Hydrogeologic processes in saline systems: playas, sabkhas, and saline lakes
Hydrogeologic processes in saline systems: playas, sabkhas, and saline lakes
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DOI：
10.1016/s0012-8252(02)00067-3
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发表时间：
2002-10
影响因子：
12.1
通讯作者：
Y. Yechieli;W. Wood
中科院分区：
文献类型：
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作者：
Y. Yechieli;W. Wood
平原、盐沼、盐湖、盐湖和盐滩在水文上是相似的，只是边界条件不同。因此，在评价这些系统中的地球化学过程时，可以采用一般的水和溶质质量平衡方法。以阿拉伯湾附近沿海sabkha的概念模型为例，说明各种水通量和溶质通量。对该模型的分析表明，地下地层的地下水向上流动可能是sabkha溶质的主要来源，但只贡献了一小部分水。在模拟的sabkha系统中，当地降雨是水的主要来源，其补给与降雨的比例惊人地高，超过50%。海水对溶质收支的贡献取决于潮上带的宽度与总宽度的比率，一般限于典型沿海sabkha海岸线附近的一个狭窄地带。由于水的停留时间较短，预计在短时间内（<100年）就能达到稳态流动，而溶质的稳态可能需要更长的时间（约5万年）。封闭盐水系统中卤水的溶质组成在很大程度上取决于输入水的原始组成。盐水中总离子的高含量限制了水岩相互作用和吸收的效率。由于大多数自然系统在水文上是开放的，因此盐水和相关的蒸发岩沉积物的化学性质可能与水文封闭系统的预测结果有很大不同。非饱和带温度的季节性变化引起盐碱地系统中矿物质的沉淀，并进行蒸发。因此，在炎热的干旱季节，矿物表现出逆行溶解度，因此石膏，硬石膏和方解石沉淀。如果大气的相对湿度小于水的活度，地表附近的蒸发也是导致不饱和带上部矿物降水（如盐岩和光卤石）的一个主要过程。咸水湖系统中淡水/咸水界面的坡度较淡水/海水界面浅，这是由于淡水/咸水水体之间的密度差较大。sabkha盐水和海水之间的界面向海倾斜，不像一般的海洋淡水系统向陆地倾斜。此外，盐水/海水界面不能达到稳定状态，因为它被sabkha的盐水推向大海。
Pans, playas, sabkhas, salinas, saline lakes, and salt flats are hydrologically similar, varying only in their boundary conditions. Thus, in evaluating geochemical processes in these systems, a generic water and solute mass-balance approach can be utilized. A conceptual model of a coastal sabkha near the Arabian Gulf is used as an example to illustrate the various water and solute fluxes. Analysis of this model suggests that upward flux of ground water from underlying formations could be a major source of solutes in the sabkha, but contribute only a small volume of the water. Local rainfall is the main source of water in the modeled sabkha system with a surprisingly large recharge-to-rainfall ratio of more than 50%. The contribution of seawater to the solute budget depends on the ratio of the width of the supratidal zone to the total width and is generally confined to a narrow zone near the shoreline of a typical coastal sabkha. Because of a short residence time of water, steady-state flow is expected within a short time (<100 years), while steady state for solutes may take much longer (>50,000 years). The solute composition of the brine in a closed saline system depends largely on the original composition of the input water. The high total ion content in the brine limits the efficiency of water–rock interaction and absorption. Because most natural systems are hydrologically open, the chemistry of the brines and the associated evaporite deposits may be significantly different than that predicted for hydrologically closed systems. Seasonal changes in temperature of the unsaturated zone cause precipitation of minerals in saline systems undergoing evaporation. Thus, during the hot dry season months, minerals exhibit retrograde solubility so that gypsum, anhydrite and calcite precipitate. Evaporation near the surface is also a major process that causes mineral precipitation in the upper portion of the unsaturated zone (e.g. halite and carnallite), provided that the relative humidity of the atmosphere is less than the activity of water. The slope of the fresh/brine-water interface in saline lake systems is shallower than in fresh/seawater interface because of the greater density difference between the fresh/brine-water bodies. The interface between sabkha brines and seawater slopes seaward, unlike normal marine–fresh water systems that slope landward. Moreover, the brine/seawater interface does not achieve steady state because it is pushed toward the sea by the sabkha's brine.