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

智力优势：河流系统的水文、地貌和生物地球化学动力学在几个小时到几千年的时间尺度上是耦合的。汇水输入和流道特性通过对水和溶质输送动力学的影响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对水文、形态和生物地球化学具有相互的控制作用。这些耦合的生物-非生物相互作用导致复杂的非线性响应，需要高时空密度的数据才能理解。在泉水供养的喀斯特河流中，由于植物产量高，流速低，预计会发生强烈的生物-非生物相互作用，并被假设控制N和DO的动态，具有重要的生态系统后果，并且河流的pH值对矿物溶解和喀斯特河道发育具有影响。生物对溶质输送的控制程度，以及与河道溶解的联系，目前还知之甚少。因此，本提案解决了3个问题，这些问题与泉水喀斯特河道的生物和非生物过程有关：1)地下水流路径如何随气候和水流状况而变化，它们如何控制泉水输送的大小，以及水的溶质化学性质？2)水文地貌对河流氮加工的控制作用是什么？3)低起伏喀斯特河流河道溶蚀的生物和水文控制因素是什么？研究地点是佛罗里达州北部的伊切塔克尼河，在那里，多个测量泉水汇合形成一条8公里长的河流，在泉水下游5公里处也测量了这条河流。工作计划包括：1)在战略选择的泉口和河流地点使用最先进的传感器对水化学进行连续测量，2)对非连续测量或非传感器地点的分析物进行天气性水取样，以及3)分析伊切塔克尼和其他区域重要泉的档案数据，以更普遍地测试假设。连续记录传感器，测量DO浓度、T、级、比电导率和pH值，将部署在两个弹簧上，代表Ichetucknee复合体的两个水化学组。这些传感器以及连续的NO3和浊度传感器也将部署在下游的三个位置。连续测量的数据将用于在日、期、季和年际时间尺度上评估氮的输送变异性和流中处理（例如同化吸收与异化损失）。每月的天气取样将把生物过程与碳酸盐饱和状态和溶解联系起来。对整个地区的弹簧档案数据进行分析，将允许统计分析（自动/相互关联）跨越更大的弹簧种群的流量与化学关系。更广泛的影响：佛罗里达？温泉是重要的区域文化、经济、生态资源；观察到的生态衰退使泉水成为当前监管考虑的主题，重点是氮污染。由于监管选择是有争议的，对弹簧如何处理N的机械理解不足，限制了对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，伊切塔克尼斯普林斯盆地工作组、佛罗里达州环境保护部、佛罗里达州斯普林斯工作组）允许将科学知识转化为政策和公共教育。这项拟议工作的结果将定期在公众和机构会议上向利益攸关方提出。研究的很大一部分将在少数民族服务机构（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。在初步研究期间，将这项工作与WATERS试验台地点共同定位，将扩大在传感器网络和数据基础设施方面获得的专业知识。这项工作将为建立传感平台提供额外的技术进步，允许跨过程和管理相关时间尺度收集有关河流系统的关键信息。

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.