Understanding Dissolved Organic Matter Reactivity and Composition in Lakes and Streams Using Proton-Transfer-Reaction Mass Spectrometry (PTR-MS)

Abstract

Here, we present a novel approach for investigating dissolved organic matter (DOM) composition using thermal desorption protontransfer-reaction mass spectrometry (PTR-MS), a technique that provides insight into the molecular composition of DOM < m/z 500 (termed "PTR-DOC"). The applicability of PTR-MS for understanding the relationship between DOM composition and reactivity has yet to be explored. We present results from a synoptic sampling campaign of streams and lakes in a Swedish forest catchment where we measured DOM composition using PTR-MS and traditional optical methods and conducted DOM biodegradability assays. PTR-DOC comprised ≤12% of the total DOC pool. We found significant relationships between PTR-DOC and DOM degradability; reduced chemodiversity and low concentrations of PTR-DOC were both associated with the total DOM pool being more susceptible to microbial degradation. Furthermore, molecular differences were apparent among headwater lakes, headwater streams, and lakes further down the catchment. Direct linkages between PTR-DOC and optical methods were observed. Using the quantitative data that PTR-MS generates, it could become possible to identify the fluorescing components of DOM, and the method may be particularly informative in low-DOC waters such as marine environments where PTR-DOC may dominate the total DOM pool.

Presence of nanoplastics in rural and remote surface waters

“…All analyses on the Swedish samples were originally conducted for an experiment investigating dissolved organic matter (DOM) composition and reactivity [66]. Water samples were collected by hand (wearing no gloves) and were filtered in-situ with PE syringes (note that the same type of syringe was used for treatment of lab blanks) and 0.45 µm cellulose nitrate filters (pre-rinsed with lake/stream water) and stored in 100 ml glass bottles (also pre-rinsed with filtered lake/stream water).…”

“…All the steps of the data analysis (including all the mass spectra, subtractions, detection limit calculation, and final mass spectra) are provided in the permanent repository (see the SI). Further details on the analysis are provided in Peacock et al [66], where the PTR-MS data were used to investigate the molecular composition of DOM.…”

Presence of nanoplastics in rural and remote surface waters

“…All analyses on the Swedish samples were originally conducted for an experiment investigating dissolved organic matter (DOM) composition and reactivity 54 . Water samples were ltered in-situ with 0.45 µm lters (pre-rinsed with lake/stream water) and stored in 100 ml glass bottles in the dark at 4°C until analysis…”

“…All the steps of the data analysis (including all the mass spectra, subtractions, detection limit calculation, and nal mass spectra) are provided in the permanent repository (see the SI). Further details on the analysis are provided in Peacock et al (2018) 54 , where the PTR-MS data were used to investigate the molecular composition of DOM.…”

“…The concentration of the detected plastics was then calculated based on the known kinetics of the reaction chamber 58,59 , as explained in our previous work 19,54,56,60 .…”