COLLABORATIVE RESEARCH: Salinity of Groundwater in Continental Sedimentary Basins as a Record of Quaternary Paleoclimatic Conditions

[805446]汉娜：了解含水层盐渍化的自然和人为控制具有重要的社会意义，因为它对世界上淡水供应短缺的半干旱地区的灌溉农业和饮用水供应产生影响。由于地下水补给的溶解固体浓度代表了降水减去蒸散的一种度量，因此浅层含水层系统中盐度的数量和空间分布可能是过去气候的一个有用指标。提出了在104 ~ 105年时间尺度上研究沉积盆地盐度演化的研究计划。一个新的数学模型（MWT3D SALT）正在开发中，用于求解代表地下水、盐运移、地下水/地表水相互作用和根区蒸发蒸腾的控制方程。该三维模型将能够表示四种含水层盐渍化机制：1)盐湖盐的蒸发浓度和回流；2)根区和地下水位附近深根的渗透植物的盐浓度；3)海洋围封单元原生地下水的扩散；4)地下水在地下水位侵蚀地表的毛细边缘直接蒸发。该模型将应用于一般敏感性研究，以及在水文地质学和古嵌合学上研究得很好的澳大利亚默里盆地。一般敏感性研究将有助于确定哪些特定的陆地表面、地下和植被条件在含水层盐渍化中起重要作用。对于Murray盆地的应用，该模型将首先使用现代水文应力、已公布的含水层参数和长期（~50年）地下水水位波动记录进行校准/验证。一旦我们确信Murray盆地模型能够在区域尺度上再现历史水文变化，我们将尝试重建第四纪记录，包括古湖泊水位波动、浅层蒸发岩矿床的空间分布以及盆地内地下水盐度的现今分布。古水文模型将由澳大利亚和塔斯马尼亚州合成湖芯记录的地下水补给估计和古全球环流模型（古gcm）输出驱动。如果我们能够利用湖芯记录和/或古gcm输出来重建当今沉积盆地的盐度分布，那么我们将为世界半干旱地区的区域第四纪古气候研究发现一种强有力的新方法。PIs Person和Hanor在盆地尺度数学建模和地下水盐水地球化学方面已经证明了自己的优势，非常适合开展拟议的研究。

9805446HanorUnderstanding the natural and anthropogenic controls on aquifer salinization is of great societal relevance because of its impact on irrigated agriculture and drinking water supplies within semi-arid regions of the world where fresh water is in short supply. Because the dissolved solids concentration of groundwater recharge represents a measure of precipitation minus evapotranspiration, the amount and spatial distribution of salinity within shallow aquifer systems may represent a useful indicator of past climate. A research plan is outlined in this proposal to study salinity evolution within sedimentary basins on time scales of 104-105 years. A new mathematical model (MWT3D SALT) is in the process of being developed to solve governing equations representing groundwater, salt transport, groundwater/surface water interactions and evapotranspiration within the root zone. This three-dimensional model will be capable of representing four aquifer salinization mechanisms: 1) evaporative concentration and reflux of salts from saline lakes; 2) concentration of salts within the root zone and near the water table by deeply rooted phreatophytes; 3) diffusion of connate groundwater from marine confining units; 4) direct evaporation of groundwater across the capillary fringe where the water table encroaches upon the land surface. The model will be applied both in a generic sensitivity study and to the hydrogeologically and paleochimatologically well studied Murray Basin, Australia. The generic sensitivity study will help to determine what specific land surface, subsurface, and vegetation conditions play an important role in aquifer salinization. For the Murray Basin application, the model will first be calibrated/validated using modern hydrologic stresses, published aquifer parameters, and records of long-term (~50 years) groundwater level fluctuations. Once we are satisfied that the Murray Basin model can reproduce historical hydrologic changes at the regional scale, we will attempt to reconstruct Quaternary records of paleo-lake level fluctuations, the spatial occurrence of shallow evaporite deposits, and the present-day distribution of groundwater salinity across the basin. The paleohydrologic model will be driven either by estimates of groundwater recharge taken from composite lake core records for Australia and Tasmania and by paleo global circulation model (Paleo-GCM) output. If we can use lake core records and/or paleo-GCM output to reconstruct the present-day salinity distribution across sedimentary basins, then we will have discovered a powerful new approach for regional Quaternary paleoclimate studies in semi-arid regions of the world. PIs Person and Hanor have proven strengths in basin-scale mathematical modeling and groundwater brine geochemistry and are well suited to carry out the proposed study.