Sky Lake water level data, 2016-2018, Humphreys County, Mississippi

Lake stage, wetland stage, and groundwater levels in 11 wells collected by Michael C. Gratzer at the University of Mississippi Department of Geology & Geological Engineering. Data used in the following with abstract below: Gratzer, M.C., Davidson, G.R., O'Reilly, A.M., and Rigby, J.R., (in press 12/2019), Groundwater recharge from an oxbow lake-wetland system in the Mississippi Alluvial Plain, Hydrological Processes, https://doi.org/10.1002/hyp.13680 The Mississippi River Valley Alluvial Aquifer ranks among the most over-drafted aquifers in the United States due to intensive irrigation. Concern over declining water levels has increased focus on understanding the sources of recharge. Numerous oxbow lakes overlie the aquifer which are often considered hydraulically disconnected from the groundwater system due to fine-grained bottom sediments. In the current study, groundwater levels in and around a 445-ha oxbow lake-wetland in Mississippi were monitored for a two-year period that included an unusually long low-water condition in the lake (>17 months), followed by a high-water event lasting over four months before returning to earlier low water levels. The high water pulse (>4 m rise) provided a unique opportunity to track the impact in the underlying alluvial aquifer. During low-water conditions, groundwater flowed westward beneath the lake. Following the lake rise, groundwater beneath and near the perimeter responded as quickly as the same day, with more delayed responses moving away from the lake. Within two months, a groundwater mound formed near the center of the oxbow (>3 m increase), with a reversal in the local hydraulic gradient toward the east. Flow returned to a westward gradient when the lake level dropped back below 0.3 m. Analysis of precipitation and nearby river stage could not account for the observed behavior. Recharge to the aquifer is attributed to rising water levels spreading over point bar deposits and into surrounding forested wetlands where preferential flow pathways are likely to exist due to buried and decomposing tree remains. An earlier study in the wetland demonstrated increasing redox potential in isolated zones, consistent with the existence of preferential flow pathways through the bottom sediments (Lahiri & Davidson, this issue). Retaining high water levels in oxbow lakes could be a relatively low-cost water-management practice for enhancing aquifer recharge.本数据集包含密西西比大学地质与地质工程系Michael C. Gratzer采集的11口监测井的湖泊水位、湿地水位与地下水水位数据。本数据集所用内容源自如下2019年12月付印的研究论文摘要：Gratzer, M.C.、Davidson, G.R.、O'Reilly, A.M. 及 Rigby, J.R.（2019年12月付印）：《密西西比冲积平原牛轭湖-湿地系统的地下水补给》，《水文过程》，https://doi.org/10.1002/hyp.13680 密西西比河河谷冲积含水层（alluvial aquifer）因高强度农业灌溉，成为美国超采程度最为严重的含水层之一。针对地下水位持续下降的担忧，使得厘清地下水补给来源的研究备受关注。该含水层之上广泛分布牛轭湖（oxbow lake），由于湖底发育细粒沉积物，这类湖泊长期被认为与地下水系统水力不连通。 本研究针对密西西比州一处面积达445公顷的牛轭湖-湿地及其周边区域开展了为期两年的地下水水位监测。监测期间，湖泊先后经历了异常持久的低水位状态（时长超17个月）、持续四个月以上的高水位事件，最终水位回落至此前的低水平。此次水位抬升幅度超4米的高水位脉冲，为追踪其对下伏冲积含水层的影响提供了独一无二的研究契机。 在低水位阶段，地下水沿湖体下方向西流动。当湖泊水位抬升后，湖体下方及周边区域的地下水响应迅速，最快可在当日出现水位变化，而远离湖体的区域则呈现滞后响应。监测开始后的两个月内，牛轭湖中心附近形成了地下水丘（groundwater mound），水位累计抬升超3米，当地水力梯度（hydraulic gradient）发生逆转并向东偏移。当湖泊水位回落至0.3米以下时，地下水流向重新恢复为西向。 对研究区域降水及邻近河流水位的分析，无法解释上述观测到的水文行为。本次含水层补给被归因于抬升的湖体水体漫过点坝沉积物，并渗入周边的森林湿地——由于埋藏且正在分解的树木残体，这类区域大概率存在优势流通道。此前针对该湿地的研究显示，孤立区域的氧化还原电位呈上升趋势，这与湖底沉积物中存在优势流通道的结论相符（Lahiri & Davidson, 本期）。维持牛轭湖的高水位，可作为提升含水层补给效率的低成本水资源管理手段。