Collaborative Research: Salinity of Groundwaters in Continental Sedimentary Basins as a Record of Quaternary Paleoclimatic Conditions

9805456了解含水层盐碱化的自然和人为控制具有重大的社会意义，因为它影响到世界上淡水短缺的半干旱地区的灌溉农业和饮用水供应。 由于地下水补给的溶解固体浓度代表降水减去蒸散量的量度，浅层含水层系统内的盐度的量和空间分布可能代表过去气候的有用指标。 该建议概述了一项研究计划，以104-105年的时间尺度研究沉积盆地内的盐度演变。 一个新的数学模型（MWT 3D SALT）正在开发过程中，以解决控制方程代表地下水，盐的运输，地下水/地表水的相互作用和蒸发蒸腾在根区。 该三维模型可模拟4种含水层盐渍化机制：1）盐湖蒸发浓缩和回流，2）深根潜水植物对根区和地下水位附近盐分的浓缩，3）海洋封闭单元原生地下水的扩散，4）地下水的蒸发浓缩和回流。（4）地下水通过毛细边缘直接蒸发，地下水位侵入地表。 该模型将应用于一般的敏感性研究和水文地质和古生物学研究的默里盆地，澳大利亚。 一般敏感性研究将有助于确定哪些具体的地表、地下和植被条件在含水层盐碱化中发挥重要作用。 对于墨累盆地的应用，将首先使用现代水文应力、已公布的含水层参数和长期（约50年）地下水位波动记录对模型进行校准/验证。 一旦我们感到满意，墨累盆地模型可以重现历史水文变化在区域尺度上，我们将试图重建第四纪记录的古湖水位波动，浅层蒸发沉积物的空间分布，以及现今的地下水盐度分布在整个盆地。 古水文模型将驱动从复合湖芯记录澳大利亚和塔斯马尼亚的地下水补给的估计和古全球循环模型（古GCM）的输出。 如果我们能够利用湖芯记录和/或古GCM输出来重建现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。 PI Person和Hanor在盆地规模的数学建模和地下水卤水地球化学方面具有优势，非常适合开展拟议的研究。

9805456PersonUnderstanding 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.