Zone Sediments Research Articles

Nitrogen removal and performance deterioration in digested effluent treatment by partial nitrification-anammox (PNA) process based on aeration sedimentation integrated microaerobic reactor (ASIMR)

The existing microaerobic reactors for PN/A process have the drawbacks of complex structure and hard to scale-up in full scale application. Aiming at these problems, we have designed new aeration sedimentation integrated microaerobic reactor (ASIMR). The feasibility of ASIMR for PN/A processes and the optimal HRT were explored by gradually reducing the hydraulic retention time (HRT). When the HRT was 4.45 h and the NLR was 3.98 kg·(m3·d)-1, ASIMR achieved the highest nitrogen removal performance, with the ammonia nitrogen removal efficiency (ARE) and total nitrogen removal efficiency (NRE) of 90.5 % and 79.2 %, respectively, and the total nitrogen removal rate (NRR) could reach 3.15 kg·(m3·d)-1. When HRT decreased to 3.60 h with the NLR of 4.76 kg·(m3·d)-1, the performance deterioration was observed, with ARE and NRE decreasing to 35.9 % and 12.4 %, and NRR decreasing to 0.59 kg·(m3·d)-1. The main reasons for the decrease in nitrogen removal performance were overhigh hydraulic load in the sedimentation zone which led to the loss of nitrifying sludge. The loss of nitrifying sludge in turn reduced the efficiency of ammonia nitrogen removal resulting in the accumulation of free ammonia (FA) which inhibited the activity of nitrogen removal functional bacteria. Although reactor performance deteriorated at too low HRT, when the HRT was much than 4.45 h, ASIMR could achieve a good performance for nitrogen removal owe to the combined action of reactor design, enriched nitrified and anammox sludge as inoculum, and dissolved oxygen control. Except good nitrogen removal performance, ASIMR has another advantage, such as simple structure, low cost for manufacture, and more suitable for engineering scale-up in full scale application.

Organic contaminants levels, distribution and risk assessment in Jeddah marine coastal zone sediments

Herein, various organic contaminants were determined in surface sediments collected from the Jeddah coastal zone, Saudi Arabia, to assess their levels, origin and probable toxic effects on marine organisms. High hydrocarbons concentrations, indicative of an enhanced pollutant burden, were recorded in the Jeddah Lagoon (mean value 4100 mg/kg for total aliphatic hydrocarbons (∑AHC) and 5800 μg/kg for total polycyclic aromatic hydrocarbons (∑PAH)), whereas mean values in Mena Jeddah were 258 mg/kg for ∑AHC and 615 μg/kg for ∑PAH. By using molecular diagnostic ratios/indices and applying Positive Matrix Factorization, petroleum related pollution seems to predominate in Jeddah lagoons, whereas carcinogenic contaminants of pyrolytic origin were dominant in Mena Jedda. Additionally, municipal wastewaters were identified as a major source of pollution in Jeddah lagoons. Comparison of the concentrations of individual PAHs and polychlorinated biphenyls with sediment quality guidelines indicates that, despite their high total values, adverse biological effects are unlikely to occur.

Mercury distribution, mobilization and bioavailability in polluted sediments of Scheldt Estuary and Belgian Coastal Zone

In this study, the vertical distribution of mercury (Hg) in estuarine and marine sediment porewaters and solid phases was assessed by conventional and passive sampling techniques in the historically polluted Scheldt Estuary and Belgian Coastal Zone (BCZ). The Diffusive Gradients in Thin-films (DGT) measured labile Hg concentrations (HgLA) were mostly lower than the porewater Hg concentrations (HgPW), and they also presented different vertical distribution patterns. Still high Hg concentrations in the sediment solid phases, comparable to the historical ones, were observed. Even though pH, redox potential and dissolved sulfide concentration could influence the Hg biogeochemical behaviour, organic matter (OM) played a key role in governing Hg mobilization from sediment solid phase to porewater and in its partitioning between porewater and solid phase over depth. In the marine sediments, where OM had a marine signature, higher labile Hg concentrations in the porewater and faster resupply from the solid phase were observed. The DGT technique showed significant potential not only for the measurement of bioavailable Hg fractions in porewater, but also for the assessment of kinetic parameters governing the release of labile Hg species from the solid phase with the assistance of the DGT Induced Fluxes in Sediments (DIFS) model.

Numerical simulation on the coupling of the elliptical particle motion and phase change

The particle sedimentation and phase change in the mushy zone are accompanied by a variety of complex transfer processes involving momentum, heat, and mass. It is very important to investigate the coupling process of particle settling and melting in the mushy zone for revealing the mechanism of the solid-liquid phase change. In this paper, the motion process and heat transfer characteristics of an elliptic particle as well as two particle interactions in the vertical channel were solved by the finite element method with the consideration of coupling of the phase change and motion. The Arbitrary Lagrangian-Euler Method (ALE) was employed to track the interface of the moving particle and fluid. Results show that the elliptical particle settles along the channel's center line vertically under gravity and undergoes phase change simultaneously. Uneven velocity and temperature fields surrounding the particle are generated by sedimentation, resulting in the particle with an irregular shape. When the initial position of the particle deviates from the center line, the particle deflects during the sedimentation and shifts both left and right in the X-direction. The different initial angles of settling also affect the sedimentation velocity and melting rate. When two particles settle simultaneously, they will lead to complex movement and heat transfer due to the interaction between each other. If the arrangement is eccentric, both particles undergo complex deflections during sedimentation, leading to different melting rates for the two particles.

Sedimentary records of megafloods in the Yarlung Tsangpo Gorge in the eastern Himalaya since the Last Glacial Period

The megaflooding caused by outbursts from Late Quaternary glacially-dammed lakes in the Yarlung Tsangpo Gorge (YTG) potentially shaped the fluvial landscape and controlled the geodynamic evolution of the Namche Barwa Syntaxis in the eastern Himalaya. However, the sedimentary evidence for such flooding in the narrow reaches of the Yarlung Tsangpo River (YTR) valley has been lacking. In this study we conducted geomorphological and sedimentological analyses of the Motuo stretch of the YTR downstream of the Yarlung Tsangpo Gorge and combined these with dating results to identify multistage high magnitude outburst paleofloods. One megaflood event was found to have occurred at ∼5 ka, with a minimum discharge of ∼1.1–4.4×106 m3/s. Our results suggest that this event exceeded 1000 km in range, and was consistent with the age of flood deposits downstream, where the YTR becomes the Siang-Brahmaputra River. Evidence of older and younger flood deposits was also obtained. The erosion caused by this megaflood was stronger in the steep river channel that flows through the uplift center of the Namche Barwa Massif. This may have been principally a response to the differential uplift caused by the main boundary faults. The megaflood event also gave rise to the headward erosion of the YTR's northern tributaries. The megaflood sediment zone is concentrated in the middle and lower reaches of the YTR where the valley widens. Here, the gradient of the river channel is shallower, potentially reflecting weaker tectonic activity accompanied by slower fluvial erosion. Furthermore, multistage catastrophic floods from the Yarlung Tsangpo Gorge may have significantly impacted any downstream prehistoric human settlements.

Ecological State of Bottom Sediments in the Coastal Zone of the Eastern Part of the Gulf of Finland

Ecological State of Bottom Sediments in the Coastal Zone of the Eastern Part of the Gulf of Finland

Beach and Dune Subsurface Hydrodynamics and Their Influence on the Formation of Dune Scarps

AbstractErosive beach scarps influence beach vulnerability, yet their formation remains challenging to predict. In this study, a 1:2.5 scale laboratory experiment was used to study the subsurface hydrodynamics of a beach dune during an erosive event. Pressure and moisture sensors buried within the dune were used both to monitor the water table and to examine vertical pressure gradients in the upper 0.3 m of sand as the slope of the upper beach developed into a scarp. Concurrently, a line‐scan lidar tracked swash bores and monitored erosion and accretion patterns along a single cross‐shore transect throughout the experiment. As wave conditions intensified, a discontinuity in the slope of the dune formed; the discontinuity grew steeper and progressed landward at the same rate as the R2% runup extent until it was a fully formed scarp with a vertical face. Within the upper 0.15 m of the partially saturated sand, upward pore pressure gradients were detected during backwash, influencing the effective weight of sand and potentially contributing to beachface erosion. The magnitude and frequency of the upward pressure gradients increased with deeper swash depths and with frequency of wave interaction, and decreased with depth into the sand. A simple conceptual model for scarp formation is proposed that incorporates observations of upward‐directed pressure gradients from this study while providing a reference for future studies seeking to integrate additional swash zone sediment transport processes that may impact scarp development.

Influence of Beach Slope on Morphological Changes and Sediment Transport under Irregular Waves

This paper presents new data from large-scale wave flume experiments. It shows the beach profile evolution and sediment transport for two different bed slopes (1:15 and 1:25), and three irregular high-energy erosive wave conditions and one low-energy accretive wave condition. The bulk cross-shore net sediment transport was investigated for the total active profile and for the surf and swash zone separately. It is shown that the steep slope is morphologically more active than the gentle slope, with faster and more pronounced morphological changes and larger sediment transport rates. For both slopes, the total and surf zone net sediment transport were offshore-directed for erosive waves and onshore-directed for the accretive wave condition. However, the net swash zone transport for the erosive wave conditions was offshore-directed for the steep slope and onshore-directed for the gentle slope. The direction and magnitude of the total and surf zone sediment transport correlate well with the slope-corrected Dean criterion with increasing offshore-directed sediment transport (erosion) observed for increasing wave energy and bed slope. This relation does not hold for the swash zone sediment transport along the gentle slope, suggesting that swash zone sediment transport processes are not well captured when using a simple predictor such as the (modified) Dean number. Differences in sediment transport in the swash for the different slopes are likely influenced by differences in incoming wave energy, wave–swash interactions and the relative importance of long- and short-waves.

A machine learning-based strategy for predicting the mechanical strength of coral reef limestone using X-ray computed tomography

Different sedimentary zones in coral reefs lead to significant anisotropy in the pore structure of coral reef limestone (CRL), making it difficult to study mechanical behaviors. With X-ray computed tomography (CT), 112 CRL samples were utilized for training the support vector machine (SVM)-, random forest (RF)-, and back propagation neural network (BPNN)-based models, respectively. Simultaneously, the machine learning model was embedded into genetic algorithm (GA) for parameter optimization to effectively predict uniaxial compressive strength (UCS) of CRL. Results indicate that the BPNN model with five hidden layers presents the best training effect in the data set of CRL. The SVM-based model shows a tendency to overfitting in the training set and poor generalization ability in the testing set. The RF-based model is suitable for training CRL samples with large data. Analysis of Pearson correlation coefficient matrix and the percentage increment method of performance metrics shows that the dry density, pore structure, and porosity of CRL are strongly correlated to UCS. However, the P-wave velocity is almost uncorrelated to the UCS, which is significantly distinct from the law for homogenous geomaterials. In addition, the pore tensor proposed in this paper can effectively reflect the pore structure of coral framework limestone (CFL) and coral boulder limestone (CBL), realizing the quantitative characterization of the heterogeneity and anisotropy of pore. The pore tensor provides a feasible idea to establish the relationship between pore structure and mechanical behavior of CRL.

Crustal electrical structure and seismicity of the Weiyuan shale gas block in Sichuan Basin, southwest China

Abstract Hydraulic fracturing, a significant contributor to seismic activity within and around operational fields, has been extensively used in shale gas production. Magnetotelluric (MT) sounding is an effective geophysical tool for identifying high-conductivity fluid-filled and/or molten regions. In this study, we deploy a dense grid of rectangular MT sites to investigate the 3D geoelectrical resistivity structure beneath the Weiyuan shale gas block (WSGB) and subsequently examine the causes of seismic activity. The resistivity data, obtained through 3D inversion accounting for topography using ModEM, reveals a shallow low-resistivity layer (<10 Ω-m) within the WSGB, ranging from ∼2 to 5 km in depth. This layer exhibits multiple isolated areas with very low resistivity (<5 Ω-m), indicative of fluid-filled zones associated with hydraulic fracturing or shale gas-bearing formations. In the northwestern WSGB, the Weiyuan anticline presents a high-resistivity dome extending possibly to depths beyond 20 km, without extending beyond the northern boundary of our study area. Conversely, the sedimentary zone in the southeastern WSGB displays a low-resistivity feature, with an extremely low-resistivity center (<1 Ω-m). Since a consistent high-resistivity zone exists beneath each fault and its top depth is <5 km, so faults might not extend downward below 5 km. Earthquakes with magnitudes (ML) of 3.0 or higher predominantly occur close to the faults, when considering industrial production data, we found a noteworthy correlation between earthquakes with ML < 3.0 and annual shale gas production within the WSGB. Tectonic faulting is not the leading cause for ML < 3.0 earthquakes but likely the primary contributor to seismic events with ML ≥ 3.0.

Redox gradients drive microbial community assembly patterns and molecular ecological networks in the hyporheic zone of effluent-dominated rivers

The impacts of effluent discharge on receiving waterbodies have been a research hotspot. Nonetheless, limited information is available on the microbial community assembly patterns in the hyporheic zones (HZ) responding to the changes in the microenvironments, e.g., solute transport and redox gradient variations. Using two representative effluent-dominated rivers as model systems, the spatio-temporal bacterial community dynamics and assembly patterns in oxic and suboxic zones in the shallow riverbed sediments were disentangled via null model- and neutral model-based approaches. Bacterial dynamics in community composition were observed driven by environmental filtering, i.e., impacts of environmental variables, more than geographic distances, i.e., the depths of sediments. The communities in samples collected in summer were largely shaped by stochasticity, in which homogeneous selection occupied a higher proportion in oxic (∼39%) than in suboxic zone (∼23%). Deterministic processes contributed to a more complex community structure for samples from oxic zones, whereas weakened the interspecies interactions in suboxic zones. The richness and abundances of non-neutral community were confirmed governing the deterministic assembly in oxic zones. Key species ascribed to ‘connectors’ and ‘network hubs’ dominated the community assembly variations in samples collected in winter, and in oxic zones, respectively. Significant positive relationships between β-nearest taxon index and dissolved organic nitrogen (DON) and nitrate highlighted their vital roles in community assembly via deterministic selective pressures in oxic zones. The significance thresholds of nitrogen species for community transition in winter (ΔDON: 2.81 mg-N/L, ΔNO3−: 1.09 mg-N/L) were lower than in summer, probably implying that stricter effluent quality standards should be established in colder seasons. Combined, our work poses first insights on the roles of redox zonation in driving microbial community assembly in HZ, which is of significance in guiding ecological remediation processes in effluent-dominated rivers.

Experimental investigation of local scour around complex bridge pier of sea-crossing bridge under tidal currents

To study the process of local scour around the large-scale complex bridge pier under tidal currents, local scour experiments were carried out using the pile group-cap of the Hong Kong-Zhuhai-Macao Bridge (HZMB) as prototypes. The geological conditions at the bridge site were explored and the sampled soil was experimentally analyzed to determine the model sand. Based on the long-term observation data of tidal currents at the bridge site, a harmonic analysis of tidal currents was conducted to obtain the hydrodynamic characteristics of the tidal currents. Then a flume experiment of local scour around the large-scale pile groups under tidal currents was carried out. Research results indicate that the tidal currents velocity at the HZMB site exhibits the characteristic that the falling tide velocity is greater than the rising tide velocity. The frequency of the flow direction in the N and S directions is more significant. The tidal currents at the bridge site belong to the irregular semi-diurnal tide. The maximum depth of scour under tidal currents occurs on the side with highest velocity in the rising and falling tide process, and its value is slightly lower than the value under unidirectional flow. The duration of equilibrium scour under tidal currents is longer than under unidirectional flow. The shape of the equilibrium scour pit under tidal currents has changed from a circular arc shape on the upstream side to a saddle shape with deep ends and shallow middle, and has formed a longer sedimentation zone at both ends of the rising and falling tides compared to the situation under unidirectional flow. The size and layout of the pile foundation have a significant impact on the shape of the scour pits that achieve equilibrium scour.

Hydrocarbons in bottom sediments of coastal waters of the Kazantip peninsula (Azov Sea)

The aim of the article is to study the bottom sediments of the coastal zone of Kazantip peninsula in the Sea of Azov of complexes of hydrocarbon pollution. This water area is a site with a high level of recreational load, despite the presence of a nature reserve there, and is also characterized by a rugged coastline, which causes the accumulation of pollution in bottom sediments. The material for the study was samples of the upper layer of bottom sediments, which were taken in the summer of 2021 in the coastal waters of Cape Kazantip (Sea of Azov) with a manual sampler from depths of up to 1.5 m both within the protected area and beyond its borders. Determination of hydrocarbons in bottom sediments was carried out by gas and liquid chromatography in accordance with certified methods. The paper presents new original materials on the distribution of hydrocarbons in bottom sediments in the area of Kazantip peninsula, as well as an assessment of the local level of pollution of marine soils in this area. The ratio of hydrocarbons of different origin in bottom sediments is given. In addition, possible ways and sources of pollution are indicated. As a result of the study, it was shown that the bottom sediments of the coastal zone of Kazantip peninsula are not polluted and the concentrations of the main groups of hydrocarbons are within the range of average values for the Sea of Azov. But, despite this, there are traces of fresh inflows of petroleum hydrocarbons, which can be of both anthropogenic and natural origin.

Bacterial community driven nitrogen cycling in coastal sediments of intertidal transition zone

Microorganisms inhabiting in coastal sediments significantly affect the nitrogen cycling in coastal waters and ecosystems. However, the bacterial community that related to the key active nitrogen transformation processes in intertidal transition zone are still not understood. Across a long flat intertidal zone at depths from 0 to 3 m in Daya Bay, China, the bacterial communities in sediments and their driven nitrogen cycling potential were evaluated with environmental factors and 16S rRNA sequencing. The results showed that the intertidal zone is a divide for environmental factors as pH, salinity and C/N ratio, instead of an average shift from freshwater to salt water. At the same time, the environmental factors influenced the abundance of bacterial community related to nitrogen cycling. Across the intertidal zone, the dominant nitrogen transformation processes were different. At the high tide and middle tide sites, the primary nitrogen cycling process was nitrification that worked with Nitrosomonadaceae, Nitrospiraceae, 0319-6A21, and wb1-A12. At the low tide sites, nitrogen fixation was the dominant function conducted by Bradyrhizobiaceae. The reduction of nitrate was carried out with the help of Xanthomonadales but relatively weak in all sampling sites especially for low tide sites. This was mostly because the richness and evenness of bacterial community were the lowest at the low tide sites. Meanwhile, the pH, Cl−, salinity, NH4+, NO3− and C/N ratio were the important factors that shaped the composition of local bacterial community. Further, the nonmetric multidimensional scaling results indicated that there were significant statistical differences in the composition of bacterial community among samples at different layers. The dominant nitrogen cycling processes in coastal sediments at different tide levels were revealed in this study, which offered an extended concept of nitrogen transformation along the groundwater discharge path in the intertidal transition zone. The distributions and compositions of bacterial communities and predicted functions provided a new insight for coastal environment and ecosystem management.

Numerical modeling of vadose zone electrical resistivity to evaluate its hydraulic parameters

Studying and determining the physical properties and hydraulic parameters of vadose zone sediments is an important key to evaluate the infiltration rate into them and assessing the extent to which aquifer sediments benefit from rainwater harvesting in arid and semi-arid areas. Due to the lack of sufficient data on the characteristics of this zone depths, a numerical modeling was used to simulate the electrical resistivity of these sediments by applying the electrical resistivity method, because it is the most affected by the physical properties of dry and wet sediments. This study was applied as a proposal for application in northwestern KSA to calculate the vertical hydraulic conductivity and transmissivity for the vadose zone. This was implemented by assuming a three-layer model using COMSOL Multiphysics model with different electrical resistivity values depending on some in situ electrical resistivity measurements for shallow depths. Hence, the infiltration rate of sediments in this area can be predicted with depth and its effect on aquifer recharge. The focus was on calculating the vertical hydraulic parameters of the most widespread surface sediments with depth and comparing the results of calculating these parameters for some sediments laboratory-wise to ensure their accuracy. Then, their infiltration rate was inferred separately with depth, predicting their ability to aquifer recharge and make the most of rainwater harvesting. Finally, this study can be considered as a preliminary study to determine the expected forward model of electrical resistivity and hydraulic parameters values for the vadose zone sediments with depth along the area and in any other areas, and then apply them accurately in situ to estimate the extent of its usefulness in rainwater harvesting, especially aquifer recharge.

Gley catagenesis of Devonian red-colored rocks on the Middle Timan

Research subject. The article presents the results of morphological, mineralogical, and geochemical studies into gley zones in the Devonian red-colored sediments of the Middle Timan. Aim. Determination of the timing of gleization processes in the formation history of the Devonian sedimentary strata; identification of morphological, mineralogical and geochemical features of gley zones. Methods. A macroscopic study of the morphology of gley zones in successive sections of the sediments was carried out in field conditions. Thin sections were studied using a Nikon eclipse LV100 ND polarization microscope with a Nikon DS Fi2 camera; polished samples were characterized using a TESCAN electron microscope VEGA3 with an Oxford instruments X-Max energy dispersion attachment; the chemical composition was determined by an X-ray fluorescent silicate method on a MESA-500W spectrometer; X-ray diffraction analysis was performed using a Shimadzu XRD-6000 diffractometer under the CuKα radiation. Results. In terms of size and morphological features, the gley zones under study are divided into four types: point, veined, lens-shaped, and bed-shaped. The similarity between the forms of gley zones and core organics fragments was established both in plan and vertically. The lithological heterogeneity of rocks (stratification) does not have any effect on the development of gley processes. Changes in the content of rock-forming elements during gleization are confined to intensive iron removal and a slight decrease in the potassium content; the silica content remains almost unchanged. An increase in the content of aluminum, titanium, and magnesium was observed. Among the contents of microelements, trends towards accumulation of Y and Yb, removal of Ga, V, Co, Ni are noticeable. Conclusions. Gleization processes proceeded for a very long time until the sedimentary sequence was completely formed and compacted; the main mechanism of chemical element migration was diffusion.

Using compound-specific isotope analysis to identify the mechanism of acetochlor degradation during oxygenation of hyporheic zone sediment

Biodegradation is recognized as the main pathway for acetochlor attenuation in aquatic environments. However, the potential abiotic degradation of acetochlor by hydroxyl radicals (•OH) generated during oxygenation of hyporheic zone sediments has not been investigated. This study aims to examine the production of •OH during oxygenation of hyporheic zone sediments and its effects on acetochlor attenuation. A significant decrease of acetochlor, ranging from 77.9% to 100%, was observed in the water-sediment systems with extensive •OH production. The primary sources of •OH production were found to be the oxidation of Fe(II) and reduced humic acids. Furthermore, a •OH quenching experiment suggests that •OH driven oxidation is the dominant pathway for acetochlor attenuation. Carbon isotope fractionation of acetochlor degradation during oxygenation of sediments (εbulk,C ranged from −1.5‰ to −0.5 ± 0.3‰) was close to that during acetochlor degradation by •OH in a H2O2–Fe3O4 Fenton system (εbulk,C = −0.5 ± 0.1‰), but significantly smaller than that during acetochlor biodegradation (εbulk,C = −5.8 ± 0.9‰). Compound-specific isotope analysis (CSIA) further suggests that •OH produced by sediment oxygenation plays a critical role in acetochlor attenuation in aquatic environments. Results of calculated apparent kinetic isotope effect of carbon (AKIEC) and transformation products indicate that SN1 and SN2-type nucleophilic substitution are the first steps in acetochlor attenuation through •OH driven oxidation (AKIEC = 1.007 ± 0.001) and aerobic biodegradation (AKIEC = 1.088 ± 0.013), respectively. Our findings highlight the potential of CSIA to assess the acetochlor degradation in water-sediment system, which can help to elucidate the fate of herbicide in aquatic environments.

Evidence of cryptic methane cycling and non-methanogenic methylamine consumption in the sulfate-reducing zone of sediment in the Santa Barbara Basin, California

Abstract. The recently discovered cryptic methane cycle in the sulfate-reducing zone of marine and wetland sediment couples methylotrophic methanogenesis to anaerobic oxidation of methane (AOM). Here we present evidence of cryptic methane cycling activity within the upper regions of the sulfate-reducing zone, along a depth transect within the Santa Barbara Basin, off the coast of California, USA. The top 0–20 cm of sediment from each station was subjected to geochemical analyses and radiotracer incubations using 35S–SO42-, 14C–mono-methylamine, and 14C–CH4 to find evidence of cryptic methane cycling. Methane concentrations were consistently low (3 to 16 µM) across the depth transect, despite AOM rates increasing with decreasing water depth (from max 0.05 nmol cm−3 d−1 at the deepest station to max 1.8 nmol cm−3 d−1 at the shallowest station). Porewater sulfate concentrations remained high (23 to 29 mM), despite the detection of sulfate reduction activity from 35S–SO42- incubations with rates up to 134 nmol cm−3 d−1. Metabolomic analysis showed that substrates for methanogenesis (i.e., acetate, methanol and methylamines) were mostly below the detection limit in the porewater, but some samples from the 1–2 cm depth section showed non-quantifiable evidence of these substrates, indicating their rapid turnover. Estimated methanogenesis from mono-methylamine ranged from 0.2 to 0.5 nmol cm−3 d−1. Discrepancies between the rate constants (k) of methanogenesis (from 14C–mono-methylamine) and AOM (from either 14C–mono-methylamine-derived 14C–CH4 or from directly injected 14C–CH4) suggest the activity of a separate, concurrent metabolic process directly metabolizing mono-methylamine to inorganic carbon. We conclude that the results presented in this work show strong evidence of cryptic methane cycling occurring within the top 20 cm of sediment in the Santa Barbara Basin. The rapid cycling of carbon between methanogenesis and methanotropy likely prevents major build-up of methane in the sulfate-reducing zone. Furthermore, our data suggest that methylamine is utilized by both methanogenic archaea capable of methylotrophic methanogenesis and non-methanogenic microbial groups. We hypothesize that sulfate reduction is responsible for the additional methylamine turnover, but further investigation is needed to elucidate this metabolic activity.

Influencing Factors and Nutrient Release from Sediments in the Water Level Fluctuation Zone of Biliuhe Reservoir, a Drinking Water Reservoir

Significant amounts of nitrogen and phosphorus in sediments will be released into the overlying water during the flood season in the water level fluctuation zone (WLFZ) of reservoirs that undergo periodic drying and flooding. This will result in water quality deterioration of the reservoir. In order to clarify the distribution characteristics and release behavior of nitrogen (N) and phosphorus (P) from sediments in the WLFZ of a reservoir, this study analyzed the sediment distribution characteristics and potential exchange flux sediment–water interface(SWI) through field investigations and sediment core incubation experiments. And the main factors affecting the release of N and P through the incubation experiments in sediments of the WLFZ in the reservoir were determined. Our findings indicated that the sediment in the WLFZ serves as the primary source of NH4+-N and acts as a sink for NO2-N in the overlying water of sediment. The concentration of NH4+-N in the interstitial water of sediments is the key factor that affects the water quality of Biliuhe Reservoir. Total nitrogen content of surface sediments in the WLFZ of Biliuhe Reservoir ranges from 1052.52 ± 49.39 to 3520.54 ± 30.31 mg/kg. High concentrations of N pollution are the primary increased risk of eutrophication in Biliuhe Reservoir during summer. The sediment N and P release flux of BLH1 located in the main stream is 1.67 ± 1.06 and 12.32 ± 2.42 mg·(m2·d)−1, respectively, which is smaller than that of BLH2 (3.27 ± 2.15 and 15.19 ± 2.36 mg·(m2·d)−1, respectively), BLH3 (4.24 ± 1.74 and 17.02 ± 2.47 mg·(m2·d)−1, respectively) and BLH4 (7.78 ± 2.03 and 20.56 ± 2.38 mg·(m2·d)−1, respectively) located in the tributary. It indicates that the water conveyance project located in BLH1 has an impact on nutrient scouring of sediments in the WLFZ at this site. The main water environment factor affecting the release of N and P in the sediment of the WLFZ is dissolved oxygen (DO). And the Pearson correlation coefficients between TN and TP with DO were −0.838 and −0.777, respectively (p < 0.05). At the same time, the diffusion of nutrients in the sediments can be effectively inhibited by maintaining a certain DO concentration in the overlying water.

Tropicibacter oceani sp. nov., a novel sulfur-metabolizing bacteria isolated from the intertidal zone sediment of Chinese Yellow Sea.

In this study, we reported a Gram-stain-negative, rod-shaped, atrichous, and aerobic bacterial strain named YMD87T, which was isolated from the intertidal zone sediment of Chinese Yellow Sea. Growth of strain YMD87T occurred at 10.0-40.0°C (optimum, 25-30°C), pH 4.0-12.0 (optimum, 8.0) and with 0-6.0% (w/v) NaCl (optimum, 0.0-2.0%). Phylogenetic tree analysis based on 16S rRNA gene sequence indicated that strain YMD87T belonged to the genus Tropicibacter and was closely related to Tropicibacter alexandrii LMIT003T (97.2% sequence similarity). Genomic analysis indicated that strain YMD87T contains a circular chromosome of 3,932,460bp with G + C content of 63.8% and three circular plasmids of 116,492bp, 49,209bp and 49,673bp, with G + C content of 64.3%. Genomic functional analysis revealed that strain YMD87T is potential a novel sulfur-metabolizing bacteria. The predominant respiratory quinone of YMD87T was ubiquinone-10 (Q-10). The major polar lipids of YMD87T contained phosphatidylglycerol, phosphatidylethanolamine, five unidentified lipids, five unidentified phospholipids, phosphatidylcholine, unidentified glycolipid and five unidentified aminolipids. The major fatty acids of strain YMD87T contained C12:1 3-OH, C16:0, and summed feature 8 (C18:1 ω7c or/and C18:1 ω6c). Phylogenetic, physiological, biochemical and morphological analyses suggested that strain YMD87T represents a novel species of the genus Tropicibacter, and the name Tropicibacter oceani sp. nov is proposed. The type strain is YMD87T (= MCCC 1K08473T = KCTC 92856T).