青海湖泉湾镭同位素的空间分布与沿岸地下水排放评价

Evaluation of the groundwater discharge and the spatial distribution of radium isotope in Quanwan Bay of Lake Qinghai

青海湖是青藏高原的重要组成部分,它是维系青藏高原东北部生态安全的重要水体.其沿岸地下水的排放直接影响了青海湖的水文生物地球化学过程,然而对该问题的研究仍然不充分.本研究于2014年对青海湖泉湾湖水、河水和地下水进行223Ra和224Ra活度的测定分析,并对泉湾湖水水平向和垂直向的Ra活度分布进行深入分析,最后估算并探讨了泉湾水体的停留时间和布哈河口沿岸地下水的排放通量.表层湖水、河水、地下水不同端元的水体223Ra和224Ra活度值分别为0.441和0.026 dpm/100 L、0.22和0.016 dpm/100 L以及0.061和1.30 dpm/100 L,最高值为地下水,其次湖水,河水最小;总体上泉湾湖水223Ra和224Ra活度随离岸距离增加分别由0.047到0.011 dpm/100 L和1.4到0.2 dpm/100 L的减小,垂向上Ra活度呈楔形分布,Ra活度在不同方向上的非保守性分布主要受到悬浮颗粒物解析的影响;通过水体滞留时间模型计算获得青海湖泉湾水体的平均停留时间为1.8天,进一步分析泉湾水体Ra的源汇项,应用镭同位素质量平衡模型获得泉湾布哈河口沿岸地下水排放通量为0.054~0.109 m^3/(m^2·d).

Lake Qinghai is an important part of the Qinghai-Tibet Plateau. It is important to maintain the ecological security in the northeast of Qinghai-Tibet Plateau. The discharge of groundwater along the lake shore directly affects the hydrobiogeochemical process of Lake Qinghai. However, research on this issue is still inadequate. In the study, we measured and analyzed the activity of 223Ra and 224Ra in the lake water, river water and groundwater in Quanwan Bay of Lake Qinghai in 2014. We discussed the horizontal and vertical distribution of activity of Ra, and also estimated the residence time of Quanwan Bay water and the discharge flux of groundwater in the Buha Estuary. The activity values of 223Ra and 224Ra at different end elements are 0.441 dpm/100 L and 0.026 dpm/100 L, 0.22 dpm/100 L and 0.016 dpm/100 L, 0.061 dpm/100 L and 1.30 dpm/100 L, respectively. The activity of Ra from high to low was followed by groundwater, lake water and river water. In general, the activity of 223Ra and 224Ra in Quanwan Bay were decreased with the increase of offshore distance from 0.047 to 0.011 dpm/100 L and 1.4 to 0.2 dpm/100 L, respectively. The activity of Ra was presented wedge in the vertical of lake water. Ra activity in different directions of conservative distribution mainly affected by the suspended particle resolution. The average residence time of Quanwan Bay water was calculated by using the water retention time model, and the source and sink term of Ra in Quanwan Bay was further analyzed. The discharge flux of groundwater was 0.054-0.109 m^3/(m^2·d) in the Buha Estuary which was calculated by the radium isotope mass balance model.