Search

Micro- and nanoplastic (MNP) pollution in aquatic ecosystems requires investigation on its source, transport, and extent to assess and mitigate its risks. Chitosan is a potential biomolecule for water treatment, but its interaction with MNP is undefined. In this work, chitosan-nanoplastic interaction was explored in the laboratory under environmentally relevant conditions using polystyrene (PS) nanoplastic (NP) as model particle to identify conditions at which PS-chitosan interaction resulted in aggregation. Aggregation limits NP transport and allows separation of NP for targeted remediation. The effect of environmental conditions (pH, salinity, dissolved organic matter (DOM) content), chitosan particle size and NP surface modification on chitosan-NP interaction was studied at various chitosan doses. PS aggregated at chitosan doses as low as 0.2 % w/w, while higher doses of chitosan resulted in re-stabilization of NP in solution, restoring the particle size to its initial value. Increasing pH, DOM, or carboxyl modification of the NP surface also improved NP stability in solution. Increased salinity of the solution caused aggregation of unmodified PS independent of chitosan, but carboxyl-modified PS remained stable and aggregated at the same chitosan doses across all salinity levels. Chitosan with low molecular weight promoted PS aggregation at lower doses. Notably, zeta potential (ZP) alone did not indicate chitosan-induced PS aggregation, which occurred independently of changes in ZP. DLVO calculations based on ZP, however, still indicated attractive interaction due to charge differences, albeit with less contrast at high pH, salinity, and DOM content. Additional insights gained in the work recommend caution when using spectrophotometric methods to assess NP removal. Overall, this study demonstrates that chitosan impacts NP transport and holds potential for water remediation of NP.

Atmospheric oxygen (O2) concentrations likely remained below modern levels until the Silurian–Devonian, as indicated by several recent studies. Yet, the background redox state of early Paleozoic oceans remains poorly constrained, hampering our understanding of the relationship between early animal evolution and O2. Here, we present a multi-proxy analysis of redox conditions in the Caledonian foreland basin to Baltica from the early to the mid-Silurian. Our results indicate that anoxic to severely hypoxic bottom waters dominated during deposition of the Silurian sediments cored in the Sommerodde-1 well (Bornholm, Denmark), and regional comparison suggests that these conditions persisted across the Baltoscandian foreland basin. Indeed, even during times of relative oxygenation, ichnological observations indicate that conditions were, at most, very weakly oxic. The results suggest that dissolved O2 was generally scarce in the bottom waters of the extensive Silurian seaway between Baltica and Avalonia, even between Paleozoic “Anoxic Events”. In light of delayed oxygenation of the atmosphere–hydrosphere system, it may be time to consider that early animals were adapted to “hypoxia” and thrived through ∼100 million years of low-O2 conditions after the Cambrian.

Microbe-mineral interactions, such as mineral substrate utilization and aggregate formation, have played a key role in the cycling of elements through Earth evolution. In water, soils, and sediment biogeochemistry modulates microbial community composition and mineral formation over spatial and temporal scales. Plastic is a new material that is now widespread in the environment. Both microbial and mineral associations with plastic comprise the Plastisphere, which influences the fate of plastic. This study focuses on how the biogeochemical environment defines microbial and mineral association with polyethylene (PE) and polystyrene (PS) over a 12-month period in a temperate coastal harbor. The coastal harbor environment was separated into 3 conceptual compartments defined by physical and biogeochemical conditions, that allow transfer of electrons between species e.g., light penetration and redox setting. Microbe and mineral association were investigated in the water column, top sediment, and bottom sediment by applying a range of modern analytical techniques to identify changes in the chemical structures of plastics, microbial community development, metal, salt and mineral formation. The epiplastic microbial community was distinct to that of the surrounding environment across changing redox conditions. The type and oxidation state of metallic minerals formed on plastics or entrapped in the biofilm matrix related to the dominant abiotic and biotic processes across redox conditions. FTIR spectroscopy indicated the occurrence of PE and PS oxidation in the various biogeochemical environments. Combined, these findings demonstrate that redox conditions and surrounding biogeochemistry mediate the composition of mineralogical and biological loading of PE and PS in coastal marine environments. This suggests that the biogeochemical setting in which the plastics are stored constrains the development of plastic interfacial biogeochemistry and the potential for plastic degradation, Microbe-mineral interactions, such as mineral substrate utilization and aggregate formation, have played a key role in the cycling of elements through Earth evolution. In water, soils, and sediment biogeochemistry modulates microbial community composition and mineral formation over spatial and temporal scales. Plastic is a new material that is now widespread in the environment. Both microbial and mineral associations with plastic comprise the Plastisphere, which influences the fate of plastic. This study focuses on how the biogeochemical environment defines microbial and mineral association with polyethylene (PE) and polystyrene (PS) over a 12-month period in a temperate coastal harbor. The coastal harbor environment was separated into 3 conceptual compartments defined by physical and biogeochemical conditions, that allow transfer of electrons between species e.g., light penetration and redox setting. Microbe and mineral association were investigated in the water column, top sediment, and bottom sediment by applying a range of modern analytical techniques to identify changes in the chemical structures of plastics, microbial community development, metal, salt and mineral formation. The epiplastic microbial community was distinct to that of the surrounding environment across changing redox conditions. The type and oxidation state of metallic minerals formed on plastics or entrapped in the biofilm matrix related to the dominant abiotic and biotic processes across redox conditions. FTIR spectroscopy indicated the occurrence of PE and PS oxidation in the various biogeochemical environments. Combined, these findings demonstrate that redox conditions and surrounding biogeochemistry mediate the composition of mineralogical and biological loading of PE and PS in coastal marine environments. This suggests that the biogeochemical setting in which the plastics are stored constrains the development of plastic interfacial biogeochemistry and the potential for plastic degradation

Three sedimentary systems tracts (LST, TST, and HST) have been identified in Nha Phu Bay and the adjacent shelf, Khanh Hoa Province, Vietnam. These have been deposited since the Last Glacial Maximum (LGM) and interpreted in this study via the analysis of high-resolution acoustic data and sediment cores. The lowstand systems tract (LST) comprises sandy sediments exposed at seabed on the outer shelf as sand ridges, and underlying the transgressive systems tract (TST) on the middle shelf. The LST developed under shallow-marine settings during the sea-level lowstand and early sea-level rise before 14.6 cal kyr BP. The TST comprises primarily fine-grained sediments deposited during the transgression between 14.6 and 8.0 cal kyr BP in an incised trough of the outer shelf, on the middle shelf, and in Nha Phu Bay. Erosion of the seaward portion of the TST on the middle shelf might occur during the late transgression (9.0–8.0 kyr BP). The highstand systems tract (HST) comprises sediments deposited during the sea-level highstand between 8.0 and 0.0 cal kyr BP and is distributed widely in the bay, on the inner-middle shelf, and partially on the outer shelf. A paleo-coast zone, located in 100–120 m present-day water depth, is recognized through the appearance of sand ridges and sandy sediments. The seafloor sediment distribution is mapped via four major acoustic echo types, combined with seabed sediment samples. The coarse-grained sediment distribution, subaqueous outcrops, and thin deglacial sediment thickness on the inner shelf indicate erosion-dominated processes under vigorous hydrodynamic conditions. Nha Phu Bay and the middle shelf are interpreted as the depocentres. The estimated sediment load deposited in Nha Phu Bay is 0.18 Mt./yr, accounting for 15–35% of the annual sediment discharge from the Dinh River. The seabed morphology, muddy sediment distribution, and deglacial sediment thickness reveal a dominant sediment-transport pathway, across the inner shelf to the m

Oxygen minimum zones (OMZs) have been suggested as a suitable niche for the oxygen-sensitive process of biological fixation of dinitrogen (N2) gas. However, most N2 fixation rates reported from such waters are low. This low N2 fixation activity has been proposed to result from the unusual community of N2 fixers, in which cyanobacteria were typically underrepresented. The Northern Benguela Upwelling System (North BUS) is part of one of the most productive marine ecosystems and hosts a well-developed OMZ. Although previous observations indicated low to absent N2 fixation rates, the community composition of diazotrophs needed to understand the North BUS has not been described. Here, we present a first detailed analysis of the diazotrophic diversity in the North BUS OMZ and the Angola tropical zone (ATZ), based on genetic data and isotope speciation. Consistent with a previous study, we detected a slight N deficit in the OMZ, but isotope data did not indicate any active or past N2 fixation. The diazotroph community in the North BUS was dominated by non-cyanobacterial microbes clustering with members of gamma-proteobacteria, as is typical for other OMZ regions. However, we found a strikingly high diversity of Cluster III diazotrophs not yet described in other OMZs. In contrast to previous observations, we could also identify cyanobacteria of the clades Trichodesmium sp., UCYN-A and Cyanothece sp., in surface waters connected to or above the OMZ, which were potentially active as shown by the presence of genes and transcripts of the key functional marker gene for N2 fixation, nifH. While the detection of diazotrophs and the absence of active N2 fixation (based on isotopic speciation) are consistent with other OMZ observations, the detected regional variation in the diversity and presence of cyanobacteria indicate that we still are far from understanding the role of diazotrophs in OMZs, which, however, is relevant for understanding the N cycle in OMZ waters, as well for pre

Microorganisms drive the biogeochemical cycles that link abiotic and biotic processes in the aqueous environment and are intricately associated with plastic debris. The presence of microplastics in water and sediment introduces new concerns as small particle size allows for increased pathways of microplastics in the food web and element cycles. In this review, we present the current state of knowledge on microbe-plastic interactions and summarize the potential impact of biogeochemical processes on plastic distribution, cycling, transport, and sedimentation. We explore how microbe-plastic interactions influence the exposure of consumers to microplastics and plastic degradation products. Key methods used to elucidate biofilm development, microbial biodegradation, and microplastic detection in the aqueous environment are discussed. Finally, we comment on potential future questions and research directions needed to further define the role of microorganisms in the environmental fate of microplastics.

The toxicity of arsenic (As) towards life on Earth is apparent in the dense distribution of genes associated with As detoxification across the tree of life. The ability to defend against As is particularly vital for survival in As-rich shallow submarine hydrothermal ecosystems along the Hellenic Volcanic Arc (HVA), where life is exposed to hydrothermal fluids containing up to 3000 times more As than present in seawater. We propose that the removal of dissolved As and phosphorus (P) by sulfide and Fe(III)(oxyhydr)oxide minerals during sediment-seawater interaction, produces nutrient-deficient porewaters containing<2.0ppb P. The porewater arsenite-As(III) to arsenate-As(V) ratios, combined with sulfide concentration in the sediment and/or porewater, suggest a hydrothermally-induced seafloor redox gradient. This gradient overlaps with changing high affinity phosphate uptake gene abundance. High affinity phosphate uptake and As cycling genes are depleted in the sulfide-rich settings, relative to the more oxidizing habitats where mainly Fe(III)(oxyhydr)oxides are precipitated. In addition, a habitat-wide low As-respiring and As-oxidizing gene content relative to As resistance gene richness, suggests that As detoxification is prioritized over metabolic As cycling in the sediments. Collectively, the data point to redox control on Fe and S mineralization as a decisive factor in the regulation of high affinity phosphate uptake and As cycling gene content in shallow submarine hydrothermal ecosystems along the HVA.

Lake Cadagno (26 ha) is a crenogenic meromictic lake located in the Swiss Alps at 1921 m asl with a maximum depth of 21 m. The presence of crystalline rocks and a dolomite vein rich in gypsum in the catchment area makes the lake a typical “sulphuretum ” dominated by coupled carbon and sulphur cycles. The chemocline lies at about 12 m depth, stabilized by density differences of salt-rich water supplied by sub-aquatic springs to the monimolimnion and of electrolyte-poor surface water feeding the mixolimnion. Steep sulphide and light gradients in the chemocline support the growth of a large bacterial plume (up to 107 cells ml−1) dominated by green sulphur bacteria (GSB) of the genus Chlorobium and purple sulphur bacteria (PSB) of the Chromatiaceae family. Since the early Holocene (10.5–8 cal kyr BP), PSB and GSB are showing long-term alternation in abundance and relative dominance. Key species are Chlorobium clathratiforme , Thiocystis chemoclinalis , Thiocystis cadagnonensis , Candidatus “ Thiodictyon syntrophicum ” and Chromatium okenii ; the latter represents only 0.3 % of the total cell number but due to its big size and high activity can contribute up to 70 % of the total carbon uptake in the chemocline. Small-celled PSB together with the sulfate-reducing bacterium Desulfocapsa thiozymogenes sp. form stable aggregates in the lake, which represent small microenvironments with an internal sulphur cycle. Eukaryotic primary producers in the anoxic zones are dominated by Cryptomonas phaseolus , whereas eukaryotic heterotrophs are represented by ciliates and choanoflagellates, but a clade of heteroloboseans and two novel clades distantly related to opisthokonts and Cercozoa are also present. Zooplankton and fish abundance in the mixolimnion of this model ecosystem are linked via food web to the chemocline microbial plume, consequently anaerobic primary production supports relative high fish productivity in the lake.

Post-depositional diagenetic alteration makes the accurate interpretation of key precipitation processes in ancient sediments, such as Precambrian banded iron formations (BIFs), difficult. While microorganisms are proposed as key contributors to BIF deposition, the diagenetic transformation of precursor Fe(III) minerals associated with microbial biomass had not been experimentally tested. We incubated mixtures of ferrihydrite (proxy for biogenic ferric oxyhydroxide minerals) and glucose (proxy for microbial biomass) in gold capsules at 1.2kbar and 170??C. Both wet chemical analysis and mineralogical methods (microscopy, X-ray diffraction and M??ssbauer spectroscopy) were used to analyze the reaction products. Under these conditions, ferrihydrite (FeIII(OH)3) transforms to hematite (Fe2IIIO3), magnetite (FeIIFe2IIIO4), and siderite (FeIICO3). Silica-coated ferrihydrite prepared at conservative Si:Fe ratios (as predicted for the Precambrian oceans) and mixed with glucose yielded hematite and siderite, whereas magnetite could not be identified microscopically. Our results show that electron transfer from organic carbon to Fe(III) minerals during temperature/pressure diagenesis can drive the production of key BIF minerals. Our results also demonstrate that the post-depositional mineralogy of BIF does not directly archive the oceanic or atmospheric conditions present on Earth during their lithification. As a consequence, atmospheric composition regarding concentrations of methane and CO2 during the time of BIF mineral deposition cannot be directly inferred from BIF mineralogical data alone. ?? 2013 Elsevier B.V.

Sedimentary deposits of alternating iron-rich (20–40% Fe) and iron-poor, siliceous (40–50% SiO2) mineral layers that primarily precipitated throughout much of the late Archean (2.7–2.5 Ga) and Paleoproterozoic (2.5– 1.8 Ga), but then remerged in the Neoproterozoic (0.8 Ga).

Phototrophic iron(II) [Fe(II)]-oxidizing bacteria are present in modern environments and evidence suggests that this metabolism was present already on early earth. We determined Fe(II) oxidation rates depending on pH, temperature, light intensity, and Fe(II) concentration for three phylogenetically different phototrophic Fe(II)-oxidizing strains (purple nonsulfur bacterium Rhodobacter ferrooxidans sp. strain SW2, purple sulfur bacterium Thiodictyon sp. strain F4, and green sulfur bacterium Chlorobium ferrooxidans strain KoFox). While we found the overall highest Fe(II) oxidation rates with strain F4 (4.5 mmol L(-1) day(-1), 800 lux, 20 degrees C), the lowest light saturation values [at which maximum Fe(II) oxidation occurred] were determined for strain KoFox with light saturation already below 50 lux. The oxidation rate per cell was determined for R. ferrooxidans strain SW2 to be 32 pmol Fe(II) h(-1) per cell. No significant toxic effect of Fe(II) was observed at Fe(II) concentrations of up to 30 mM. All three strains are mesophiles with upper temperature limits of c. 30 degrees C. The main pigments were identified to be spheroidene, spheroidenone, OH-spheroidenone (SW2), rhodopinal (F4), and chlorobactene (KoFox). This study will improve our ecophysiological understanding of iron cycling in modern environments and will help to evaluate whether phototrophic iron oxidizers may have contributed to the formation of Fe(III) on early earth.

Precambrian banded iron formations provide an extensive archive of pivotal environmental changes and the evolution of biological processes on early Earth. The formations are characterized by bands ranging from micrometre- to metre-scale layers of alternating iron- and silica-rich minerals. However, the nature of the mechanisms of layer formation is unknown. To properly evaluate this archive, the physical, chemical and/or biological triggers for the deposition of both the iron- and silica-rich layers, and crucially their alternate banding, must be identified. Here we use laboratory experiments and geochemical modelling to study the potential for a microbial mechanism in the formation of alternating iron–silica bands. We find that the rate of biogenic iron(III) mineral formation by iron-oxidizing microbes reaches a maximum between 20 and 25 °C. Decreasing or increasing water temperatures slow microbial iron mineral formation while promoting abiotic silica precipitation. We suggest that natural fluctuations in the temperature of the ocean photic zone during the period when banded iron formations were deposited could have led to the primary layering observed in these formations by successive cycles of microbially catalysed iron(III) mineral deposition and abiotic silica precipitation.

Nicole Posth and colleagues spent a month touring South African rock formations in their quest to understand the origin of ancient iron and silicate layers.

Oxidized Fe minerals in Archean-Paleoproterozoic banded iron formations (BIFs) are commonly taken to indicate the presence of biogenic O2 or photosynthetic Fe(II)-oxidizing bacteria in the oceans' photic zone. However, at least one viable abiogenic oxidation mechanism has been proposed. Prior to the rise of atmospheric oxygen and the development of a protective ozone layer, the Earth's surface was subjected to high levels of ultraviolet radiation. Bulk ocean waters that were anoxic at this time could have supported high concentrations of dissolved Fe(II). Under such conditions, dissolved ferrous iron species, such as Fe2+ and Fe(OH)+, would have absorbed radiation in the 200-400??nm range, leading to the formation of dissolved ferric iron [Fe(III)], which in turn, would have hydrolyzed to form ferric hydroxide [Fe(OH)3] at circumneutral pH [Cairns-Smith, A.G., 1978, Precambrian solution photochemistry, inverse segregation, and banded iron formations. Nature 76, 807-808; Braterman, P.S., Cairns-Smith, A.G., and Sloper, R.W., 1983, Photo-oxidation of hydrated Fe2-Significance for banded iron formations. Nature 303, 163-164]. This process has been invoked to account for BIF deposition without need for biology [Fran??ois, L.M., 1986, Extensive deposition of banded iron formations was possible without photosynthesis. Nature 320, 352-354]. Here, we evaluate the potential importance of photochemical oxidation using a combination of experiments and thermodynamic models. The experiments simulate the chemistry of ambient Precambrian seawater mixing with Fe(II)-rich hydrothermal fluids with, and without, UV irradiation. We find that if Fe(II) was effused from relatively shallow seamount-type vent systems directly into an anoxic photic zone, the photochemical contribution to solid-phase precipitation would have been negligible. Instead, most of the Fe(II) would have precipitated rapidly as an amorphous precursor phase to the ferrous silicate mineral greenalite ((Fe)3Si2O5(OH)4)