Biogeochemical Cycling Of Elements Research Articles

Interannual Variability of Marine Nitrogen Fixation in the Western Tropical Atlantic

AbstractN2 fixation is a central process of the marine nitrogen cycle, yet little is known about how this process varies from year‐to‐year. Here, we investigate this variability in the Western Tropical Atlantic (WTA), a region where N2 fixation is prevalent, fueled, in part, by the nutrient input from the Amazon River. We use hindcast simulations from 1983 through 2019 with the Regional Oceanic Modeling System (ROMS) coupled to the Biogeochemical Elemental Cycling (BEC) model expanded to include Diatom‐Diazotroph Assemblages (DDAs). Throughout the WTA, we find a substantial level of interannual variability of N2 fixation, altering it by up to 33%, and locally by up to nearly 60%. Part of this interannual variability is driven by variations in the Amazon River discharge, which during high discharge events leads to reduced rates in the upper parts of the plume and strongly enhanced rates in the downstream part. This dipole pattern is a consequence of the riverine inputs of phosphorus and the competition with non‐diazotrophs for this limiting resource. Another part of the N2 fixation variability is driven by the Atlantic Meridional Mode (AMM), and the El Niño‐Southern Oscillation (ENSO). These processes alter N2 fixation primarily through the supply of the limiting nutrients phosphorus and iron by vertical mixing, while the role of top‐down control through grazing is relatively limited in our model. The high, and so far not well recognized interannual N2 fixation variability can lead to erroneous extrapolation of field measurements and inaccuracies in the marine nitrogen budget, if unaccounted for.

Biological and paleoceanographic controls on the postglacial sulfur isotope records in Arctic shelf sediments

The Arctic Ocean has experienced environmental fluctuations during the Pleistocene glacial-interglacial cycles. Since the last deglaciation, the reinundation of the Bering Strait and regional transgression have led to dramatic changes in the western Arctic Ocean, affecting coastal landscapes, depositional processes, marine ecosystem, and, inherently, biogeochemical element cycles. Here, we investigate the records of sulfur, carbon, and iron cycles in the Chukchi Sea of the western Arctic, with a primary focus on microbial sulfate reduction and subsequent pyrite formation. Variations in the pyrite abundance and sulfur isotopic composition, derived from a 10-m sediment core, demonstrate that dynamic changes in the factors governing pyrite formation – organic electron donor, reactive iron, and sulfate – are closely linked to the regional environmental conditions. In the early Holocene sediment, pyrite precipitation was impeded by the lack of organic matter, even in the presence of abundant sulfate and reactive iron. In the overlying sediment, pyrite contents increased due to vigorous microbial sulfate reduction fueled by enhanced availability of organic substrate and additional methane from the sulfate-methane transition zone. In general, the increased supply of organic matter to the Chukchi Shelf sediments can be attributed to the resumed inflow of nutrient-rich Pacific Water through the flooded Bering Strait. The increase in pyrite content, however, does not correlate exactly with either the increase in TOC or the opening of the Bering Strait, both of which precede the increased pyrite formation. These lags reflect the balance between marine primary production and terrestrial carbon sources, as well as the balance between the Pacific Inflow and the Beaufort Gyre. While a comparable increase in pyrite and TOC contents during the Holocene deglaciation has also been reported in the Black and Baltic Sea sediments, their distinct sulfur isotope records, contingent upon the availability of sulfate and reactive iron, highlight that pyrite can serve as a valuable proxy for tracking past climate and environmental change, especially in barren sedimentary records such as those found in the Arctic Ocean.

Strong associations between dissolved organic matter and microbial communities in the sediments of Qinghai-Tibetan Plateau lakes depend on salinity

In aquatic ecosystems, dissolved organic matter (DOM) plays a vital role in microbial communities and the biogeochemical cycling of elements. However, little is known about the associations between DOM and microbial communities in lake sediments. This study investigated the composition of water-extractable organic matter and microbial communities in surface sediments of lakes with different salinities on the Qinghai-Tibet Plateau. Ultrahigh-resolution mass spectrometry and high-throughput microbial sequencing techniques were employed to assess the associations between molecular diversity and microbial diversity and the effects of salinity in 19 lakes spanning a salinity range from 0.22 ‰ to 341.87 ‰. Our results show that increasing salinity of lake water led to higher molecular diversity of DOM in surface sediments. High-salinity lakes exhibited distinct DOM characteristics, such as lower aromaticity, smaller molecular weight, and higher oxidation degree, compared to freshwater lakes. The complexity of the microbial network composition of sediments first increased and then decreased with the increase of salinity. Moreover, as salinity increases, the dominant species transitioned from Gammaproteobacteria to Bacteroidia, and this transition was accompanied by a decrease in microbial diversity and an increase in molecular diversity. Microbial factors accounted for 34.68 % of the variation in the molecular composition of DOM. Overall, this study emphasizes the significant effects of salinity on both molecular and microbial diversity in lake sediments. Furthermore, our findings underscore the importance of microbes in controlling the range of organic compounds present in lakes and deepen our knowledge of the biogeochemical cycling of DOM.

Heterogeneous Coprecipitation of Nanocrystals with Metals on Substrates.

ConspectusThe heterogeneous coprecipitation of nanocrystals with metals on substrates plays a significant role in both natural and engineered systems. Due to the small dimensions and thereby the large specific surface area, nanocrystal coprecipitation with metals, which is ubiquitous in natural settings, exerts drastic effects on the biogeochemical cycling of metals on the earth's crust. Meanwhile, the controlled synthesis of nanocrystals with metal doping to achieve tunable size/composition enables their broad applications as adsorbents and catalysts in many engineered settings. Despite their importance, complex interactions among aqueous ions/polymers, nanocrystals, substrates, and metals are far from being well-understood, leaving the controlling mechanisms for nanocrystal formation with metals on substrates uncovered.In this Account, we discuss our systematic investigation over the past 10 years of the heterogeneous formation of representative nanocrystals with metals on typical substrates. We chose Fe(OH)3 and BaSO4 as representative nanocrystals. Mechanisms for varied metal coprecipitation were also investigated for both types of nanocrystals (i.e., Fe, Al, Cr, Cu, and Pb)(OH)3 and (Ba, Sr)(SO4, SeO4, and SeO3)). Bare SiO2 and Al2O3, as well as those coated with varied organics, were selected as geologically or synthetically representative substrates. Through the integration of state-of-the-art nanoscale interfacial characterization techniques with theoretical calculations, the complex interactions during nanocrystal formation at interfaces were probed and the controlling mechanisms were identified.For BaSO4 and Fe(OH)3 formation on substrates, the local supersaturation levels near substrates were controlled by Ba2+ adsorption and the electrostatic attraction of Fe(OH)3 monomer/polymer to substrates, respectively. Meanwhile, substrate hydrophobicity controlled the interfacial energy for the nucleation of both nanocrystals on (in)organic substrates. Metal ions' (i.e., Cr/Al/Cu/Pb) hydrolysis constants and substrates' dielectric constants controlled metal ion adsorption onto substrates, which altered the surface charges of substrates, thus controlling heterogeneous Fe(OH)3 nanocrystal formation on substrates by electrostatic interactions. The sizes and compositions of heterogeneous (Fe, Cr)(OH)3 and (Ba, Sr)(SO4, SeO4, SeO3) formed on substrates were found to be distinct from those of homogeneous precipitates formed in solution. The substrate (de)protonation could alter the local solution's pH and the substrates' surface charge; substrates could also adsorb cations, affecting local Fe/Cr/Ba/Sr ion concentrations at solid-water interfaces, thus controlling the amount/size/composition of nanocrystals by tuning their nucleation/growth/deposition on substrates. From slightly supersaturated solution, homogeneous coprecipitates of microsized (Ba, Sr)(SO4, SeO4, SeO3) formed through growth, with little Sr/Se(VI) incorporation due to higher solubilities of SrSO4 and BaSeO4 over BaSO4. While cation enrichment near substrates made the local solution highly supersaturated, nanosized coprecipitates formed on substrates through nucleation, with more Sr/Se(VI) incorporation due to lower interfacial energies of SrSO4 and BaSeO4 over BaSO4. The new insights gained advanced our understanding of the biogeochemical cycling of varied elements at solid-water interfaces and of the controlled synthesis of functional nanocrystals.

Effect of the antibiotic tetracycline on structural-functional characteristics of coccolithophore Chrysotila sp. and the degree of its calcification

Coccolithophorids play a fundamental role in the marine carbon cycle, fixing inorganic carbon during photosynthesis and exporting CO2 during calcification. In the presented study, the toxic effect of tetracycline on coccolithophorids of Chrysotila sp. was evaluated and the possibility of removing the antibiotic from water using this microalga was investigated. Tetracycline at a concentration of 1–15 mg L−1 had no effect on the growth of Chrysotila sp. and at higher values (20–25 mg L−1) it stimulated the growth of the algae. As the concentration of tetracycline increased, a tendency to decrease the percentage of coccolith-covered cells in the culture was observed. At the same time, the growth of Chrysotila sp. was realized mainly at the expense of uncovered coccoliths cells, the number of covered cells changed insignificantly. Coccolith- covered and uncovered Chrysotila sp. cells showed different physiological responses to antibiotic addition. Calcified cells are more sensitive to tetracycline, which is expressed in an increase in their size and a decrease in granularity, a decrease in specific chlorophyll fluorescence and enzymatic (esterase) activity, and an increase in the production of reactive oxygen species. Reduction of cell calcification under exposure to pollutants is potentially dangerous by changes in the biogeochemical cycle of nutrient elements in the aquatic ecosystem.It is shown that the main mechanism of tetracycline removal from water is photodegradation. However, in the presence of Chrysotila sp. the rate of tetracycline degradation is significantly higher (by 7–15%) than in samples without algae.

Dynamic Changes of Dissolved Organic Matter Derived from Algal Decomposition and the Environmental Effects in Eutrophic Lakes

The global occurrences of lake eutrophication have led to algal bloom and the subsequent algal decomposition, releasing high amounts of algae-derived dissolved organic matter (DOM) into the lake water. Algae-derived DOM could regulate the quantity and composition of DOM in lake water and further impact the biogeochemical cycles of multiple elements. In this study, the dynamic changes in the quantity and quality of DOM during algal decomposition under different eutrophic scenarios (e.g., from oligotrophication to severe eutrophication) were monitored, and the corresponding environmental effects (e.g., microbial responses and greenhouse gas emissions) caused by algal decomposition were further explored. The results showed that algal decomposition significantly increased the DOM levels, bioavailability, and intensities of fluorescent components in the water. The total DOM levels gradually decreased, whereas the average molecular weight increased along the decomposition process. Furthermore, unsaturated hydrocarbon and aliphatic compounds were preferentially utilized by microorganisms during algal decomposition, and some refractory molecules (e.g., lignin, condensed hydrocarbons, and tannin with high O/C values) were synchronously generated, as evidenced by the results from ultra-high-resolution mass spectrometry. The dominant bacterial species during algal decomposition shifted from Proteobacteria (46%) to Bacteroidetes (42%). In addition, algae addition resulted in 1.2-5 times the emissions of CO2 and CH4 from water, and the emission rates could be well predicted by the optical index of a254 in water. This study provides comprehensive perspectives for understanding the environmental behaviors of aquatic DOM and further paves the ways for the mitigation of lake eutrophication.

Iron “ore” nothing: benthic iron fluxes from the oxygen-deficient Santa Barbara Basin enhance phytoplankton productivity in surface waters

Abstract. The trace metal iron (Fe) is an essential micronutrient that controls phytoplankton productivity, which subsequently affects organic matter cycling with feedback on the cycling of macronutrients. Along the continental margin of the US West Coast, high benthic Fe release has been documented, in particular from deep anoxic basins in the Southern California Borderland. However, the influence of this Fe release on surface primary production remains poorly understood. In the present study from the Santa Barbara Basin, in situ benthic Fe fluxes were determined along a transect from shallow to deep sites in the basin. Fluxes ranged between 0.23 and 4.9 mmol m−2 d−1, representing some of the highest benthic Fe fluxes reported to date. To investigate the influence of benthic Fe release from the oxygen-deficient deep basin on surface phytoplankton production, we combined benthic flux measurements with numerical simulations using the Regional Ocean Modeling System coupled to the Biogeochemical Elemental Cycling (ROMS-BEC) model. For this purpose, we updated the model Fe flux parameterization to include the new benthic flux measurements from the Santa Barbara Basin. Our simulations suggest that benthic Fe fluxes enhance surface primary production, supporting a positive feedback on benthic Fe release by decreasing oxygen in bottom waters. However, a reduction in phytoplankton Fe limitation by enhanced benthic fluxes near the coast may be partially compensated for by increased nitrogen limitation further offshore, limiting the efficacy of this positive feedback.

Invasion mechanism of Spartina alterniflora by regulating soil sulfur and iron cycling and microbial composition in the Jiuduansha Wetland.

Spartina alterniflora, an invasive plant widely distributed in China's coastal regions, has had a significant impact on the stability of wetland ecosystems and elemental biogeochemical cycles. The invasion of S. alterniflora has been found to lead to the accumulation of sulfides in the soil. The cycling of sulfur and iron in the soil is closely interconnected. Coastal estuarine wetlands are influenced by both freshwater in rivers and seawater tides, as well as the frequent variations in redox conditions caused by tidal fluctuations, which makes the cycling of sulfur and iron in the soil invaded by S. alterniflora more intricate. In this study, field surveys and laboratory experiments were conducted to explore the effects of S. alterniflora invasion and hydrological changes on the cycling of sulfur and iron as well as related functional microorganisms in the soil. The invasion of S. alterniflora showed an increase in soil reduced inorganic sulfur (RIS) components in both high and low marshes of Jiuduansha wetland, with higher content observed in summer and autumn. The tidal simulation experiments revealed abundant sulfate in seawater tidal conditions could promote the formation of acid volatile sulfides (AVS) in the soil of low marshes invaded by S. alterniflora and ensuring the continuous increase in AVS content. Diffusive gradients in-thin-films (DGT) technology indicated the existence of high-concentration soluble S2- enrichment zones in the soil of low marshes invaded by S. alterniflora, which may be related to S. alterniflora root exudates. Tidal action increased the relative abundance of sulfur-reducing bacteria (SRB) in the soil of low marshes, and under the influence of seawater tidal action, SRB exhibited higher relative abundance. However, S. alterniflora might inhibit the activity of iron-reducing bacteria (FeRB) in the soil of low marshes. In conclusion, S. alterniflora may enhance the sulfate reduction rate and promote the formation of free sulfides in tidal salt marsh ecosystems by releasing root exudates that stimulate the activity of SRB, while concurrently inhibiting the activity of FeRB and reducing their competition with SRB. This effect is particularly pronounced in low marshes under seawater tidal conditions. Thus, S. alterniflora is capable of rapidly invading tidal salt marshes by utilizing sulfides effectively.

Speciation and cycling of iodine in the subtropical North Pacific Ocean

Iodine intersects with the marine biogeochemical cycles of several major elements and can influence air quality through reactions with tropospheric ozone. Iodine is also an element of interest in paleoclimatology, whereby iodine-to-calcium ratios in marine carbonates are widely used as a proxy for past ocean redox state. While inorganic iodine in seawater is found predominantly in its reduced and oxidized anionic forms, iodide (I−) and iodate (IO3−), the rates, mechanisms and intermediate species by which iodine cycles between these inorganic pools are poorly understood. Here, we address these issues by characterizing the speciation, composition and cycling of iodine in the upper 1,000 m of the water column at Station ALOHA in the subtropical North Pacific Ocean. We first obtained high-precision profiles of iodine speciation using isotope dilution and anion exchange chromatography, with measurements performed using inductively coupled plasma mass spectrometry (ICP-MS). These profiles indicate an apparent iodine deficit in surface waters approaching 8% of the predicted total, which we ascribe partly to the existence of dissolved organic iodine that is not resolved during chromatography. To test this, we passed large volumes of seawater through solid phase extraction columns and analyzed the eluent using high-performance liquid chromatography ICP-MS. These analyses reveal a significant pool of dissolved organic iodine in open ocean seawater, the concentration and complexity of which diminish with increasing water depth. Finally, we analyzed the rates of IO3− formation using shipboard incubations of surface seawater amended with 129I−. These experiments suggest that intermediate iodine species oxidize to IO3− much faster than I− does, and that rates of IO3− formation are dependent on the presence of particles, but not light levels. Our study documents the dynamics of iodine cycling in the subtropical ocean, highlighting the critical role of intermediates in mediating redox transformations between the major inorganic iodine species.

A Young Scientist’s Perspective on GEOTRACES

GEOTRACES is an international endeavor to elucidate the biogeochemical cycles of trace elements and their isotopes in the ocean. Inherently, this interdisciplinary program provides ample opportunities for students to develop professional, academic, and seagoing skills. This perspective recalls first-hand experiences gained from five years in the GEOTRACES community, spanning undergraduate and graduate research, including international engagement in Germany and seagoing oceanography in the South Pacific and Southern Ocean. Description of these opportunities reveals the framework that makes the GEOTRACES program a success and the culture that will ensure its ongoing legacy.

Introduction to the special issue on twenty years of GEOTRACES: An international study of the marine biogeochemical cycles of trace elements and isotopes

This special issue of Oceanography celebrates the transformational findings of the international GEOTRACES program in chemical oceanography, 20 years after drafting of the GEOTRACES Science Plan in 2004 (GEOTRACES Planning Group, 2006). With the section cruise phase of the program ending soon, and a planned pivot toward smaller-​scale process studies, this is an opportune time to look back at the achievements of GEOTRACES during the last two decades and to highlight some of the advances in our understanding of the processes that determine the oceanic distributions of trace elements and isotopes (TEIs).

Ecological and geochemical features of mercury load on the territory of south of Western Siberia

Relevance. The need to study contribution of biogenic factors to migration of elements and response of ecological and geochemical system to natural and technogenic situation, which makes it possible to identify the presence of biogeochemical anomalies. Aim. To determine ecological and geochemical features of mercury load in the south of Western Siberia (Tomsk region, Kemerovo region, Altai Territory) according to research (leaves of aspen (Populus tremula L., family Salicaceae)). Objects. Aspen leaves, widely used to analyze the biogeochemical cycle of chemical elements and their migration in the "soil–plant" system, reflect the elemental composition of growing environment and can act as a biogeoindicator for biogeochemical studies. Methods. Sampling of aspen leaves, drying at room temperature, grinding, atomic absorption analysis of mercury on an RA-915M analyzer with the PIRO-915+ attachment (pyrolysis method). The application program STATISTICA 12 was used to process the data analysis and calculate eco-geochemical indicators: concentration factor, enrichment factor, bioaccumulation factor, concentration clarke. Results. The article presents original data on Hg gross concentration in aspen leaves in Tomsk, Kemerovo regions and Altai Territory. The authors have revealed the features of pollutant accumulation depending on the area of growth, geography and orography of the territory, geochemical features of the study areas, and the influence of anthropogenic factors. Calculations of the main geo-environmental indicators of the mercury load were made. The calculation results indicate that the concentrations are higher than the background, the Clarke of the noosphere, and the average for the dry matter of terrestrial plants. The presence of the element in the form available to plants was revealed in the substrate, as evidenced by the results of calculating the bioaccumulation coefficient. Geographically, Hg accumulation in aspen leaves in the south of Western Siberia is associated with the prevailing wind direction and the impact of anthropogenic sources.

Rapid diversification of a free-living protist is driven by adaptation to climate and habitat

Microbial eukaryotes (protists) have major functional roles in aquatic ecosystems, including the biogeochemical cycling of elements as well as occupying various roles in the food web. Despite their importance for ecosystem function, the factors that drive diversification in protists are not known. Here, we aimed to identify the factors that drive differentiation and, subsequently, speciation in a free-living protist, Synura petersenii (Chrysophyceae). We sampled five different geographic areas and utilized population genomics and quantitative trait analyses. Habitat and climate were the major drivers of diversification on the local geographical scale, while geography played a role over longer distances. In addition to conductivity and temperature, precipitation was one of the most important environmental drivers of differentiation. Our results imply that flushing episodes (floods) drive microalgal adaptation to different niches, highlighting the potential for rapid diversification in protists.

Geochemistry of dissolved rare earth elements in the Lancang River with cascade dams and implications for anthropogenic impacts

Anthropogenic effects like the construction of cascade dams are increasingly affecting the biogeochemical cycles of rare earth elements (REE) in rivers. However, our understanding on the REE compositions of dissolved loads in rivers under the effect of cascade dams remains limited. In this study, forty-four water samples in the Lancang River were analyzed for REE concentrations to assess the impact of cascade dams. The results showed that total dissolved REE concentrations ranged from 4.0 to 65.7 ng/L, with an average value of 21.8 ng/L. The concentrations in the middle (519.6 ng/L) and lower (331.5 ng/L) reaches were higher than those in the upper reaches (108.1 ng/L). All river samples showed (La/Yb)N values < 1, and the PAAS-normalized REE patterns indicated a substantial enrichment of heavy REE, characterized by negative Ce (0.1–0.9) and positive Eu (1.5–32.1) anomalies. The enrichment of heavy REE can be attributed to their preferential release from minerals during the weathering process and their interaction with inorganic complex anions. The negative Ce anomaly observed is likely the result of redox conditions, while the positive Eu anomaly was inherited from the REE characteristics of the source rocks. Moreover, the Ce anomaly decreased to 0.29 in the Huangdeng reservoir and 0.12 in the Dachaoshan reservoir. The value of Ce anomaly displayed a sharp decline in the middle and lower reaches affected by the cascade reservoirs. The effect of the dams played an important role in Ce anomaly by decreasing the DOC concentrations, and rivers with low DOC concentrations are commonly associated with negative Ce anomaly. This study revealed that cascade dams paly an essential role in the variation of REE in dissolved loads and REE anomaly may have the potential to track anthropogenic activities.

Local Biogeochemical Cycles of Trace Elements in Agroecosystems of Western Siberia

Local Biogeochemical Cycles of Trace Elements in Agroecosystems of Western Siberia

Local biogeochemical cycles of trace elements in agroecosystems of Western Siberia

The article presents the results of long-term field experiments (2005-2022) to study the distribution and migration of trace elements in the soil-plant-animal system on the example of agrocenoses of the southern forest-steppe of Western Siberia. A biogeochemical assessment of the content of trace elements (Pb, Cu, Zn, Ni, Cd, Cr, Se) in trophic chains under certain agroecological conditions is given. The analysis of geochemical factors affecting the accumulation of trace elements in various types of soils and plants growing on them has been carried out. Normative quantitative characteristics of the action of trace elements on the chemical composition of the soil, productivity and quality of plants of grain, fodder and vegetable crops have been established. The relationship of macro- and microelements when they enter plants is shown, depending on the level and ratio of chemical elements in the soil, the physiological needs of the plant organism at different stages of ontogenesis.The parameters of the intake of trace elements into the body of animals with plant food under the conditions of model experiments have been established. Structural and functional changes in animal organs during feeding with crop products grown with different content of trace elements are analyzed.

PHOTOCHEMICAL TRANSFORMATION OF DISSOLVED ORGANIC MATTER AND BEHAVIOR OF METALS IN THE WATERS OF THE SOUTHERN TAIGA BOG COMPLEX, WESTERN SIBERIA

Link for citation: Raudina T.V., Smirnov S.V., Istigechev G.I., Pokrovsky O.S. Photochemical transformation of dissolved organic matter and behavior of metals in the waters of the southern taiga bog complex, Western Siberia. Bulletin of the Tomsk Polytechnic University. Geo Аssets Engineering, 2023, vol. 334, no. 9, рр. 182-193. In Rus. The relevance. Dissolved organic matter is one of the largest biologically available sources of carbon in terrestrial and aquatic ecosystems, and its dynamics are critical to local and global carbon cycles. Destruction of organic matter during migration determines the biological cycle of elements and their stability. Important processes that lead to the transformation or removal of the dissolved organic matter are bio- and photodegradation. To date, enough research has been carried out to study the composition of humic substances, forms of metals, and the processes of migration of organo-mineral compounds in natural waters of the taiga zone, Western Siberia. Work is underway to study the dissolved organic carbon bioavailability, but the mechanisms of its photochemical transformations in different seasons of the year have not been studied. At the same time, photochemical mineralization of dissolved organic compounds largely regulates the biogeochemical cycles of elements by changing their bioavailability, the intensity of carbon dioxide emission from surface waters into the atmosphere, and the removal of dissolved trace elements through precipitation and coagulation. The main aim is to assess changes in the chemical composition and the rate of the dissolved organic matter and dissolved metals removal in the waters of the southern taiga bog complex (Western Siberia) under the sunlight exposure on a spatio-temporal scale. Objects: soil waters within different bog landscapes (open sedge-sphagnum fen, tall ryam (pine-shrub-sphagnum phytocenosis with high pine trees), and waterlogged mixed forest) of the Bakchar bog complex located in the southeastern part of the Ob-Irtysh interfluves, the Vasyugan plain. The waters were taken at a depth by digging a pit (40´40 cm area, 40 cm depth), which allowed the surrounding gravitational water to fill it up to the depth of 10–20 cm. The sampling took place during two field period in 2020 (June and October). Methods. pH, water temperature, specific conductivity (Cond) and dissolved oxygen were measured using a multiparameter instrument (WTW MULTI 3430 SET). The dissolved organic carbon was measured by a high-temperature thermic oxidation method using a Shimadzu TOC-LCPN analyzer, with an uncertainty of 2 %. The absorbance was measured at wavelengths up to 800 nm, 1 nm step using quartz 10 mm cuvette on a Cary-50 spectrophotometer. Major cations (Ca, Mg, Na, K), Si, and trace metals were determined with an ICP-MS Agilent CE 7500 with In and Re as internal standards and three various external ones. In the photodegradation experimental design, we followed the methodology which is sunlight exposure of sterile filtered (0,2 μm) samples in quartz reactors in the outdoor pool. Results. The authors revealed the influence of photodegradation on the qualitative and quantitative composition of dissolved organic substances and the behavior of metals in water samples of bog landscapes of the taiga zone of Western Siberia on spatiotemporal scales. It was established that from 3 to 30 % of the dissolved organic carbon can be removed from soil water under the influence of sunlight with maximum values in early June. At the same time, in autumn, despite the decrease in the amount of solar radiation, the photodegradable DOC can also reach 10–12 %. In general, there is a decrease in the percentage of the dissolved organic carbon loss in the waters in the row fen&gt;ryam&gt;forest. The dissolved organic carbon removal can be associated both with the transition of a part into an inorganic form, and with the destruction of high-molecular organic substances. A significant change (p&lt;0.05) in the optical parameters is noted, which is consistent with the behavior of the dissolved organic matter during photolysis. In addition, under the influence of insolation, the transformation of organo-mineral compounds occurs, which leads to a change in the forms of metals. The greatest losses relative to control were observed for rare earth elements (Y, La, Ce, Pr, Nd), as well as Ti, V, which in some cases reach 70 % (more significant in fen waters). These trace elements show behavior similar to dissolved organic carbon, Al and Fe, which confirms the importance of organic and organo-Fe-Al-colloids determining the behavior of most elements in acidic waters with a high content of organic matter.

Humic acid-dependent respiratory growth of Methanosarcina acetivorans involves pyrroloquinoline quinone.

Although microbial humus respiration plays a critical role in organic matter decomposition and biogeochemical cycling of elements in diverse anoxic environments, the role of methane-producing species (methanogens) is not well defined. Here we report that a major fraction of humus, humic acid reduction enhanced the growth of Methanosarcina acetivorans above that attributed to methanogenesis when utilizing the energy sources methanol or acetate, results which showed both respiratory and fermentative modes of energy conservation. Growth characteristics with methanol were the same for an identically cultured mutant deleted for the gene encoding a multi-heme cytochrome c (MmcA), results indicating MmcA is not essential for respiratory electron transport to humic acid. Transcriptomic analyses revealed that growth with humic acid promoted the upregulation of genes annotated as cell surface pyrroloquinoline quinone (PQQ)-binding proteins. Furthermore, PQQ isolated from the membrane fraction was more abundant in humic acid-respiring cells, and the addition of PQQ improved efficiency of the extracellular electron transport. Given that the PQQ-binding proteins are widely distributed in methanogens, the findings extend current understanding of microbial humus respiration in the context of global methane dynamics.

Development and validation of a real-time PCR assay protocol for the specific detection and quantification of pelagiphages in seawater samples

Earth is inhabited by numerous adaptations of cellular forms shaped by the persistent scrutiny of natural selection. Thus, as natural selection has fixed beneficial adaptations of functional traits, cellular life has conquered almost all environmental niches on our planet. However, cellular life succumbs in number and genetic diversity to viruses. Among all viruses, phages are highly prevalent in diverse environments, and due to their vast genetic diversity and abundance, their relevant role as significant players in several ecological processes is now fully recognized. Pelagiphages, bacteriophages infecting bacteria of the SAR11 clade, are the most abundant viruses in the oceans. However, the ecological contribution of pelagiphages on populations of Pelagibacterales remains largely underestimated. An essential aspect of estimating the impact of bacteriophages is their absolute and precise quantification, which provides relevant information about the host-virus interactions and the structure of viral assemblages. Consequently, due to its abundance and claimed influence in the biogeochemical cycling of elements, the accurate quantification of pelagiphages results in an essential task. This study describes the development and validation of a sensitive, specific, accurate and reproducible qPCR platform targeting pelagiphages. Moreover, this method allowed the detection and quantification of pelagiphages in the Gulf of California for the first time.

Anaerobic methanotrophy is stimulated by graphene oxide in a brackish urban canal sediment.

Anthropogenic activities are influencing aquatic environments through increased chemical pollution and thus are greatly affecting the biogeochemical cycling of elements. This has increased greenhouse gas emissions, particularly methane, from lakes, wetlands, and canals. Most of the methane produced in anoxic sediments is converted into carbon dioxide by methanotrophs before it reaches the atmosphere. Anaerobic oxidation of methane requires an electron acceptor such as sulphate, nitrate, or metal oxides. Here, we explore the anaerobic methanotrophy in sediments of three urban canals in Amsterdam, covering a gradient from freshwater to brackish conditions. Biogeochemical analysis showed the presence of a shallow sulphate-methane transition zone in sediments of the most brackish canal, suggesting that sulphate could be a relevant electron acceptor for anaerobic methanotrophy in this setting. However, sediment incubations amended with sulphate or iron oxides (ferrihydrite) did not lead to detectable rates of methanotrophy. Despite the presence of known nitrate-dependent anaerobic methanotrophs (Methanoperedenaceae), no nitrate-driven methanotrophy was observed in any of the investigated sediments either. Interestingly, graphene oxide stimulated anaerobic methanotrophy in incubations of brackish canal sediment, possibly catalysed by anaerobic methanotrophs of the ANME-2a/b clade. We propose that natural organic matter serving as electron acceptor drives anaerobic methanotrophy in brackish sediments.