Ongoing and amplified climate change in the Arctic is leading to glacier retreat and to the exposure of an ever-larger portion of non-glaciated permafrost-dominated landscapes. Warming will also cause more precipitation to fall as rain, further enhancing the thaw of previously frozen ground. Yet, the impact of those perturbations on the geochemistry of Arctic rivers remains a subject of debate. Here, we determined the geochemical composition of waters from various contrasting non-glacial permafrost catchments and investigated their impact on a glacially dominated river, the Zackenberg River (Northeast Greenland), during late summer (August 2019). We also studied the effect of rainfall on the geochemistry of the Zackenberg River, its non-glacial tributaries, and a nearby independent non-glacial headwater stream Gr ae nse. We analyzed water properties, quantified and characterized dissolved organic matter (DOM) using absorbance and fluorescence spectroscopy and radiocarbon isotopes, and set this alongside analyses of the major cations (Ca, Mg, Na, and K), dissolved silicon (Si), and germanium/silicon ratios (Ge/Si). The glacier-fed Zackenberg River contained low concentrations of major cations, dissolved Si and dissolved organic carbon (DOC), and a Ge/Si ratio typical of bulk rock. Glacial DOM was enriched in protein-like fluorescent DOM and displayed relatively depleted radiocarbon values (i.e., old DOM). Non-glacial streams (i.e., tributaries and Gr ae nse) had higher concentrations of major cations and DOC and DOM enriched in aromatic compounds. They showed a wide range of values for radiocarbon, Si and Ge/Si ratios associated with variable contributions of surface runoff relative to deep active layer leaching. Before the rain event, Zackenberg tributaries did not contribute notably to the solute export of the Zackenberg River, and supra-permafrost ground waters governed the supply of solutes in Zackenberg tributaries and Gr ae nse stream. After the rain event, surface runoff modified the composition of Gr ae nse stream, and non-glacial tributaries strongly increased their contribution to the Zackenberg River solute export. Our results show that summer rainfall events provide an additional source of DOM and Si-rich waters from permafrost-underlain catchments to the discharge of glacially dominated rivers. This suggests that the magnitude and composition of solute exports from Arctic rivers are modulated by permafrost thaw and summer rain events. This event-driven solute supply will likely impact the carbon cycle in rivers, estuaries, and oceans and should be included into future predictions of carbon balance in these vulnerable Arctic systems.

Soil organic carbon (SOC) rapidly accumulates during ecosystem primary succession in glacier foreland. This makes it an ideal model for studying soil carbon sequestration and stabilization, which are urgently needed to mitigate climate change. Here, we investigated SOC dynamics in the Kuoqionggangri glacier foreland on the Tibetan Plateau. The study area along a deglaciation chronosequence of 170-year comprising three ecosystem succession stages, including barren ground, herb steppe, and legume steppe. We quantified amino sugars, lignin phenols, and relative expression of genes associated with carbon degradation to assess the contributions of microbial and plant residues to SOC, and used FT-ICR mass spectroscopy to analyze the composition of dissolved organic matter. We found that herbal plant colonization increased SOC by enhancing ecosystem gross primary productivity, while subsequent legumes development decreased SOC, due to increased ecosystem respiration from labile organic carbon inputs. Plant residues were a greater contributor to SOC than microbial residues in the vegetated soils, but they were susceptible to microbial degradation compared to the more persistent and continuously accumulating microbial residues. Our findings revealed the organic carbon accumulation and stabilization process in early soil development, which provides mechanism insights into carbon sequestration during ecosystem restoration under climate change.

Microplastics (MPs) affect the carbon cycle in coastal salt marsh soils. However, studies on their effects on CHCl3 and CHBr3, which are volatile halohydrocarbons that can damage the ozone layer, are lacking. In this study, indoor simulation experiments were conducted to explore the effects of MPs invasion on the source and sink characteristics of soil CHCl3 and CHBr3. The results showed that different concentrations of polyethylene (PE)MPs promoted CHCl3 and CHBr3 emissions. Emission peaks of the two gases appeared on days 3 and 15 during the culture cycle. CHCl3 and CHBr3 fluxes were mainly affected by soil physicochemical properties and microbial communities. PE-MPs caused changes in soil properties, microorganisms, and related functional genes. Soil total organic carbon, which was significantly and positively correlated with CHCl3. Dissolved organic matter, which was one of the main factors affecting CHBr3, its relative content increased after the addition of PE-MPs. The abundances of Methylocella and Dehalococcoides, which mediate dechlorination reduction, decreased with the addition of PE-MPs. The addition of PE-MPs also significantly varied the abundance of ctrA, which controls dechlorination in soil microorganisms. The gene pceA greatly influenced CHCl3 emissions. In addition, CHBr3 flux was influenced by the interactions between sediment redox and microbial co-metabolic reactions under the control of genes such as TC.FEV.OM and soxB. This study provides theoretical and data support for the source and sink characteristics of volatile halohydrocarbons in coastal salt marshes and highlights the environmental hazards of MPs.

Anthropogenic activities such as the over-application of road deicers are causing an increase in the concentration of salts in historically fresh waters. Experimental and field investigations demonstrate that freshwater salinization disrupts ecosystem functions and services, causing the death of freshwater organisms and changes to nutrient conditions. Wetland habitats are one system negatively affected by salt pollution, including ephemeral wetlands (vernal pools) that fill with salt-polluted water after snowmelt. In urbanized areas, the degradation of these ecosystems could result in irreversible ecological damage including reduced water quality and a reduction in biodiversity. To investigate the effects of freshwater salinization on vernal pool communities, we exposed soils from vernal pools to water containing no salt (control), or four concentrations of three salts standardized by chloride concentration (50 mg Cl- L-1, 100 mg Cl- L-1, 200 mg Cl- L-1, and 400 mg Cl- L-1; magnesium chloride, calcium chloride, and sodium chloride). The results of this experiment suggest that emerging zooplankton communities in vernal pools are sensitive to low concentrations of salt pollution, and that alternative salts such as magnesium chloride and calcium chloride are more toxic than sodium chloride. We did not find positive or negative changes in the abundance of eukaryotic phytoplankton but did find negative effects of salt on cyanobacteria abundance, possibly due to corresponding reductions in turbidity which might be needed as a fixation site for cyanobacteria to form heterocysts. Finally, we found that salt pollution likely caused flocculation of Dissolved Organic Matter (DOM), resulting in reduced concentrations of DOM which could alter the buffering capacity of freshwater systems, light attenuation, and the populations of planktonic heterotrophs.

The ecological risks of biochar-derived dissolved organic matter (DOM) to soil invertebrates at different organismal levels remains limited. This study comprehensively explored the ecological risks of biochar-derived DOM on earthworm gut through assessments of enzyme activity response, histopathology, gut microbiomes, and metabolomics. Results demonstrated that DOM disturbed the digestive enzymes in earthworm, especially for 10% DOM300 groups. The integrated biomarker response v2 (IBRv2) indicated that the perturbation of earthworm digestive enzymes induced by DOM was both time-dependent and dose-dependent. Pathological observations revealed that 10% DOM300 damaged intestinal epithelium and digestive lumen of earthworms. The significant damage and injury to earthworms caused by DOM300 due to its higher concentrations of heavy metal ions and organic substrates (e.g., toluene, hexane, butanamide, and hexanamide) compared to DOM500 and DOM700. Analysis of 16S rRNA from the gut microbiota showed a significant decrease in genera (Verminephrobacter, Bacillus, and Microbacteriaceae) associated with inflammation, disease, and detoxification processes. Furthermore, 10% DOM300 caused the abnormality of metabolites, such as glutamate, fumaric acid, pyruvate, and citric acid, which were involved in energy metabolism, These findings contributed to improve our understanding of the toxic mechanism of biochar DOM from multiple perspectives.

Climate warming is predicted to change the fluxes of dissolved organic matter and nitrate by increasing active layer thickness, plant productivity, and organic matter decomposition. These changes are hypothesized to in-crease mineral weathering and soil acidification rates. We investigated whether acidification rates and solute leaching fluxes are variable between permafrost-affected soils with different active layer thicknesses. We compared the fluxes of dissolved organic carbon (DOC) and total dissolved N and the ion fluxes associated with solute leaching and plant uptake to calculate proton budgets in the soils that differed in slope positions (upper slope and lower slope) and soil texture (clayey and sandy soils) in NW Canada. We found the wide variation in DOC and nitrate-N fluxes, depending on slope positions and soil texture. The nitrate-N fluxes were higher at the lower slope position of the sandy soil, compared to the upper slope position. Compared to sandy soils, the DOC fluxes from the organic horizons were higher in the clayey soils on shallower permafrost table. Organic acids were major proton sources in the organic horizons at all sites, but acidity was also contributed by nitrate (sandy and clayey soils at lower slope position) and carbonic acid (clayey soil at upper slope position). The weathering by carbonic acid lead to accumulation of short-range-order minerals in the clayey soils, while incipient podzolization of the sandy soils included the weathering of illite to vermiculite and the dissolution of short-range-order minerals. The shallower active layer thickness at the lower slope position resulted in lower plant productivity and acidification rates. In the permafrost-affected soils, the active layer thickness, the DOC and nitrate-N fluxes, and their contribution to acidification are dependent on the local variation in slope position and soil texture, as well as climate change.

Accelerated melting of mountain glaciers due to global warming has a significant impact on downstream biogeochemical evolution because a large amount of labile dissolved organic matter (DOM) is released. However, the DOM evolution processes from glacier to downstream are not well understood. To investigate these processes, samples from the glacial surface and terminating runoff of a mountain glacier on the Tibetan Plateau were collected simultaneously throughout the melting season. The samples were analyzed to determine the dissolved organic carbon (DOC) contents and chemical compositions by means of a combination of fluorescence excitation-emission matrix coupled with parallel factor analysis (EEM-PARAFAC) and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). The results indicate that the DOC concentrations were higher in the snow samples than in the glacial runoff samples, although a significantly higher concentration of inorganic ions was found in the glacial runoff samples, suggesting the dominant source of DOM in the glacial runoff was the glacier. The EEM-PARAFAC revealed four fluorescent components in both the snow and glacial runoff samples. However, significantly different ratios between the four components of these two categories of samples suggested chemical, physical and/or biological evolution of DOM during transport. Molecular chemical composition analyses by FT-ICR MS revealed that the DOM composition varied dramatically between the glacier and the glacial runoff. More than 50 % of the molecules were transformed from aliphatic and peptide-like compounds in the snow samples into highly unsaturated and phenolic-like compounds in the glacial run-off samples. The potential chemical transformation of DOM was likely related to biological and/or photolytic evolution during transport. Our results suggest that chemical evolution of glacial DOM could occur during the downstream transport, which is expected to be useful for further research exploring the fate of DOM and carbon cycling from the ciyaspheric environment and evaluating the biogeochemical effects.

Climate change is dramatically altering Arctic ecosystems, leading to shifts in the sources, composition, and eventual fate of riverine dissolved organic matter (DOM) in the Arctic Ocean. Here we examine a 6-year DOM compositional record from the six major Arctic rivers using Fourier-transform ion cyclotron resonance mass spectrometry paired with dissolved organic carbon isotope data (Delta C-14, delta C-13) to investigate how seasonality and permafrost influence DOM, and how DOM export may change with warming. Across the pan-Arctic, DOM molecular composition demonstrates synchrony and stability. Spring freshet brings recently leached terrestrial DOM with a latent high-energy and potentially bioavailable subsidy, reconciling the historical paradox between freshet DOM's terrestrial bulk signatures and high biolability. Winter features undiluted baseflow DOM sourced from old, microbially degraded groundwater DOM. A stable core Arctic riverine fingerprint (CARF) is present in all samples and may contribute to the potential carbon sink of persistent, aged DOM in the global ocean. Future warming may lead to shifting sources of DOM and export through: (1) flattening Arctic hydrographs and earlier melt modifying the timing and role of the spring high-energy subsidy; (2) increasing groundwater discharge resulting in a greater fraction of DOM export to the ocean occurring as stable and aged molecules; and (3) increasing contribution of nitrogen/sulfur-containing DOM from microbial degradation caused by increased connectivity between groundwater and surface waters due to permafrost thaw. Our findings suggest the ubiquitous CARF (which may contribute to oceanic carbon sequestration) underlies predictable variations in riverine DOM composition caused by seasonality and permafrost extent.

Organic matter, upon dissolution into the aqueous state as dissolved organic matter (DOM), can undergo mineralization by microbes. There has been increasing effort to characterize DOM released from thawing permafrost because it may perpetuate a permafrost carbon feedback. Permafrost-derived DOM often has a composition that can be highly susceptible to mineralization by microbes, but most studies to date that characterize permafrost-derived DOM have been limited to select regions, and tend to focus on a single type of permafrost (sometimes unspecified) that reflects a particular deposit type. Importantly, diversity in the nature of the deposit, formation of permafrost, and thaw modification processes leads to spatial and stratigraphic variability in its properties, but our understanding of variation in the composition of DOM derived from differing permafrost types (end-members) is poor. Here, we used ultrahigh-resolution mass spectrometry to characterize DOM composition derived from a series of permafrost end-member types that are commonly found within the thaw-vulnerable western Canadian Arctic, including: tills (glacially deposited), diamicton (thawed and remobilized material of mixed origin), lacustrine (lake basin sediments into which permafrost has aggraded), peat (partially decomposed organic material), and Yedoma (syngenetic silty loess) deposits. We identified marked variation in DOM composition among permafrost end-member types. Tills were compositionally dissimilar to all other permafrost end-members. Compounds unique to Yedoma were predominantly aliphatic, while compounds unique to peat, lacustrine, and diamicton spanned saturation and oxygenation gradients. All permafrost leachates were generally higher in aliphatics, lower in aromatics, and less oxygenated than active layer leachates. Compositional differences appear to reflect variation in permafrost parent materials, and particularly strong effects from past modification processes while in the unfrozen or thawed state. Constraining DOM composition and assessing its stratigraphic variability will become more pressing as the spatial and stratigraphic extent of thaw increases with future warming.

Recent studies have revealed the abundance of dissolved organic matter (DOM) in snow/glaciers of the Tibetan Plateau (TP). Here, we present a comprehensive study on the chemical compositions of snowpit samples collected from widely distributed eight glaciers in the western China (six from the TP) to investigate the spatial variation of deposited atmospheric aerosols. An Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) was used to chemically characterize the DOM in snow samples which can offer chemical properties of DOM. Highest mass concentration of dissolved species mass was observed in Tienshan Baishui No 1 glacier (TS, 6.55 +/- 0.85 mg/L) close to Takalamagan Desert, whereas lowest (0.89 +/- 0.18 mg/L) was observed in Zadang Glacier (ZD) in the central TP. DOM (8-40%) and calcium as well as magnesium (9-67%) were generally the most abundant chemical species. Average DOM concentration in the TP glaciers among the investigated sites were comparable. DOM was found highly oxidized with an oxygen to carbon ratio (O/C ratio) ranging from 0.82 to 1.03. Highly oxidized DOM could have related with aerosol aqueous processes as illustrated by observed organic acids. This study provides insights into the spatial variations of the DOM and dissolved inorganic matter, as well as oxidized organic aerosol, were most likely due to local and regional contribution. (C) 2019 Elsevier B.V. All rights reserved.