Sediment Depth Research Articles

Sediment Bacteria in the Alpine Lake Sayram: Vertical Patterns in Community Composition.

Bacterial communities inhabiting alpine lakes are essential to our understanding of ecosystem processes in a changing climate, but little has been reported about the vertical patterns of sediment bacterial communities in alpine lakes. To address this knowledge gap, we collected the 100 cm long sediment core from the center of Lake Sayram, the largest alpine lake in Xinjiang Uygur autonomous area, China, and used 16S rRNA gene-targeted amplicon sequencing to examine the bacterial populations. The results showed that bacterial diversity, as estimated by the Shannon index, was highest at the surface (6.9849 at 0-4 cm) and gradually decreased with depth up to 3.9983 at 68-72 cm, and then increased to 5.0927 at 96-100 cm. A total of 56 different phyla and 1204 distinct genera were observed in the sediment core of Lake Sayram. The bacterial community structure in the sediment samples from the various layers was dissimilar. The most abundant phyla in alpine Lake Sayram were Proteobacteria, Firmicutes, and Planctomycetes, accounting for 73%, 6%, and 4% of the total reads, respectively; the most abundant genera were Acinetobacter, Hydrogenophaga, and Pseudomonas, accounting for 18%, 12%, and 8% of the total reads, respectively. Furthermore, the relative abundance of Acinetobacter increased with sediment depth, while the relative abundance of Hydrogenophaga and Pseudomonas decreased with sediment depth. Our findings indicated that the nitrate-reducing bacteria (Acinetobacter, Hydrogenophaga, and Pseudomonas) may be prevalent in the sediment core of Lake Sayram. Canonical correspondence analysis showed that carbonate and total organic carbon (TOC) may be the main environmental factors affecting the vertical patterns of bacterial community composition (BCC) in the sediment of Lake Sayram. This work significantly contributes to our understanding of the BCC of sediments from alpine lakes in arid and semiarid regions.

Disentangling artificial and natural benthic weathering in organic rich Baltic Sea sediments

Enhanced mineral dissolution in the benthic environment is currently discussed as a potential technique for ocean alkalinity enhancement (OAE) to reduce atmospheric CO2 levels. This study explores how biogeochemical processes affect the dissolution of alkaline minerals in surface sediments during laboratory incubation experiments. These involved introducing dunite and calcite to organic-rich sediments from the Baltic Sea under controlled conditions in an oxic environment. The sediment cores were incubated with Baltic Sea bottom water. Findings reveal that the addition of calcite increased the benthic alkalinity release from 0.4 μmol cm−2 d−1 (control) to 1.4 μmol cm−2 d−1 (calcite) as well as other weathering products such as calcium. However, these enhanced fluxes returned to lower fluxes after approximately 4 weeks yet still higher than the un-amended controls. Microbial activity appeared to be the primary driver for lowering pore water pH and thus enhanced weathering. In several sediment cores, pH profiles taken at the start of the experiments indicated activity of sulfur oxidizing Beggiatoa spp, which was verified by RNA-profiling of 16S rRNA genes. The pH profiles transitioned to those commonly associated with the activity of cable bacteria as the experiments progressed. The metabolic activity of cable bacteria would explain the significantly lower pH values (~5.6) at sediment depths of 1–3 cm, which would favor substantial calcite dissolution. However, a high abundance of cable bacteria was not reflected in 16S rRNA sequence data. Total alkalinity (TA) fluxes in these cores increased by a factor of ~3, with excess TA/calcium ratios indicating that the enhanced flux originated from calcite dissolution. The dissolution of dunite or the potential formation of secondary minerals could not be identified due to the strong natural flux of silicic acid, likely due to biogenic silica dissolution. Furthermore, no accumulation of potentially harmful metals such as nickel was observed, as highlighted as a potential risk in other studies concerning OAE. Given the complexity of sediment chemistry and changes of the benthic conditions induced by the incubation, it remains challenging to distinguish between natural and enhanced mineral weathering. Further investigation, including the identification of suitable tracers for mineral dissolution, are necessary to assess the feasibility of benthic weathering as a practical approach for OAE and climate change mitigation.

Metal and non–metal dynamics and distribution in soil profiles across selected pans in the Ramsar declared subtropical within a national protected area

ABSTRACT The study investigated the spatial distributions of selected metals, semi–metals and non–metals within a floodplain pan ecosystem in the Ramsar declared Makuleke Wetlands within the Makuleke Contractual National Park, in the northern Kruger National Park (South Africa), along varying soil depths (0–120 cm) at 20 cm intervals. The study identified significant differences in metal concentrations (i.e. Ca, Mn, Fe) and non–metals (i.e. C, S) across sediment depths. Metal and non–metal concentrations in surface sediments (0–40 cm) were generally high. Compared with the sediment quality guidelines, all measured metals were within the ‘no effect’ level across different sites and depths, except for one site (i.e. Mambvumbvanyi pan). In contrast, enrichment factors showed that K, Ca and Mg were enriched in sediments across all the floodplain pans and depths. Principal component and cluster analyses indicated that various metals originated from different sources. Although a high concentration of metals was found in the topsoil, no potential detrimental effects on the aquatic systems could be observed. Based on the findings, this study provides a baseline overview of sediment metal pollution that can inform effective management of these floodplain wetlands systems.

Communities of macrozoobenthos on soft sediments in the coastal areas of open parts of Peter the Great Bay, Japan Sea and their ecological status

At least 10 communities of macrozoobenthos are determined by modern statistical methods on soft sediments in the coastal areas of Peter the Great Bay with the depth of ≥ 5 m surveyed in 1992, 1993 and 1996. They were: I. Scoletoma spp. + Ophiura sarsii; II. Aphelochaeta pacifica (I–II — in the Strelok Bay and Rifovaya Inlet); III. O. sarsii + Amphiodia fissa; IV. Scoletoma spp. + Mactra chinensis; V. Scoletoma spp. + Maldane sarsi; VI. Acila insignis (III–VI — in the Posyet Bay and adjacent area); VII. Scoletoma spp. + Echinocardium cordatum; VIII. Dipolydora cardalia + M. sarsi + O. sarsii; IX. Spiophanes uschakovi + E. cordatum, and X. Ampelisca macrocephala (VII–X — in the area at the Tumannaya/Tumen River mouth). Their development was determined by such environmental imperatives as the bottom sediments properties (silting degree, mean grain size), depth, and level of pollution and eutrophication. Majority of these communities (I, III, IV, V, VII, VIII, IX, and X) were in good ecological condition. Their habitats were slightly disturbed (intact or almost intact) and rare or never polluted and eutrophicated. The community II occupied more disturbed habitats with moderate ecological status reflected in higher indices of pollution. This community was rather likely formed in the process of succession in conditions of decreasing pollution. The community VI had a lower ecological status; its differentiation was probably caused by specific oceanographic regime of the Posyet Bay and anthropogenic impacts.

Depth-Dependent Distribution of Prokaryotes in Sediments of the Manganese Crust on Nazimov Guyots of the Magellan Seamounts.

Deep ocean polymetallic nodules, rich in cobalt, nickel, and titanium which are commonly used in high-technology and biotechnology applications, are being eyed for green energy transition through deep-sea mining operations. Prokaryotic communities underneath polymetallic nodules could participate in deep-sea biogeochemical cycling, however, are not fully described. To address this gap, we collected sediment cores from Nazimov guyots, where polymetallic nodules exist, to explore the diversity and vertical distribution of prokaryotic communities. Our 16S rRNA amplicon sequencing data, quantitative PCR results, and phylogenetic beta diversity indices showed that prokaryotic diversity in the surficial layers (0-8 cm) was > 4-fold higher compared to deeper horizons (8-26 cm), while heterotrophs dominated in all sediment horizons. Proteobacteria was the most abundant taxon (32-82%) across all sediment depths, followed by Thaumarchaeota (4-37%), Firmicutes (2-18%), and Planctomycetes (1-6%). Depth was the key factor controlling prokaryotic distribution, while heavy metals (e.g., iron, copper, nickel, cobalt, zinc) can also influence significantly the downcore distribution of prokaryotic communities. Analyses of phylogenetic diversity showed that deterministic processes governing prokaryotic assembly in surficial layers, contrasting with stochastic influences in deep layers. This was further supported from the detection of a more complex prokaryotic co-occurrence network in the surficial layer which suggested more diverse prokaryotic communities existed in the surface vs. deeper sediments. This study expands current knowledge on the vertical distribution of benthic prokaryotic diversity in deep sea settings underneath polymetallic nodules, and the results reported might set a baseline for future mining decisions.

Mercury concentrations in sediments and oysters in a temperate coastal zone: a comparison of farmed and wild varieties.

Oyster aquaculture has progressively increased to meet growing demands for seafood worldwide; however, its effects on methylmercury (MeHg) production in sediment and accumulation in oysters are largely unknown. In this study, total Hg (THg) and MeHg in sediments collected from aquaculture and reference sites and in farmed and wild oysters were measured and compared to explore potential factors that regulate MeHg production and bioaccumulation at the aquaculture sites. The results showed that the mean concentrations of THg and MeHg in varying sediment depths at the aquaculture site were 34 ± 4.1 ng g-1 and 16 ± 12 pg g-1, respectively. In comparison, the mean concentrations of THg and MeHg in sediments at the reference site were 25 ± 2.5 ng g-1 and 63 ± 28 pg g-1, respectively. While the MeHg/THg in the aquaculture sediments increased with organic carbon content, the slope of MeHg/THg versus organic carbon content was suppressed by high concentrations of dissolved sulfide in the pore water. Multiple parameters (total sulfur, total nitrogen and acid volatile sulfide in sediment, and dissolved sulfide in pore water) showed significant negative relationships with MeHg/THg in the sediment, and the total sulfur content in the sediment showed the highest inverse correlation factor with MeHg/THg (r = - 0.83). The mean concentrations of THg and MeHg in farmed oysters (mean weight 3.2 ± 1.5 g) were 36 ± 10 ng g-1 and 15 ± 6.7 ng g-1, respectively, while those in wild oysters (mean weight 0.92 ± 0.32 g) were 47 ± 9.9 ng g-1 and 15 ± 6.7 ng g-1, respectively. Concerning oysters of the same size range, THg and MeHg levels were higher in farmed oysters than in wild oysters despite the faster growth rate of farmed oysters, suggesting that the Hg content of food sources is more important than growth dilution rates in the control of Hg levels. The mean hazardous quotient for MeHg in farmed oyster was calculated as 0.044 ± 0.020, suggesting no expected health risk from farmed oyster consumption.

ALTERNATIVE RADIOCARBON AGE-DEPTH MODEL FROM LAKE BAIKAL SEDIMENT: IMPLICATION FOR PAST HYDROLOGICAL CHANGES FOR LAST GLACIAL TO THE HOLOCENE

ABSTRACT We present an alternative radiocarbon (14C) age-depth model using IntCal20 to calibrate new accelerator mass spectrometry (AMS) data applied to a Lake Baikal sediment core (VER99G12) in southern Siberia. 14C dating showed that the core extends to 31 ka. To take into account uncertainties in 14C age and sedimentation depth in the core, a new age-depth modeling routine, undatable, was used in this study. Undatable revealed that significant changes in sedimentation rate correspond to global climate events, either warm or cold, which periods are likely close to the timing of the occurrence of the Meltwater pulses (MWP) at 19 and 14 ka, and the Last glacial Maximum (LGM) at 21–20 ka. Since the Selenga River accounts for 50% of the total river inflow to Lake Baikal, we interpret that these changes in sedimentation rate could be signals of significant changes in Selenga River discharge to the lake, which is expected to be affected by global climate change. Based on pollen analysis, it is highly probable that the sudden influx of the Selenga River to Lake Baikal, particularly at 19 ka, was due to the thawing of permafrost water through the Selenga River, which had developed in the region. Total organic carbon content and mean grain size increases concurrent with sedimentation rate, suggesting river inflow increased available nutrients for biological activity. Our results indicate that hydrological changes corresponding to MWP events can be observed in continental areas of the Northern Hemisphere.

Seasonal variation regulate the endogenous phosphorus release in sediments of Shijiuhu Lake via water-level fluctuation

Freshwater lakes undergo substantial alterations of the phosphorus (P) cycle in the water-sediment ecosystem due to thermal change. The impact process of seasonal fluctuation on P cycling in sediments has been scarcely investigated. P forms in sediments from a freshwater lake in China were analyzed using sequential extraction technique. The vertical distribution of soluble reactive P (SRP), Fe2+, and S2− in the interstitial water was measured using diffusion gradient technique (DGT). Fick's Law and DIFS model were used to obtain the diffusion fluxes of SRP and the kinetic parameters in the water-sediment system. The results showed that total P (TP) concentrations in the solid sediments varied from 207.5, 266.6 and 130.3 mg/kg to 614.7, 1053.1, and 687.6 mg/kg in winter, spring, and summer, respectively. The concentrations of individual P forms in spring were higher than those in other seasons, with Fe-bound P (Fe–P) concentration being the highest across all seasons. Notably, significant variations of SRP concentrations were found in the interstitial water between sedimentary depths of approximately 2 cm and 6 cm, particularly in the summer. Furthermore, higher diffusion fluxes of SRP through the interface were found in summer. A stable anaerobic environment failed to develop in spring with high water level, preventing the desorption of solid Fe–P and diffusion of Fe2+ into the water due to the afflux and deposition of P-containing particulate into deeper sediment layers along with organic material. Under extreme high-temperature in summer, decreased rainfall and rising temperatures boosted the activity of aquatic organisms in the water, thereby reducing P fixation by sediments and leading to P release. This process increased the risk of P excess and potential eutrophication in the water. Generally, clarifying the resupplying processes of endogenous P in sediment systems experiencing seasonal variations is critical for eutrophication management of lakes.

The coupling effects of carbon fractions, bacteria, and protists on carbon emissions among various ditch levels in the Lower Yellow River

Inland waters are receiving increasing attention due to their importance in the global carbon cycle. However, the dynamics of CO2 emissions and the related mechanisms from ditches remain unclear. In this study, field sampling and an incubation experiment were conducted to explore the effects and mechanisms, especially the coupling effects between carbon fractions, bacteria, and protists on carbon dynamics of different ditch levels (sublateral ditch, farm ditch, and lateral ditch) and sediment depths (0-20cm, 20-40cm) in the Lower Yellow River. Results indicated that sublateral ditches nearest to farmland had the highest accumulative carbon mineralization (0–20 cm 1.38 g C kg−1; 20–40 cm 0.89 g C kg−1), equivalent to that of farmland, followed by the lateral ditch (0–20 cm 0.84 g C kg−1; 20–40 cm 0.50 g C kg−1) and the farm ditch (0–20 cm 0.67 g C kg−1; 20–40 cm 0.26 g C kg−1). Carbon emissions from ditches are mainly regulated by SOC (36.97 %), bacteria (29.2 %), and protists (18.95 %). Specifically, the mineralization of flooded lateral ditches is attributed to protist diversity. SOC, bacterial and protistan diversity in the farm ditch significantly impacted carbon emissions, with SOC as the dominant factor, while the bacterial composition and SOC contributed more to CO2 emissions in the sublateral ditch. Our results highlight the importance of carbon emissions from ditches, especially those closest to farmland. This study provides new insights into the construction and management of farmland irrigation and drainage in the aspects of carbon sequestration.

Variations in Water and Deposited Sediment Qualities in the Tidal River Basins of Bangladesh and Their Implications for TRM Success

The tidal river management (TRM) in coastal areas of Bangladesh has been successful in varying degrees. Though there are many studies on the social, institutional, hydrological and hydraulic factors in relation to TRM, there is no study that investigated the relationship between the water and soil qualities and the TRM success. This paper investigates the variations of water and deposited sediment qualities vis-à-vis the TRM success in selected tidal basins in the southwest coastal delta of Bangladesh. The basins were selected based on the level of success in TRM operation: Beel Bhaina (a successful TRM), East Beel Khuksia (a partially successful TRM), and Beel Pakhimara (an unsuccessful TRM). The level of success in TRM was decided from the local community’s perception and how the TRM operation reduced the drainage congestion and increased the sedimentation depth inside a tidal basin. Fifteen water quality parameters with seven indices and eight soil quality parameters were analyzed to evaluate their suitability for agricultural purposes. The analysis reveals that the water of Beel Bhaina and East Beel Khuksia has high salinity, TDS, TSS, SAR and Na% than that of Beel Pakhimara due to the presence of an active tidal current. The most dominant cation is Na+ in almost all the water samples due to the seawater influence. The most dominant anion is Cl− in Beel Bhaina and East Beel Khuksia, and HCO3− in Beel Pakhimara. The deposited sediment quality parameters are worse in the dry season than in the monsoon, except for organic matter. The soil EC of Beel Bhaina and East Beel Khuksia is low, which may be one of the reasons for good yield in these basins. The average yields of boro rice were 7.2, 7.7 and 6.4 ton/ha in Beel Bhaina, East Beel Khuksia and Beel Pakhimara, respectively, which might be related to the quality of the deposited sediment in the tidal basins and also to the level of TRM success.

Micro-pressure promotes endogenous phosphorus release in a deep reservoir by favouring microbial phosphate mineralisation and solubilisation coupled with sulphate reduction

Deep reservoirs vary in their hydrostatic pressure owing to artificial water level control. The potential migration of phosphorus (P) in reservoir sediments raises the risk of harmful algal blooms. To ascertain the mechanisms of endogenous P release in reservoirs, we characterised aquatic microbial communities associated with coupled iron (Fe), P and sulphur (S) cycling at the sediment–water interface. The responses of microbial communities to hydrostatic pressures of 0.2–0.7 mega pascals (MPa; that is, micro-pressures) were investigated through a 30-day simulation experiment. Our findings unravelled a potential mechanism that micro-pressure enhanced the solubilisation of Fe/aluminium (Al)-bound P caused by microbially-driven sulphate reduction, leading to endogenous P release in the deep reservoir. Although the vertical distribution of labile Fe was not affected by pressure changes, we did observe Fe resupply at sediment depths of 2–5 cm. Metagenomic analysis revealed increased abundances of functional genes for P mineralisation (phoD, phoA), P solubilisation (pqqC, ppx-gppA) and sulphate reduction (cysD, cysC) in sediments subjected to micro-pressure, which contrasted with the pattern of S oxidation gene (soxB). There was a tight connection between P and S cycling-related microbial communities, based on significant positive correlations between labile element (P and S) concentrations and functional gene (phoD, cysD) abundances. This provided strong support that Fe–P–S coupling processes were governed by micro-pressure through modulation of P and S cycling-related microbial functions. Key taxa involved in P and S cycling (for example, Bradyrhizobium, Methyloceanibacter) positively responded to micro-pressure and as such, indirectly drove P release from sediments by facilitating P mineralisation and solubilisation coupled with sulphate reduction.

Microbial diversity and authigenic siderite mediation in sediments surrounding the Kedr-1 mud volcano, Lake Baikal.

The gas hydrate-bearing structure-mud volcano Kedr-1 (Lake Baikal, southern basin)-is located near the coal-bearing sediments of the Tankhoy formation of Oligocene-Miocene age and can be an ideal source of gas-saturated fluid. A significant amount of siderite minerals (FeCO3 ) were collected from sediments at depths ranging from 0.5 to 327 cm below the lake floor (cmblf). An important feature of these carbonate minerals is the extremely strong enrichment in the heavy 13 C isotope, reaching values of +33.3‰ VPDB. The δ13 C of the siderite minerals, as well as their morphology and elemental composition, and the δ13 CDIC of the co-existing pore water, differed across layers of the core, which implies at least two generations of siderite formation. Here, we leverage mineralogical and geochemical data with 16S rRNA data from the microbial communities in sediments surrounding layers containing siderite minerals. Statistical data reveal the formation of three clusters of microbial communities based on taxonomical composition, key taxa among bacteria and archaea, and environmental parameters. Diversity and richness estimators decrease with sediment depth, with several similar prevailing clades located at the bottom of the core. Most of the taxa in the deep sediments could be associated with putative metabolisms involving organotrophic fermentation (Bathyarchaeia, Caldatribacteriota, and Chloroflexota). Various groups of methanogens (Methanoregulaceae, Methanosaetaceae, and Methanomassiliicoccales) and methanotrophic (Methanoperedenaceae) archaea are present in the sediment at variable relative abundances throughout the sampled depth. Based on the physicochemical characteristics of the sediment, carbon isotope analysis of carbonate minerals and DIC, and phylogenetic analysis of individual taxa and their metabolic potential, we present several models for subsurface siderite precipitation in Lake Baikal sediments.

Sediment depth-related variations of comammox Nitrospira: Evidence in the Three Gorges Reservoir, China

The recent discovery of comammox Nitrospira as complete ammonia-oxidizing microorganism has fundamentally revolutionized our understanding of nitrogen cycling in sediment environments. However, knowledge regarding their abundance, biodiversity, community structure, and interactions is predominantly limited to the upper layers (0–20 cm). To address this gap, we collected sediment samples along profiles ranging from 0 to 300 cm in depth at three locations within the middle segment of the Three Gorges Reservoir (TGR), China. Quantitative real-time PCR (qPCR) analyses suggested that comammox bacteria were not only ubiquitous in deep sediments but also more abundant than ammonia-oxidizing bacteria (AOB). Ammonia monooxygenases subunit A (amoA) gene amplicon sequencing illuminated that comammox bacteria were more sensitive to sedimental depth compared to AOB and ammonia-oxidizing archaea (AOA), as evidenced by a more significant decline in community diversity and similarity over distance along sediment vertical profiles. Notably, we discovered that the amoA gene abundance, alpha- and beta-diversity of comammox bacteria exerted an essential contribution to potential nitrification rates according to random forest model. Phylogenetic analysis indicted that most comammox bacteria within sediment samples belonged to clade A.2. Intriguingly, the average relative abundance of comammox clade A.2 displayed a noteworthy rise with sediment depth, whereas clade A.1 demonstrated a converse pattern, unveiling distinct ecological niche adaptations of these two clades along the sediment profile. Ecological network analysis further revealed closer interactions between comammox bacteria and canonical ammonia oxidizers in the superficial layer (0–40 cm), with the network structure gradually simplifying from superficial to deep sediment (200–300 cm). Overall, these findings broaden the current recognition of the geographic distribution and niche segregation of comammox bacteria at the fine scale of the sediments ecosystems and provide insights into sediment depth-related variations of their coexistence network patterns in large freshwater reservoirs.

Behaviors of redox-sensitive tungsten and molybdenum in the northern South China Sea: From the Pearl River to the continental slope

To increase the proxy toolbox for the reconstruction of redox conditions, the transition metal tungsten (W) has been increasingly suggested as a promising new candidate during the last few years. However, compared to other trace metals such as molybdenum (Mo), studies on the redox behavior of W in the brackish/marine environment are relatively rare and mainly limited to euxinic settings. To contribute to our understanding of the behavior of W in modern aquatic ecosystems, we here present a water column W and Mo dataset that follows the salinity gradient of the Pearl River Estuary towards the adjacent coastal and offshore waters of the northern South China Sea (water depths range from 36 m to 3735 m) with the latter also including mostly anoxic porewater and rather oxic sediment surface data. Except for deviations of W in the low-salinity reaches of the Pearl River Estuary, both metals are conservatively introduced to the coastal ocean. The contribution of dissolved W via the Pearl River plume was identified in surface waters along the coastline. In line with previous open ocean studies, the conservative behavior of W proceeds towards the remote parts of the study area with surface waters that are possibly also affected by the South China Sea Warm Current. Within the short core porewater profiles, W concentrations increased with sediment depth and reached the highest levels at the more distal sites. These trends are not linked to the formation of more soluble thiotungstate species as indicated by generally non-sulfidic porewaters. Along with porewater gradients of W, the W concentrations in near-bottom waters suggest effective trapping of W at the sediment/water interface by Mn oxides especially at greater water depths and limited contribution to the open water column W inventory. In contrast to W, Mo concentrations show little variation in the reducing porewaters and remain close to or slightly above the ocean level. Enrichments of W and Mo in the surface sediments from the upper and lower continental slope reflect the known affinity of both trace metals to Mn oxides. Positive correlations of W with the heavy mineral-associated metals titanium (Ti) and zirconium (Zr) in sand-rich deposits of the outer continental shelf subjected to stronger near-bottom currents, further indicate a relation of sedimentary W abundances to the depositional environment.

Microbial gene expression in Guaymas Basin subsurface sediments responds to hydrothermal stress and energy limitation.

Analyses of gene expression of subsurface bacteria and archaea provide insights into their physiological adaptations to in situ subsurface conditions. We examined patterns of expressed genes in hydrothermally heated subseafloor sediments with distinct geochemical and thermal regimes in Guaymas Basin, Gulf of California, Mexico. RNA recovery and cell counts declined with sediment depth, however, we obtained metatranscriptomes from eight sites at depths spanning between 0.8 and 101.9 m below seafloor. We describe the metabolic potential of sediment microorganisms, and discuss expressed genes involved in tRNA, mRNA, and rRNA modifications that enable physiological flexibility of bacteria and archaea in the hydrothermal subsurface. Microbial taxa in hydrothermally influenced settings like Guaymas Basin may particularly depend on these catalytic RNA functions since they modulate the activity of cells under elevated temperatures and steep geochemical gradients. Expressed genes for DNA repair, protein maintenance and circadian rhythm were also identified. The concerted interaction of many of these genes may be crucial for microorganisms to survive and to thrive in the Guaymas Basin subsurface biosphere.

ESTIMATION OF METHANE FLOW FROM THE BOTTOM OF THE KARA SEA

During the expedition on the R/V “Akademik Mstislav Keldysh” (81st cruise) in 2020, extensive material was selected, representing columns of bottom sediments up to 6 meters deep in the Kara Sea. After lithological description of the columns, sediment samples were taken from different horizons for degassing of pore gases. The extracted gas samples were analyzed for the content of the main gases – methane (CH4), carbon dioxide (CO2) and light hydrocarbons. The characteristic features of CH4 and CO2 content changes with depth of bottom sediment at station 6879 (Kara Sea shelf) were studied. A model of gas diffusion was constructed taking into account the biochemical reactions of methanogenesis and methane oxidation. The rate of methane formation can be estimated by the value J ≈ 3 × 10–10 μg sec–1 L–1 (per liter of sediment). The rate coefficient of methane consumption by microorganisms is K ≈ 0.5 × 10–10 sec–1. The methane flux from the bottom surface of the Kara Sea near station 6879 is q ≈ 3.47 × 10–2 μL m–1 year–1.

Microplastic pollution distribution: Differences between marine reserves and urbanised areas

Microplastic particles (<5 mm) have been observed to be widely distributed in the oceans, from estuaries the deep ocean trenches. While plastic pollution in the marine environment is a growing concern worldwide, relatively little is known about microplastic distribution and accumulation on the seafloor, particularly in marine protected area (MPAs). The delimitation of MPAs frequently follow jurisdictional or political boundaries, however the distribution of species, habitats and ecosystems does not always follow these same confines. Likewise, pollution in the marine environment do not have boundaries.This study compares microplastic content in sediment cores from two sites: an urbanised area, near the coastal township of Picton; and a site distal from the township (∼30 km) but proximal to open ocean, adjacent to the Kokomohua Marine Reserve, in the region of Queen Charlotte Sound/Tōtaranui (QCS), Aotearoa/New Zealand.Microplastic particles were identified throughout the sediment cores from both locations, reaching depths of ∼45 cm below the seabed. Our findings revealed that marine sediments adjacent to the marine reserve had four times the microplastic accumulation of marine sediments from near the coastal township. The abundance of microplastics across the sediment depth profiles also varied between the two sites, suggesting different accumulation of microplastics on the seafloor due to differences in the frequency and extent of seabed disturbance experienced by the two locations.Our study demonstrates the extent to which human stressors such as microplastic pollution proliferate and concentrate in the environment, particularly in areas considered to be near-pristine with strict environmental protections.

Microtremor analysis around Jari mud volcano, Bojonegoro

The earthquake that occurred in the Mount Pandan area in 2016 is thought to have triggered the emergence of a mudflow mixed with water and gas. The research area is in the Kendeng Zone with a complex geological structure. In this zone, there is a very fast sedimentation process so the buried material is not fully compacted. In this study, measurements were made of 6 microtremor data points around Jari Mud Volcano, Bojonegoro, East Java, Indonesia. Furthermore, the data obtained were processed using the HVSR analysis method. HVSR analysis is a method of processing microtremor signals to determine soil characteristics based on information on natural frequency values and its amplification. The result shows the natural frequency parameter and its amplification is slightly variated around Jari Mud Volcano, caused by sedimentary depth variation and/or the presence of existing rock. Based on 6 processed data, the natural frequency values range from 1.9 to 9.1 Hz. Meanwhile, the amplification value ranges from 2.6 to 4.4. Based on the amplification value, the research area is classified as low and medium amplification zones (low value dominance). This is because the amplification value is related to geomorphological conditions, in which the research area is located in the mountains and is composed of volcanic sediments.

Evaluation of Maturity (Late Diagenesis) in Source Rocks of Jaisalmer Basin in Rajasthan, India using 57Fe Mössbauer Spectroscopy

Abstract The potential of a source rock for hydrocarbon generation depends on several factors such as the amount, type and maturity level of the organic matter present in it as well as the redox conditions in which the sediments containing the source rocks were deposited. Organic-rich sediments deposited in reducing environment have better prospects for a good quality source rock as compared to those deposited in oxidizing environments. The information about the oxidizing/reducing environment at the time of deposition can be obtained from the presence or absence of certain iron-bearing minerals in sediments. The presence of oxide minerals goethite (α-FeOOH) and/or hematite (α-Fe2O3) indicates that sediments were deposited in an oxidizing environment. Therefore the study of iron-bearing minerals in sediments can be used to understand the qualities of the source rocks. Sedimentary samples were collected from different depths of three wells BT-3, DND-1 and LNR-1 located in different structures of the Jaisalmer basin were investigated to understand the chemical state of iron by using Mössbauer spectroscopy. In most of the samples, iron was found mainly in the form of pyrite (FeS2), siderite (Fe, Mg) CO3, 2:1 layer silicates in high spin Fe3+ and high spin Fe2+ state and (Ca, Fe, Mg) carbonates. In the samples from Lathi and Shumarwali formations that belong to the lower Jurassic and Triassic sequences, α-Fe2O3 (hematite) was indeed observed. It was present in a narrow sedimentary depth interval in the wells BT-3 and DND-1 and in a much broader thickness in well LNR-1. The other sedimentary sequences younger than the Lower Jurassic sediments have not shown the presence of any oxide mineral. The present study indicates that oxidizing environment was present in the entire basin in the Lower Jurassic era at least for some duration. However, the degree of oxidation was not uniform as evident from the distribution pattern of iron oxide mineral (α-Fe2O3). Mössbauer studies of source rocks can also be used as a fingerprint to get information about the thermal history (Palaeo-temperature) of sedimentary sequence which is crucial in hydrocarbon prospecting.

Stok Karbon Organik Sedimen di Kawasan Ekosistem Mangrove Pesisir Kabupaten Kolaka Sulawesi Tenggara

Mangrove ecosystem can absorb and store carbon stock in their biomass and sediment. This ecosystem plays an important role in the carbon cycle. This study aimed to analyze the C-organic content and organic carbon stock of sediment, also CO2 absorption. The sediment sampling was conducted in the Kolaka Coastal line mangroves using a Peat Auger for 1 m of sediment depth. Then the sediment was separated into four layers. Then the sediment samples were oven dried at 50°C for 1 week for sediment bulk density analysis (SBD). The analysis of the C-organic content of sediment was done by the LOI method. The estimation of sediment carbon stock using sediment C-organic data and SBD data. The results showed that the highest average of C-organic content was in station 3 (4.12±0.15%). In the othher hand, the highest average of SBD was in station 1 (0.67±0.02 g cm-3). Overall, the total of sediment C-organic stock in station 1 was higher than other station (233.67±11.90 Mg C ha-1). The total capacity of CO2 absorption by sediment in the station 1 was also higher than other station (856.77±37.66 Mg CO2 ha-1). The sediment C-organic stock was influenced by C-organic content and SBD value.