青藏高原多年冻土区热喀斯特湖水量平衡机制及定量化研究

With climate warming and wetting, and permafrost degradation, the scale and number of thermokarst lakes are significantly increasing in the Qinghai-Tibet Plateau (QTP). The expand of thermokarst lakes accelerate the water cycles, greenhouse gas emissions and ecological disturbances, and hold potential impacts on stability of regional projects. The water balance is the core issue for comprehensive evaluation the hydrology-environment-project effects of thermokarst lakes. However, the regime of thermokarst lake water balance were not well studied in the QTP due to the restrict of technicals and Plateau environments. The project plans to choose the Beiluhe basin as the study region. The methods of dynamic monitoring, geophysical prospecting, isotopic tracing and numerical simulation are employed to (1) establish the quantitative relationship between thermokarst lakes and air-ground factors, and illuminate the influencing mechanism of permafrost degradation coupled with groundwater distribution on thermokarst lake evolution; (2) clarify the recharge and discharge rules of a typical thermokarst lake, and quantitatively evaluate the contribution of hydrological processes to changes of the thermokarst lake water; (3) combined with the monitoring results and permafrost water-heat models, the future changing trends of thermokarst lake water will be forecasted. The results will help to deeply understand the hydrological cycles in the Three Rivers’ headwater region of the QTP, and get the references for protecting the ecological environments and scientific planning to permafrost projects.

随着气候暖湿化和多年冻土退化，青藏高原热喀斯特湖的规模和数量均显著增加，其持续发展加速了水文循环、温室气体释放和生态环境扰动，并对区域工程的稳定性构成潜在影响。水量平衡作为评估热喀斯特湖水文-环境-工程效应的核心问题，由于受技术手段和高原环境的限制，目前在青藏高原多年冻土区的研究仍存在不足。本项目拟选取北麓河盆地为研究区域，运用动态监测、物探勘察、同位素示踪及数值模拟等方法：（1）建立热喀斯特湖动态变化与地-气要素的定量关系，揭示冻土退化协同地下水分布对热喀斯特湖变化的影响机制；（2）针对典型热喀斯特湖进行剖析，厘清热喀斯特湖补给、排泄过程的变化规律，定量化评估不同水文过程对热喀斯特湖水量变化的贡献；（3）结合监测结果及冻土水-热模型对青藏高原热喀斯特湖未来变化趋势进行预测。研究成果将有助于深入理解青藏高原江河源区的水文循环过程，并对生态环境保护及冻土工程科学规划具有参考意义。

热喀斯特湖作为寒区典型地貌单元，其形成演化过程会引起一系列生态、水文、环境效应。阐明热喀斯特湖水量平衡过程及影响机制是研究其水-热-碳耦合过程的关键。因此，本研究结合野外观测、区域调查及室内分析等方法，系统研究了青藏高原热喀斯特湖的水量平衡过程及影响机制。结果显示：1）青藏高原热喀斯特湖主要发育在亚稳定多年冻土区，目前处于快速形成及扩张阶段，能量收支的不平衡导致湖底下伏多年冻土快速融化，极易形成贯穿性湖泊；2）湖面降水、水面蒸发、湖冰升华、冻结层上地下水渗流、地表径流及湖底渗漏等过程影响热喀斯特湖的水量平衡，其中降水和地表径流是主要来源，而冻结层上地下水的渗流量相对较小。下伏多年冻土的完全融化导致湖水以0.8 mm/d的速率渗漏。3）基于LAKE2.6模型对热喀斯特湖温度进行模拟与预测，发现2050和2100年，年平均湖面温度在SSP126、SSP245、SSP370和SSP585气候模式下分别升温2.86℃，2.91℃，3.00℃，3.02 ℃和3.01℃，3.85℃，4.62℃和5.10℃，该模型对湖底夏季温度模拟较好，而对湖底冬季温度模拟效果欠佳。研究成果将有助于深入理解青藏高原的水文循环过程及产汇流机制。未来气候暖湿化伴随着多年冻土的融化，将导致热喀斯特湖的演化更为迅速，其频繁的水-热-碳交换过程所引起的环境效应需要进一步深入研究。