Dissolved organic compounds with synchronous dynamics share chemical properties and origin

Abstract

The temporal dynamics of dissolved organic matter (DOM) are inherently linked with the functioning of aquatic ecosystems. Because DOM represents a complex mixture of millions of different compounds, the statistical analysis of DOM dynamics poses a huge challenge. Here, we present a statistical approach based on hierarchical clustering of time series that groups DOM compounds with synchronous dynamics. We applied this approach to time series of Fourier-transform ion cyclotron resonance mass spectrometry data of DOM sampled over a period of 26 months near Helgoland, an island in the Southern North Sea. We identified three DOM clusters, which represented a total of 1392 different molecular formulae and showed distinct chemical properties and noticeably compound matches within the PubChem database. Correlations of the three DOM clusters with abundance data of prokaryote and phytoplankton species and with environmental parameters provided consistent indications on the potential origin of the clustered compounds. The first cluster integrated terrestrial DOM originating from riverine discharge reaching Helgoland waters. The second cluster was attributed to DOM related to phytoplankton and microbial activity, whereas the third cluster was interpreted as representing the marine refractory DOM background. Accordingly, while further partitioning divided each of the first two clusters into five sub-clusters with distinct temporal dynamics and molecular characteristics, the third cluster persisted as a stable feature. Applying a purely mathematical approach, we thus confirmed the differential dynamics of individual DOM compounds and compound groups and showed that temporal dynamics of dissolved molecules are linked to their origin and transformation history.

Biodegradation of Terrigenous Organic Matter in a Stratified Large-Volume Water Column: Implications of the Removal of Terrigenous Organic Matter in the Coastal Ocean

“…FDOM accumulation with incubation time, thus, suggests that highly unsaturated, highly oxygenated DOM accumulated via microbial transformation of DOM in the bottom layer . Highly unsaturated, highly oxygenated DOM molecules are usually restricted to microorganism degradation. , Therefore, the accumulation of FDOM may indicate carbon storage in the bottom water; meanwhile, it should be noted that DOM fluorescence does not necessarily equal carbon content.…”

“…22 Highly unsaturated, highly oxygenated DOM molecules are usually restricted to microorganism degradation. 75,76 Therefore, the accumulation of FDOM may indicate carbon storage in the bottom water; meanwhile, it should be noted that DOM fluorescence does not necessarily equal carbon content.…”

Reviews and syntheses: Use and misuse of peak intensities from high resolution mass spectrometry in organic matter studies: opportunities for robust usage

“…If we continue with the bird community example and assume that the detectability of a given bird species is consistent across sampled locations (or times), then it would be appropriate to examine variation in within-species call counts. This within-species analysis is directly analogous to the HRMS within-peak time series analysis in Merder et al (2021), discussed below. However, if call counts of a given species are suppressed by the presence/abundance of other species, then call counts of a given species do not indicate an increase in its abundance.…”

“…Such within-peak comparisons may be repeated independently for each peak of interest in a given dataset. For example, Merder et al (2021) quantified temporal dynamics of individual HRMS peaks and then binned peaks into different groups with characteristic temporal fluctuations. In those analyses, peak intensities were not compared between peaks.…”

Will various interpretation strategies of the same ultrahigh‐resolution mass spectrometry data tell different biogeochemical stories? A first assessment based on natural aquatic dissolved organic matter

“…The solid‐phase extraction (SPE) column can concentrate and desalinate DOM from filtered nature water, which adapts well to the measured standard requiring high carbon amount and avoiding the impacts of halogen elements (Dittmar et al 2008). Recently, with the demand for high resolution and sensitivity from the molecular perspective, the Fourier ion cyclotron resonance mass spectrometry (FT‐ICR MS) has become one of the most effective tools and is widely used in studying DOM (Barrow et al 2004; Bao et al 2017; He et al 2020 b ; Merder et al 2021; Qi et al 2022 b ). However, different FT‐ICR MS settings could contribute to less comparable results in semi‐quantitative comparison, like weighted mass to charge ( m / z ) ratio, H/C, and O/C (oxygen to carbon ratio) of DOM (Kim et al 2003; Hawkes et al 2020), even though their specific comparisons between formulas are still highly comparable, like molecular composition and targeted formulas (Stubbins et al 2010; Medeiros et al 2016; Kellerman et al 2021).…”