Total Organic Carbon Ratio Research Articles

Petroleum Potentiality and Petrophysical Evaluation of Late Triassic Baluti Formation, Northern Iraq

Source rock potentiality and reservoir characteristics of the Baluti Formation (Late Triassic), Northern Iraq were examined in order to determine the hydrocarbon generation potential and reservoir properties. A combination of geochemical analyses, stable carbon isotope, 1D-basin modeling and digital log data were used to evaluate the formation. The Total Organic Carbon ratios range from 0.39 to 0.61 wt%, while the quantity of free hydrocarbon and residual hydrocarbon are low (0.05-0.11, 0.40-0.90 mg/g respectively). The average of oxygen index is 318 mg CO2/g TOC, while the hydrogen index is less than 200 mg HC/g TOC, which indicates type III kerogen. The outcomes of the pristane/phytane and Pr/n-C17 with Ph/n-C18 ratios suggest that the formation was deposited under oxic environment. This conclusion is also supported by trace elemental data. According to the average of Ro% of 0.58 and Tmax of 430.1oC, the formation is in immature to early mature stage. From a plot of 1D-modeled Ro% versus time, it is inferred that the organic matter of the formation had reached early maturation in the Early Paleocene (63Ma). The Baluti is waxier formation and the degree of waxiness ranges from 1.99-2.55. Regarding to, Triterpanes (Tm/Ts) and regular sterane C27-C29 the studied formation has deposited in terrestrial environment with high terrigenous input with hot and arid to semiarid climates. This result is supported by stable carbon isotopic data and clay mineralogy. Porosity of the dolomite beds is 10-15%. Based on the cutoff results, the Baluti Formation has only 1.13m net pay of 72m thickness, which means that the formation has poor porosity and permeability in the reservoir beds.

Lower Cretaceous calcareous nannofossils and their biostratigraphic and paleoceanographic implications in Southern Tibet

Lower Cretaceous marine strata are widely distributed and well exposed in the Tingri area of Southern Tibet, which includes the Gucuocun and the overlying Gambacunkou Formations. However, the age of the boundary between these two lithologic formations is poorly constrained due to a scarcity of macrofossils. A detailed biostratigraphic study was carried out on the abundant, moderately preserved calcareous nannofossil assemblages obtained from the lower part of the Gambacunkou Formation and the underlying Gucuocun Formation in the Kangsha Section, Tingri. The first occurrence of the marker species Tranolithus orionatus (110.73 Ma) constrains the Gucuocun/Gambacunkou boundary to slightly below the lower boundary of Subzone NC8c (early Albian age), which correlates with Ocean Anoxic Event (OAE) 1b. The absence of Axopodorhabdus albianus and Eiffellithus turriseiffelii throughout the section suggests that the lower part of the Gambacunkou Formation mostly falls within nannofossil Subzone NC8c (110.73–109.94 Ma; early Albian), with a mean sedimentation rate of 12.7 cm/kyr, which is higher than that typical of the open ocean. The consistently high total organic carbon (TOC) and CaCO3 contents in Interval I (Gucuocun Fm.) indicate that productivity was higher during OAE1b, possibly due to increased terrigenous input (as evidenced by elevated C/N and nutrient/fertility indices) that carried nutrients to promote productivity during this event. Nannofossil assemblages and geochemical proxies, including TOC and elemental ratios (Ti/Al, Zr/Al, K/Al), reveal a parallel upsection increase in surface water fertility and continental weathering intensity from Interval II-1 (0–60 m) to the overlying Interval II-2 (60–102 m) in the Gambacunkou Fm., suggesting that enhanced continental weathering contributed to increase the surface water fertility and dilute the sediment carbonate content. These data also indicate that the depositional environment in the Tingri area was aerobic to hypoxic during the early Albian. Our result confirms the presence of OAE1b at the top of the Gucuocun Formation.

Vertical SOC distribution and aromatic carbon in centuries old charcoal‐rich Technosols

AbstractCharcoal‐rich Technosols on century‐old relict charcoal hearths (RCHs) are the subject of ongoing research regarding potential legacy effects that result from historic charcoal production and subsequent charcoal amendments on forest soil properties and forest ecosystems today. RCHs consist mostly of Auh horizons that are substantially enriched in soil organic carbon (SOC), of which the largest part seems to be of pyrogenic origin (PyC). However, the reported range of SOC and PyC contents in RCH soil also suggests that they are enriched in nonpyrogenic SOC. RCH soils are discussed as potential benchmarks for the long‐term influence of biochar amendment and the post‐wildfire influences on soil properties. In this study, we utilised a large soil sample dataset (n = 1245) from 52 RCH sites in north‐western Connecticut, USA, to quantify SOC contents by total element analysis. The contents of condensed highly aromatic carbon as a proxy for black carbon (BC) were predicted by using a modified benzene polycarboxylated acid (BPCA) marker method in combination with diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy‐based partial least square regression (r2 = 0.89). A high vertical spatial sampling resolution allowed the identification of soil organic matter (SOM) enrichment and translocation processes. The results show an average 75% and 1862% increase in TOC and BPCA‐derived carbon, respectively, for technogenic Auh horizons compared to reference soils. In addition to an increase in aromatic properties, increased carboxylic properties of the RCH SOC suggest self‐humification effects of degrading charcoal and thereby the continuing formation of leachable aromatic carbon compounds, which could have effects on pedogenic processes in buried soils. Indeed, we show BPCA‐derived carbon concentrations in intermediate technogenic Cu horizons and buried top/subsoils that suggest vertical translocation of highly aromatic carbon originating in RCH Auh horizons. Topmost Auh horizons showed a gradual decrease in total organic carbon (TOC) contents with increasing depth, suggesting accumulation of recent, non‐pyrogenic SOM. Lower aliphatic absorptions in RCH soil spectra suggest different SOM turnover dynamics compared to reference soils. Furthermore, studied RCH soils featured additional TOC enrichment, which cannot be fully explained now.Highlights BC to TOC ratio and high resolution vertical SOC distribution in 52 RCH sites were studied. RCH soils non‐BC pool was potentially different to reference soils. RCH soils feature TOC accumulation in the topmost horizon. There is BC translocation into buried soils on RCH sites.

Relationships between regulated DBPs and emerging DBPs of health concern in U.S. drinking water

A survey was conducted at eight U.S. drinking water plants, that spanned a wide range of water qualities and treatment/disinfection practices. Plants that treated heavily-wastewater-impacted source waters had lower trihalomethane to dihaloacetonitrile ratios due to the presence of more organic nitrogen and HAN precursors. As the bromide to total organic carbon ratio increased, there was more bromine incorporation into DBPs. This has been shown in other studies for THMs and selected emerging DBPs (HANs), whereas this study examined bromine incorporation for a wider group of emerging DBPs (haloacetaldehydes, halonitromethanes). Moreover, bromine incorporation into the emerging DBPs was, in general, similar to that of the THMs. Epidemiology studies that show an association between adverse health effects and brominated THMs may be due to the formation of brominated emerging DBPs of heath concern. Plants with higher free chlorine contact times before ammonia addition to form chloramines had less iodinated DBP formation in chloraminated distribution systems, where there was more oxidation of the iodide to iodate (a sink for the iodide) by the chlorine. This has been shown in many bench-scale studies (primarily for iodinated THMs), but seldom in full-scale studies (where this study also showed the impact on total organic iodine. Collectively, the THMs, haloacetic acids, and emerging DBPs accounted for a significant portion of the TOCl, TOBr, and TOI; however, ∼50% of the TOCl and TOBr is still unknown. The correlation of the sum of detected DBPs with the TOCl and TOBr suggests that they can be used as reliable surrogates.

Humus Transformation and Compost Maturity Indexes in High-Temperature Composting of Livestock and Poultry Manure

Based on the variations of total humus, humic acid (HA), and fulvic acid (FA) during the manure composting process, the transformation of substances in humus was analyzed, and the compost maturity indexes were constructed by using the TC-TN ratio (C/N), ratio of total humus and total organic carbon (TOC), and humification index (HI). The results showed that: (1) The total humus content in the compost heap decreased firstly and then increased. When compost finished, the total humus content of R1, R2, and R3 was 8.33±0.31, 7.56±0.21, and 7.14±0.35%, respectively; (2) The changes of humic acid (HA) and fulvic acid (FA) concentrations in the three kinds of manure were basically consistent with the changes in total humic acid, which decreased first and then increased; (3) When experiments finished, the ratio of total humus and TOC decreased firstly and then increased. At the end of day 30, HI index was 1.25, 1.15, and 1.01, respectively, increasing by 48.8, 45.56, and 31.16%, respectively.

Reconstructing the paleoceanographic and redox conditions responsible for variations in uranium content in North American Devonian black shales

The uranium (U) content, and more recently, the ratio between 238 U and 235 U in black shales are commonly applied as a proxy to determine redox conditions and infer organic-richness. Uranium contents typically display a linear relationship with total organic carbon (TOC) in shales. This relationship is due to the processes and mechanisms responsible for the incorporation of U into the sediment during the deposition and remineralization of organic matter. This U/TOC relationship can vary, however, and some shales display uncharacteristically low U content despite having high TOC content, while others show large enrichments of U relative to TOC. Here we examine the U to TOC ratios and U-isotope compositions of three Upper Devonian-Lower Mississippian shales: the Woodford Shale, the Cleveland Shale, and the Bakken Shale, with two study sites in Oklahoma, one site in eastern Kentucky, and three sites in eastern Montana and western North Dakota, respectively. The U/TOC ratios of each shale are distinct from one another exhibiting average ratios ranging from 3 in the Cleveland Shale, to over 10 in the Bakken Shale. The distinct geochemical composition of the three shales suggests that, although lithologically similar, each study site represents a markedly different and dynamic depositional environment. The low average U/TOC (~3) along with the relatively high δ 238 U values (~0.03‰) of the Cleveland Shale core suggests deposition along the basin margin under normal marine conditions with periods of reduced bottom water oxygenation, likely due to fluctuations in the location of the pycnocline. The Woodford Shale on the other hand, shows higher U/TOC ratios (~4, George core, ~9, Poe core) and δ 238 U (~0.02‰ average, George core, ~0.06‰ average, Poe core), which suggests an unrestricted setting with intermittent euxinic conditions. In contrast, high U/TOC ratios (2–15), and very high δ 238 U values (up to 0.55‰) in the Bakken Shale cores indicate intense metal draw-down into sediments under sulfidic waters. The results show that when the U/TOC ratios and U-isotopic compositions of each studied shale are compared to modern anoxic basins and upwelling areas, it allows for an enhanced understanding of the paleoenvironmental conditions such as basin restriction and redox state of waters within the Late Devonian epicontinental seas of North America. • U/TOC ratios of Late Devonian shales vary due to basin restriction. • Bottom water euxinia does not require strong basin restriction. • δ 238 U values provide new insight into the paleogeography of N. American basins.

Efficient degradation of tetracycline by persulfate activation with Fe, Co and O co−doped g−C3N4: Performance, mechanism and toxicity

In this work, the porously thin layered Fe, Co and O co − doped g − C3N4 (FCOCN) was synthesized as persulfate (PS) activator for tetracycline (TC) degradation. The characterization demonstrated that Fe, Co and O doping could boost the specific surface area and modulate the electronic structure of g − C3N4. With addition of PS, the FCOCN2 exhibited the maximum TC removal efficiency of 90.1 % after 120 min reaction, and the kinetic constant was 2.67 times that of pure g–C3N4. Meanwhile, the removal ratio of total organic carbon and reaction stoichiometric efficiency of PS could reach to 68.6% and 5.2%, respectively. When the addition of catalyst and PS were 0.6 g/L and 10.5 mM, respectively, the lower pH and TC concentration, as well as higher temperature were conducive to degradation reaction with activation energy at 23.88 kJ.mol−1. As indicated by work function, a lower internal electronic excitation energy barrier enhanced electron transfer, so the active species of •O2−, 1O2, SO4•−, SO5•− and •OH could be favorably generated on over metal (II/III) redox shuttles, electron − rich O/N and electron–deficient C active sites. The quantitative structure − toxicity relationship prediction of intermediates and the acute toxicity experiment showed that the toxicity of water treated for 60 min to V. fischeri, E. coli and B. subtilis was significantly reduced. Moreover, after five consecutive degradation cycles, the removal efficiency of TC still remained at 72.7%. Besides, even in matrices of tap water, river water, municipal wastewater and medical wastewater, the elimination proportion of TC by FCOCN2/PS were 90.0%, 88.6%, 74.0% and 81.5%, respectively. Hence, the FCOCN2/PS system may be a promising alternative for highly effective treatment of antibiotic contained wastewater and environmental protection.

Soil microbial biomass carbon and nitrogen in historic convent gardens under long‐term horticultural cultivation in Krakow, Poland

AbstractThis paper evaluates the seasonal changes of microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN) contents as an indicator of urban soil health. Our research was conducted in six horticultural urban soils in Krakow that have been cultivated for centuries. We investigated the temporal dynamics of microbial biomass C and N in soil samples from 0 to 20 cm depth taken in spring, summer and autumn. The study plots were placed in suburban areas as well as in the centre of the city to distinguish whether the detected effect of altered soil properties is similar to suburban areas. Soil microbial biomass was determined by the chloroform fumigation–extraction (CFE) method. The concentrations of MBC and MBN were measured in the field‐moist soil samples. MBC in the soil ranged from 226.5 to 742.7 mg kg−1 and MBN from 62.7 to 359.6 mg kg−1 expressed in dry mass. Repeated‐measures analysis of variance (ANOVAR, match‐model) was performed to test the main effects and interactions of temporal changes for MBC and MBN. There were significant differences only between MBN concentration in summer and autumn (p < .05). Principle component analysis (PCA) gave insightful results for the whole soil profile. Detrended canonical correspondence analysis (DCCA) indicated that the most explanatory variables in the studied time period were concentration of silt, total nitrogen, MBN and MBC content in the surface layer. Molar ratios of total organic carbon and total nitrogen (TOC:TN) indicated that microbial activity for C and N is enhanced by stoichiometry demands and therefore may be important for vegetation.

Energy composting allows rapid degradation of food waste using a water bath heated with electricity or solar energy

Food waste is a major issue in the context of pollution, climate change, and the future circular economy. Composting kitchen waste is a promising method to recycle elements, yet the efficiency of composting is limited, calling for new processes that degrade rapidly and thoroughly organic matter. Here, we built a rapid laboratory-scale aerobic composting system, equipped with a water bath fueled with either solar energy, or electricity under low sunlight. We tested compositing with and without energy. Results show that only three days are needed to raise the temperature to over 45 °C by energy composting in winter, leading to notable increases in pH, total nitrogen, and cation exchange capacity after 7 days. Composting materials were thoroughly decomposed and mature in 10 days, displaying pH of 7.5, ratio of total organic carbon to total nitrogen of 9.9, cation exchange capacity of 65.61 cmol kg−1, and germination index of 80.4%. Overall, energy composting starts biodegradation quickly in 2 days, reduces effectively the inhibition from some waste compounds, decomposes organic substances well, and yields mature compost.

Anomalously high enrichment of mercury in early Cambrian black shales in South China

The widespread lower Cambrian black shales reflect a significant anoxic event during a global transgression, recording synergistic changes in the marine environment and biological evolution. Extremely high Hg (714–6187 ppb, average is 3380 ppb) contents and Hg to total organic carbon ratios (Hg/TOC: 120–765 ppb/wt.%) were observed in the Danquan section of South China, suggesting that extensive volcanic activities may occur during the early Cambrian. The redox condition of the Danquan section is euxinic as evidenced by multiple redox proxies, which include U/Th, V/Cr, Corg/P and authigenic enrichment of redox sensitive elements (MoEF, UEF). The Co*Mn – Al crossplot revealed that black shale developed in different geographical settings (upwelling setting for the Interval I, and restricted condition for the Interval II). Besides, the sedimentary Hg is hosted in different phases in the two intervals: in organic matter for the Interval I, and in sulfides for the Interval II. Moreover, the anomalous enrichment of Hg in both intervals document the Hg controlled by geographical settings and host phases. Thus, volcanic activities and geographical settings both constrain the evolution of life, as well as redox conditions.

Sedimentary exhalative venting of bioavailable nitrogen into the early ocean

Ore deposits found in Proterozoic marine sedimentary basins supply much of the world's zinc. Many of the deposits formed contemporaneously with their host sediments when saline brines circulating from deeper in the basin reached the sea floor. Textural, geochemical and isotopic features of these SEDEX (‘sedimentary-exhalative’) deposits and their host sediments indicate that biologically active seeps, vents and brine pools were a feature of many ore-forming systems. In mineralised pockets of mid-Proterozoic basins, these ‘microbial oases’ were productive areas in an otherwise low productivity, anoxic, deep marine realm. Here we hypothesize that these metal-rich brines which circulated through organic matter-rich substrate also carried high levels of fixed nitrogen and stimulated distinct ecosystems at sites of mineralisation, or enhanced productivity more broadly in the basin. We tested this hypothesis with organic carbon and nitrogen analyses of samples of carbonaceous siltstone and shale from the 1.64 Ga Barney Creek Formation of northern Australia. The Barney Creek Formation hosts several SEDEX Zn systems, including one of the world's largest deposits at McArthur River Mine (the HYC deposit). Samples come from the mineralised edge of HYC and from correlated strata in drill cores at varying distances (1-60 km) from the deposit. The data reveal lower ratios of total organic carbon (TOC) to total nitrogen (TN) closer to the ore body. Strong correlations (r2>0.7) between TOC and TN and the absence of excess N in the samples suggest that most N was buried as bound to organic matter. Bioavailable N was thus probably more abundant closer to HYC, consistent with fixed nitrogen input by hydrothermal fluids. If correct, our data may suggest that such a hydrothermal nitrogen point source enabled microbes to develop lower C:N ratios in their biomass. A hydrothermal nitrogen source is also supported by a gradient in δ15N values from = +4‰ proximal to the vent to +7.5‰ in distal sites, which may point towards recycling of ammonium from the underlying Wollogorang Formation (1.73 Ga). This unit has previously been identified as a source of over-mature hydrocarbons to the ore-forming fluid. We speculate that, during the mid-Proterozoic, fixed nitrogen carried by SEDEX hydrothermal brines may have locally offset the lack of aerobic nutrient remineralization that characterized most of the anoxic Precambrian deep ocean and thus stimulated biological productivity in areas where the brines reached the sea floor, and, possibly, more broadly as spent brines mixed into the water column.

Cryogenian interglacial greenhouse driven by enhanced volcanism: Evidence from mercury records

An ice-free greenhouse interval (ca. 660 ∼ 650 Ma) occurred between the global Sturtian (ca. 717 Ma ∼ 660 Ma) and Marinoan glaciation (ca. 650 Ma ∼ 635 Ma) during the Cryogenian. While volcanic CO2 emissions have been suggested as a trigger for this ice-free interval, evidence for volcanism has been lacking. In this study, spikes in both Hg concentration (76 to 366 ppb) and Hg to total organic carbon ratio (Hg/TOC: 114 to 717 ppb/wt.%) were observed in the Wuhe section of South China, suggesting that extensive volcanic emissions of Hg occurred during the Cryogenian interglacial period. Positive Δ199Hg (0.02 to 0.18‰) values were observed in these Hg-rich shales, indicating that the volcanic Hg was cycling in the atmosphere, deposited in seawater, and sequestered to sediment via organic matter burial. Combined with other geochemical proxies (e.g., organic carbon isotope and chemical index of alteration), our results provide the first direct evidence that volcanism played a key role in forming the brief Cryogenian interglacial period.

Total and Hot-Water Extractable Organic Carbon and Nitrogen in Organic Soil Amendments: Their Prediction Using Portable Mid-Infrared Spectroscopy with Support Vector Machines

Against the background of climate change mitigation, organic amendments (OA) may contribute to store carbon (C) in soils, given that the OA provide a sufficient stability and resistance to degradation. In terms of the evaluation of OA behavior in soil, total organic carbon (TOC), total nitrogen (TN), and the ratio of TOC to TN (CN-ratio) are important basic indicators. Hot-water extractable carbon (hwC) and nitrogen (hwN) as well as their ratios to TOC and TN are appropriate to characterize a labile pool of organic matter. As for quickly determining these properties, mid-infrared spectroscopy (MIRS) in combination with calibrations based on machine learning methods are potentially capable of analyzing various OA attributes. Recently available portable devices (pMIRS) might replace established benchtop devices (bMIRS) as they have potential for on-site measurements that would facilitate the workflow. Here, we used non-linear support vector machines (SVM) to calibrate prediction models for a heterogeneous dataset of greenwaste composts and biochar compost substrates (BCS) (n = 45) using bMIRS and pMIRS instruments on ground samples. Calibrated models for both devices were validated on separate test sets and showed similar results. Ten OA were sieved to particle size classes (psc’s) of >4 mm, 2–4 mm, 0.5–2 mm, and <0.5 mm. A universal SVM model was then developed for all OA and psc’s (n = 162) via pMIRS. Validation revealed that the models provided reliable predictions for most parameters (R2 = 0.49–0.93; ratio of performance to interquartile distance (RPIQ) = 1.19–5.70). We conclude that (i) the examined parameters are sensitive towards chemical composition of OA as well as particle size distribution and can therefore be used as indicators for labile carbon and nitrogen pools of OA, (ii) prediction models based on SVM and pMIRS are a feasible approach to predict the examined C and N pools in organic amendments and their particle size class, and (iii) pMIRS can provide valuable information for optimized application of OA on cultivated soils at low costs and efforts.

Greigite as an Indicator for Salinity and Sedimentation Rate Change: Evidence From the Yangtze River Delta, China

AbstractFerrimagnetic greigite (Fe3S4) is widespread in the sedimentary environment. Despite abundant reports of greigite occurrence in marine and lacustrine deposits, its formation mechanisms in deltaic deposits remain poorly studied. Here we investigate greigite in Holocene Yangtze River Delta deposits using granulometric, magnetic, and geochemical methods. The studied cores consist of tidal river, estuary, shallow marine, and delta facies in ascending order. The greigite‐bearing layers are found predominantly in the accreting tidal flat facies during the transgression stage and secondarily in the shallow marine facies during the regression stage of the delta's Holocene development. These sedimentary intervals have a higher total sulfur (TS) content and TS to total organic carbon ratios (TS/TOC) suggesting the accumulation of iron sulfides, including greigite, under reducing estuarine and shallow marine conditions. The greigite‐bearing layers in the tidal flat facies have lower Sr/Ba ratios, in comparison to the shallow marine facies, indicating a lower salinity environment. Supported by the dating results, it is suggested that the higher sedimentation rate of the tidal flat facies, caused by rapid sea‐level rise during the early Holocene, favors the formation and preservation of greigite. Our results indicate that the magnetic detection of greigite provides a simple and useful tool for inferring salinity and sedimentation rate changes, and hence better an understanding of the heterogeneity of depositional processes in Holocene delta environments.

Coupled relationships among anammox, denitrification, and dissimilatory nitrate reduction to ammonium along salinity gradients in a Chinese estuarine wetland

Salinization in estuarine wetlands significantly alters the balance between their nitrogen (N) removal and retention abilities but these processes have not yet been characterized effectively. In the present study, the potential rates of sediment denitrification, anaerobic ammonium oxidation (anammox), and dissimilatory nitrate reduction to ammonium (DNRA) were mapped using N isotope tracing methods along salinity gradients across the Yellow River Delta wetland (YRDW) in China. The contribution of anammox to total dissimilatory N transformations in YRDW was merely 6.8%, whereas denitrification and DNRA contributed 52.3% and 40.9%, respectively. The potential rate of denitrification (5.82 μmol/kg/h) decreased significantly along salinity gradients and markedly exceeded DNRA potential rate (2.7 μmol/kg/h) in fresh wetlands, but was lower than that of DNRA in oligohaline wetlands (3.06 and 3.18 μmol/kg/h, respectively). Moreover, a significantly positive relationship between salinity and DNRA/denitrification was obeserved, indicating that increased salinity may favor DNRA over denitrification. Furthermore, total sulfur (TS) content and ratio of total organic carbon to total nitrogen (C/N) increased with the salinity gradient and showed evident positive relationships with the DNRA/denitrification ratio. In this study, we proved that increased salinization resulted in the dominance of DNRA over denitrification, possible through the addition of S and alteration of the C/N in estuarine wetlands, leading to increased N retention in estuarine wetlands during salinization, which would enhance the eutrophication potential within wetlands and in downstream ecosystems.

Anthropogenic impact on the organic carbon sources, transport and distribution in a subtropical semi-enclosed bay

Suspended particulate organic carbon (POC) and sedimentary total organic carbon (TOC) in coastal areas play critical roles in the global carbon cycle, yet sources and dynamics of coastal POC and TOC have been affected by various anthropogenic activities such as aquaculture, sewage discharge, dam construction and land reclamation. To better understand the anthropogenic impacts on coastal organic carbon, this study was carried out in a representative semi-enclosed bay, Dongshan Bay, Southeast China. Through analyses of stable isotopic compositions of both POC (δ13CPOC and δ15NPN) and TOC (δ13CTOC and δ15NTN), the ratio of total organic carbon vs. total nitrogen (C/N), grain size, Chl-a concentrations and hydrological parameters, our study led to the following main findings: 1) During flood season, the distribution of δ13CPOC, δ13CTOC, δ15NPN and δ15NTN values within the bay did not follow the conventional land-sea transition pattern. This distribution pattern indicated more terrestrial organic matter input seaward, which contrasts with the conventional organic matter distribution along the estuarine gradient. 2) Using the organic δ13C, δ15N and C/N signatures of different endmembers, we found that the sources of organic matter deposited in the bay were strongly related to anthropogenic activities, including municipal wastewater discharge, aquaculture, land reclamation and sluice-dyke construction. Furthermore, 3) by applying the Grain Size Trend Analysis Model and the previously-estimated residual current directions, we suggested that human activities have not only altered the sources of organic matter to the semi-enclosed bays, but also significantly modified their transportation and deposition patterns, and might influence the ultimate fate of organic matter into and out of Dongshan Bay. The conclusions of this study should be applicable to similar coastal bays around the world.

Improved denitrification in surface flow constructed wetland planted with calamus

The calamus type surface-flow constructed wetland (SFCW) is widely used for treating low-polluted water bodies, such as effluents from wastewater treatment plants. The calamus biomass is considered a potential carbon source for denitrification, integrating plant biomass into the carbon cycle in SFCWs. This study conducted experiments on the calamus biomass decomposition and evaluated its potential application for denitrification in an SFCW system. We showed that decomposition of the biomass could release a high ratio of total organic carbon (TOC) to total nitrogen (TN), reaching 26.9, 27.7, and 23.6 at biomass doses of 0.1, 0.5, and 1.0 g L −1 . A continuous-flow experiment on the SFCW system revealed that higher TN removal efficiency and load were obtained after the addition of biomass, approximately three times before the biomass addition. Microbial community analysis revealed an increase in heterotrophic denitrifying bacteria (i.e., Flavobacterium , Dechloromonas , and Bacillus ) content throughout the period of biomass addition. This study demonstrated an excellent enhancement of the denitrification efficiency in the SFCW caused by the addition of calamus biomass, suggesting its potential application as an excellent plant carbon source for biological denitrification. • A high C/N ratio (26.9) was released from decomposing 0.1 g L −1 of calamus biomass. • Calamus biomass can be used as carbon source in denitrification processes. • Denitrification efficiency was enhanced by about 200% with the addition of biomass. • Content of denitrifying bacteria was increased by 8 times via adding the biomass.

Mobility of carbohydrates, proteins, phenol and eutrophication assessment in a brackish Egyptian lake; predicted equations

ABSTRACT Although great efforts have been devoted in assessing the ecological risks in aquatic environments, a lack of information is still present. An integrative approach was proposed concerning the mobility of carbohydrates, proteins and phenol among water, sediments and macrophytes in relation to the physical, chemical and geochemical parameters of Lake Mariout. Total carbohydrates, proteins and phenol showed averages of 6.80 mg L−1, 116.90 mg L−1 and 19.46 µg L−1; 89.82 mg g−1; 29.21 mg g−1 and 1.80 µgg−1; and 60.80 mg g−1, 15.27 mg g−1 and 9.29 mg g−1 in water, sediments and macrophytes, respectively. Protein/carbohydrate ratios in sediments were used as the trophic indicator. This study cleared out that all stations had ratios (<1) refereeing to aged organic matter. Station 6 indicated fresh organic matter. Moreover, the ratio of total organic carbon to total nitrogen (TOC/TN) suggested a primarily marine origin at eleven stations (<10) and a mixture of terrestrial input and marine materials (>10) at stations 1 and 7 located in the North-West Basin. Relatively high phenol concentrations of 54.5, 38.25 and 45.37 µgL−1 in water were measured at stations (3 & 5) located in the Main Basin, and station 11 located at El-Qalaa drain, respectively. The partition coefficient of phenol (Kd) varied from 0.053 to 0.199 (<1 Lg−1) revealing high mobility and an underground disposal facility. The low biodiversity of phytoplankton (38 spp.), seagrasses (4 spp.) and seaweed (3 spp.) inside the lake reflected the impact of wastewater discharged. Two phytoplankton blooms were observed at stations 3 and 7. According to the Diversity Index of Boyd, all Mariout stations (<4) are moderately polluted. Multivariate analyses were adopted to describe the lake chemistry. This study gives a conceptual framework helps decision-makers to express the problem of sustainability at Lake Mariout.

Scale‐dependent effects of environmental factors on soil organic carbon, soil nutrients and stoichiometry under two contrasting land‐use types

AbstractVariations in and control of soil total organic carbon (TOC), total nitrogen (TN) and total phosphorus (TP) and their stoichiometric ratios (C:N, C:P and N:P) are critical in agricultural nutrient management. This study examined the scale‐dependent effects of environmental factors on these soil properties under two contrasting land‐use types (tea versus. bamboo) at plot scale (70 × 70 m) and landscape scale (2 × 2 km). Results showed that at both scales, the tea garden generally had higher TOC and nutrient concentrations and lower stoichiometric ratios than the bamboo forest, because of fertilizer and green manure applications in the tea garden. Influences of topography and soil texture on TOC, nutrients and stoichiometric ratios were scale‐dependent. In the tea garden plot, as scale increased, influences of topography and soil texture on TOC, TN and C:N ratio increased, whereas their influence on TP, C:P ratio and N:P ratio decreased. Similar patterns were observed in the forest plot. At the landscape scale, the effects of influences of topography and soil texture on TOC and nutrients were not obvious. The spatial variations in TOC, nutrients and stoichiometric ratios were controlled by both topography and soil texture at the plot scale but were mainly influenced by soil texture at the landscape scale. The influences of topography and soil texture on TOC, nutrients and stoichiometric ratios were generally weaker at landscape than at plot scale. This study confirmed that the effect of scale must be considered when predicting the spatial variations in TOC and nutrients.

Integrated bio-chemostratigraphy of Lower and Middle Triassic marine successions at Spiti in the Indian Himalaya: Implications for the Early Triassic nutrient crisis

In this paper we study the Lilang Super Group in the Spiti area, Indian Himalaya to understand environmental changes in the aftermath of the end-Permian mass extinction. We focus on the Mikin and Kaga Formations, which span the Induan to Ladinian stages of the Lower and Middle Triassic. These strata formed on the southern mid-palaeolatitude margin of East Gondwana and are interpreted as condensed, mixed carbonate – siliciclastic ramp deposits that deepened distally. Carbon isotope ratios of carbonate (δ13Ccarb) show an increase from −2.6 to 0‰ from the Griesbachian substage to the Dienerian-Smithian transition, followed by a negative shift to −3‰ in the Smithian substage and a large positive excursion from −3.0 to 3.5‰ across the Smithian-Spathian boundary. A short negative shift to −1.0‰ occurred in the early Spathian substage, and is followed by a positive trend from ~−1.0 to 1.0‰ in the Middle Triassic, with several minor excursions occurring during the Aegean substage. Carbon isotope ratios of total organic carbon (δ13Corg) co-vary with δ13Ccarb, suggesting that both proxies represent the original isotopic signatures. Sedimentary and palaeontological evidence, as well as trace metal geochemistry (Mo/Al ratio), indicate anoxic conditions developed from the late Griesbachian to the Dienerian substages, and dysoxic to probably fully oxic conditions from the late Dienerian substage onward. Anoxic conditions only very briefly reoccurred in the late Smithian substage. Ti/Ca and Zr/Al ratios suggest a consistently high terrestrial input in the first three substages of the Early Triassic, followed by a decrease across the Smithian–Spathian boundary. Thus, in the Spiti area, the positive δ13Ccarb excursion across the Smithian–Spathian boundary is recorded in generally well‑oxygenated sediments and coincides with a decrease in terrestrial input. While evidence for enhanced weathering is lacking, observations are strongly at odds with studies postulating eutrophication as a universal kill mechanism for the Smithian–Spathian crisis. The strata in the Spiti area contain an Early Triassic gap in phosphorite deposition indicating a ~ 5 Myr waning of coastal upwelling in an otherwise persistent (>100 Myr) upwelling zone of the East Gondwana margin. The phosphorite gap suggests low P availability, low rates of organic matter degradation, and a reduction in nutrient exchange between deep and surface water masses. Altogether, the phosphorite gap, the paucity of sessile and filtering fauna in oxygenated waters, and low organic carbon burial rates indicate a collapse in marine productivity in the aftermath of the end-Permian mass extinction.