Reversals of karst springs: Implications for water budgets, water quality, and speleogenesis

该奖项是根据2009年《美国复苏和再投资法案》(公法111-5)资助的。智力上的功绩。河流泛滥期间泉水的逆转(例如，河口的形成)可能会将有机碳带到营养稀少的环境中，在那里它将被重新矿化，改变营养物质和终端电子受体的浓度，如溶解氧(DO)、NO3以及铁和锰氧化物，并增加二氧化碳。二氧化碳浓度升高应该会在排泄点而不是在下沉的溪流中驱动溶解。逆转将由泉水、管道、地下水和河流之间的水头梯度控制，但这种简单化的观点因之前的条件、扩散补给与异质补给的速率、含水层的水力特性和含水层限制而变得复杂。泉水倒流的这些潜在影响导致了这里讨论的问题，包括：(1)含水层中的水头、流量、扩散补给和含水层限制之间的关系是什么？(2)回灌水返回地表的速度是多少？(3)控制回灌水成分的主要固液反应是什么？这些问题将在佛罗里达州中北部苏万尼河沿岸的四个泉(麦迪逊蓝泉、特洛伊泉、孔雀泉和范宁泉)解决，所有这些泉都经历了频繁的反转。麦迪逊蓝、特洛伊和范宁泉是正在进行的监测项目的地点，这些项目已经产生了许多关于流动和化学的遗留数据，这些数据将补充作为该项目的一部分收集的新数据。将在基流期间以低频率采集样品，以观察背景化学成分，并在反转事件期间以高分辨率采集样品，以构建洪水化学图。将使用可靠的现成测井仪器监测特定的电导率、温度、DO和pH。数据收集和分析将包括利用现有的和新的排放数据估计反转幅度。将使用锶同位素比率和水的年龄(~3H/~3He比率和氯氟化碳浓度)来分离洪水和地下水的不同部分。主要元素浓度将被用来评估水的饱和状态。DO、NO3、NH4、Fe2、Fe3、Mn、硫酸盐、硫化物、溶解无机和有机碳浓度以及13CDIC值的测量将被用来估计有机质再矿化的程度。数据建模将包括模拟流动的MODFLOW和估计氧化还原和饱和状态的PHREEQC。与许多喀斯特地区一样，苏万尼河流域正在经历快速的土地利用变化和地下水开采。该盆地也是各种濒临灭绝的茎栖动物的家园。这些问题需要认真管理水质和水量，这两者都将受到春季逆转的影响。苏万尼河也被提议作为水网的选址，其最大的支流圣达菲河是一个受资助的“试验台”项目的选址。试验台项目将通过水文信息系统(HIS)的综合数据处理和存储与该项目相联系。研究地点位于州立公园，允许与普通民众互动。洞穴潜水在公园里很常见，潜水员会自愿采集样本。该项目将为本科生和研究生提供培训，这些本科生将使用遗留数据，研究生将为他们的论文或学位论文从事该项目。结果将被用作佛罗里达大学目前教授的几门课程的正式课堂培训的范例。

ABSTRACTThis award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). Intellectual Merit. Reversal of springs during river flooding (e.g., formation of estavelles) are likely to carry organic carbon to oligotrophic environments where it will be remineralized, changing concentrations of nutrients and terminal electron acceptors such as dissolved oxygen (DO), NO3, and Fe and Mn oxides, and increase pCO2. Elevated pCO2 should drive dissolution at the discharge point rather than at sinking streams. Reversals will be controlled by head gradients between the spring, conduits, groundwater, and rivers, but this simplistic view is complicated by antecedent conditions, the rates of diffuse versus allogenic recharge, hydraulic properties of the aquifer, and aquifer confinement. These potential effects of spring reversals lead to questions addressed here including: (1) What are the relationships between hydraulic head in the aquifer, discharge, diffuse recharge, and aquifer confinement? (2) At what rate is backflooding water returned to the surface? (3) What are the primary solid-fluid reactions controlling backflooded water compositions? These questions will be addressed at four springs (Madison Blue, Troy, Peacock, and Fanning) along the Suwannee River in north-central Florida, all of which experience frequent reversals. Madison Blue, Troy and Fanning springs are sites of on-going monitoring programs that have generated much legacy data about flow and chemistry, which will supplement new data collected as part of this project. Samples will be collected at low frequency during base flow to observe background chemical compositions and at high resolution during a reversal event to construct flood chemographs. Specific conductivity, temperature, DO, and pH will be monitored with reliable off the shelf logging instruments. Data collection and analyses will include estimates of reversal magnitudes using available and new discharge data. Sr isotope ratios and age of water (3H/3He ratios and CFC concentrations) will be used to separate fractions of flood water and groundwater. Major element concentrations will be used to assess saturation states of the water. Measurements of DO, NO3, NH4, Fe2+, Fe3+, Mn, sulfate, sulfide, dissolved inorganic and organic carbon concentrations, and ?Ô13CDICvalues will be used to estimate the magnitude of organic matter remineralization. Data modeling will include MODFLOW to simulate flow and PHREEQC to estimate redox and saturation states.Broader impacts. Similar to many karst areas, the Suwannee River Basin is experiencing rapid land use changes and elevated groundwater withdrawals. The basin is also home to a variety of endangered stygobitic fauna. These issues require careful management of water quality and quantity, both of which will be affected by spring reversals. The Suwannee River has also been proposed as a site for the WATERS network, and its largest tributary, the Santa Fe River, is the site of a funded ¡§test-bed¡¨ project. The test bed project will be linked to this project through combined data handling and storage using Hydrologic Information System (HIS).Study sites are located in state parks, allowing interaction with the general population. Cave diving is common at the parks, and divers will volunteer for sample collection. The project will provide training for undergraduates, who will work with legacy data, graduate students, who will work on the project for their thesis or dissertations. Results will be used as examples in formal classroom training in several courses currently taught at the University of Florida.