Mapping Spatial and Temporal Heterogeneity of Lake Seepage

[609827]利用电阻率和感应电位绘制湖泊渗漏的时空异质性图天普大学地质学系aura Toran和Jonathan Nyquist了解地下水-湖泊相互作用需要详细了解渗透模式，以确定水收支，跟踪从湖泊流入地下水或地下水流入湖泊的污染物，并研究富含营养的地下水对湖泊微栖息地的影响。但是详细测量整个湖泊的渗漏是一项艰巨的任务。利用质量平衡和模拟计算出的通量估计处理的是整个湖泊，但没有指出地下水排放和补给的区域。使用渗透计进行的点测量，或根据压力计数据和沉积物水力传导性计算得出的点测量，通常间隔很宽，而且往往难以重现。地质变异性控制着渗漏，但地质变异性的特征很差，因为很难在湖下绘制地图。该项目将研究连续电阻率剖面（CRP），这是一项很有前途的海洋沉积物和基岩测绘新技术。通过在船后拖曳电极拖缆进行电阻率测量，可以在数据反演期间将GPS和测深数据结合起来，生成连续的二维电阻率剖面。电阻率的变化对应于孔隙度、孔隙流体离子强度和粘土含量的变化。在宾夕法尼亚州拉卡瓦克湖使用最先进的CRP系统收集的初步数据表明，湖泊水电导率（2 uS/cm）和地下水电导率（40 uS/cm）之间的适度对比可以直接检测到。地下水上涌以低电阻率带的形式出现在充满阻性湖水的沉积物中。即使在湖泊和地下水导电性几乎没有对比的地方，如新罕布什尔州的镜湖，CRP也可以提供影响渗透模式的孔隙度和粘土含量等沉积物特性变化的信息。CRP数据的快速收集允许收集广泛的空间和时间数据，以改善用于直接测量通量变化的渗透仪的放置，提供更好的空间覆盖，地质特征与渗漏之间的联系，以及用于检查系统对风暴和季节变化的响应的时间数据。将详细比较CRP数据与使用一系列低成本人工渗流仪收集的点测量数据，以及水文数据、湖泊沉积物岩心分析和地下水建模，以评估该方法的实用性和局限性。通过比较重复地球物理调查与新开发的测井渗流仪数据之间的差异，还将研究用于变化检测的实用CRP。由于淡水资源的压力越来越大，这项研究对社会很重要。更好地了解地下水和地表水的相互作用将改进对水收支和化学转移（营养物质或污染物）的预测。此外，渗流界面往往是生物活性的热点，在养分和碳循环中起着重要作用。这项研究的目的是为了转移到其他地点，因为它通过地下水流动模型研究了地球物理信号与观测到的水文地层之间的基本关系。这项研究对教育的影响体现在多个层面。将为三名硕士研究生提供第二年学习经费。此外，本科生将担任现场助理并负责研究子项目。为了进一步提高他们的研究经验，资助本科生参加科学会议并展示他们的研究成果。天普经常吸引第一代大学生，少数民族人口占30%；在地质系，学生的性别比例很好。因此，坦普尔能够接触到科学界代表性不足的群体。除了大学教育外，该项目还将提供有关地下水-湖泊相互作用重要性的教育材料，用于在所研究湖泊的旅游中。

0609827ToranMapping spatial and temporal heterogeneity of lake seepageusing electrical resistivity and induced potentialLaura Toran and Jonathan Nyquist, Department of Geology, Temple UniversityUnderstanding groundwater-lake interactions requires detailed knowledge of seepage patterns todetermine water budgets, to track contaminants flowing from lakes into groundwater, or groundwater into lakes, and to study the influence of nutrient-rich groundwater on lake micro-habitats. But measuring lake-wide seepage in detail is a daunting task. Flux estimates calculated using mass balance and modeling address the lake as a whole, but do not indicate the regions of groundwater discharge and recharge. Point measurements made using seepage meters, or calculated from piezometer data and sediment hydraulic conductivity, are typically widely spaced and often difficult to reproduce. Geologic variability controls seepage, but geologic variability is poorly characterized because it is difficult to map beneath a lake.This project with investigate continuous resistivity profiling (CRP), a promising new technologyfor mapping marine sediments and bedrock. Electrical resistivity measurements made by towing an electrode streamer behind a boat can be combined with GPS and bathymetry data during data inversion to produce continuous 2-D resistivity profiles. Resistivity changes correspond to variations in porosity, ionic strength of pore fluids, and clay content. Preliminary data collected at Lake Lacawac, Pennsylvania, using a state-of-the-art CRP system suggest that modest contrasts between lake water conductivity (2 uS/cm) and groundwater conductivity (40 uS/cm) are directly detectable. Groundwater upwelling appeared as a low-resistivity zone within sediments saturated with resistive lake water. Even at sites with almost no contrast between lake and groundwater conductivity, such as Mirror Lake, New Hampshire, CRP may provide information on variability in sediment properties such as porosity and clay content that influence seepage patterns. The rapidity of CRP data collection permits extensive spatial and temporal data to be collected to improve the placement of seepage meters used for direct measurements of changesin flux, providing better spatial coverage, linkages between geologic features and seepage, and temporal data to examine system response to storms and seasonal change. Detailed comparison will be made between CRP data and point measurements collected using an array of low cost manual seepage meters, as well as hydrologic data, lake sediment core analysis, and groundwater modeling to assess the utility and limitations of the method. The utility CRP for change detection will also be investigated by comparing differences between repeated geophysical surveys with data from newly-developed logging seepage meters.This research is important to society because of the increasing pressures on freshwater resources.Better understanding of groundwater-surface water interactions will improve prediction of water budgets and chemical transfer (nutrients or contaminants). Furthermore, seepage interfaces are often hot spots of biological activity and play an important role in nutrient and carbon cycling. This study is designed for transfer to other sites because it looks at the fundamental relationships between the geophysical signals and the observed hydrostratigraphy through groundwater flow modeling. The educational impact of this research occurs at multiple levels. Funds will be provided for three masters students during their second year of study. In addition, undergraduates will act as field assistants and take ownership of research sub-projects. To further enhance their research experience, funding is included to permit undergraduate students to attend a scientific conference and present their research. Temple often attracts first-generation college students and has a 30% minority population; in the geology department, there is a good gender balance among students. Thus, Temple is able to reach underrepresented groups in the sciences. In addition to university education, the project will contribute educational materials on the importance of groundwater-lake interaction for tours at the lakes studied.