The use of strontium isotopes in determining groundwater mixing and brine fingering in a playa spring zone, Lake Tyrrell, Australia. J..Hydrol. 167, 225-239
The use of strontium isotopes in determining groundwater mixing and brine fingering in a playa spring zone, Lake Tyrrell, Australia. J..Hydrol. 167, 225-239
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DOI：
10.1016/0022-1694(94)02601-7
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发表时间：
1995-05
影响因子：
6.4
通讯作者：
W. Lyons;S. Tyler;H. Gaudette;D. T. Long
中科院分区：
文献类型：
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作者：
W. Lyons;S. Tyler;H. Gaudette;D. T. Long
干旱半干旱区Playas是重要的区域性地下水排放区。蒂勒尔湖位于澳大利亚维多利亚州西北部，是一个大型盐湖，是该地区地下水的主要排放区。该地区地下水的化学成分是独特的，其盐度约为30 g 1−1，pH值低至2.8。当区域地下水沿着盐湖西部边缘的“泉水区”排出时，它被蒸发浓缩成密集的盐水，通过盐湖沉积物下沉。Macumber在该地区地质水文方面的开创性工作表明，盐湖表面以下的这种密度更大的“回流”盐水是由区域地下水的蒸发演变而来的。我们测量了沿盐湖边缘泉水带浅层地下水样品的87sr /86Sr比值，并与区域地下水和回流盐水进行了比较。我们的数据揭示了与playa系统相关的各种水团混合的相当复杂的模式，最有可能是密度驱动的对流羽流的结果。根据87sr /86Sr值可以识别出两种类型的区域地下水，其中南部地下水的放射性成因小于北部地下水（0.7108 vs 0.7142）。在邻近泉水带的井中观测到的区域地下水中87sr /86Sr的垂直变化也可以沿着泉水带的垂直梯度进行识别。除了这些测量提供的水文地质信息外，锶同位素的变化使我们能够评估这些水域的锶来源。南湖区域地下水87sr /86Sr比值与回流盐水非常接近，而北湖区域地下水87sr相对富集。这一增强的87sr特征表明，锶通过含水层材料中新世Parilla砂的风化作用沿流动路径添加。南部海域的87sr /86Sr值更接近现今海水和/或中新世海水的87sr /86Sr值，表明该体系Sr的主要来源是这两个来源中的一个或两个。我们的研究结果表明，锶同位素在研究地表水-地下水相互作用的动力学和地球化学方面非常有用。
Playas in arid and semi-arid regions can be important regional groundwater discharge zones. Located in the northwestern portion of Victoria, Australia, Lake Tyrrell is a large playa that serves as a major discharge zone of regional groundwater. The chemistry of the regional groundwater is unique, having salinities of approximately 30 g 1−1and pH values as low as 2.8. As the regional groundwater is discharged along the western edge of the playa in the ‘spring zone’, it is evapo-concentrated into a dense brine which sinks through the playa sediments. Macumber's pioneering work on the geohydrology of this region established that this denser, ‘reflux’ brine below the playa surface has evolved from the evaporation of regional groundwaters. We have measured the87Sr/86Sr ratio of a number of groundwater samples taken at shallow depths along the spring zone at the playa edge and compared them with the regional groundwaters and the reflux brine. Our data reveal a rather complex pattern of mixing of the various water masses associated with the playa system, most probably the result of density driven convective plumes. Two types of regional groundwater can be identified based on their87Sr/86Sr values, with groundwater from the south being less radiogenic than that flowing from the north (i.e. 0.7108 vs. 0.7142). Vertical variations in87Sr/86Sr in the regional groundwaters observed in wells adjacent to the spring zone can also be identified along a vertical gradient in the spring zone. Besides the hydrogeological information provided by these measurements, the strontium isotope variations allow us to evaluate the source of strontium to these waters. The regional groundwaters south of the lake are very similar in87Sr/86Sr ratio to the reflux brines, whereas the northern regional groundwaters are comparatively enriched in87Sr. This enhanced87Sr signature indicates the addition of Sr along the flow path via the weathering of the aquifer material, the Miocene Parilla Sand. The southern waters have87Sr/86Sr values closer to that of present-day seawater and/or Miocene seawater, indicating that the major source of Sr to the system is from one or both of these sources. Our results demonstrate that strontium isotopes can be extremely useful in studying the dynamics as well as the geochemistry of surface-water-groundwater interactions.