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

了解对含水层盐碱化的自然和人为控制具有重大的社会意义，因为它对淡水短缺的世界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降水减去蒸散量的量度，因此浅层含水层系统内盐度的数量和空间分布可能代表过去气候的有用指标。这一建议概述了一个研究计划，即在104-105年的时间尺度上研究沉积盆地内的盐度演化。正在开发一种新的数学模型(MWT3D SALT)，以求解代表地下水、盐分运移、地下水/地表水相互作用和根区内蒸散的控制方程。这个三维模型将能够描述四种含水层盐化机制：1)盐湖盐分的蒸发浓缩和回流；2)深植植根植物在根带内和地下水位附近的盐分浓缩；3)来自海洋封闭单元的联合地下水的扩散；4)地下水穿过地下水位侵蚀地表的毛管边缘的直接蒸发。该模型将应用于一般性敏感性研究以及澳大利亚默里盆地的水文地质和古生物研究。一般敏感性研究将有助于确定哪些特定的地表、地下和植被条件对含水层盐碱化起着重要作用。对于Murray盆地的应用，首先将使用现代水文应力、已公布的含水层参数和长期(~50年)地下水位波动记录来校准/验证模型。一旦我们对Murray盆地模型能够在区域尺度上再现历史水文变化感到满意，我们将尝试重建古湖平面波动的第四纪记录、浅层蒸发岩沉积的空间分布以及整个盆地的地下水盐度今天的分布。古水文模型将由澳大利亚和塔斯马尼亚综合湖芯记录中的地下水补给量估计和古全球环流模型(Paleo-GCM)的输出驱动。如果我们能够利用湖泊岩心记录和/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找到一条强有力的新途径。PIS 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已被证明具有优势，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.