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起着关键作用，因为它们是生物活动和化学转化的热点，位于陆地、海洋和大气之间的界面。当物质从陆地运输到海洋时，河口通过各种过程深刻地转化或过滤这些物质，其中最主要的是光合作用和呼吸作用，统称为新陈代谢，以及河口与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、空间和时间的高度可变性、不一致的方法以及缺乏统一的模型，这些过程受到的约束很差。这项研究将通过实地活动、模型开发和历史数据分析的新颖结合，促进对这些过程的理解。目前可用于量化这些过程的数据是对溶解氧的连续测量，由于潮流的影响而变得复杂。因此，研究的一个主要目的是评估和改进消除潮流（称为平流）影响的方法。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。这项研究的成果将提供给高中教师、大学生和研究专业人员。将开发基于开源R编程语言的易于使用的软件来分析溶解氧数据。教师研究经验将聘请一名高中教师进行河口代谢和气体交换研究。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。该软件将集成到当前的软件套件中，用于分析来自国家数据库的溶解氧数据。博士后研究人员将参与更广泛影响的各个方面，并获得教学和推广方面的经验。拟议研究的前两个目标是在四个为期一个月的实地活动中评估和改进平流去除技术和气体传输参数化，这些活动分别发生在不同的河口（哈德逊河和阿巴拉契科拉湾）和季节（春季和夏末）。将采用控制体积的方法，为完全限制河口位置的溶解氧预算提供难得的机会。实现这两个目标将允许测试以下假设：（H1）平流去除误差随着太阳角度和潮汐高度之间相关性的增加而增加，（H2）浊度和fetch可测量地影响气体传递速度。第三个目标是开发一种新的溶解氧数据同化方法——河口贝叶斯单站估计（EBASE），用于同时确定总初级产量、生态系统呼吸、净生态系统产量和气体交换。EBASE将把平流去除技术（及其在第一个目标中估计的确定误差）与湖沼学中最近发展的贝叶斯代谢技术结合起来。EBASE还将检索模型参数，如光合作用-辐照度曲线的初始斜率、呼吸的温度依赖性以及气体传递速度的获取依赖性。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）高质量溶解氧时间序列，该时间序列还包含温度、盐度、浊度、风速、风向和表面辐照度的关键连续测量，以及叶绿素和营养物质的月度测量。EBASE将应用于NERRS数据的一个月段，促进对河口代谢和气体交换的季节性、年际和跨系统可变性的驱动因素的分析。该分析将允许进一步测试H2以及测试与代谢相关的假设：（H3a）光合作用-辐照曲线的初始斜率随营养物质和叶绿素增加而增加，随浊度降低而降低；（H3b）呼吸-温度关系的斜率随盐度（溶解有机物的代表）和叶绿素（细菌丰度的代表）而增加。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识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.