Groundwater-surface water connectivity in the presence of riparian wetlands

近三分之一的加拿大人口依赖地下水资源，农业区的人口比例高达80%。全球地下水开采率在过去50年中至少增加了两倍，我们才刚刚开始评估使用量增加对饮用水供应和生态系统的影响。在大多数情况下，与地表水水库有关的含水层的补给和排放仍然知之甚少。这导致对含水层的可持续开采以及水资源的综合管理缺乏控制。这项研究计划的长期目标是确定地下水和地表水水库是如何连接的，以及它们如何应对自然和人类引起的变化。具体目标是(1)确定在存在河岸湿地的情况下驱动地下水补给和排放的参数和过程，(2)量化不同尺度上含水层、河岸湿地和河流之间的交换通量，以及(3)了解环境变化对水文连通性的影响。研究计划分为三个部分。在第一部分中，将描述湿地存在时地下水补给-排放设置的特征。这将在现有试验场上实现，方法是利用详细的实地数据和水样(主要离子、222Rn、稳定同位素和水温)测量地质和河流走廊条件。统计分析将有助于查明控制地下水补给-排放连通性的参数，而时间序列分析(水位、温度和电导率)将有助于确定交换过程。在第二部分中，将使用完全耦合的三维模型和局部补给模型来模拟含水层、河岸湿地和河流之间的通量，以精确地确定这些交换所涉及的尺度。全球敏感性分析将从数值上确定驱动含水层-湿地-河流相互作用的过程。在第三部分中，将量化环境变化对湿地存在时水文连通性驱动因素的影响。这将通过土地利用变化和气候变化情景下的完全耦合流动模拟来实现。还将模拟实施河流走廊等缓解措施对地下水位、洪水和河流枯水的影响。将在地方和区域尺度上进行运输模拟，以更好地了解河岸湿地作为污染物通量有效屏障的作用。这项研究计划将查明河岸湿地地下水补给和排放的驱动因素和制约因素。它还将大大有助于查明现有方法的局限性，并确定在有河岸湿地的情况下研究含水层-河流通量的新技术。将对涉及通过河岸湿地补给和排放地下水的通量的规模进行科学的理解，以充分评估所涉及的过程。这项研究还将大大有助于更好地确定人为压力和气候变化对流域的影响，并更好地了解河岸系统的水文和水质功能。这些最初的贡献将通过对许多总部基地人员的培训而成为可能，这些总部基地人员准备面对水文地质学和环境研究中常见的现场和建模工作的复杂性。这项研究计划有可能极大地改变地下水和湿地的管理方式，并有助于维持它们在河流走廊内的长期弹性。

Nearly a third of the Canadian population, and up to 80% in agricultural areas, relies on groundwater resources. The global groundwater extraction rate has at least tripled over the past 50 years and we are only beginning to assess the impacts of increased usage on drinking water supplies and ecosystems. In most cases, recharge and discharge of aquifers in connection with surface water reservoirs remain poorly understood. This leads to a lack of control for the sustainable exploitation of aquifers as well as for the integrated management of water resources. The long-term objective of this research program is to determining how groundwater and surface water reservoirs are connected and how they respond to natural and human-induced changes. Specific objectives are (1) to identify the parameters and processes that drive groundwater recharge and discharge in the presence of riparian wetlands, (2) to quantify the fluxes exchanged between aquifers, riparian wetlands, and rivers at various scales and (3) to understand the impacts of environmental change on hydrological connectivity. The research program is divided in three parts. In Part I, groundwater recharge-discharge settings in the presence of wetlands will be characterized. This will be achieved on existing experimental sites by measuring geology and river corridor conditions using detailed field data and water sampling (major ions, 222Rn, stable isotopes and water temperature). Statistical analyses will help discern which parameters control groundwater recharge-discharge connectivity and time series analyses (water levels, temperature and electrical conductivity) will contribute to the identification of exchange processes. In Part II, the fluxes between aquifer, riparian wetlands and river will be simulated with fully-coupled 3D modeling and with local recharge modeling to pinpoint the scales involved in these exchanges. Global sensitivity analysis will determine numerically the processes that drive aquifer-wetland-river interactions. In Part III, the effects of environmental change on the drivers of hydrological connectivity in the presence of wetlands will be quantified. This will be done through the fully-coupled flow simulations under land use change and climate change scenarios. The effect of mitigation measures such as the implementation of river corridors leading to additional wetland areas on groundwater levels, floods and river low flows will also be simulated. Transport simulations will be performed at the local and regional scales to better understand the role of riparian wetlands as effective barriers for contaminant fluxes. This research program will pinpoint the drivers and constraints of groundwater recharge-discharge through riparian wetlands. It will also contribute significantly to identify the limits of existing approaches and to define new techniques for the study of aquifer-river fluxes in the presence of riparian wetlands. Science-based understanding of the scales at which fluxes involved in groundwater recharge and discharge through riparian wetlands need to be considered to fully assess the processes involved will be developed. The research will also significantly contribute to better define the impact of anthropogenic pressures and climate change on watersheds, and to better understand hydrological and water quality functions of riparian systems. These original contributions will be made possible by the training of numerous HQPs prepared to face the complexity of field and modeling work common to hydrogeology and environmental studies. This research program has the potential to drastically change the way groundwater and wetlands are managed and to help sustain their long term resilience within the river corridor.