Dissolved Organic Matter Processing in Pristine Antarctic Streams

Accelerated glacier melt and runoff may lead to inputs of labile dissolved organic matter (DOM) to downstream ecosystems and stimulate the associated biogeochemical processes. However, still little is known about glacial DOM composition and its downstream processing before entering the ocean, although the function of DOM in food webs and ecosystems largely depends on its composition. Here, we employ a set of molecular and optical techniques (UV–vis absorption and fluorescence spectroscopy, 1H NMR, and ultrahigh-resolution mass spectrometry) to elucidate the composition of DOM in Antarctic glacial streams and its downstream change. Glacial DOM consisted largely of a mixture of small microbial-derived biomolecules. 1H NMR analysis of bulk water revealed that these small molecules were processed downstream into more complex, structurally unrecognizable molecules. The extent of processing varied between streams. By applying multivariate statistical (compositional data) analysis of the DOM molecular data, we identified molecular compounds that were tightly associated and moved in parallel in the glacial streams. Lakes in the middle of the flow paths enhanced water residence time and allowed for both more DOM processing and production. In conclusion, downstream processing of glacial DOM is substantial in Antarctica and affects the amounts of biologically labile substrates that enter the ocean

Occurrence of arsenic in the riverbed sediments of the Selenga river system

Over the past few decades, anthropogenic activities have concentrated in the transboundary Selenga River basin, especially in the two-thirds of it located in the Mongolian territory. In this study, we measure the concentration of arsenic (As) in riverbed sediments and the mobilization and accumulation of this metalloid in sediments of the Selenga River system. Higher concentrations of As were detected in the sediments collected from the Orkhon River system than those from downstream of Selenga River in Russia. The observed difference indicates that the Orkhon River watershed is highly affected by anthropogenic activities involving soil excavation. In particular, high concentrations of As (3.6-4.9 mg kg^), in comparison with the average for the entire Selenga River system (2.8 mg kg^), were detected in sediment samples collected downstream of gold mining areas and near Darkhan City. Around this city, As pollution might be related to the combustion of coal with high As content. Gold mining is a main source of As pollution in rural areas. Notably, the content of fine fractions in sediment samples collected downstream of the Zaamar mining area was half that measured in samples collected upstream of it. However, no correlation was observed between As concentration and fine particle content in sediment samples collected throughout the whole research area, suggesting that the proportion of fine particle sediments is not a controlling factor in As distribution in the riverbed. Heavy and coarse particles released by mining sites seem to quickly deposit on the riverbed near their source. However, fine particles can co-precipitate at river junctions due to changes in water quality. These deposition processes can limit the extent to which As pollution can spread in a large area, but redissolution of As from secondary minerals is now recognized as a key factor in the widespread groundwater As contamination observed around the world

Spatial variations in the molecular diversity of dissolved organic matter in water moving through a boreal forest in eastern Finland

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Characterization of volcanic ash soils in southwestern Tanzania: Morphology, physicochemical properties, and classification

This study examined the characteristics of volcanic ash soils in southwestern Tanzania. Twelve pedons of volcanic origin were studied, and 66 soil samples were analyzed. Soil morphology revealed volcanic ash layers of varying thicknesses. Most pedons had a dark thick humus surface and buried A, AB, and BA horizons with melanic indices of 1.7 or less. Except in two pedons, the NaF pH was 9.4 or more, reflecting an exchange complex dominated by amorphous materials and/or Al–humus complexes. The phospate-retention capacity ranged from 65 to 100%, except in two pedons, and was positively correlated with NaF pH. Both Tanzanian and Japanese volcanic ash soils showed comparable ranges of base saturation (BS) values, but the distribution patterns of BS basic cations, for example, showed some differences. Some Tanzanian volcanic ash soils had higher BS values than their Japanese counterparts. While the Japanese soils were generally more calcic and magnesic, the Tanzanian soils were more potassic and sodic than their counterparts, most likely reflecting lithological differences among parent materials in the two study areas. According to the USDA Soil Taxonomy, nine pedons satisfied the requirements for andic properties and were classified as Andisols at the order level, whereas according to FAO World Reference Base (WRB) soil classification, eight pedons were classified as Andosols at the level of reference soil groups

Dissolved organic matter composition in Antarctic streams (Sôya Coast, Lützow-Holm Bay, East Dronning Maud Land, East Antarctica) derived from FT-ICR-MS analyses during JARE58

The sampling campaign was conducted during the austral summer in January 2017 as a part of the 58th Japanese Antarctic Research Expedition. There are several ice-free areas on Sôya Coast with hundreds of lakes and several streams, which were formed during the last 7,000 years under the glacier retreat and iso-static uplifts that occurred after the Last Glacial Maximum. The Langhovde ice-free area is located ~25 km away from Japan's Syowa Station. The Yukidori and Yatsude Valleys in Langhovde run from the edge of the continental ice sheet to Lutzow-Holm Bay. At each stream of the valleys, water samples were directly collected into 550-mL volume polyethylene terephthalate bottles after rinsing more than three times with the collected water. The collected waters were filtered in a field laboratory within a few hours after sampling. Samples were filtered through pre-combusted (450dc, >3 h) glass-fiber filters (nominal pore size 0.3mm, GF-75, Advantec, Tokyo, Japan) into pre-combusted glass bottles (see doi:10.1016/J.WATRES.2019.114901). The filtered samples were immediately spiked with sodium azide (final concentration of 0.02%) for preservation, stored dark at 5dc, and shipped back to Japan. DOM was extracted and desalted prior to FT-ICR MS analysis following an established method using cartridges filled with a styrene-divinylbenzene copolymer (Agilent Bond Elut PPL, 100 mg). Depending on the DOC concentration, the volume used for extraction was adjusted such that 4 µmol C was applied to each cartridge. We performed a mass spectrometric analysis of DOM extracts via FT-ICR MS on a 15 Tesla solariX XR Fourier-transform ion cyclotron resonance mass spectrometer (Bruker Daltonik GmbH, Bremen, Germany). The system was equipped with an electrospray ionization source (ESI, Bruker Apollo II) applied in negative ionization mode. Methanol extracts were mixed with ultrapure water (50:50 v/v) for FT-ICR MS analysis and diluted to a final DOC concentration of 2.5 mg C/L. 200 single scans with an ion accumulation time of 0.1 s were recorded over a mass range of m/z 92 to 2,000 Da and added to one spectrum. Data processing, molecular formulae assignments, and compound category classifications were done with the software package ICBM-OCEAN

Molecular formulae assignments and compound category classifications from the 58th Japanese Antarctic Research Expedition

The sampling campaign was conducted during the austral summer between December 2016 and February 2017 as a part of the 58th Japanese Antarctic Research Expedition. On Sôya Coast (Lützow-Holm Bay, East Dronning Maud Land, East Antarctica), there are hundreds of lakes with variable water chemistry which were formed during the last 7,000 years under the glacier retreat and iso-static uplifts that occurred after the Last Glacial Maximum. Water samples were collected either at the center of the lakes or at the shore into 550-mL PET bottles after rinsing more than three times with the collected water. Within a few hours after sampling, samples were filtered through pre-combusted (450dc, >3 h) glass-fiber filters (nominal pore size 0.3mm, GF-75, Advantec, Tokyo, Japan) into pre-combusted glass bottles (see doi:10.1016/J.WATRES.2019.114901). The filtered samples were immediately spiked with sodium azide (final concentration of 0.02%) for preservation, stored dark at 5dc, and shipped back to Japan. DOM was extracted and desalted prior to FT-ICR MS analysis following an established method using cartridges filled with a styrene-divinylbenzene copolymer (Agilent Bond Elut PPL, 100 mg). Depending on the DOC concentration, the volume used for extraction was adjusted such that 4 µmol C was applied to each cartridge. We performed a mass spectrometric analysis of DOM extracts via FT-ICR MS on a 15 Tesla solariX XR Fourier-transform ion cyclotron resonance mass spectrometer (Bruker Daltonik GmbH, Bremen, Germany). The system was equipped with an electrospray ionization source (ESI, Bruker Apollo II) applied in negative ionization mode. Methanol extracts were mixed with ultrapure water (50:50 v/v) for FT-ICR MS analysis and diluted to a final DOC concentration of 2.5 mg C/L. 200 single scans with an ion accumulation time of 0.1 s were recorded over a mass range of m/z 92 to 2,000 Da and added to one spectrum. Data processing, molecular formulae assignments, and compound category classifications were done with the software package ICBM-OCEAN