Collaborative Research: Controls on Delivery and Fate of Water, Nitrogen and Calcium in a Spring-Fed Karst River

知识价值：河流系统的水文、地貌和生物地球化学动力学在从几个小时到几千年的时间尺度上相互耦合。流域输入和径流特性通过对水和溶质输送动力学的影响来影响地貌和生物地球化学过程。同时，河流生物群的代谢过程可以对水文、形态和生物地球化学产生相互控制作用。这些耦合的生物-非生物相互作用导致复杂的、非线性的反应，需要高时空密度的数据才能理解。在泉水补给的喀斯特河流中，由于高植物产量和低流速，预计会有强烈的生物-非生物相互作用，并被假设控制N和DO的动态，具有重要的生态后果，以及河水pH影响矿物溶解，从而影响岩溶河道的发育。生物控制溶质输送的大小，以及与河道溶解的联系，人们知之甚少。因此，这项建议解决了三个问题，这些问题将生物和非生物处理联系在一起：1)地下水流路径如何随气候和水流状况变化，以及它们如何控制泉水输送的大小和水的溶质化学；2)河流氮处理的水文和地貌控制是什么？3)在低起伏的岩溶河流中，生物和水文控制是什么？研究地点是佛罗里达州北部的伊切特基尼河，多个测量过的泉水汇合成一条8公里长的河流，也被测量到泉水下游5公里处。工作计划包括：1)在战略上选定的泉口和河流地点利用最先进的传感器对水化学进行连续测量，2)对没有连续测量或在非传感器地点进行分析物的天气观测水样，以及3)对Ichetucny和其他区域重要泉水的档案数据进行分析，以更全面地检验假设。连续记录传感器，测量DO浓度、T、阶段、比电导率和pH，将部署在两个泉水，代表Ichetucny复合体的两个水化学类群。这些传感器，连同连续的N3和浊度传感器，也将部署在下游的三个地点。连续测量的数据将被用来评估在日、季、季和年际时间尺度上N的交付变异性和流中处理(例如，同化吸收与异化损失)。每月的天气采样将把生物过程与碳酸盐饱和状态和溶解联系起来。对该地区泉水档案数据的分析，将允许对跨越更多泉水种群的流量与化学关系的统计分析(自动/交叉关联)。更广泛的影响：佛罗里达州？S泉水是重要的区域文化、经济和生态资源；观察到的生态衰退使泉水成为当前监管考虑的对象，重点是N污染。随着监管选择的争论，对弹簧如何处理N的机械性理解不足，限制了就如何管理它们提出建议的能力。多个地方和州监管机构和利益相关者团体(例如，Ichetucny Springs盆地工作组、佛罗里达州环境保护部、佛罗里达州斯普林斯特别工作组)允许将科学知识转化为政策和公共教育。这项拟议工作的成果将定期在公共和机构会议上提交给利益攸关方。很大一部分研究将在少数族裔服务机构(佛罗里达国际大学)进行；代表性不足的群体将被招募为学生和博士后候选人。将这项工作与水域试验台位置合并将扩大在初步研究期间获得的关于传感器网络和数据基础设施的专业知识。这项工作将在建立传感平台方面提供更多的技术进步，使有关河流系统的关键信息能够跨过程和管理相关的时间尺度收集。

Intellectual Merit: Hydrologic, geomorphic and biogeochemical dynamics of river systems are coupled over time scales ranging from hours to millennia. Catchment inputs and flowpath properties influence geomorphic and biogeochemical processes through effects on water and solute delivery dynamics. Simultaneously, metabolic processes of river biota can exert reciprocal control on hydrology, morphology, and biogeochemistry. These coupled biotic-abiotic interactions lead to complex, non-linear responses that require high spatiotemporal density of data to understand. In spring-fed karst rivers, strong biotic-abiotic interactions are expected due to high plant production and low flow velocity, and are hypothesized to control both N and DO dynamics, with important ecosystem consequences, and also river water pH with implications for mineral dissolution and thus karst channel development. The magnitude of biotic controls on solute delivery, and links to stream channel dissolution, are poorly understood. Consequently, this proposal addresses 3 questions that link biotic and abiotic processing of spring-fed karst channels: 1) How do sub-surface flow paths vary with climate and flow regime, and how do they control the magnitude of spring water delivery, and the solute chemistry of the water? 2) What are the hydrologic and geomorphic controls on riverine N processing? 3) What are the biotic and hydrologic controls on channel dissolution in low-relief karst rivers?The study site is the Ichetucknee River in north Florida where multiple gauged springs merge to form an 8-km long river, which is also gauged 5 km downstream of the springs. The work plan includes: 1) continuous measurements of water chemistry, utilizing state-of-the-art sensors at strategically selected spring vent and river sites, 2) synoptic water sampling for analytes not continuously measured or at non-sensor sites, and 3) analysis of archival data at Ichetucknee and other regionally important springs to test hypotheses more generally. Continuously recording sensors, that measure DO concentrations, T, stage, specific conductivity, and pH, will be deployed at two springs, representing two hydrochemical groupings of the Ichetucknee complex. These, along with continuous NO3 and turbidity sensors, will also be deployed at three locations downstream. The continuously measured data will be used to assess delivery variability and in-stream processing of N (e.g. assimilatory uptake versus dissimilatory loss) at diel, episodic, seasonal, and inter-annual time scales. Monthly synoptic sampling will link the biological processes to carbonate saturation state and dissolution. Analyses of archival data from springs across the region, will allow statistical analyses (auto/cross-correlation) of discharge vs. chemistry relationships spanning a larger population of springs.Broader Impacts: Florida?s springs are significant regional cultural, economic, and ecological resources; observed ecological declines have made springs the subject of current regulatory consideration, with a focus on N pollution. As regulatory options are debated, poor mechanistic understanding of how springs process N limits the ability to make recommendations for how to manage them. Multiple local and state regulatory agencies and stakeholder groups (e.g., Ichetucknee Springs Basin Working Group, Florida Department of Environmental Protection, Florida Springs Task Force) allow translation of scientific knowledge into policy and public education. Results from this proposed work will be presented regularly to stakeholders at public and agency meetings. A significant portion of the research will be conducted at a minority serving institution (Florida International University); under-represented groups will be recruited to work as students and post-doctoral candidates. Co-locating this work with a WATERS test-bed location will expand the expertise gained about sensor networks and data infrastructure during the preliminary studies. This work will provide additional technological advances toward building sensing platforms, allowing critical information about river systems to be collected across process and management relevant time-scales.