Collaborative Research: Estuarine metabolism and gas exchange determined from dissolved oxygen time series: method development, field evaluation, and application to historical data

河口在全球元素循环中发挥着关键作用，因为它们是位于陆地、海洋和大气之间的界面上的生物活动和化学转化的热点。随着物质从陆地运输到海洋，河口通过各种过程深刻地转化或过滤这些物质，其中主要是光合作用和呼吸作用，统称为新陈代谢，以及河口和大气之间的气体交换(如二氧化碳和氧气)。然而，由于缺乏足够的数据、空间和时间上的高度可变性、方法不一致以及缺乏统一的模型，这些过程受到的约束很少。这项研究将通过实地活动、模型开发和历史数据分析的新组合来促进对这些过程的理解。目前可用于量化这些过程的数据因潮流而变得复杂，这些过程是对溶解氧的连续测量。因此，这项研究的一个主要目标是评估和改进消除潮流影响的方法，这被称为平流。这一目标将通过在不同季节对两个不同河口的平流进行直接测量来实现。这项研究的产品将提供给高中教师、大学生和研究专业人员。将开发基于开源R编程语言的简单易用的软件来分析溶解氧数据。教师的研究体验将邀请一名高中教师从事河口新陈代谢和气体交换的研究。使用该软件的高中和大学课程材料将与教育专家一起开发。该软件将被整合到当前的软件套件中，该软件套件用于分析来自国家数据库的溶解氧数据。一名博士后研究员将参与更广泛影响的所有方面，并获得教育学和外展方面的经验。拟议研究的前两个目标是评价和改进在河口(Hudson River和Apalachicola Bay)和季节(春季和夏末)对比的4个月现场活动中的平流消除技术和气体输送参数。将采用控制体积的方法，这将提供一个难得的机会来完全限制河口位置的溶解氧收支。实现这两个目标将允许检验以下假设：(1)平流去除误差随着太阳角和潮汐高度之间的相关性的增加而增加；(2)浊度和取气对气体传输速度有明显的影响。第三个目标是开发一种新的溶解氧数据同化方法，即河口贝叶斯单站估计(EBASE)，用于同时确定总初级生产力、生态系统呼吸、净生态系统生产力和气体交换。EBASE将结合平流去除技术(及其在第一个目标中估计的确定误差)与最近在湖泊学中发展的贝叶斯新陈代谢技术。EBASE还将恢复模型参数，如光合作用-辐照度曲线的初始斜率、呼吸作用的温度依赖关系以及气体传输速度的获取依赖关系。第四个目标是将EBASE应用于野外活动数据和美国国家河口研究储备系统(NERRS)内的16个长期(至少14年)、高质量的溶解氧时间序列，该系统还包含对温度、盐度、浊度、风速、风向和地表辐照度的关键连续测量以及对叶绿素和营养物质的每月测量。EBASE将应用于NERRS数据的一个月段，有助于分析河口新陈代谢和气体交换的季节性、年际和跨系统变异性的驱动因素。这一分析将允许对H2以及与新陈代谢相关的假设进行进一步的测试：(H3a)光合作用-辐射曲线的初始斜率随营养物质和叶绿素的增加而增加，并随浊度的增加而减小；(H3b)呼吸-温度关系的斜率随盐度(溶解有机物的替代物)和叶绿素(细菌丰度的替代物)而增加。该奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

Estuaries play a key role in the global cycling of elements because they are hot spots of biological activity and chemical transformations that lie at the interface between land, ocean, and atmosphere. As materials are transported from land to ocean, estuaries profoundly transform or filter these materials through various processes, chief among which are photosynthesis and respiration, collectively referred to as metabolism, and the exchange of gases (such as carbon dioxide and oxygen) between the estuary and the atmosphere. However, these processes are poorly constrained due to lack of sufficient data, high variability in space and time, inconsistent methodology, and lack of a unified model. This research will advance understanding of these processes through a novel combination of field campaigns, model development, and historical data analysis. The data currently available to quantify these processes, which are continuous measurements of dissolved oxygen, are complicated by tidal currents. Hence a main objective of the research is to evaluate and improve methods that remove the influence of tidal currents, which is called advection. This objective will be achieved by direct measurements of advection in two contrasting estuaries in contrasting seasons. Products of this research will be made available to high school teachers, college students, and research professionals. Easy-to-use software based on the open-source R programming language will be developed to analyze the dissolved oxygen data. A Research Experience for Teachers will engage a high school teacher in estuarine metabolism and gas exchange research. Curricular materials for high school and college employing the software will be developed with education specialists. The software will be integrated into the current software suite that is used to analyze dissolved oxygen data from a national data base. A postdoctoral researcher will be involved in all aspects of the broader impacts and gain experience in pedagogy and outreach. The first two objectives of the proposed research are to evaluate and improve advection-removal techniques and gas transfer parameterizations in four one-month field campaigns in contrasting estuaries (Hudson River and Apalachicola Bay) and seasons (spring and late summer). A control volume approach will be adopted, providing a rare opportunity to completely constrain the dissolved oxygen budget at an estuarine location. Achieving these two objectives will allow the following hypotheses to be tested: (H1) advection-removal errors increase as the correlation between sun angle and tidal height increases and (H2) turbidity and fetch measurably influence the gas transfer velocity. The third objective is to develop a new dissolved-oxygen data assimilation method, Estuarine BAyesian Single-station Estimation (EBASE), for simultaneously determining gross primary production, ecosystem respiration, net ecosystem production, and gas exchange. EBASE will combine the advection-removal technique (and its determined errors estimated in the first objective) with Bayesian metabolism techniques recently developed in limnology. EBASE will also retrieve model parameters, such as the initial slope of the photosynthesis-irradiance curve, the temperature dependence of respiration, and the fetch dependence of the gas transfer velocity. The fourth objective is to apply EBASE to the field campaign data and to 16 long-running (at least 14 years), high-quality dissolved oxygen time series within the U.S. National Estuarine Research Reserve System (NERRS), which also contains critical continuous measurements of temperature, salinity, turbidity, wind speed, wind direction, and surface irradiance as well as monthly measurements of chlorophyll and nutrients. EBASE will be applied to one-month segments of the NERRS data, facilitating an analysis of the drivers of seasonal, interannual, and cross-system variability in estuarine metabolism and gas exchange. This analysis will allow further testing of H2 as well as testing of metabolism-related hypotheses: (H3a) the initial slope of the photosynthesis-irradiance curve increases with nutrients and chlorophyll and decreases with turbidity and (H3b) the slope of the respiration-temperature relationship increases with salinity (a proxy of dissolved organic matter) and chlorophyll (a proxy of bacterial abundance).This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.