Negligible Quantities of Particulate Low-Temperature Pyrogenic Carbon Reach the Atlantic Ocean via the Amazon River

Fates of Terrigenous Dissolved Organic Carbon in the Gulf of Maine

A significant amount of organic carbon is transported in dissolved form from soils to coastal oceans via inland water systems, bridging land and ocean carbon reservoirs. However, it has been discovered that the presence of terrigenous dissolved organic carbon (tDOC) in oceans is relatively limited. Therefore, understanding the fates of tDOC in coastal oceans is essential to account for carbon sequestration through land ecosystems and ensure accurate regional carbon budgeting. In this study, we developed a state-of-the-art modeling approach by coupling a land-to-ocean tDOC flux simulation model and a coastal tDOC tracking model to determine the potential fates of tDOC exported from three primary drainage basins in the Gulf of Maine (GoM). According to our findings, over half a year in the GoM, 56.4% of tDOC was mineralized. Biomineralization was responsible for 90% of that amount, with the remainder attributed to photomineralization. Additionally, 37% of the tDOC remained suspended in the GoM, and 6.6% was buried in the marine sediment.

Selective extraction of levoglucosan and its isomers from complex matrices using ligand exchange-solid phase extraction for analysis by liquid chromatography-electrospray ionization-tandem mass spectrometry

The analysis of trace quantities of monosaccharide anhydrides (MAs) in sediments is complicated by the lack of fast and reliable technologies to selectively extract these water-soluble non-ionic compounds from samples of complex composition. Here we describe a solid phase extraction method that takes advantage of the affinity between monosaccharide anhydrides (MAs) and immobilized Na⁺ ions related to ligand-exchange processes (LE-SPE). The capacity factor of LE-SPE columns was enhanced by using non-aqueous mobile phases such as DCM/MeOH mixtures. We have used the unique properties of LE-SPE columns to selectively extract MAs from lacustrine, coastal, and deep-sea oceanic sediment samples. The analytical procedure produces extracts with low ion suppression effects (0-20%), resulting in ideal conditions for MAs quantification with LC-ESI-MS/MS systems irrespective of the sedimentary matrix and MAs concentration. The analytical method yields repeatable concentration values (RSD of 9-23% for levoglucosan and 15-34% for mannosan and galactosan) and an IS recovery of 45-70%. The instrumental dynamic range is 10-10000 pg injected, but in practice, the methodological lower limit of quantification is constrained by sample contamination during processing. The combination of LE-SPE and LC-ESI-MS/MS has the potential to produce sensitive and reliable technologies to analyze saccharides and amino acids in environmental and biological samples.

Effect of leaching time on phytotoxicity of dissolved organic matter derived from black carbon based on spectroscopy

Black carbon (BC) exports huge amounts of its derived DOM from terrestrial ecosystems annually through a variety of ways (i.e., erosion or runoff migration). The pyrolytic feedstock type and temperature resulted in DOM derived from highly condensed aromatic and non-aromatic BC. However, the behaviors of low aromatic BC-derived DOM at diverse leaching time are poorly understood. In this work, low aromatic BCs were prepared by pyrolysis corn straws at 250 °C, 350 °C and 450 °C. Extraction experiments for four leaching time (6 h, 10 h, 15 h and 21 h) were set up to simulate BC-derived DOM generative process in nature. The phytotoxicity of BC-derived DOM was evaluated via germination index (GI). Spectral characteristics were discussed to analyze the phytotoxicity variations of fluorescence components composition at different time, including the excitation-emission matrix-parallel factor, two-dimensional correlation spectra and Fourier transform infrared spectroscopy. The results suggested that low aromatic BC-derived DOM might contain aromatic phenolic compounds. A longer time contributed to accumulate the complex, hard-to-use organic matters, leading to lower GI. These results would supplement the dynamic spectral characteristics of low aromatic BC-derived DOM and its environmental risks during the leaching process.