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大量示例表明，研究岩溶地区的水循环有重要作用。一方面，研究岩溶地区地下水在流域中对降水输入的响应不仅可以反映植被-土壤-岩石这一复杂含水系统的性质，评价含水系统中植被-土壤-岩石对水循环过程的影响；另一方面，由于水-碳循环的耦合，定量研究岩溶地区的水量对全球水循环和碳循环的研究有重要意义。此外，近年来人为活动的加剧使大量的土地利用方式发生了转变，造成原有的水循环受到破坏而引发一系列的环境问题，因此研究不同土地利用下的水循环规律有着十分重要的意义。然而在自然的岩溶流域中，由于植被种类的多样性、边界和水文地质条件等的复杂性，我们往往不能单纯的研究土地利用因子对流域水循环的影响；此外，在对自然流域水循环进行量化研究时，将流域蒸散发进行蒸发和蒸腾的分割往往是最难也是最为关键的，然而由于缺乏对自然流域蒸发真值的认识，人们在用不同的方法对流域蒸发进行定量研究时缺乏相应检验的标准。基于氢氧稳定同位素在研究流域水循环的天然优越性，本研究选取边界、水文地质条件可控的贵州普定沙湾模拟试验场作为研究对象，通过气象因子（降雨量、温度、湿度）、流域地下水的水文因子（流量、水位）、降雨和地下水的氢氧同位素等指标，来研究2015年11月至2018年10月三个水文年中五种不同土地利用下（裸岩地、荒地、耕地、草地、灌木地）模拟流域的水循环规律，分别通过水文因子、氢氧同位素来研究地下水对降雨输入的响应，在对流域水循环的定量研究时，通过同位素方法（氢氧单同位素和氘盈余双同位素）来对流域蒸发进行定量，其中由于裸岩地和荒地没有植被，因此二者通过水均衡法得到的流域蒸散发就是流域蒸发，这可以对不同同位素法的计算结果进行对比验证。通过本研究，我们得到以下一些新认识：（1）研究区不同土地利用下的流量和水位对降雨量的输入没有明显的滞后，呈季节同步响应，但五个不同土地利用下模拟流域地下水的流量和水位存在一定的差异，因此不同土地利用下的地下水水文要素对降雨的输入在响应时间快慢上没有明显的区别，但在响应幅度上具有明显的差异；由于研究区降雨主要集中在雨季，不同土地利用下的地下水补给均主要来自于雨季降雨，雨季入渗补给率在70.9%~110.0%之间，总体上地下水的全年入渗补给量有80%以上来自雨季降雨；（2）降雨的氢氧同位素和氘盈余均有明显的季节变化规律，均表现为雨季偏负，旱季偏正，并且在地下水主要补给的雨季，雨水氢氧同位素的变化幅度比氘盈余的更明显，即氘盈余呈现出比氢氧同位素更好的稳定性；研究区不同土地利用下模拟流域地下水的氢氧同位素也具有明显的季节变化规律，但与降雨的季节变化相反。地下水中的氘盈余没有明显的季节变化在水文年内整体是相对稳定的，而地下水氘盈余的稳定性主要是继承了雨季降雨中氘盈余的特性；（3）不同土地利用对流域地下水氢氧同位素相对于降雨的削弱程度和地下水滞留时间都有重要影响，其中不同土地利用下地下水削弱程度的大小关系是：裸岩地<耕地<草地<灌木地<荒地；地下水滞留时间的关系：裸岩地<灌木地<荒地<草地<耕地，因此流域地下水的滞留时间越长不能代表地下水氢氧同位素对降雨氢氧同位素输入信号的削弱程度越大，也就是二者不构成正比例关系；（4）通过扣除各模拟流域地下水的滞留时间发现地下水氢同位素和氧同位素的季节变化规律和雨水的同位素季节变化规律相同，并且在不同水文年的雨季模拟流域地下水氢氧同位素偏负的程度明显不同，即具有明显的年际变化规律，而地下水氢氧同位素偏负的程度主要是受不同水文年雨季降雨氢氧同位素偏负程度的控制；（5）在流域水循环定量研究上，通过水均衡法分别得到了不同土地利用下模拟流域的蒸散系数和入渗系数，结果表明当流域的植被不是很发育时，流域的水循环主要以径流为主，如裸岩地、荒地、耕地，但当流域的植被很发育时，流域的水循环则主要以蒸散发为主，不同土地利用下模拟流域的蒸散系数和入渗系数有所不同，表明土地利用在流域水循环的水量分配中起重要调节作用；（6）通过和水均衡法计算的裸岩地和荒地的蒸散系数对比，氘盈余双同位素计算流域蒸发的结果比氢氧单同位素计算的结果能更好地反映流域真实的蒸发，并且不同土地利用下的模拟流域其蒸发率不同；这两种同位素方法的应用表明：当利用同位素信号来量化流域蒸发时，输入信号的稳定性对量化结果的准确性有至关重要的作用，所以相比氢氧单同位素，氘盈余双同位素更适用于流域蒸发的定量研究；（7）通过流域水均衡法得到的蒸散结果和氘盈余双同位素计算得出的蒸发可以计算出不同土地利用下模拟流域的蒸腾，同时估算出了不同土地利用下模拟流域的蒸腾相对蒸散发的占比分别是：在2015年11月至2016年10月，耕地占39.4%，草地占81.9%，灌木地占62.4%；在2016年11月至2017年10月，耕地占43.1%，草地占84.6%，灌木地占47.0%，表明在植物生物量较大的草地，地表的水汽循环通量主要受植物蒸腾作用的控制，而在植被较为稀疏的灌木地中，受蒸腾作用和蒸发作用共同控制，而玉米只在生长季（5月至8月）发育的耕地中，地表水汽通量主要受蒸发作用的控制。

A large number of studies have shown that it is important to study the water cycle in karst areas. On the one hand, researching on the response of groundwater to precipitation in watersheds can not only reflect the nature of vegetation-soil-rock complex aquifer system, but also evaluate the impact of vegetation-soil-rock on the water cycle process in watersheds. On the other hand, due to the coupling of water cycle and carbon cycle, it is significant to quantitatively study the water cycle in karst areas for global water cycle and carbon cycle. In addition, as the intensification of human activities in recent years, a large number of land use patterns have been changed, resulting in the destruction of the original water cycle and a series of environmental problems. Therefore, it is of great significance to study the water cycle under different land uses in karst areas. However, in natural karst watersheds, owing to the diverse vegetation types, the complexed boundary and hydrogeological conditions, we usually unable to discuss the impact of land use patterns on watersheds water cycle only. Besides, quantifying the evapotranspiration into the evaporation and transpiration is often the most difficult and critical part when quantifying the water cycle in natural watersheds. However, due to the lack of understanding of the true value of evaporation in natural watersheds, we couldn't test the validity of evaporation results calculated by different methods.Based on the advantages of stable hydrogen and oxygen isotopes in the study of watersheds water cycle, the Puding Shawan test site with controlled boundary and hydrogeological conditions was selected to study the water cycle of five different land uses （bare rock land, bare soil land, cultivated land, grassland and shrub land） through the meteorological factors （rainfall, temperature, humidity）, the hydrological factors （discharge, water level） and hydrogen and oxygen isotopes of precipitation and groundwater during November 2015 to October 2018. We have studied the response of groundwater to rainfall input through hydrological factors, hydrogen and oxygen isotopes. In the quantitative study of watersheds water cycle, the isotope methods （single hydrogen or oxygen isotope and deuterium excess dual isotopes） were used to quantify the watersheds evaporation, as there is no vegetation in bare rock and bare soil lands, so the evapotranspiration of the both lands obtained by water balance method is the evaporation. As a result, it could allow us to verify the validity of the evaporation results derived from different isotope methods. In the following are some conclusions from this study: (1) In the study area, there are no obvious lags between rainfall and discharge and water level under different land uses, indicating similar seasonal synchronous response to rainfall, but differences exist between the discharge and water level of groundwater in the five simulated watersheds under different land uses. Because the rainfall in the study area is mainly concentrated in the rainy season, the groundwater recharge under different land uses mainly comes from the rainfall in the rainy season. The infiltration recharge rates in rainy season are between 70.9% and 110.0%. Overall, more than 80% of the annual groundwater infiltration recharge comes from the rainy season rainfall; (2) The hydrogen and oxygen isotopes and deuterium excess of rainfall have obvious seasonal variations, which are relatively negative in rainy season and positive in dry season. What’s more, in the rainy season when groundwater is mainly supplied, the hydrogen and oxygen isotopes are more varied than that of deuterium excess, indicating the deuterium excess is more stable than that of hydrogen and oxygen isotopes. The hydrogen and oxygen isotopes of groundwater in the five simulated watersheds also have obvious seasonal variations, but contrary to the rainfall. The deuterium excess in groundwater has no obvious seasonal variations and is relatively stable in the whole hydrological year, which is mainly due to the inheritance of the characteristics of deuterium excess of rainy season rainfall; (3) Land use patterns have important effects on the attenuation ratio of hydrogen isotope and oxygen isotopes of groundwater over those of rainfall and groundwater residence time of the five simulated watersheds with different land uses. The relationship between the attenuation ratio is as follows: bare rock land < cultivated land < grassland < shrub land < bare soil land; the groundwater residence time is: bare rock land < shrub land < bare soil land < grassland < cultivated land. Therefore, the residence time and attenuation ratio of hydrogen and oxygen isotopes of groundwater are not proportional to each other; (4) By subtracting the groundwater residence time in each simulated watershed, we found that the seasonal variations of hydrogen and oxygen isotopes in all groundwater are the same as that in rainwater, and the degree of negative skewness in hydrogen and oxygen isotopes of groundwater is different during rainy season in different hydrological years. We found that the depleted degree of hydrogen and oxygen isotopes in groundwater is mainly controlled by the depleted degree of hydrogen and oxygen isotopes in rainfall during rainy season in different hydrological years;(5) In the quantitative study of water cycle in watershed, evapotranspiration coefficient and infiltration coefficient of five simulated watersheds were obtained by water balance method. The results show that when the vegetation in a watershed is not well developed, the water cycle is mainly controlled by runoff, such as bare rock land, bare soil land and cultivated land, but when the vegetation in the basin is well developed, the water cycle is mainly composed by evapotranspiration. This demonstrates that land use patterns play an important role in regulating water distribution in watersheds water cycle;(6) The deuterium excess dual isotope is more acceptable than those of hydrogen or oxygen single isotope when we compare to the evapotranspiration coefficients of bare rock and bare soil lands calculated by water balance method. The application of these two isotope methods shows that the stability of input signals plays an important role in the accuracy of quantification when using them to quantify watershed evaporation, so the deuterium excess dual isotope is more suitable for studying watershed evaporation than hydrogen or oxygen single isotope;(7) Based on the evapotranspiration results obtained by water balance method and evaporation results through deuterium excess method, we have calculated the watershed transpiration, and then estimated the ratios of transpiration to evapotranspiration under different land uses. They are: 39.4% for cultivated land, 81.9% for grassland and 62.4% for shrub land from November 2015 to October 2016; 43.1% for cultivated land, 84.6% for grassland and 67.0% for shrub land from November 2016 to October 2017. The results show that in grassland with dense vegetation, the vapor flux was mainly controlled by plant transpiration, and in shrub land with sparse vegetation which was mainly controlled by both transpiration and evaporation, while in cultivated land, where the corn only develops in growing season （May-August）, the vapor flux was mainly controlled by evaporation.