Transformation Of Organic Matter Research Articles

Land use impact on the levels of fluorescent dissolved organic matter, phytoplankton and zooplankton in urban lakes

Urban lakes are vulnerable ecosystems, sensitive to environmental challenges, such as pollution, land use transformation and climate change. Closed and open lakes play relatively different roles in the accumulation, transport and transformation of pollutants and organic matter. Land use can influence the concentration of dissolved organic matter and the abundance of phytoplankton. Little is known about the relationship between fluorescent dissolved organic matter (FDOM), phytoplankton and zooplankton in open and closed lakes, relative to the impact of land use. This study aims to determine the connection between various types of land use and FDOM characteristics, as well as phytoplankton and zooplankton abundances in urban lakes. For the closed lakes samples, results showed positive associations between Bacillariophyceae and Testacea, and the protein-like fraction, while for open lakes, positive associations were found between these groups and the microbial humic-like fraction. Also, copepods and rotifers were associated with the humic-like fraction, in closed lakes, but in open lakes copepods correlated with the biological index, and rotifers with the humification index and fluorescence T/C ratio. Results suggested that discontinuous urban fabric, dump sites and abandoned lands decreased the abundance of protein-like fraction and phytoplankton. However, lakes with the highest quantity of protein-like FDOM also had the highest coverage of continuous urban fabric around the lake. Green urban areas decreased the quantity of humic-like FDOM. No impact by land use type was observed on zooplankton groups, suggesting that zooplankton may be less vulnerable to land use. Our findings will contribute to an improved urban water management and to an effective control of FDOM and phytoplankton abundances in urban lakes.

Preservation of molecular fossils in carbonate concretions in cretaceous shales in the songliao basin, northeast China

Paleoenvironmental information is better preserved in carbonate concretions. In this study, carbonate concretions in the Cretaceous Nenjiang shale, Songliao Basin, were examined to determine whether molecular fossils reflective of the paleoenvironment were better preserved at these sites. Organic and inorganic geochemical characteristics of the concretions and surrounding rocks were analyzed using a series of techniques, including SEM, LA-ICP-MS, GC-MS-MS, and GC-IRMS. The concretions are composed of high content microcrystalline dolomite. The δ13Ccarb and δ18Ocarb values of the concretionary dolomite were significantly higher than those of the surrounding rocks. The dolomite show enrichment in the LREEs and have a negative Eu anomaly. The concretion biomarkers showed distribution characteristics similar to those of surrounding rocks. This suggested that the molecular fossils preserved in concretions were mainly inherited from surrounding rocks. However, the concretions contained more C27 sterane and hopanes, with the hopane/sterane ratio being significantly higher than that of surrounding rocks (1.49 v. 0.86). Moreover, the relative content of 2-methylhopane was 2.4–6.6 times that of the surrounding rocks. This indicated changes in the biological equilibrium of source organisms within and outside the concretions. It was possible that the unstable organic matter at the core increased the bacterial concentration and activity inside the concretions. Both the hydrogen index and biomarker-derived indicators implied that the transformation of organic matter in concretions was minimized when compared with their host rock. The isotope δ13C16-30 was 1‰–3‰ more prevalent in individual N-alkane hydrocarbons in the concretions than in surrounding rocks, likely owing to differences in lithology, bacterial action, and degree of weathering. The study concluded that carbonate concretions could preserve molecular fossils better than the surrounding rocks, and the in-depth organic geochemical analysis of concretions could provide a valuable reference for research into early life forms.

Insights into the influence of digestate-derived biochar upon the microbial community succession during the composting of digestate from food waste

The by-product from the anaerobic digestion of food waste (FW) called the digestate (DFW) needs proper disposal because of its high environmental burden. Composting can transform DFW into a nutrient-containing soil improver via a series of microbial metabolic activities. However, the long composting time and high amount of ammonia emission are the key concerns of DFW composting. In the present study, the effect of DFW-derived biochar (BC-DFW) on microbial succession and its involvement in nitrogen transformation and humification during DFW composting were investigated. The results indicated that the BC-DFW accelerated bacterial and fungal evolution, and the bacterial diversity was augmented by increasing the amount of BC-DFW. In particular, Cryomorpha, Castellaniella, Aequorivita, and Moheibacter were enriched by the addition of BC-DFW, thereby enhancing the degradation of organic matter and nitrogen transformation and increasing the germination index. The group with 25% BC-DFW contained a higher relative abundance of Cryomorpha (2.08%, 2.47%) than the control (0.39%, 1.72%) on days 19 and 35 which benefited the degradation of organic matter. The group with 25% BC-DFW quickly enhanced the growth of Nitrosomonas, thereby accelerating the conversion of ammonium-nitrogen to nitrate-nitrogen and reducing the phytotoxicity of the composting product.

Emerging investigator series: aqueous photooxidation of live bacteria with hydroxyl radicals under cloud-like conditions: insights into the production and transformation of biological and organic matter originating from bioaerosols.

Live bacteria in clouds are exposed to free radicals such as the hydroxyl radical (˙OH), which is the main driver of many photochemical processes. While the ˙OH photooxidation of organic matter in clouds has been widely studied, equivalent investigations on the ˙OH photooxidation of bioaerosols are limited. Little is known about the daytime encounters between ˙OH and live bacteria in clouds. Here we investigated the aqueous ˙OH photooxidation of four bacterial strains, B. subtilis, P. putida, E. hormaechei B0910, and E. hormaechei pf0910, in microcosms composed of artificial cloud water that mimicked the chemical composition of cloud water in Hong Kong. The survival rates for the four bacterial strains decreased to zero within 6 hours during exposure to 1 × 10-16 M of ˙OH under artificial sunlight. Bacterial cell damage and lysis released biological and organic compounds, which were subsequently oxidized by ˙OH. The molecular weights of some of these biological and organic compounds were >50 kDa. The O/C, H/C, and N/C ratios increased at the initial onset of photooxidation. As the photooxidation progressed, there were few changes in the H/C and N/C, whereas the O/C continued to increase for hours after all the bacterial cells had died. The increase in the O/C was due to functionalization and fragmentation reactions, which increased the O content and decreased the C content, respectively. In particular, fragmentation reactions played key roles in transforming biological and organic compounds. Fragmentation reactions cleaved the C-C bonds of carbon backbones of higher molecular weight proteinaceous-like matter to form a variety of lower molecular weight compounds, including HULIS of molecular weight <3 kDa and highly oxygenated organic compounds of molecular weight <1.2 kDa. Overall, our results provided new insights at the process level into how daytime reactive interactions between live bacteria and ˙OH in clouds contribute to the formation and transformation of organic matter.

INVESTIGATION ON THE NATURE AND PROVENANCE OF PAH FOUND IN SEDIMENTS OF THE SOLIMÕES RIVER AND SOME ASSOCIATED LAKES

The present work aimed at evaluating indicators of hydrocarbon sources to sediments from the Solimões River region, in the central Amazon. The 16PAH, the alkylated homologs and molecular markers were investigated. The entire series of alkylated PAH were present and, in some cases, with a distribution observed when oil residues dominate. Nevertheless, hopanes characterizing immature environments undergoing diagenetic transformation were identified in samples from the Solimões River and in surface as well as in core sediment samples from Preto Lake, in the Coari-Manaus stretch. Investigation suggests early diagenesis of the organic matter confirmed by identifying biogenic markers produced during organic matter transformation. Some of these markers derive from incomplete combustion of biomass and are contained in particulate matter formed during forest burning. In the sediments of an industrial area near the city of Manaus, the entire series of mature hopanes was present indicating anthropogenic source of hydrocarbons. The results so far obtained point out the complexity of PAH source appraisal.

Transformation characteristics of organic matter and phosphorus in composting processes of agricultural organic waste: Research trends

Agricultural waste is rich in organic matter and an important secondary source of phosphorus, which can be converted into valuable products through various technologies. Composting is an effective way to treat agricultural waste and further produce organic fertilizer, achieving waste minimization and stabilization. This paper reviews the current situation of agricultural waste pollution and composting technology, introduces the parameters that influence of the composting process and the optimal conditions, and presents the indicators for evaluating the decay of compost products and the evaluation criteria as well. In the composting process, small-molecule organic acids produced by the degradation of easily degradable organic matter such as sugars and lipids and various enzymes produced by microorganisms (phytase, phosphatase, etc.) can mineralize organic phosphorus such as phytate and phospholipids, promote phosphorus activation and provide phosphorus sources for microorganisms, so the conversion of organic matter and phosphorus is related to the fertilizer effect of composted products. Therefore, the clarification of the characteristics of organic matter and phosphorus transformation in the composting process is an important prerequisite for the resource utilization of agricultural organic waste. This paper provides theoretical support for the sustainable utilization of agricultural organic waste resources.

Transformation of plant residues into a humus-like substance using biological means of multifunctional action

Purpose. Justification of the technology of biological transformation of plant remains into a humus-like substance thanks to the microbial agents of the drug Extrakon, ensuring the improvement of the soil and the initiation of its biological cycles. Methods. Complex of modern and generally accepted physicochemical, microbiological, physiological and biochemical research methods; methods of laboratory and field research; statistical analysis of the data. Results. A promising, innovative scientific-methodological development and technology for the use of the multifunctional biological preparation Extrakon has been created, which is guaranteed to improve the soil, nourish plants and accelerate the processes of transformation of organic matter (plant residues) into a humus-like substance. Scientifically substantiated expediency of using the drug Extrakon in the processes of accelerated composting of crop production waste (according to indicators of biothermal processes, kinetics of temperature regimes and decomposition of organic matter of siderate, as well as changes in the physical and chemical properties of compost depending on the duration of its preparation). The transformation of straw and plant residues with the help of a consortium of natural soil microorganisms takes from 30 days to 6–8 months. Conclusions 1. Loose and liquid preparations based on a consortium of soil microorganisms (CSM) are effective for preparing and improving substrates and soil, pre-sowing seed treatment, feeding plants during the growing season; post-harvest use – to activate the transformation of plant residues, composting organic cellulose-containing residues. 2. The duration of the plant residues transformation is from 30 days to 6–8 months, which is 2-3 times less than when using existing biodestroyers. The effect of biological preparation in the agricultural cluster is from 80 % to complete transformation of organic substances into a humus-like substance. 3. The proposed preparation can be used both for the transformation of plant residues into a humus-like substance, composting, and for the preparation and improvement of various substrates, soil, as well as for the purpose of eliminating toxicity, for growing plants in closed and open soils. Keywords: humus-like substance, consortium of soil microorganisms, plant remains, transformation.

Combined Effect of Chlorella vulgaris Beijer. (Chlorophyta) and Silicon-Containing Organic Fertilizer on Bell Pepper Productivity, Microbiocenosis, Allelopathic and Agronomic Soil Characteristics

The combined effect of the culture medium of green microalgae (&lt;i&gt;Chlorella vulgaris&lt;/i&gt;) and organosilicon fertilizer (analcite &amp;#43; peat (pH 5.8) in a ratio of 1 : 3) on characteristics of growth, development, photosynthetic productivity, yield and quality of bell pepper (&lt;i&gt;Capsicum annuum&lt;/i&gt; L., cv. "Bilozyorka"), as well as microbiocenosis, allelopathic and agronomic characteristics of the soil were studied in pot experiments. The culture medium of microalgae was added at a rate of 10 mL per pot (0.7 L) to sifted and sterile gray podzolid soil. Plants were grown in a phytochamber under controlled conditions of light, temperature and soil moisture. The vitality of pepper plants was assessed by morphometric growth characteristics (shoot height, stem diameter, surface area of leaves, root length, dry weight of shoots and roots, number and weight of fruits), the content of photosynthetic pigments in leaves, and protective antioxidants (carotenoids, flavonoids and anthocyanins) in fruits. At the end of the experiment, the content of phenolic compounds, electrical conductivity, redox potential, pH, content of NH&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;+&lt;/sup&gt;, NO&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;-&lt;/sup&gt; and HCO&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;-&lt;/sup&gt; ions in the soil solution were determined. Eco-trophic groups of soil microorganisms were also determined. A synergistic enhancement of the positive effect of microalgae and organosilicon fertilizer on the growth, development, productivity and fruit quality in bell pepper was established. The combined application of the microalgae with organosilicon fertilizer more effectively improved the agronomic and allelopathic characteristics of the soil, stimulated the development of agronomically useful eco-trophic groups of microorganisms, incresed the intensity of the mineralization and transformation of organic matter compared to the control and treatments in which microalgae or fertilizer were applied separately.

Quantitative and Qualitative Characteristics of Organic Matter Under Long-Term Exposure to Natural and Anthropogenic Factors

Studies have found that the increase in differences between the amount of energy subsidies invested in agrobiocenoses and alienated from them over a 105-year period changes the direction of biochemical processes of organic matter transformation, which leads to significant losses of organic carbon reserves, which amount to 17.5 t/ha in highly degraded soils, 7.3 t/ha in poorly cultivated soils, and in highly cultivated increases them by 2.8 t /ha, respectively, compared with the initial content. Long-term use of arable land affects the qualitative characteristics of the state of organic matter of sod-podzolic soil, which are expressed in a change in the ratio of the peripheral and central parts, the enrichment of humus with nitrogen. The humus substances of medium (57%) and highly cultivated soils (54%) are characterized by the highest degree of participation of peripheral groupings in the construction, and the least highly degraded (29%).

АКТУАЛЬНЫЕ АСПЕКТЫ ИЗУЧЕНИЯ ПЕРИОДИЧЕСКИ ПЕРЕСЫХАЮЩИХ АКВАТОРИЙ В КОНТЕКСТЕ УГЛЕРОДНОГО ЦИКЛА (НА ПРИМЕРЕ БАССЕЙНА НИЖНЕГО ДОНА)

Investigations were carried out in the reservoirs of the Don delta and Western Manych to study the biogeochemical cycles of elements, mainly carbon, in the transition zones between land and water. The main physical and geographical processes that determine the supply, transfer and transformation of organic matter and the connectivity of aquatic and terrestrial ecosystems are identified. A decrease of the surface area, based on a comparison of remote sensing data in ArcGIS for the period 1985–2021, of the water surface of reservoirs in average of 15– 16 % was established (in the Don delta, mainly due to the destruction of man-made ponds, in Manych – due to a decrease in the water level). It is possible to slow down biogeochemical processes in drained areas and change one type of process to another as a result of the absence of a hydrological flow. A shift of geochemical barriers towards the river during surges and an increase of mineralized underground runoff during negative surges was recorded under the influence of surge phenomena in the Don Delta. For the system of reservoirs of the Western Manych, the presence of salinity gradients between its individual parts was noted. Investigations have established that the mixing zones of fresh and salt water – biogeochemical “hot spots”, are characterized by a contrasting chemical composition and very different concentrations of organic and suspended matter. A tendency to a significant change in the structure of the upper part of the profile of alluvial soils of the river delta was noted with the continuing low water in the Lower Don. Areas with varying degrees of manifestation of soil-forming processes, as well as the main natural and anthropogenic factors that control these processes, have been identified.

Highly efficient transformation of slowly-biodegradable organic matter into endogenous polymers during hydrolytic fermentation for achieving effective nitrite production by endogenous partial denitrification

The utilization of slowly-biodegradable organic matter (SBOM) to provide nitrite efficiently for anaerobic ammonia oxidation (anammox) process is an essential topic. High nitrite concentration without inhibition of exogenous organic matter is optimal condition for anammox process. In this study, hydrolytic fermentation (HF) of SBOM was applied to drive an endogenous partial denitrification (EPD) process (nitrate to nitrite) during an anaerobic-anoxic operation in a starch-fed system. With a limited production of exogenous organic matter (22.3 ± 4.9 mg COD/L), 79.0% of SBOM was transformed into poly-hydroxyalkanoates (PHA) through a pathway of simultaneous HF-absorption and endogenous polymer synthesis, corresponding to a hydrolytic fermentation ratio of 86.0%. A high nitrate to nitrite transformation ratio of 85.4% was achieved under an influent carbon to nitrogen ratio of 4.8. Denitrifying glycogen-accumulating organisms (DGAOs) was enriched from 0.6% to 10.9%, with an increase from 0.7 to 1.0 of nitrate reductase genes to nitrite reductase genes ratio. Subsequently, nitrate reduction rate was 5.6-fold higher than the nitrate reduction rate. A prominent migration of exogenous complete denitrification to EPD was accomplished. Furthermore, the starch-fed system exhibited performance with significant adaptability and stability in the presence of different SBOMs (dissolved protein and primary sludge). Therefore, the HF-EPD system achieved efficient nitrite production through EPD with the addition of various SBOMs, providing a potential alternative to anammox systems for the treatment of SBOM-rich wastewater.

Soil organic matter transformation influenced by silver birch (Betula pendula Roth) succession on abandoned from agricultural production sandy soil

A chronosequence approach was applied to evaluate the effects of silver birch succession on soil organic matter (SOM). The studies covered five plots (arable field [AF], fallow [FA] and three birch stands aged 8, 33 and 40 years), and all located in the same complex of Brunic Arenosols in central Poland. The O and A horizons of the soils were sampled and analysed using the standard procedures in soil science. It was found that the birch succession was accompanied by dynamic changes in the stock and quality of the SOM. The transition from AF to FA soils did not significantly change the content or pool of SOM in the A horizon; however, it did modify its fractional composition and internal structure. This was reflected by an increase in the humic acids content and a decrease in the fulvic acid, as well as in the values of the elemental and 13C-NMR analyses. Rapid losses in the SOM content and stock in the A horizon were recorded after entering the silver birch. The soils under the young birches were characterised by lower contents of low-molecular humus fractions, which are more susceptible to microbial degradation, than the FA soils. In addition, the birch succession contributed to a lower internal oxidation of the humic acids and an increase in the content of aliphatic structures in their molecules. The next stages of succession were characterised by gradually increasing SOM contents and stocks, accompanied by the increasing internal oxidation and maturity of the humic acids.

Close relationship between the gene abundance and activity of soil extracellular enzyme: Evidence from a vegetation restoration chronosequence

Extracellular enzymes (EEs) play vital roles in the transformations of soil organic matter, yet the regulators of EE activity remain unclear. Inducible EE production predicts that EE activity is determined by microbial nutrient status. Alternatively, EE production can be constitutive (continuous and baseline-level expression of EE gene regardless of the nutrient status), and in this case EE gene abundance potentially affects EE activity. Here, we examined whether EE gene abundance was a key regulator of EE activity along a vegetation restoration chronosequence. For the four hydrolytic EEs related to microbial acquisition of carbon, nitrogen and phosphorus, their gene abundance ratios (obtained from metagenomic sequencing) were positively related to corresponding activity ratios (R2 = 0.43–0.94). These relationships were maintained in the structural equation modeling when the effects of microbial nutrient status and soil property were considered. The gene-enzyme link was further confirmed by the positive relationship between the absolute abundance of phoD gene (obtained from qPCR analysis) and the alkaline phosphomonoesterase activity. Overall, our results suggest that constitutive EE production may contribute significantly to soil EE activity. The direct gene-enzyme link highlights the development of gene-informed Earth system models to better predict the soil carbon dynamics under global change.

Oxygen Vacancy-Mediated Activates Oxygen to Produce Reactive Oxygen Species (ROS) on Ce-Modified Activated Clay for Degradation of Organic Compounds without Hydrogen Peroxide in Strong Acid.

The treatment of acid wastewater to remove organic matter in acid wastewater and recycle valuable resources has great significance. However, the classical advanced oxidation process (AOPs), such as the Fenton reaction, encountered a bottleneck under the conditions of strong acid. Herein, making use of the oxidation properties of CeAY (CeO2@acid clay), we built an AOPs reaction system without H2O2 under a strong acid condition that can realize the transformation of organic matter in industrial wastewater. The X-ray photoelectron spectroscopy (XPS) proved that the CeAY based on Ce3+ as an active center has abundant oxygen vacancies, which can catalyze O2 to produce reactive oxygen species (ROS). Based on the electron spin-resonance spectroscopy spectrum and radical trapping experiments, the production of •O2- and •OH can be determined, which are the essential factors of the degradation of organic compounds. In the system of pH = 1.0, when 1 mg CeAY is added to 10 mL of wastewater, the degradation efficiency of an aniline solution with a 5 mg/L effluent concentration is 100%, and that of a benzoic acid solution with a 100 mg/L effluent concentration is 50% after 10 min of reaction. This work may provide novel insights into the removal of organic pollutants in a strong acid water matrix.

From biogenic silica and organic matter to authigenic clays and dolomite: Insights from Messinian (upper Miocene) sediments of the Northern Mediterranean

AbstractThe biogeochemical cycles of carbon and silicon are tightly coupled in modern marine environments due to the pivotal role of planktonic diatoms. Once diatoms are sedimented, the fate of organic matter and biogenic silica is initially governed by bottom water oxygen levels and bacterial communities involved in remineralization processes. The early diagenesis of biosiliceous sediments may result in drastic changes in composition, sometimes hampering palaeoenvironmental reconstruction. Sedimentary successions deposited in the Mediterranean region during the Messinian salinity crisis (5.97–5.33 Ma) allow to explore the early diagenetic transformation of organic matter and biogenic silica in a restricted basin experiencing a severe palaeoceanographic turnover. Sedimentological and petrographic observations coupled to elemental, mineralogical, inorganic and organic geochemical analyses were carried out on biosiliceous (diatomaceous shales and diatom‐bearing mudstones) and associated clay‐rich and dolomite‐rich sediments (dolomitic mudstones) interbedded with primary gypsum layers in the Piedmont Basin (north‐west Italy). The state of preservation of biogenic silica was governed by different pathways of organic matter remineralization, depending on bottom and pore water redox conditions, which were controlled by the structure of the water column. Aerobic respiration of organic matter in a mixed water column and an oxygenated seafloor promoted biogenic silica preservation. In contrast, bottom water anoxia induced by permanent stratification of the water column favoured the concomitant formation of dolomite and authigenic clays. In particular, organic matter degradation through bacterial sulphate reduction increased pore water alkalinity, promoting the precipitation of dolomite. At the same time, the rise in pH promoted the dissolution of biogenic silica which, reacting with pore water cations, ultimately caused the formation of authigenic clays. This study suggests that the apparent annihilation of Mediterranean marine biota during the Messinian salinity crisis partially reflects an early diagenetic bias produced by interactions of the carbon, silicon and sulphur biogeochemical cycles in a restricted basin.

Particulate Organic Matter Mobilization and Transformation Along a Himalayan River Revealed by ESI‐FT‐ICR‐MS

AbstractTracing pathways and transformations of particulate organic carbon from landscape sources to oceanic sinks is commonly done using the isotopic composition or biomarker content of particulate organic matter (POM). However, similarity of source characteristics and complex mixing in rivers often preclude a robust deconvolution of individual contributions. Moreover, these approaches are limited in detecting organic matter transformations. This impedes understanding of carbon cycling. Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT‐ICR‐MS) can simultaneously identify many molecular formulas from mixtures of organic matter, and provide direct information on its compositional variability. Here, we investigate how FT‐ICR‐MS can give insight into POM dynamics on a landscape scale, focusing on the trans‐Himalayan Kali Gandaki River, Nepal. Using molecular information, we identify source tracers in the solvent extractable lipid fraction of riverine POM, finding up to 102 indicative molecular formulas for individual sources. Further, we assess molecular transformations of the lipid fraction of POM during its transfer from litter into topsoil, and onwards into the river. A large number of shared mass formulas and a well‐preserved isoprenoidal patterns suggest efficient incorporation of litter into topsoil. In contrast, we observe a selective loss of mass formulas and a preferential export of formulas with low double bond equivalents and a low nominal oxidation state of carbon after organic matter entrainment in the river. Our results demonstrate the potential of FT‐ICR‐MS for source‐to‐sink studies, allowing detailed organic matter source characterization and discrimination, and tracking of molecular transformations along organic matter pathways spanning different spatial and temporal scales.

Stable Carbon Isotopic Composition (δ13C) as a Proxy of Organic Matter Dynamics in Soils on the Western Shore of Lake Baikal

Abstract Assessing the main factors that control carbon dynamics in soils is an urgent problem in the context of modern climate change. The analysis of stable carbon isotope (δ13С) composition is one of the approaches to understanding this dynamics. The study was carried out in the landscapes of the southeastern slope and foothills of the Primorskii Range, characterized by contrasting physico-geographical conditions. Climatic parameters, spatial variations in the composition of stable carbon isotopes and their distribution in soil profiles, and soil physicochemical properties controlling carbon dynamics have been analyzed. The soil humus horizons formed in mountainous tundra and steppe landscapes manifest the highest δ13С values (–24.72 and –23.97…–24.75‰); whereas the lowest (–25.61…–27.18‰) values are registered in the mountainous taiga soils. Based on the calculation of linear dependence between δ13С values and the total carbon content in soil, which varies with the depth, the carbon turnover intensity was determined using the slope of linear regression. It was revealed that under the contrasting conditions of mountainous tundra and steppe landscapes, the climate (deficiency of heat and moisture) has a significant impact on the intensity of organic matter transformation, blocking the effect of edaphic (soil profile) factors. Under more favorable climatic conditions of mountainous taiga landscapes, the dynamics of organic matter in soils is controlled mainly by edaphic factors.

Transformation of soil organic matter subjected to environmental disturbance and preservation of organic matter bound to soil minerals: a review

Transformation of soil organic matter subjected to environmental disturbance and preservation of organic matter bound to soil minerals: a review

Differences in the composition, source, and stability of suspended particulate matter and sediment organic matter in Hulun Lake, China.

The occurrence, migration, transformation, and stability of sediment (SOM) and suspended particulate (SPOM) organic matters have important effects on the environmental behaviors of carbon, nitrogen, phosphorus, and other pollutants in a water environment. The content, composition, fluorescence characteristics, source, and stability of SOM and SPOM in Hulun Lake, a typical lake in cold and arid region of China, were compared by sequential extraction, three-dimensional fluorescence spectroscopy, parallel factor technique, carbon-nitrogen ratio, and stable carbon isotope. Contents of SOM and SPOM in north and west were higher than those in east and south. The average content of SPOM (24.70 ± 4.63g/kg) was slightly higher than that of SOM (23.04 ± 10.27g/kg), but the difference was not significant. Humin was the dominant component in SOM and SPOM, accounting for 73.7% and 61.2%, respectively. Humus was the main fluorescence component of water-extractable organic matter in SOM and SPOM, accounting for 79.9% and 70.4%, respectively, of the total fluorescence intensity. SOM and SPOM were derived from terrestrial sources with a relative contribution rate of about 70%. SPOM was more influenced by autochthonous sources and had a significantly lower humification degree and stability than SOM. Effects of climate changes on migration, transformation, stability, and bioavailability of organic matters and endogenous pollutants closely related to organic matters in lakes of cold and arid regions should be paid attention in the future.

Effects of exogenous Fe addition on soil respiration rate and dissolved organic carbon structure in temperate forest swamps of northeastern China

Fe as an important redox-active transition metal plays a key role in the carbon cycle of ecosystems. To date, the mechanisms by which Fe affects organic carbon (soil respiration rate [Rs] and dissolved organic carbon [DOC] structure) remain unclear, because most studies only focused on the effect of Fe on soil organic carbon content. To understand these effects, a 30-day laboratory incubation experiment was conducted using forest swamp soils from northeastern China amended with different concentrations of exogenous Fe (no exogenous Fe added [L0], add exogenous Fe at 1 time the soil background value [L1], add exogenous Fe at 2 times the soil background value [L2]). Our results showed that exogenous Fe addition reduced the soil respiration rate by 54.8% during the incubation time. The DOC concentration decreased by 40.5% with exogenous Fe addition during the incubation time. The dissolved organic matter (DOM) characteristic parameters showed apparent variations (p < 0.05), including significant increases in the fluorescence and biological index and significant decreases in the humification index, which indicate that exogenous Fe addition reduced humification, which may lead to the increased fixation of dissolved organic carbon. In addition significant increases in tryptophan-like DOM was observed when exogenous Fe addition resulted in a soil Fe concentration of twice the background value (p < 0.05). These findings indicate that exogenous Fe addition promotes the production of endogenous soil DOC by microorganisms. Overall, Our study uses three-dimensional fluorescence spectroscopy techniques combined with the parallel factor analysis (PARAFAC) to characterize the dissolved organic matter components in soil samples under exogenous Fe addition conditions, with a view to exploring the differences in the effects of Fe on the DOC concentration and structure of wetland soils, providing a theoretical basis for the mechanisms of soil carbon fixation and soil organic matter transformation in wetland soils.