Supply Of Organic Matter Research Articles

The heterogeneous characteristics and their influencing factors of organic matter of saline lacustrine hydrocarbon source rocks

The heterogeneous characteristics and their influencing factors of organic matter are still the research focuses of saline lacustrine hydrocarbon source rocks. This paper examined the heterogeneous characteristics of organic matter richness and type. The effects of tectonic activities, sedimentary facies, climate, biological sources, and preservation conditions on organic matter richness and type were examined in the Yiliping Depression, Qaidam Basin, northwestern China. Organic matter enrichment models for the Yiliping Depression were developed. Total organic carbon (TOC) content, extractable organic matter (EOM) content, and free hydrocarbon and kerogen thermal cracking hydrocarbon yield of mudstones are higher than 0.5%, 0.05% and 0.5 mg/g in the condensed sections and the early stage of high stand systems tracts while lower in other intervals. The heterogeneity of organic matter richness and type in the Pliocene is displayed. With the uplift of the A-erh-chin mountains, influenced by the Himalayan tectonic movement during the Neogene, the sedimentary facies were mainly saline lakes with braided river deltas, and their depocenters gradually migrated eastward. Climatic conditions changed from humid in the lower Pliocene to dry in the middle and upper Pliocene. Multiple water transgressive and regressive cycles formed multiple condensed sections and high stand systems tracts, where enough accommodation space, organic matter supply, favorable preservation conditions resulting from relatively deep and quiet water brought more organic matter accumulation. Mixed input of aquatic algae and terrestrial plants formed type II2 and type III kerogen in the depression, and there are more type II1 and type I hydrocarbon source rocks around lacustrine centers. The saline lacustrine evolution and organic matter accumulation models were developed, showing that the peak saline lacustrine period in the middle Pliocene was the most favorable for organic matter enrichment. The results indicate that there are active hydrocarbon source rocks (TOC content more than 0.4% and reflectance of vitrinite more than 0.5%) from the Neogene around the Jianshishan and Hongsanhan structures, and the Yikeyawuru and Taijinaier structures in the Yiliping Depression.

Roles of sediment supply, geochemical composition and monsoon on organic matter burial along the longitudinal mud belt in the East China Sea in modern times

Terrestrial sediment supply and its composition, aquatic productivity and coastal hydrodynamics together control the nature of organic matter (OM) that buried in ocean margins. Distinguishing their individual roles in river-dominated continental margins is challenging, but crucial for understanding (i) the regional carbon cycle in modern times and (ii) the OM burial-climate link on shorter timescales. Here we investigate the contents of total organic carbon (TOC) and total nitrogen (TN) and stable carbon isotopic composition of TOC (δ13C), along with grain size and calcium carbonate, in three short, 210Pb- and 137Cs-dated, sediment cores (DH1-1, DH3-3 and DH5-1) from the Yangtze distal mud belt in the East China Sea to delineate the spatiotemporal distribution, origin and burial flux of sedimentary OM for the last ca. 130 years. We also use selected inorganic elements (Si, Al, Ca, Na, K, Rb and Sr) and geochemical proxies derived from them (i.e. chemical index of alteration-CIA, molar Al/Si, molar K/Na, K/Rb and Rb/Sr) to elucidate the importance of detrital composition and chemical weathering on the supply, transport and burial of OM.Bulk organic geochemical and grain size data suggest a longer transport of fine sediments-laden OM, indicating the role of China Coastal Current on hydrodynamic sorting in the study area. Spatial distribution of Al/Si, K/Na, Rb/Sr and CIA in all cores corroborates the selective transport of fine-grained minerals from the Yangtze estuary to the distal mud belt. Less variable molar C/N ratios (5.6–7.7) and δ13C values (–22.4 to –21.2‰) in our cores and the results of δ13C mixing model indicate the predominance of marine OM burial over the last century in the study area. Relationships of TOC, δ13C and mean grain size and spatial evolution of δ13C along the river-mud belt continuum show that adsorption of marine OM on the Yangtze-derived fine sediments during their southward transport. Estimated mean burial fluxes of terrestrial and marine OC (0.73 ± 0.21 and 1.88 ± 0.29 Tg C yr−1) indicate that the Yangtze distal mud belt, despite covering ~18% of the shelf area, acts as a key OM sequestration center (>50%) in the East China Sea. Comparison of records of riverine OC burial and geochemical weathering and grain size proxies of our cores with East Asian winter monsoon index, and sediment and water discharges in the Yangtze River confirms that hydrodynamics associated with the winter monsoon winds-driven China Coastal Current predominantly controlled the sediment accumulation and OM burial along the mud belt before 1970s. Nonetheless, human activities especially the construction of Three Gorges Dam have reduced the burial flux of terrestrial OC from 0.93 to 0.54 Tg yr−1, significantly affecting the supply and burial of OM and thus the regional carbon cycle since 1970s.

The organic, inorganic and isotope geochemistry of the holocene sapropel units in the sea of Marmara and their paleoceanographic significance

The ocean redox structure and nitrogen utilization are investigated in the Holocene sapropel depositions in the Sea of Marmara, based on inorganic, organic, and isotopic analyses and grain-size distribution of the sediments of a piston core from Çınarcık Basin. Two sapropel units are identified in the core studied, the lower (main) sapropel of the early Holocene and the upper sapropel of the middle-late Holocene. Relatively high C/N ratios (10–11) and smaller δ13Corg values (~−26‰) in the lower Holocene sapropel unit indicate that the organic matter is mainly of terrestrial origin. Up to 5.5‰ δ15N values and Mo concentration (6.5 ppm) above crustal values in the bottom of the lower sapropel unit strongly suggest that bottom-water conditions were denitrifying and suboxic-dysoxic, suitable for the preservation and burial of the organic matter. Such bottom-water conditions were induced by water stratification that resulted from the transgression from the Aegean Sea coupled with a riverine influx from the Black Sea that provided the terrestrial organic matter. A progressive upward decrease of C/N ratios and increase of δ13Corg values in the upper sapropel unit might have been caused by the additional supply of organic matter of mainly marine origin and improved ventilation of the lower water, which resulted in the oxidation of the organic nitrogen pool and a decrease of δ15N values (below 3‰) under nitrate-rich conditions. Mn enrichment in the upper sapropelic sediments also supports a relatively oxidative environment.

Structure and dynamics of a Pampa plain, (Argentina) shallow lake over the last 600 years

A multi-proxy analysis, including pollen, non-pollen palynomorphs and plant macrofossil remains was performed to reconstruct the paleoenvironmental history of the Cabeza de Buey shallow lake (36°17′S, 61°10′W) over the last 600 years. We identified the main forcing factors behind changes in the structure and dynamics of the lake communities. Given the relatively low intensity of human activity during the early period of the lake history (prior to 1880 AD), changes in dominant communities were mainly controlled by climate. Afterwards, changes probably resulted from a combination of climate and human impacts that generated an accelerated eutrophication. Four periods in the lake’s evolution were recognized based on changes in macrophyte and algae communities’ structure. Between ca. 1320 and ca. 1630 AD a shift was evidenced from an oligotrophic brackish with low nutrient content (dominated by Botryococcus braunii) to a mesotrophic fresh water body (dominated by Pediastrum and Scenedesmus), due to an increase in the water level associated with an increase in precipitation. At ca. 1840 AD a transition towards a phase dominated by Myriophyllum spicatum was noted, induced by a low water level as a consequence of low precipitation. Later, at ca. 1880 AD, the current lake conditions were established, and the increase in nutrient and organic matter supply influenced plant community structure towards organic tolerant species of submerged macrophytes (Potamogeton pectinatus). Towards the beginning of the twenty-first century, the lake turned to a more eutrophic state, which is evidenced by the dominance of the phytoplankton community. The last hundred years of the lake history were characterized by the eutrophication process related to the impact of agriculture and cattle breeding implemented in the landscape as well as to the urban settlement. This study made it possible to infer changes in the structure and dynamics of Cabeza de Buey lake and to elucidate the forcing factors that induced these changes on a high-resolution scale.

Enhanced terrestrial organic matter burial in the marine shales of Yangtze platform during the early Carboniferous interglacial interval

The supply and preservation of terrestrial organic matter (TOM) during early Carboniferous glacial-interglacial intervals in South China were investigated with respect to their roles in paleo-environmental variation and organic matter (OM) accumulation in black shales. The marine redox proxies such as V/Cr, Corg/P ratios, and Mo–U covariation indicate a fully oxic water condition during the earliest Visean, while dominant oxic with occasional suboxic water conditions prevailed during the early to middle Visean. High sedimentary δ15N values (1.9–6.3‰) suggest the existence of enhanced water-column denitrification in the expanded oxygen minimum zones (OMZs) during the earliest Visean, whereas lower δ15N values (avg. 2.6‰) during the early to middle Visean indicate a decreasing water column denitrification in the reduced OMZs. Both the organic matter compositions and the relationship between Corg/N ratios and δ13Corg values indicate a significant contribution of terrestrial OM in the marine sediments, and the low abundance of marine OM is mainly attributed to the low paleoproductivity as evidenced by low P/Ti and Ba/Al ratios. One reason for such a high contribution of TOM is that a large amount of plant debris and wildfire-derived OM was preserved during Tournaisian glacier time and then released and buried rapidly in the marine sediments during the interglacial interval of Visean due to the temperature-driven glacial melting. The rapid transportation of large quantity of TOM from land to ocean may have resulted in remarkable drawdown of atmospheric pCO2 and subsequent cool climate, as evidenced by the decoupled relationship between δ13Corg and δ13Ccarb values. In summary, the sinking of TOM flux during the sea level lowstand and highstand may be the controlling factor for the paleo-environmental variation as well as OM accumulation in the Visean black shales.

Interaction Between Oxygen Consumption and Carbon Dioxide Emission in a Subtropical Hypoxic Reservoir, Southeastern China

AbstractIt is well recognized that dam construction aggravates eutrophication and hypoxia in river reservoirs, but the interaction between oxygen dynamics and carbon cycling is often unclear. Here we investigated the external and internal controls on oxygen consumption and effects of hypoxia on carbon dioxide (CO2) emission in a subtropical reservoir in southeast China based on detailed field measurements during 2017 and 2018. Hypoxia lasted 4 months starting in mid‐July and expanded from the bottom to near surface water. Rainstorm hyperpycnal flow and unusual hydraulics (outflow exit 40 m from the bottom) resulted in two thermoclines and enhanced the oxygen deficit in deeper water. Microbial respiration accounted for 67.4%–96.5% of total oxygen consumption in the bottom water. The increased supply of organic matter from storm runoff and to a lesser extent primary production in summer enhanced subsequent oxygen consumption. We observed an imbalance between excess CO2 production and oxygen depletion in summer and winter which was likely associated with other processes in the hypolimnion (e.g., chemoautotrophy, anaerobic degradation of organic matter, proton buffering, and nitrification). The water‐air CO2 fluxes suggest that the surface reservoir usually served as a CO2 source, but was a sink in summer due to high primary productivity. CO2 was always oversaturated in the hypolimnion; this layer was at the depth of the dam outflow and ultimately released 68% of annual CO2 efflux to the atmosphere. This research confirmed that construction of a hydropower dam has substantially altered reservoir metabolism and regulated the CO2 emission pathway.

Contribution of anecic and epigeic earthworms to biological control of Fusarium graminearum in wheat straw

Earthworms have proved to contribute to plant health indirectly, by improvement of soil physical and chemical properties, as well as directly, through suppression of plant pathogens. Fusarium Head Blight, caused primarily by Fusarium graminearum, is one of the most important cereal diseases, with severe detrimental effects on yield and grain quality worldwide, and significant effect on grain safety due to the accumulation of mycotoxins produced by the fungus. Earthworms could reduce the residue-borne inoculum density of F. graminearum through different mechanisms, including direct competition by residue consumption, growth inhibition caused by the earthworm coelomic fluid, mechanical disruption of fungal hyphae, and burying crop residue which reduce the chances for the fungus to release spores for head infection. Thus, the aim of this study was to assess the effects of anecic and epigeic earthworms on wheat straw and on F. graminearum inoculum. For this, PVC cylinders (microcosms 14.5 cm diameter, 30 cm height) were filled with moist soil mix, wheat straw was evenly distributed on the soil surface (inoculated with Fusarium, soil microorganisms or sterile) and three earthworm species (Aporrectodea longa, Lumbricus rubellus or Lumbricus terrestris) were tested. Since the response of earthworms may change according to conditions of soil moisture and food availability, two different experiments were arranged. The first Experiment represented a sub-optimal situation for earthworms regarding soil moisture and feeding conditions, which was obtained by scarce watering of the microcosms with a consequent decrease in soil water content during incubation, and by not adding cow manure as supplementary food source. In the second experiment, soil was enriched with cow manure as feed for the earthworms and soil moisture was maintained above 25%. Results from qPCR analysis revealed that F. graminearum inoculum on straw was reduced to undetectable amounts by L. rubellus and A. longa when the feeding conditions were limited, while no significant differences compared with the control without earthworms were found when earthworms had high food availability (α = 0.05). Straw coverage on soil surface was reduced by L. rubellus (epigeic) in both experiments (p < 0.0001), while A. longa (anecic) just did so under optimal conditions. L. terrestris (anecic), only tested under optimal conditions, reduced soil cover significantly more than the other two species (p < 0.0001). Negative effect of this fungus was not observed on the studied earthworms. Both anecic and epigeic earthworms tested showed potential to contribute to biological control of F. graminearum in wheat straw. This control may occur by reducing straw on surface, reducing the pathogen inoculum on straw, or both, depending on the environmental conditions and their response according to their ecological group and species. The possibilities to optimize earthworm capacity for biological control of fungal diseases in practical agriculture, under changing weather and organic matter supply conditions, are discussed.

Spatial and temporal dynamics of nitrogen exchange in an upwelling reach of a groundwater‐fed river and potential response to perturbations changing rainfall patterns under UK climate change scenarios

AbstractWe report the complex spatial and temporal dynamics of hyporheic exchange flows (HEFs) and nitrogen exchange in an upwelling reach of a 200 m groundwater‐fed river. We show how research combining hydrological measurement, geophysics and isotopes, together with nutrient speciation techniques provides insight on nitrogen pathways and transformations that could not have been captured otherwise, including a zone of vertical preferential discharge of nitrate from deeper groundwater, and a zone of rapid denitrification linking the floodplain with the riverbed. Nitrate attenuation in the reach is dominated by denitrification but is spatially highly variable. This variability is driven by groundwater flow pathways and landscape setting, which influences hyporheic flow, residence time and nitrate removal. We observed the spatial connectivity of the river to the riparian zone is important because zones of horizontal preferential discharge supply organic matter from the floodplain and create anoxic riverbed conditions with overlapping zones of nitrification potential and denitrification activity that peaked 10–20 cm below the riverbed. Our data also show that temporal variability in water pathways in the reach is driven by changes in stage of the order of tens of centimetres and by strength of water flux, which may influence the depth of delivery of dissolved organic carbon. The temporal variability is sensitive to changes to river flows under UK climate projections that anticipate a 14%–15% increase in regional median winter rainfall and a 14%–19% reduction in summer rainfall. Superimposed on seasonal projections is more intensive storm activity that will likely lead to a more dynamic and inherently complex (hydrologically and biogeochemically) hyporheic zone. We recorded direct evidence of suppression of upwelling groundwater (flow reversal) during rainfall events. Such flow reversal may fuel riverbed sediments whereby delivery of organic carbon to depth, and higher denitrification rates in HEFs might act in concert to make nitrate removal in the riverbed more efficient.

The molecular composition of extractable soil microbial compounds and their contribution to soil organic matter vary with soil depth and tree species

Recent findings on soil organic matter (SOM) revealed that soil microorganisms are not only crucial for SOM formation through plant litter degradation but soil microbial biomass (SMB) may also directly contribute to SOM and its composition. However, the role and interactions of litter quality, microbial turnover and composition of SMB and SOM remain unclear. Hence, soil profiles (organic forest floor and mineral soil layers) at a recultivated and afforested post-mining site were investigated for the influence of litter quality from different tree species (Fagus sylvatica, Pseudotsuga menziesii, Pinus nigra) and soil depth – representing different degrees of organic matter (OM) turnover – on the molecular composition of chloroform fumigation extracted SMB-derived compounds in comparison with easily extractable (non-fumigated) SOM-derived compounds. The SMB extracts were analyzed for microbial biomass carbon (MBC), nitrogen (MBN) and phosphorus (MBP). The molecular composition of SMB and SOM compounds were determined by electrospray ionization Fourier transformation ion cyclotron resonance mass spectrometry (ESI-FT-ICR-MS) complemented by the determination of nine monosaccharides representing microbial or plant origin.Van Krevelen diagrams obtained from the ESI-FT-ICR mass spectra revealed the substantial contribution of microbial-derived compounds to extractable SOM that further increased with soil depth. Analysis of the easily extractable monosaccharides implied that >99% were of microbial origin. Microbial sugars as well as MBC, MBN and MBP explained best depth-related variations of extractable SMB compounds indicating that supply and availability of C-rich OM drive these parameters. Furthermore, the contribution of microbial sugar C to MBC increased with depth, suggesting that recycling of carbohydrates is an adaptation strategy of microorganisms in C-limited environments. The supply of tree species-specific substrates resulted in different chemical composition of SMB with largest differences between deciduous and coniferous stands and vice versa, microorganisms contributed to SOM resulting in large similarity in the composition of extractable SOM and SMB.

Terrestrial Dissolved Organic Matter Mobilized From Eroding Permafrost Controls Microbial Community Composition and Growth in Arctic Coastal Zones

Climate warming is accelerating erosion along permafrost-dominated Arctic coasts. This results in the additional supply of organic matter (OM) and nutrients into the coastal zone. In this study we investigate the impact of coastal erosion on the marine microbial community composition and growth rates in the coastal Beaufort Sea. Dissolved organic matter (DOM) derived from three representative glacial deposit types (fluvial, lacustrine, and moraine) along the Yukon coastal plain, Canada, were used as substrate to cultivate marine bacteria using a chemostat setup. Our results show that DOM composition (inferred from UV-Visible spectroscopy) and biodegradability (inferred from DOC concentration, bacterial production and respiration) significantly differ between the three glacial deposit types. DOM derived from fluvial and moraine types show clear terrestrial characteristics with low aromaticity (Sr: 0.63 ± 0.02 and SUVA254: 1.65 ± 0.06 L mg C−1 m−1 &amp;amp; Sr: 0.68 ± 0.01 and SUVA254: 1.17 ± 0.06 L mg C−1 m−1, respectively) compared to the lacustrine soil type (Sr: 0.71 ± 0.02 and SUVA254: 2.15 ± 0.05 L mg C−1 m−1). The difference in composition of DOM leads to the development of three different microbial communities. Whereas Alphaproteobacteria dominate in fluvial and lacustrine deposit types (67 and 87% relative abundance, respectively), Gammaproteobacteria is the most abundant class for moraine deposit type (88% relative abundance). Bacterial growth efficiency (BGE) is 66% for DOM from moraine deposit type, while 13 and 28% for DOM from fluvial and lacustrine deposit types, respectively. The three microbial communities therefore differ strongly in their net effect on DOM utilization depending on the eroded landscape type. The high BGE value for moraine-derived DOM is probably caused by a larger proportion of labile colorless DOM. These results indicate that the substrate controls marine microbial community composition and activities in coastal waters. This suggests that biogeochemical changes in the Arctic coastal zone will depend on the DOM character of adjacent deposit types, which determine the speed and extent of DOM mineralization and thereby carbon channeling into the microbial food web. We conclude that marine microbes strongly respond to the input of terrestrial DOM released by coastal erosion and that the landscape type differently influence marine microbes.

Effect of forest and agricultural land use on the accumulation of polycyclic aromatic hydrocarbons in relation to soil properties and possible pollution sources

This study investigated the effects of forest and agricultural land use on the accumulation of polycyclic aromatic hydrocarbons (PAHs) in relation to the chemical and biochemical properties of soil. The heavy metal content in soil samples was also determined; PAH diagnostic ratios were used to identify pollution emission sources. Soils from the Rybnik Forest District of Poland, which has suffered some of the most intense impacts from industrial PAH emissions in Europe, were investigated. Six 200-m-long transects were designated for the experiment, with samples taken every 50 m. These transects were located across forest, agricultural land, and ecotone zones. The organic C and total N contents, pH, hydrolytic acidity and base cation content of the soil samples were determined, as well as the microbial biomass of C, N and P, the enzymatic activity, and the PAH and heavy metal content. A significant impact of land management on the PAH content of the soil due to the supply of organic matter was confirmed. The forest soils were more contaminated with PAHs than the agricultural soils, with an average PAH content in the forest soils of 565.18 µg·kg−1, almost six times higher than in agricultural soils (91.42 µg·kg−1). In addition, soil biological activity, expressed by enzymatic activity, depended on the amount and quality of the soil organic matter and, to a lesser extent, on the PAHs and heavy metals accumulated in the soils. This study confirmed that organic matter has a significant impact on PAH accumulation and is the main soil component involved in the sorption and ageing of PAHs.

Stratigraphic Variations of Fe–Mn Micronodules and Implications for the Formation of Extremely REY-Rich Mud in the Western North Pacific Ocean

The origin of deep-sea sediments in the western North Pacific Ocean, which are significantly enriched in rare-earth elements and yttrium (REY), and its paleoceanographic implications have been poorly constrained. Here, we investigated stratigraphic variations in the chemical compositions and textures of ferromanganese (Fe–Mn) micronodules separated from western North Pacific sediments. The characteristics of the micronodules of an extremely REY-rich mud layer vary from almost purely diagenetic to relatively hydrogenetic. This indicates the abundant supply of organic matter to the sediment together with fish debris that accumulates REY at the onset of the REY-enrichment of the mud, followed by the exposure of the seafloor to oxic water masses during the latter half of the formation of the REY-rich mud. These results support a previously proposed formation mechanism based on which enhanced bottom water currents caused pelagic fish proliferation via the upwelling of nutrients and fish debris was physically sorted and selectively accumulated on the seafloor. After the main REY-enrichment, the micronodules exhibit varying diagenetic signatures, suggesting changes in the bottom current intensities after the main REY-enrichment. However, the bulk REY contents do not increase. This implies that a sufficient increase in the fish productivity is an essential factor affecting the formation of REY-rich mud.

A Flux‐Based Threshold for Anaerobic Activity in the Ocean

AbstractAnaerobic microbial activity in the ocean causes losses of bioavailable nitrogen and emission of nitrous oxide to the atmosphere, but its predictability at global scales remains limited. Resource ratio theory suggests that anaerobic activity becomes sustainable when the ratio of oxygen to organic matter supply is below the ratio required by aerobic metabolisms. Here, we demonstrate the relevance of this framework at the global scale using three‐dimensional ocean datasets, providing a new interpretation of existing observations. Evaluations of the location and extent of anoxic zones and a diagnostic rate of pelagic nitrogen loss are consistent with previous estimates. However, we demonstrate that a threshold based on substrate‐supply fluxes is qualitatively different from a threshold based solely on the ambient oxygen concentration. This implies that use of the flux‐based threshold in global biogeochemical models can result in different predictions of anaerobic activity and nitrogen loss.

Latitudinal changes in the trophic structure of benthic coastal food webs along the Antarctic Peninsula

Stable isotopes of C and N have been used to assess the effect of the duration of the sea ice season on the structure of benthic, Antarctic coastal food webs. Samples of suspended particulate organic matter, macroalgae and macroinvertebrates were collected at five subtidal rocky sites across a latitudinal gradient along the western Antarctic Peninsula and among the South Shetland Islands. We tested the hypotheses that trophic positions of omnivores decrease, and food web structure becomes more redundant at higher latitudes. A latitudinal shift in the isotope baseline was detected for both δ13C and δ15N, but the trophic positions of macroinvertebrates and their relative positions along the δ13C axis and were basically constant across sites, even after rescaling stable isotope ratios to account for shifts in the baseline. Although the northernmost and southernmost study sites differed significantly in most of the metrics of the food web structure, changes with latitude and the duration of the sea ice season were non-monotonic. Highly productive phytoplankton blooms during the ice-free season at Esperanza Bay and Rothera Point may explain the observed pattern, as they result in a massive supply of planktonic organic matter to the detritus bank in the seabed and, hence, shorten the C range and increase trophic redundancy. If this hypothesis is correct, the intensity of the summer phytoplankton bloom can be as relevant for the structure of the benthic marine food web as the duration of the sea ice season.

Transformation of jarosite during simulated remediation of a sandy sulfuric soil

Aeration of wetland soils containing iron (Fe) sulfides can cause strong acidification due to the generation of large amounts of sulfuric acid and formation of Fe oxyhydroxy sulfate phases such as jarosite. Remediation by re-establishment of anoxic conditions promotes jarosite transformation to Fe oxyhydroxides and/or Fe sulfides, but the driving conditions and mechanisms are largely unresolved. We investigated a sandy, jarosite-containing soil (initial pH = 3.0, Eh ~600 mV) in a laboratory incubation experiment under submerged conditions, either with or without wheat straw addition. Additionally, a model soil composed of synthesized jarosite mixed with quartz sand was used. Eh and pH values were monitored weekly. Solution concentrations of total dissolved organic carbon, Fe, S, and K as well as proportions of Fe2+ and SO42− were analysed at the end of the experiment. Sequential Fe extraction, X-ray diffraction, and Mössbauer spectroscopy were used to characterize the mineral composition of the soils. Only when straw was added to natural and artificial sulfuric soils, the pH increased up to 6.5, and Eh decreased to approx. 0 mV. The release of Fe (mainly Fe2+), K, and S (mainly SO42−) into the soil solution indicated redox- and pH-induced dissolution of jarosite. Mineralogical analyses confirmed jarosite losses in both soils. While lepidocrocite formed in the natural sulfuric soil, goethite was formed in the artificial sulfuric soil. Both soils showed also increases in non-sulfidized, probably organically associated Fe2+/Fe3+, but no (re-)formation of Fe sulfides. Unlike Fe sulfides, the formed Fe oxyhydroxides are not prone to support re-acidification in the case of future aeration. Thus, inducing moderately reductive conditions by controlled supply of organic matter could be a promising way for remediation of soils and sediments acidified by oxidation of sulfuric materials.

Paleo-ecological changes and sedimentary evolution of the Hainan Delta, NW South China Sea

The Hainan Delta, a paleo-delta was penetrated by a 101-meter-long core (ZBW) off the southwestern shore of Hainan Island, in the Beibu Gulf, northwestern South China Sea. Grain size, dinoflagellate cysts, diatoms, and bulk carbon stable isotopes and C/N ratios of the Hainan Delta clearly support four stages of the delta development. Those stages, along the core profile of ca. 74.50–27.0 m below seafloor (mbsf), were reconciled with the deltaic facies; their depth ranges and dates are as follows: 74.50–56.80 mbsf (ca. 65.07–62.01 kyr. BP), 56.80–42.10 mbsf (ca. 62.01–58.61 kyr. BP), 42.10–30.95 mbsf (ca. 58.61–57.02 kyr. BP), and 30.95–27.00 mbsf (ca. 57.02–55.60 kyr. BP). Core ZBW is composed mainly of fine to medium sand, with admixture of coarse sand and shell debris throughout the deltaic facies. The C/N ratio in the sediment indicates mixed terrigenous and marine origin of the organic matter. The bulk carbon isotope record clearly indicates domination of terrigenous sources. The dinoflagellate cyst ('dinocyst') assemblages provided information on in-situ produced marine organic matter delivered to the deltaic sediments. The abundant presence of dinocysts indicates a high nutrient supply and favorable trophic conditions of the waters the donor species dwelled in. A constant supply of organic matter from terrigenous sources and its rapid mineralization is interpreter as factors conducive to a higher abundance of dinocysts. The low abundance of fossil diatoms is attributed to high dilution and the lateral transport of strongly silicified coastal diatoms down the Continental slope.

Biofumigation with species of the Brassicaceae family: a review

ABSTRACT: Biofumigation involves the release of volatile biocidal compounds in the soil through the incorporation of certain plants and their residues. Species of the Brassicaceae family are the most widely used plants for biofumigation. These plants contain glucosinolates, which produce compounds, such as isothiocyanates, following enzymatic hydrolysis, with scientifically proven fungicidal effects. The most commonly used brassica species belong to the genera Brassica, Raphanus, Sinapis, and Eruca. In addition to the release of compounds in the soil, complementary mechanisms, such as the supply of organic matter and nutrients, and improvement of the soil structure, also play a role in biofumigation. In the past two decades, several studies on the use of brassica residues in biofumigation have been published, showing promising results in the management of soil pathogens (fungi and oomycetes, nematodes, bacteria, and protozoa), weed seeds, and insects. Usage of new biofumigation compounds has also been validated in recent years, including the development of patented technological products such as liquid formulations and pellets. The objective of this article was to review these new developments, beginning with concepts related to biofumigation, and to discuss the mechanisms of action of compounds involving brassica species and the recommendations on usage. Promising examples of the use of this technique are also presented, further detailing the advances in basic and applied knowledge on the subject.

Relevance and magnitude of 'Blue Carbon' storage in mangrove sediments: Carbon accumulation rates vs. stocks, sources vs. sinks

Mangrove ecosystems store large amounts of 'Blue Carbon', in particular in the sediment. Research in the past decade has emphasized the quantitative significance of carbon storage in mangrove forests in climate change mitigation, mainly by determining carbon stocks and calculating potential CO2 emissions caused by mangrove degradation. However, while this approach focuses on the total amount of carbon that can be lost to degradation, it fails to capture the amount that is sequestered annually. Therefore, carbon accumulation in mangrove sediments also needs to be taken into account. This study (i) explains the differences between carbon stocks and carbon accumulation rates (CAR), (ii) it addresses the geographical variation of carbon storage and underlying factors and (iii) it assesses the global relevance of 'Blue Carbon' sequestration in mangrove sediments. Results indicate that reducing uncertainties in carbon storage estimates of individual systems requires a representative set of data that covers within-system variability. An example from Indonesia illustrates that a mangrove ecosystem with a high C stock can have a low CAR and vice versa. It is therefore conceivable that coastal environmental settings with high allochthonous supply of mineral sediment, organic matter and nutrients mostly have low carbon stocks, but high CARs. As these settings represent >80% of the global mangrove area they are most important in terms of long-term carbon storage. While a C stock is a measure of the "vulnerability potential" in the case of ecosystem degradation or total loss, a CAR is rather a measure of the "mitigation potential" of carbon storage in mangrove ecosystems. The global carbon storage in mangrove sediments of 32 Tg yr−1 estimated from CARs in this study is at the upper end of the range of global budgets (14.6–31.1 Tg yr−1, mean 22.9 Tg yr−1). It highlights that the mangrove carbon sink may be larger than previously thought, but the high variation in the global average CAR of 233 ± 280 g C m−2 yr−1 also indicates the need for further data.

Researching of indicators of agroecosystem without external energy supply

The agroecosystem without external energy supply can provide compensation for the needs of the agroecosystem in liquid fuel, heat and electricity at the expense of plant biomass as a renewable energy source. Based on the analysis of the energy balance of the agroecosystem, the area under rapeseed needed for biodiesel production and the area under crops needed for bioethanol production were calculated for the needs of the agroecosystem, as well as additional quantities of straw to compensate for the loss of humus in crop rotation, which sets the amount of plant biomass that can be used to produce heat and electricity using cogeneration gas plants. It was found that the average typical needs of the agroecosystem in diesel fuel from 60 to 80 kg/ha, and the ratio of the area under rapeseed needed for biodiesel production for the needs of agroecosystem to the total area of crop rotation with grain yield of canola from 1500 to 2500 kg/ha is from 8.3 to 18.5%. At the average typical demand of the agroecosystem for gasoline is from 15 to 16 kg/ha, the ratio of the area under wheat, barley and corn required to produce bioethanol for the needs of the agroecosystem to the total area of crop rotation with a crop yield of 3000 to 5000 kg/ha is from 0.7 to 0.9%. The increase in grain yield from 3000 to 5000 kg/ha causes an increase in the supply of organic matter to soil to a greater extent than its mineralization, and accordingly, the deficit of organic matter and humus decreases from 507 to 180 kg/ha, the volume of plant biomass (mainly straw) to compensate for the deficit of organic matter and humus decreases from 1867 to 217 kg/ha, which causes an increase in the possible volumes of plant biomass for energy production for sale from 27 to 2963 kg/ha. Respectively, electricity production increases from 48 to 2301 kWh/ha and heat power from 0 to 25,5 GJ/ha, while providing its own needs for heat and electricity by burning biogas in a cogeneration plant.

Nutrient Stocks Study in Agroecosystems Located near the Steel Industry, Galati, Romania

It is well known the role of nutrients in growing crops and obtaining cost-effective production, but also to ensure a nutritious contribution to humans and animals alike, in food safety conditions. This study aims to evaluate both the supply of nutrients and the main parameters of agricultural soils, in 0-30 cm layer, under intensive agricultural practices pressure, undertaken in an agricultural area influenced by steel industry activities. The soil samples were collected from three sites and different plots grown with wheat, corn and sunflower, and subjected to analysis protocols within Galati County Soil Survey Office. Soil supply with the main macronutrients indicates imbalances in all studied sites, regardless of the cultivated plants. Overall, soils have a high nitrogen deficiency, correlated with the low level of soil organic matter supply. Total Kjeldahl nitrogen values are between 0.076-0.258 % for all surveyed plots. Mobile phosphorus is low to very high (8-276 ppm), while mobile potassium is low to very high (70-600 ppm). This is due on the one hand to the natural process of soil degradation through water and wind erosion, and on the other to anthropogenic activities. Most of the time, out of the desire to obtain large harvests, farmers apply non-compliant amounts of fertilizers, which translates into the physical and chemical degradation of agricultural soils and poor management of crop nutrition. Other investigated soil parameters were pH, particle size fractions, as they are related to the dynamics of chemical elements in soil. It could be concluded that, the studied agricultural soils are characterized by imbalances in terms of providing chemical elements accessible to plants, in relation to the main investigated physico-chemical parameters and environmental conditions.