青海湖流域河流体系多元稳定同位素（B、Li和Sr）季节和年际变化特征及控制因素

As a useful geochemical tracer, Lithium, Boron and Strontium isotopes have been used to study some important geological or geochemical issues. It has a very important significance to reveal these isotopes fractionation mechanisms of continental weathering processes and accuratly estimate marine mass flux. However, lithium-boron-strontium source, fractionation characteristics and control factors is still unclear or controversial. In this project, Buha River and Shaliu Rive of Lake Qinghai were chose due to its largest hydrologically closed lake in China and its unique location sensitive to climate changes. Seasonal variation of B-Li-Sr concentrations and its isotopic ratio will be investigated and compared in these two river sub-catchments with different rock types at same climatic conditions. By combined with geochemistry, mineralogy and hydrogeology, we try to obtain seasonal source difference, migration and isotope fractionation of solute- and particle-form B-Li-Sr concentrations and its isotopic ratio in river systems at Lake Qinghai area. The constraints of climate, lithology and river sediments of the river basin system on B-Li-Sr concentrations and their isotopes in river systems under natural background conditions will be revealed, which will provide geochemical theoretical basis by using B-Li-Sr concentrations and their isotopes to trace catchment weathering.

河流体系B、Li和Sr同位素是揭示大陆风化过程分馏机制和准确估算物质通量的有效示踪剂，但单一同位素获得的认识只是河流体系风化物质来源及主控因素中的某一侧面，存在不确定性或多解性，因此需要多元同位素相互补充与验证。本项目选择气候条件一致、而地质和地形差异明显的青海湖流域内布哈河和沙柳河为对象，采集两河全流域不同季节样品水体、悬浮物、沉积物，通过多元同位素相结合的手段，发挥δ11B对pH、δ7Li对温度及87Sr/86Sr对物源敏感的优势，开展系统的青海湖河流体系B、Li和Sr多元同位素季节和年际变化特征研究。重点辨析岩性、大气输入、次生矿物形成和矿物吸附／解吸过程对同位素分馏影响。在此基础上示踪河流体系风化物质来源，提炼两个河流体系不同季节化学风化的控制因素。本项目将为半干旱区表生地球化学过程中B、Li和Sr多元同位素地球化学特征及其对流域风化的示踪和环境变化的响应提供新的认识和研究范例。

河流体系B、Li和Sr同位素对揭示大陆风化过程分馏机制和准确估算海洋物质通量具有重要意义。目前利用B、Li或Sr单同位素研究手段已无法满足示踪河流体系风化物质来源及提炼主控因素的需要。本课题通过对青海湖流域气候条件一致，地质和地形差异明显的最大两条河流（布哈河和沙柳河）季节性采集样品，实验室对常微量元素含量、B、Li和Sr同位素测定，获得青海湖河流体系B、Li和Sr多元同位素季节和年际变化特征。研究结果表明，流域岩性是控制河水B、Li和Sr同位素组成的主要因素，布哈河溶解态同位素变化主要由碳酸盐分布地层控制，而沙柳河则由硅酸盐地层控制；特殊事件对布哈河和沙柳河溶解态元素和同位素组成具有重要影响作用，春季粉尘输入对河水化学组成有着不容忽视的贡献，并可能诱发了自生碳酸盐的沉淀，夏季雨水冲刷和稀释作用则河水中元素含量降低的主要原因。这些研究将为半干旱区表生地球化学过程中B、Li和Sr多元同位素地球化学特征及其对流域风化的示踪和环境变化的响应提供科学依据。