Award: OCE-1335622

Collaborative Research: Calibration and application of vascular plant and aqueous microbial biomarkers to examine transformations of dissolved organic matter Scientific Merit. Biomarkers have a long history of use in the aquatic sciences for examining the source, processing and fate of organic matter. This research aimed to advance our understanding of specifically dissolved organic matter (DOM) dynamics by improving the way the scientific community applies biomarker tools. To achieve this we developed and calibrated DOM source biomarkers for both vascular plant and microbial sources using microbial and coupled photochemical-microbial incubations of vascular plant leachates. We also developed a suite of data processing tools and novel database management to catalogue and identify any potential vascular plant and microbial markers released by the commonly used cupric oxide oxidation technique. These approaches highlight that despite our incubations starting with different source materials (i.e. different leachate endmembers) throughout the incubations convergence of DOM composition to a common composition was apparent. This highlights that despite differences in the composition of starting plant material, bio- and photo-degradation mechanisms produce DOM of similar compositions. Such convergence provides a compositional buffering capacity for aquatic systems where terrestrial material is a major contributor to DOM. Large-scale surrounding landscape changes may alter DOM source endmembers in riverine or lake systems, but initial differences in composition are quickly eliminated by degradation mechanisms such that the origin of the terrestrially-derived DOM is significant only when the material is fresh. As anthropogenic impacts (e.g. deforestation, conversion of lands to agriculture) and changes in climate alter the distribution of global terrestrial vegetation, compositional buffering will become a critical mechanism to maintain stability in aquatic DOM cycling. With the recalibration of biomarkers we also conducted sampling transects across the salinity gradient in the San Francisco Bay estuary in winter and summer to estimate degradation and production rates with and without significant photooxidation present using the calibrated biomarkers. Ultimately, our results highlight that terrestrially-derived DOM is more reactive than historically thought as biomarker data was interpreted incorrectly in previous studies. Project data are publicly available through the NSF BCO-DMO web site at: https://www.bco-dmo.org/project/732791 Broader Impacts. In addition to research this project supported a host of broader impacts, most noticeably in terms of opportunities for training and professional development of young scientists. As part of this project two MS degrees in Oceanography were successfully defended at Texas A&M University at Galveston as well as data from this project contributing toward a PhD students thesis at Texas A&M. At the University of California, Davis data from this research forms the core of a PhD student?s thesis and she has developed new protocols for peak integration and quantification of biomarkers which is of general use to the scientific biomarker community as a whole. Also at University of California, Davis this project supported one undergraduate student who is now completing graduate school as a result of his experience with this project. Finally, at Florida State University two post-doctoral scholars who worked on this project have gone on to Faculty positions, and a third post-doctoral scholar who was at the University of California, Davis has also gone on to a Faculty position. Several presentations at both national and international conferences have been given and this project has already resulted in several publications. Outcomes summary: Coastal ecosystems carry tremendous economic value, control fluxes of organic carbon on a global scale, and are increasingly vulnerable to climate change and environmental degradation in general. Our research investigated the origins and transformations of riverine and estuarine soluble organic matter, which is the base of the microbial foodweb and captures significant changes in the landscape through compositional changes. We sought to understand the controls on any potential detrimental impacts to these systems, including changes in nutrient runoff as it relates to primary production, changes in hydrologic management, changes in plant succession on the landscape that can result from climate change or fire, as well as changes in overall hydrology related to climate change. The approaches relied on experimental work to develop and calibrate specific biomolecules and to capture microbial and photoxidation degradation pathways, and on field work to capture biochemical conditions along a salinity gradient in the San Francisco Bay Estuary in three seasons. The unique combination of molecular tracers, optical measurements, and high-resolution mass spectroscopy allow for rare intercalibration of all these techniques on a single study. In addition to research, this project provided a highly collaborative research, training and learning environment for undergraduates, graduate students, and postdoctoral fellows at the University of California, Davis, Texas A&M Galveston, and Florida State University. Last Modified: 12/21/2018 Submitted by: Peter J Hernes