⁸O-12.08（R²=0.97,n=21）。该方程斜率和截距均小于当地降水线方程的斜率和截距,氢氧同位素值大多数位于当地降水线右下方且与降水线接近,说明河流水来源于降水,并且受不同程度非平衡蒸发较小。河水的氢氧同位素组成受降雨的影响较大,也与前期河水同位素组成及流量有关。河水不同部位所受非平衡蒸发程度不同,导致河流水体不同部位氢氧同位素值不同,但经不同水体充分混合后,出现从上游至下游同位素值逐渐增大的趋势。井水与泉水的氢氧同位素组成较降水和土壤水变化范围明显都小。井水和泉水的δD和δ18O均落在当地降水线右下方且与降水线接近,与降水的平均δD和δ¹8O也很接近,说明井水和泉水均来源于大气降水,且在降水补给过程中由于非平衡蒸发引起的同位素分馏较小。降雨对泉水的补给滞后30天左右。降雨对井水的补给滞后时间以及土壤水对地下水的补偿作用还需进一步研究。更多还原

【Abstract】 Soil water is the demanded facter for plant growth in ecosystem, and it is also the most active part which affects plant growth, ecological construction and reasonable distribution and effective utility of water resource. Most areas of the loess plateau are located in semi-arid and semi-humid area. The soil water reservoir constructed during characteristic soil formation is an irreplaceable factor in the ecological construction. Soil water storage decreased as the vegetation reconstruction developed. So, the continuous utilization of soil water is an urgent problem in ecological construction. In this research, temporal and spatial variations and deficits of soil water was studied under different land uses in Yangou catchment located in loess hilly region. Combined with stable isotope technique, the isotope composition of precipitation, soil water, river and ground water in this area was investigated, and the main conclusions were drawn as follows:（1） Yearly precipitation pateern had definite effects on the seasonal variation and profile distribution of soil moisture. In normal year, soil moisture in dry farmland had a gentle seasonal variation; in dry year, it decreased slowly before rainy season but increased markedly after rainy season; while in rainy year, it had an overall increase and the increment was remarkable after rainy season. The soil moisture in R. psendoacacia forestland, Hippophae shrubland, and B. ischaemun grassland decreased as a whole in normal year. In dry year, soil moisture in Hippophae shrubland decreased first and increased then, while that in R. psendoacacia forestland and B. ischaemun grassland varied in“W”type, with the minimum in June and August. In rainy year, the seasonal variation of soil moisture in R. psendoacacia forestland and Hippophae shrubland presented“V”type, and that in B. ischaemun grassland fluctuated markedly, with the minimum in August. In dry farmland, the active and sub-active layers of soil moisture were deeper in dry year than in normal year, and the sub-active layer disappeared in rainy year. In R. psendoacacia forestland and B. ischaemun grassland, the active layer of soil moisture was deeper in dry and rainy years than in normal year; while in Hippophae shrubland, this active layer was shallower in dry and rainy years than in normal year.（2） Landuses made soil moisture in vertical layer quite different. In terrace land, the variational trend of soil moisture in different layers was accordant, that is, the fluctuation of soil moisture in vertical layer was little. Under different landuses, the variation of soil moisture between surface layer （0-30cm） and middle layer （30-100cm） was accordant, and landuse, in terms of the accordant degree, ranks in the descendant order of terrace land, pasture land, forestland, and shrub land. Except shrub land, the grey relational grade of the landuses between surface land （0-30cm） and deep layer （100-200cm） was least, which means that soil moisture varied remarkably. The grey relational grade of soil moisture in each month was different. In shrub land, except December, the variational trend of soil moisture was similar. By contraries, grass land had the different trend, and the fluctuation of soil moisutre in growth season was great. It can be seen that the different landuses resulted in the difference of dynamic characteristics of soil moisture.（3） No matter before or after rainy season, soil water storage under different measures of soil and water conservation was deficient and then increased in July. The increment for crop land and terraced land was the highest. In August, soil water storage deficit in surface layer increased. After rainy season, soil water storage deficit was restored by precipitation in October. Soil water storage deficit degree of crop land decreased with increased soil depth, while for fish-scale-pit land, it increased with increased soil depth. Soil water storage deficit degree of terraced land and narrow level-belt land was the highest in the 100-200 cm soil layer, the second place in the 0-50 cm, and the lowest in the 50-100 cm. The compensation effect of precipitation on soil water storage of crop land and terraced land was positive and the compensation depth was 160 cm. The compensation effect of precipitation on soil water storage of narrow level-belt land was negative at the depth of 90 cm and below 160 cm. The compensation effect in fish-scale-pit land was negative just at the depth of 30 cm and the compensation depth was at the depth of 100 cm. In the whole 0-200 cm soil layer, land types were in the descendant order of crop land, terraced land, fish-scale-pit land, and narrow level-belt land, in terms of compensation degree of soil water storage deficit. That is to say, soil and water conservation measures can influence the seasonal and vertical variations of soil water storage and the compensation impact of precipitation on soil water.（4） Compared with the global and Chinese meteoric water lines, slope and intercept of meteoric water line in loess hilly region was lower due to the lower individual rainfall, lower air humidity, inland location and strong evaporation of rainfall during the descent. The variation of soil water isotope composition was far lower than precipitation. TheδD andδ¹⁸O of soil water located at the right-down of the local water line. It showed a remarkable fractionation due to the strong imbalance evaporation before precipitation compensated for the soil water. The hydrogen and oxygen isotopic composition of soil water in different layers existed significant differences, which in 0-30cm layer was affected more by precipitation while in deeper layers by soil water evaporation driving more. Average value and standard deviation of hydrogen and oxygen isotope of ground water were all lower than precipitation. The relationship of hydrogen and oxygen isotope of ground water showed that slope and interception of which was lower than local water line’s, and the values were mostly at the right-down of the line approach to the local water line closely. This indicated that river stream water came from the precipitation affected by the imbalanced evaporation less. Hydrogen and oxygen isotopic composition of ground water affected bigger by the precipitation, which was related to the former composition and fluxes. There was an increasing trend of isotopic value from upriver to lower river after the mixing of different water resource, despite the different isotopic values of varied part of river which was lead to by the different imbalanced evaporation. Variation of hydrogen and oxygen isotopic composition of well water and spring water were both lower than precipitation and soil water,δD andδ18O values of which were at the right-down of local line approach to the line closely, and the two values were close each other. This indicated that well and spring water were all come from precipitation and isotopic fractionation was less caused by the imbalanced evaporation in the course of compensation of precipitation. Replenishment of precipitation to spring water lagged about 30 days. The lagged time of precipitation replenishment to well water and the compensation of soil water to ground water demand for further investigation.更多还原