Dissolved organic matter (DOM) is an ultra-complex mixture of chemical constituents, the reactivity, fate, and flux of which are controlled by a combination of intrinsic (i.e. quantity and quality) and extrinsic (i.e. environmental conditions and microbial processing) factors. This makes studying DOM a daunting task, particularly when working across the diverse environments of the land-ocean aquatic continuum, between deep ocean basins, or to link biotic and / or abiotic processes with shifts in DOM composition. Studying aquatic DOM often involves deconvolving a mixed signal across multiple spatial, temporal, and analytical windows. This can require diverse analytical techniques, often in combination with modelling and / or digital approaches, and we are often limited in our ability to integrate quantitative and qualitative data. For example, DOM is typically quantified relative to its DOC concentration, despite C accounting for a variable % of the DOM pool, and characterized using analytical techniques which become qualitative when applied to environmental samples (e.g. absorbance and fluorescence spectrophotometery, mass spectrometry, nuclear magnetic resonance). Most of these techniques operate over a very specific analytical window (e.g. extractable, ionizable, or chromophoric DOM), meaning that the DOM fraction identified by one method can be absent from another, and difficult to relate to bulk DOC. Absorbance, for example, is a commonly used proxy for terrigenous DOM and can be used semi-quantitatively, but the few compound classes which have been structurally defined in both freshwater and marine systems (e.g. CRAMs and terpenoid-derived structures) tend to be non-chromophic. Novel, integrative approaches and the discovery of new tracers and proxies for DOM source, reactivity, and transformation pathways are therefore pivotal in order to trace and understand DOM production via primary producers (photo- and chemoautotrophs), subsequent microbial transformation, and end-fate, whether in the atmosphere, sediments, or the deep ocean. This session therefore aims to highlight the power of combining quantitative and qualitative understanding within and between any aquatic environments, from headwater streams to deep ocean basins. We encourage submissions that integrate processes (e.g. bio- and photo-degradation and transformations) and / or work across multiple disciplines (e.g. hydrology, ecology, chemistry, and biology), and welcome studies that combine high resolution and information rich qualitative analytical methods (e.g. -omics approaches, high resolution mass spectrometery, nuclear magnetic resonance, absorbance and fluorescence spectrophotometery) with quantitative and /or modelling approaches. We also welcome submissions which develop novel approaches, tracers, or proxies for DOM source, form, and reactivity, and those which aim to better understand the methodological biases and constraints of existing techniques.
Lead Organizer: Jeffrey Hawkes, Uppsala University (jeffrey.hawkes@kemi.uu.se)
Co-organizers:
Stacey Felgate, Uppsala University (stacey.felgate@kemi.uu.se)
Michael Gonsior, UMCES (gonsior@umces.edu)
S. Leigh McCallister, VCU (slmccalliste@vcu.edu)
Leanne Powers, SUNY-ESF (lcpowers@esf.edu)
Presentations
05:00 PM
Direct analysis of dissolved organic matter from original seawater using LC-FT-ICR-MS (6602)
Primary Presenter: Boris Koch, Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung (boris.koch@awi.de)
DOM is one of the most complex natural mixtures and thus poses the greatest challenges to chemical characterization using instrumental analytics. The characterization of marine DOM is further complicated by the fact that the salt concentration in the ocean exceeds the DOM concentration by a factor of 35,000. At the same time, the low DOM concentrations challenge the analytical sensitivity. To improve sensitivity and robustness, solid-phase extraction (SPE) is often used for DOM desalting and enrichment. However, SPE is not quantitative leaving more than half of the DOM analytically undetectable. The chemical composition of the extracts obtained is strongly influenced by the type and loading of the adsorbent. Here we present a new method for characterizing DOM that allows direct injection of seawater samples with native salt and DOC concentrations. The method uses reversed-phase chromatography in combination with Fourier transform ion cyclotron resonance mass spectrometry (LC-FT-ICR MS). It allows effective salt separation and highly sensitive detection of organic compounds in as little as 100 µL of seawater. We determined analytical metrics such as reproducibility, robustness, sensitivity, and linear detection range. The method was tested with DOM samples of different carbon and salt concentrations and applied to samples from the central Arctic Ocean with DOC concentrations as low as 20 µmol / L. In addition to a quantitative DOC response, liquid chromatographic separation opens an analytical window that supports separation of structural isomers based on polarity.
05:15 PM
ENHANCING DISSOLVED ORGANIC MATTER INSIGHT BY COMBINING LC-HRMS AND IN SILICO STRUCTURAL CHARACTERIZATION (4951)
Primary Presenter: Jessica Patrone, Institute of Environmental Assessment and Water Research (IDAEA-CSIC) (jessica.patrone@cid.csic.es)
Dissolved organic matter (DOM) of aquatic systems, a diverse, complex mixture of water-soluble biogenic and anthropogenic organic compounds, constitutes one of the largest exchangeable organic carbon pools on the planet and is involved in numerous biogeochemical cycles. Although DOM characterization is challenging due to its high heterogeneity, a holistic comprehension of DOM composition is crucial to assess the health status of the ecosystem. Here, non-target liquid chromatography high-resolution mass spectrometry (LC-HRMS) was combined with novel computational tools to achieve a comprehensive data analysis workflow that allows, for the first time, an in-silico characterization of DOM at a molecular structural level. This computational workflow enabled structural annotation of 10% of the almost 20,000 molecular features detected from the analysis of three water samples (sea, river and drinking water). The LC and the prospect of DOM structural characterization enhance the understanding of the DOM pool, especially if combined with the more traditional direct infusion (DI) HRMS approach. With DI, thousands of molecular formulas were assigned, but the technique is still limited by issues such as signal suppression of multiple interfering analytes and the lacking possibility of detecting isomers or obtaining structural information. Moreover, the LC approach expands the domain of analysed DOM towards the less polar fraction of compounds. In conclusion, the combination of non-target analyses with computational MS provides new insights into DOM composition.
05:30 PM
Insights from Two Worlds: Complementary Analysis of Dissolved Organic Matter Along the River-to-Ocean Continuum in Brazilian Mangroves by NMR and FT-ICR-MS (5370)
Primary Presenter: Nico Mitschke, University of Oldenburg (nico.mitschke@uni-oldenburg.de)
Mangroves are major sources of terrigenous dissolved organic matter (DOM) to the ocean. However, our understanding of processes shaping the molecular composition of DOM at the land-ocean interface is still limited. We used a complementary approach combining ultrahigh-resolution mass spectrometry (FT-ICR-MS) and high-field nuclear magnetic resonance spectroscopy (NMR) for molecular formula and structural analysis of solid-phase extracted DOM recovered from a mangrove-fringed river-to-ocean transect in North Brazil. We hypothesized that marine, terrestrial and porewater-influenced DOM contains source-specific molecular fingerprints. We detected thousands of molecular formulas and various structural features. The increasing relative abundance of aliphatic structures from the river to the coastal ocean reflects the increasing influence of marine, microbial DOM, whereas the decreasing relative abundance of terrestrial aromatic structural motifs suggests estuarine dilution and/or removal of these compound groups by processes such as flocculation and photochemical degradation. Aromatic structural motifs were underestimated by a factor of three by 1H-detecting NMR experiments compared to FT-ICR-MS analysis. Carbohydrates were more readily detected by NMR analysis. Only two-dimensional NMR was suitable to trace porewater discharge as a major source for polycyclic aromatic hydrocarbons to the coastal ocean. Our findings highlight that combined FT-ICR-MS and NMR analyses yield highly complementary results for the characterization of DOM transformations along land-ocean interfaces.
05:45 PM
FOLLOWING THE FLOW OF WATER: THE FATE OF MICROBES AND DISSOLVED ORGANIC MATTER ALONG A BOREAL TERRESTRIAL-AQUATIC CONTINUUM (7191)
Primary Presenter: Masumi Stadler, Groupe de Recherche Interuniversitaire en Limnologie, Université du Québec à Montréal, Canada (m.stadler.jp.at@gmail.com)
Recent analytical advances have greatly enhanced our capacity to characterize aquatic microbial communities and dissolved organic matter (DOM) pools. This increased resolution comes with computational and conceptual challenges associated to disentangling the complex interactions that exist between these extremely complex assemblages. One way to disentangle their links is to assess the spatial covariation between microbes and molecules along a common flow path within interconnected networks. Here we present a study of microbial / DOM interactions at the whole network scale, where we have modelled the spatial patterns of individual microbial taxa (16S rRNA) and molecular formulae (FT-ICR-MS) along an aquatic continuum (from soil, headwater streams to reservoirs) in the Romaine river watershed in Canada. We aimed to describe the various spatial behaviours of both microorganisms and DOM molecular formulae along the flow path that undergoes major environmental changes, and eventually establish links between the two. Results indicate that around 90% and 80% of microbes and molecular patterns, respectively, do not have a consistent spatial pattern (i.e., largely passive). Within those that had significant spatial patterns, most molecular formulae were decreasing along the continuum, while microbial taxa were mostly balanced between those that increased and decreased. These preliminary results suggest that spatial patterns may provide a framework to unravel reactive microbial and DOM components, enabling us to effectively link microbial-molecular dynamics within aquatic networks.
06:00 PM
RELATING DISSOLVED ORGANIC MATTER (DOM) REACTIVITY TO COMPOSITION IN A MARSH-INFLUENCED MESOTIDAL TEMPERATE ESTUARY (6063)
Primary Presenter: Matthew Weiser, Boston University (mwweiser@bu.edu)
Dissolved Organic Matter (DOM) is ubiquitous in natural waters and represents a large, dynamic pool of organic carbon critically important to the global carbon cycle. Coastal marsh-estuary systems are located at the land-ocean interface and receive multiple types of DOM inputs from rivers, salt marshes, bottom sediments, autochthonous primary production, and mixing with the adjacent coastal waters. These systems are also influenced by tides and other physical processes that make them hydrodynamically complex. In these dynamic biogeochemical hotspots, the DOM is typically made up of a very diverse and heterogeneous mixture of compounds with varying reactivities that regulate the extent to which DOM is transformed in the estuary and exported to the adjacent coastal ocean. Predicting the photochemical and biological reactivity of DOM based on its source and degradation state in these complex systems is therefore crucial to understand the fate of organic matter moving across the land-ocean continuum and to accurately estimate carbon export to the coastal ocean. Here, we investigate the relationships between microbial and photochemical reactivities derived from controlled laboratory experiments and indicators of DOM composition, source, and degradation derived from fluorescence, absorption, and high-resolution mass spectrometry. The study focuses on the Plum Island Ecosystems LTER site, a marsh-influenced mesotidal temperate estuary located in coastal Massachusetts, and uses data and samples collected across the system and all seasons.
06:15 PM
Fluorescence proxies of the composition and reactivity of dissolved natural organic matter (7347)
Primary Presenter: Kathleen Murphy, Chalmers University of Technology (murphyk@chalmers.se)
Natural dissolved organic matter (DOM) derived from deceased and living organisms influences chemical reactions and contaminant transport in all aquatic systems. Predicting the fate of DOM and micropollutants in the environment thus depends on measuring DOM abundance and reactivity, but DOM is difficult to measure because it consists of diverse molecules that can’t be isolated or fully characterised. Fluorescence spectroscopy enables rapid and sensitive measurement of dissolved DOM in water, but this approach has been criticised because only a small fraction of NOM molecules emit fluorescence. In this talk I will discuss how despite these limitations, fluorescence spectroscopy in combination with advanced modelling approaches can inform about the bulk composition of NOM in water and help to predict how it will behave in response to physical, chemical and biological processes. Examples will be discussed from natural and engineered systems, focusing on freshwater resources and drinking water treatment plants.
SS111 Novel Analytical Approaches to Understanding Dissolved Organic Matter Reactivity, Fate, and Flux Along the Land Ocean Aquatic Continuum – Combining Qualitative and Quantitative Information
Description
Time: 5:00 PM
Date: 5/6/2023
Room: Sala Palma