青海湖流域大气降水水汽来源同位素示踪研究

The Qinghai Lake watershed lies in a critical transitional zone, where the East Asian summer monsoon, the Westerly Circulation and the Qinghai-Tibet Plateau monsoon prevail, and it is extremely sensitive to climate changes. It is very important to take the watershed as a whole to study the isotopic characteristics and moisture sources of the precipitation, which plays a key role in exploring the water cycle process of the watershed. This research selects the Qinghai Lake Watershed as study area. 20 stations for receiving precipitation and 9 locations for collecting lake water will be set up in the watershed. We analyze the spatial and temporal characteristics of stable isotope in precipitation in and around the watershed, such as LMWL (Local Meteoric Water Line), isotopic geographical effect and deuterium excess. Meanwhile, combining with the backward trajectory simulation by using Hysplit4.9, we reveal the sources and transport paths of precipitation of the Qinghai Lake Watershed. Based on the isotopic values of the atmospheric vapor and the lake water, the values of δ2H, δ18O and deuterium excess of the moisture evaporating from the lake water are calculated by using the fractionation model and the Craig-Gordon water evaporation model. On the basis of theory for estimating the contribution of evaporative vapor from surface water bodies to atmospheric vapor, we use the stable isotope values of precipitation, river water, atmospheric moisture and lake water to estimate the average contribution of evaporation from the Qinghai Lake to the local atmospheric vapor in the watershed. And we simulate the patterns of the transportation and circulation of moisture in the Qinghai Lake Watershed on different spatial and temporal scales. This study would provide scientific base for analyzing the water resources changes and discussing the causes of lake level decline. It also provides scientific guidance for the prediction and regulation of water resources in the process of ecological construction of the Qinghai Lake Watershed.

青海湖流域地处东亚季风区、西北干旱区和青藏高原高寒区的交汇地带，降水时空分布及水汽来源具有复杂性和独特性。全面系统的研究其降水同位素特征及水汽来源是探索该流域水循环过程的前提。本项目以青海湖流域为研究区，在流域内均匀布设大气降水接收点，通过对比分析流域内与流域周边大气降水同位素的地理效应及氘盈余在时间和空间上的变化规律，结合同期流域上空气流的HYSPLIT后向轨迹模拟，揭示青海湖流域大气降水来源及水汽输送过程。在青海湖湖面布设气象监测仪器，结合同位素分馏模型和Craig-Gordon水体蒸发模型，获取湖水蒸发水汽的氢氧同位素及氘盈余值，同时采集湖面上空大气水汽样品进行氢氧同位素测定，进而根据地表水体蒸发对当地大气水汽贡献的估算理论，估算青海湖蒸发水汽对流域大气水汽的贡献率。为定量分析青海湖流域水资源变化和青海湖水位下降的原因等提供科学依据，为流域生态建设中水资源预测与调控提供科学指导。

青海湖流域地处东亚季风区、西北干旱区和青藏高原高寒区的交汇地带，降水时空分布及水汽来源具有复杂性和独特性。全面系统的研究其降水同位素特征及水汽来源是探索该流域水循环过程的前提。本项目以青海湖流域为研究区，在流域内均匀布设14处大气降水接收点，通过测试分析各点降水同位素数据，获取了青海湖流域大气降水线（LMWL）为：δ2H = 7.86 δ18O + 15.01；根据各采集点降水中δ18O与高程（海拔）和距青海湖距离的关系，获得青海湖流域大气降水同位素的高程效应和“湖泊效应”，高程效应为：δ18O = -0.002 Alt – 1.025，湖泊效应为：δ18O = -0.0116 Dis – 7.65，表明地形及湖陆分布对流域的降水影响较大。通过对比分析流域内与流域周边大气降水同位素（香港、长沙、拉萨、乌鲁木齐、张掖、兰州）的地理效应及氘盈余在时间和空间上的变化规律，结合同期流域上空气流的HYSPLIT后向轨迹模拟，揭示了青海湖流域大气降水来源及水汽输送过程。结果显示，在6-8月份，青海湖流域水汽受控于东亚季风；9月-翌年5月受控于西风；东亚季风和西风交替于6月和9月份；印度季风（西南季风）因唐古拉山阻挡无法到达青海湖。同时，青海湖流域降水中氘盈余d值在4-10月份明显高于长沙、兰州、乌鲁木齐和张掖，加之流域降水δ18O湖泊效应显著，说明：青海湖水面蒸发水汽与流域大气水汽混合形成降水，且蒸发水汽对流域降水的贡献不可忽视。进一步通过对比分析上风向输入水汽与流域内降水同位素及氘盈余的时空分布差异，运用氘盈余的二元混合模型，计算了青海湖湖面蒸发对流域降水的贡献率。在月尺度上，青海湖水面蒸发对流域降水的贡献率变化在3.03%~37.93%之间，夏季较高（8月份为37.93%）。结合每月降水量，计算得青海湖蒸发对降水的年贡献率为23.42%，约为 90.54 mm/year。进而说明，青藏高原上有1500多个湖泊，总面积超过44993km2，高原内湖泊水面蒸发对局地大气水汽的贡献量很大，不可忽视。以上结论可为定量分析青海湖流域水资源变化和青海湖水位下降的原因等提供了科学依据，为流域生态建设中水资源预测与调控提供科学指导。. 在项目的支持下已发表SCI论文6篇。