Organic Matter Degradation Rates Research Articles

Short-term effects of a simulated massive river flood and its recovery on sediment biogeochemistry of a Mediterranean lagoon

ABSTRACT Strong rainfalls and river floods are becoming increasingly frequent and intense in southern Europe. Mediterranean coastal lagoons, due to their hydrological characteristics, could mitigate the consequences of such events, whose effects on sediment biogeochemistry are poorly studied, yet. To provide insights on this, we investigated short-term changes in organic matter quantity, composition, nutritional quality, degradation rates, and turnover time in a lagoonal benthocosm. Both flooding and recovery phases increased the sedimentary organic load and turnover time, whereas phytopigment contents and C degradation rates were not affected. The biochemical composition varied during both phases, with an increase in carbohydrate and lipid after the flooding, and an increase in protein and chlorophyll-a after its recovery. Our results suggest that even sudden changes in salinity caused by floods and their recovery can increase sedimentary organic loads, with minor effects on their nutritional quality. The observed effects of the flooding persist in the short-term also after the recovery of the salinity, when the substrates are pre-eminently of heterotrophic origin. Our results suggest that extreme, even if short-lasting, episodic events of flooding and recovery can severely alter the benthic trophic status of coastal lagoons, having possible effects on benthic trophodynamics.

Continuous thermophilic composting of distilled grain waste improved organic matter stability and succession of bacterial community

Continuous thermophilic composting (CTC) is potentially helpful in shortening the composting cycle. However, its universal effectiveness and the microbiological mechanisms involved are unclear. Here, the physicochemical properties and bacterial community dynamics during composting of distilled grain waste in conventional and CTC models were compared. CTC accelerated the organic matter degradation rate (0.2 vs. 0.1 d−1) and shortened the composting cycle (24 vs. 65 d), mainly driven by the synergism of bacterial genera. Microbial analysis revealed that the abundance of Firmicutes was remarkably improved compared to that in conventional composting, and Firmicutes became the primary bacterial phylum (relative abundance >70 %) during the entire CTC process. Moreover, correlation analysis demonstrated that bacterial composition had a remarkable effect on the seed germination index. Therefore, controlling the composting process under continuous thermophilic conditions is beneficial for enhancing composting efficiency and strengthening the cooperation between bacterial genera.

Predicting ruminal degradability and chemical composition of corn silage using near-infrared spectroscopy and multivariate regression.

The aim of this study was to develop and validate regression models to predict the chemical composition and ruminal degradation parameters of corn silage by near-infrared spectroscopy (NIR). Ninety-four samples were used to develop and validate the models to predict corn silage composition. A subset of 23 samples was used to develop and validate models to predict ruminal degradation parameters of corn silage. Wet chemistry methods were used to determine the composition values and ruminal degradation parameters of the corn silage samples. The dried and ground samples had their NIR spectra scanned using a poliSPECNIR 900-1700 model NIR sprectrophotometer (ITPhotonics S.r.l, Breganze, IT.). The models were developed using regression by partial least squares (PLS), and the ordered predictor selection (OPS) method was used. In general, the regression models obtained to predict the corn silage composition (P>0.05), except the model for organic matter (OM), adequately estimated the studied properties. It was not possible to develop prediction models for the potentially degradable fraction in the rumen of OM and crude protein and the degradation rate of OM. The regression models that could be obtained to predict the ruminal degradation parameters showed correlation coefficient of calibration between 0.530 and 0.985. The regression models developed to predict CS composition accurately estimated the CS composition, except the model for OM. The NIR has potential to be used by nutritionists as a rapid prediction tool for ruminal degradation parameters in the field.

Magnetite-equipped algal-rich sediments for microbial fuel cells: Remediation of sediment organic matter pollution and mechanisms of remote electron transfer

Using the bio-electrochemical methods for the restoration of high algae sediments is full of potential and challenges. How to promote extracellular electron transfer (EET) process in microbial fuel cells (MFC) is the key bottleneck. The study had explored the potential application of magnetite on accelerating electron transfer for improving the output of MFC and sediment pollution remediation. The results indicated that the organic matter degradation rate showed a remarkable increase of 27.45 %, and the voltage output was approximately 1.68 times higher compared to the MFC configured with regular sediment. Abundant electroactive bacteria (EABs), such as Geobacter and Burkholderiaceae, and fermentative bacteria were responsible for these results, accompanied by the enhanced fluorescence of humic substances (HS), increased concentration and activity of cytochrome C (25.05 % and 21.12 %), as well as elevated extracellular polymeric substance content. Moreover, the intrinsic EET mechanisms among Fe-oxides, HS, and EABs were explored. According to the electrochemical analysis and substance transformation, the EET process involved four stages: magnetite-enhanced direct electron transfer via strong conductivity, iron respiration mediating electron transfer to the electrode, the model quinone substance acting as an electron shuttle facilitating EET and iron reduction, and iron cycling mediating electron transfer. This study provides an effective strategy for pollution remediation in algal-rich sediment, which was beneficial for the harmless treatment and resource utilization of both algae and sediment, simultaneously.

Trace-metal enrichment mechanisms in Bakken Formation black shales, Williston Basin, North Dakota, USA

The Bakken black shales represent a unique sedimentary system characterized by high total organic carbon contents (TOC; Lower Bakken shale = 10.8 and Upper Bakken shale = 11.8 avg. wt%) and enrichment factors (EF) of various trace metals (TMs) such as Cu (6.2–7.7), Mo (219.7–237.8), Ni (9.4–10.2), U (20.6–29.3), V (9.9–14.2), and Zn (10.4–12.2) that are considerably higher than many other Devonian-Mississippian (D–M) black shales. In this study, raw distributions of elemental concentrations combined with bivariate and principal component analysis (PCA) were used to clarify processes that contributed to high TM EF values in the Bakken shales. Total organic carbon shares heavier PCA component loadings (>0.445) and stronger Pearson correlation coefficients (r) with Cu, Mo, Ni, U, V, and Zn than with pyrite-associated (As, Co, Fe, and S) elements, suggesting that organic matter (OM) played a primary role in the scavenging and accumulation of TMs in the sediments. Reducing conditions within bottom waters or sediment pore waters may have accelerated the accumulation of redox-sensitive Cu, Mo, Ni, V, and Zn introduced into the sediments via an OM detritus host and most likely played a secondary role in their enrichment. Deep-water renewal times for the Bakken have been estimated to be ∼10–30 yrs. based on Mo/TOC results. The high TM EF values observed in the Bakken shales may reflect frequent resupply of TMs into basin waters, enhanced primary productivity that is necessary in scavenging TMs from the water column, the presence of H2S within sediment pore or bottom waters, or possibly secondary processes associated with basin-wide fluid and hydrocarbon migration. High TOC concentrations may be the result of a possible shallow water column (∼150 m), which would limit exposure time of OM to oxidation and degradation, coupled with intermittent fluctuations between dysoxic and anoxic/euxinic bottom-water redox conditions, the latter of which would reduce rates of OM degradation by benthic organisms.

Effects of adding steel slag on humification and characteristics of bacterial community during phosphate-amended composting of municipal sludge

This study aimed to investigate the effects of different proportions (0%, 5%, 7.5%, and 10%) of steel slag (SS) on humification and bacterial community characteristics during phosphate-amended composting of municipal sludge. Compared with adding KH2PO4 alone, co-adding SS significantly promoted the temperature, pH, nitrification, and critical enzyme activities (polyphenol oxidase, cellulase, laccase); especially organic matter (OM) degradation rate (25.5%) and humification degree (1.8) were highest in the 5%-SS treatment. Excitation-emission matrix-parallel factor confirmed that co-adding SS could promote the conversion of protein-like substances or microbial by-products into humic-like substances. Furthermore, adding 5%-SS significantly improved the relative abundances of Actinobacteria, Firmicutes and the genes related to carbohydrate and amino acid metabolism, and enhanced the interactions of bacterial community in stability and complexity. The partial least squares path model indicated that OM was the primary factor affecting humification. These results provided a promising strategy to optimize composting of municipal sludge via SS.

Process Control of a Compost-Reactor Turning Operation Based on a Composting Kinetics Model

Composting is a biochemical as well as a heterogeneous process, and the turning operation is important to maintain aerobic conditions and improve the efficiency of the composting process. Therefore, the turning frequency is an important factor for the precise control of the composting reactor. It is necessary to determine the changes in the physical and chemical parameters of the composting process and to simulate them. Pretreated vinegar residue and wool washing sludge were mixed at a mass ratio of 6:4 for the composting process. The composting reactor’s temperature, CO2, CH4, and organic matter content were collected during the composting process. According to the principles of composting, a kinetic model of composting based on the change in CO2 gas concentration and heat balance in the composting reactor is developed, which provides a theoretical basis for the subsequent control of the composting reactor. The comparison of the model predictions to the measured results of the composting reactor shows that the SSE, R2, and RMSE for the organic matter content simulation are 8.122, 0.943, and 1.274 g/kg, respectively, and the SSE, R2, and RMSE for the temperature simulation are 29.54, 0.959, and 2.71 °C, respectively. Based on the prediction of the temperature in the reactor based on the composting kinetics model, the process control for the turning operation is proposed to achieve precise control of the composting process. The results show that the duration of high temperature in a composting reactor is prolonged for 2 days, the degradation rate of organic matter occurs at a more rapid speed, and the operation efficiency of the production line can be improved by more than 10%. This indicates that the decision-making method based on the composting kinetics model can improve the composting efficiency.

Drivers of pelagic and benthic microbial communities on Central Arctic seamounts

Seamounts are abundant features on the seafloor that serve as hotspots and barriers for the dispersal of benthic organisms. The primary focus of seamount ecology has typically been on the composition and distribution of faunal communities, with far less attention given to microbial communities. Here, we investigated the microbial communities in the water column (0-3400 m depth) and sediments (619-3883 m depth, 0-16 cm below seafloor) along the ice-covered Arctic ridge system called the Langseth Ridge. We contextualized the microbial community composition with data on the benthic trophic state (i.e., organic matter, chlorophyll-a content, and porewater geochemistry) and substrate type (i.e., sponge mats, sediments, basaltic pebbles). Our results showed slow current velocities throughout the water column, a shift in the pelagic microbial community from a dominance of Bacteroidia in the 0-10 m depth towards Proteobacteria and Nitrososphaeria below the epipelagic zone. In general, the pelagic microbial communities showed a high degree of similarity between the Langseth Ridge seamounts to a northern reference site. The only notable differences were decreases in richness between ~600 m and the bottom waters (~10 m above the seafloor) that suggest a pelagic-benthic coupling mediated by filter feeding of sponges living on the seamount summits. On the seafloor, the sponge spicule mats, and polychaete worms were the principal source of variation in sedimentary biogeochemistry and the benthic microbial community structure. The porewater signature suggested that low organic matter degradation rates are accompanied by a microbial community typical of deep-sea oligotrophic environments, such as Proteobacteria, Acidimicrobiia, Dehalococcoidia, Nitrospira, and archaeal Nitrososphaeria. The combined analysis of biogeochemical parameters and the microbial community suggests that the sponges play a significant role for pelagic-benthic coupling and acted as ecosystem engineers on the seafloor of ice-covered seamounts in the oligotrophic central Arctic Ocean.

Effect of different multichannel ventilation methods on aerobic composting and vegetable waste gas emissions.

Aerobic composting, especially semipermeable membrane-covered aerobic fermentation, is known to be an effective method for recycling and reducing vegetable waste. However, this approach has rarely been applied to the aerobic composting of vegetable waste; in addition, the product characteristics and GHG emissions of the composting process have not been studied in-depth. This study investigated the effect of using different structural ventilation systems on composting efficiency and greenhouse gas emissions in a semipermeable membrane-covered vegetable waste compost. The results for the groups (MV1, MV2, and MV3) with bottom ventilation plus multichannel ventilation and the group (BV) with single bottom ventilation were compared here. The MV2 group effectively increased the average temperature by 19.06% whilst also increasing the degradation rate of organic matter by 30.81%. Additionally, the germination index value reached more than 80%, 3 days in advance. Compared to those of the BV group, the CH4, N2O, and NH3 emissions of MV2 were reduced by 32.67%, 21.52%, and 22.57%, respectively, with the total greenhouse gas emissions decreasing by 24.17%. Overall, this study demonstrated a multichannel ventilation system as a new method for improving the composting efficiency of vegetable waste whilst reducing gas emissions.

Micro-aeration and leachate recirculation for the acceleration of landfill stabilization: Enhanced hydrolytic acidification by facultative bacteria

The long duration of landfill stabilization is one of the challenges faced by municipalities. In this paper, a combination of micro-aeration and leachate recirculation is used to achieve rapid degradation of organic matter in landfill waste. The results showed that the content of volatile fatty acids (VFAs) in the hydrolysis phase increased significantly and could enter the methanogenic phase quickly. Until the end of the landfill, the removal rates of chemical oxygen demand (COD), total phosphorus (TP) and ammonia nitrogen (NH4+–N) by micro-aeration and leachate recirculation reached 80.17 %, 48.30 % and 48.56 %, respectively, and the organic matter degradation rate reached 50 %. Micro-aeration and leachate recirculation enhanced the abundance of facultative hydrolytic bacteria such as Rummeliibacillus and Bacillus and the oxygen tolerance of Methanobrevibacter and Methanoculleus. Micro-aeration and leachate recirculation improved the organic matter degradation efficiency of landfill waste by promoting the growth of functional microorganisms.

Exploring the humification process of municipal sludge in hyperthermophilic composting through metagenomic and untargeted metabolomic

Hyperthermophilic composting (HC) has been widely recognized for the advantage of high treatment efficiency for organic wastes. However, the humification process is still unclear. In this study, the humification process of HC was investigated, compared to conventional composting (CK). The results showed that the highest composting temperature, organic matter degradation rate, and humification index in HC were 92.62 °C, 23.98%, and 1.59, while those in CK were 70.23 °C, 14.49 %, and 1.04, indicating HC accelerated humification process. Moreover, the results of metagenomic and untargeted metabolomic showed that the genes and metabolisms related to carbohydrate, lipid, amino acid, fatty acid, and nucleotide were more abundant in HC. Consequently, the metabolic pathways regarding organic matter degradation and microbial reproduction were enhanced in the high temperature stage of HC, further accelerating the humification reaction in the low temperature stage. This work contributes to the comprehension of the humification mechanism in HC.

Treatment of Eucalyptus chemical-mechanical pulp wastewater by coupling system of advanced catalytic oxidation and biodegradation: Synergistic effect of ozonation photocatalytic-microbial

In addressing the issues concerning the challenging treatment, extensive discharge, substantial organic pollution load, and the intricate composition of chemical-mechanical pulp (CMP) wastewater in the pulp and paper industry, an innovative coupled advanced oxidation and biodegradation techniques known as the intimate coupling of ozone oxidation and photocatalysis-biological treatment (ICOPB) was developed for CMP wastewater remediation. The focus of the present research was to explore the optimization of this system, to comprehend the degradation mechanisms, and to understand microbial reaction behavior. Moreover, the study evaluated the degradation efficiency of four potential mechanisms inherent to ICOPB, which include adsorption, photocatalysis, biological treatment, and coupled photocatalytic-biological indirect wastewater treatment. Under the optimal conditions, wherein the O3 concentration was maintained at 35 mg/min, the carrier filling rate was kept at 5 %, pH was held at 7, and aeration was kept at 0.6 L/min, the degradation efficiencies for COD, BOD, and TOC reached 80.7 %, 91.6 %, and 84.6 %, respectively. When compared with the ICOP (intimate coupling of ozone oxidation and photocatalysis) procedure, the ICOPB demonstrates a superior removal efficiency and more comprehensive mineralization. Microbial diversity results indicated that Proteobacteria actively contribute to the subsequent biodegradation of CMP wastewater treated with the ICOPB system. As revealed by the GC–MS analysis and toxicity assessments of intermediate products, ICOPB notably amplified the rate of organic matter degradation and concurrently reduced the toxicity of the effluents. In conclusion, the findings of this research offer an innovative method for the effective degradation of CMP wastewater, thereby addressing a significant environmental concern in the pulp and paper industry.

Evaluation of Biochar as an Additive in the Co-Composting of Green Waste and Food Waste

Green waste (GW) represents 11% of municipal solid waste. Managing this waste is challenging due to its physicochemical variability, low density, and presence of hard-to-degrade lignocellulosic compounds. Composting is an alternative for GW transformation and valorization. However, due to the substrate characteristics, processing times are long, and the end product typically does not meet quality standards. Incorporating additives and co-substrates are operational strategies that contribute to overcoming these challenges. An essential step is the determination of a mixture’s composition that ensures synergistic effects on the process and end-product quality. This research assessed the effect of adding biochar (Bch) in the co-composting of GW and food waste (FW). A previously studied co-composting mixture (M) of GW, raw and processed FW, sawdust (Sd), and phosphoric rock (Pr) with four treatments by duplicate were assessed at the pilot scale: T1: 100% GW, T2: M1, T3: M2 + 2% Bch, y T4: M3 + 5% Bch. The results show that Bch treatments maintained the range of thermophilic temperatures for longer than the other two treatments (between four and five additional days), showing greater biological activity and better end-product hygienization. Likewise, in the Bch treatments, the hemicellulose and cellulose degradation improved compared to treatments without Bch by 33.9% and 23.3%, respectively, and nitrogen losses were reduced by up to 70%. Regarding the end product, adding a 2% dose of Bch allowed the highest fertility index compared to the other three treatments, showing its potential for agricultural use. This work demonstrates that adding biochar to FW and GW co-composting improves organic matter degradation rates, lignocellulosic degradation, and end-product quality.

A comparison of ultrasonic, ozone, and enzyme pre-treatments on cheese whey degradation for enhancement of anaerobic digestion

Lactose in cheese whey wastewater (CWW) makes it difficult to degrade under normal conditions. The effect of ultra-sonication (US), ozonation and enzymatic hydrolysis on increasing the bioavailability of organic matter in CWW and biogas production were evaluated. The pre-treatment conditions were: specific energy input varied from 2130 to 8773KJ/KgTS for a sonication time of 4.5–18.5 min, Ozone (O3) dosages ranging from 0.03 to 0.045gO3/gTS were applied for 4–16 min, pH (3.8–7.1), temperature (35°C–55°C), enzyme dosage (0.18–0.52%), was operated from 7.75 to 53 min for enzymatic hydrolysis by β-galactosidase. The results of the US reported a maximum sCOD solubilisation of 77.15% after 18.5 min of operation, while the corresponding values for ozonation and enzymatic methods were 64.8% at 16 min and 54.79%, respectively. The organic matter degradation rates evaluated in terms of protein and lactose hydrolysis were 68.78%,46.03%; 47.83%,16.15% and 54.22%,86.2%respectively, for US, ozonation and enzymatic methods. The cumulative methane yield for sonicated, ozonised and enzymatically hydrolysed samples were 412.4 ml/g VS, 361.2 ml/g VS and 432.3mlCH4/gVS, respectively. Regardless of the lower COD solubilisation rates attained, enzymatic pre-treatment showed maximum methane generation compared to US and ozonation. This could be attributable to the increased activity of β-galactosidase in hydrolysing whey lactose. The energy calculations revealed that the pre-conditioning of organic-rich CWW with enzymatic hydrolysis is more effective and efficient, yielding a net energy gain (gross output energy-input energy) of 9166.7 KJ and an energy factor (ratio of output to input energy) of 6.67. The modified Gompertz model well simulated all experimental values.

Transformation from biofiltration unit to hybrid constructed wetland-microbial fuel cell: Improvement of wastewater treatment performance and energy recovery

This study aimed to compare the performance of biofiltration, constructed wetland, and constructed wetland microbial fuel cell (CW-MFC). The transformation from a biofiltration unit to a hybrid CW-MFC was demonstrated with the advantages of improvement of wastewater treatment while generating electricity simultaneously. The introduction of plants to the upper region of the bioreactor enhanced the DO level by 0.8 mg/L, ammonium removal by 5 %, and COD removal by 1 %. The integration of electrodes and external circuits stimulated the degradation rate of organic matter in the anodic region (1 % without aeration and 3 % with aeration) and produced 5.13 mW/m3 of maximum power density. Artificial aeration improved the nitrification efficiency by 38 % and further removed the residual COD to an efficiency of 99 %. The maximum power density was also increased by 3.2 times (16.71 mW/m3) with the aid of aeration. In treating higher organic loading wastewater (3M), the maximum power density showed a significant increment to 78.01 mW/m3 (4.6-fold) and the COD removal efficiency was 98 %. The ohmic overpotential dominated the proportion of total loss (67-91 %), which could be ascribed to the low ionic conductivity. The reduction in activation and concentration loss contributed to the lower internal resistance with the additional aeration and higher organic loading. Overall, the transformation from biofiltration to a hybrid CW-MFC system is worthwhile since the systems quite resemble while CW-MFC could improve the wastewater treatment as well as recover energy from the treated wastewater.

Experimental study on the treatment of dye wastewater by plasma coupled biotechnology

In this experiment, a gas-liquid two-phase discharge water treatment inverse device was designed independently to treat the actual workshop intermediate dye wastewater from a chemical plant. Firstly, the effects of initial concentration of wastewater, initial pH, circulation flow rate of solution, content of Fe2+, content of H2O2, and addition of tert-butanol on the organic removal rate and decolorization rate of dye wastewater treatment were investigated. The results showed that Fe2+ and tert-butanol would react with the active particles (H2O2, ·OH) and inhibit the degradation of the dye wastewater, resulting in the decrease of both organic matter degradation rate and decolorization rate. The experimentally degraded dye wastewater mainly contained benzoic acid and its derivatives in addition to dye molecules, thus the degradation mechanism of benzoic acid was mainly analyzed. Then, the actual dye wastewater treated by low-temperature plasma was combined with the traditional biological treatment technology. The biochemical properties of the wastewater treated by low-temperature plasma technology were greatly improved, and the B/C was increased from the initial 0.17 to 0.33. The effluent after the combined biological method could meet the effluent discharge standard, and the final CODcr reached 198mg/L, BOD5 reached 65mg/L, and pH and chromaticity reached 6.39 and 50, respectively.

Crushing combined with high–frequency turning can promote material degradation of sheep manure compost on the Qinghai–Tibet Plateau by improving the microbial metabolic function

Large sheep farms on the Qinghai Tibet Plateau (QTP) can produce a large amount of sheep manure annually. However, the sheep manure in this area has hard particles and high lignocellulose content, which leads to low composting efficiency and uneven internal and external fermentation. This study aimed to explore the effect of crushing pretreatment on the organic components, antibiotics degradation, and the microbial metabolic functions of sheep manure composting in the QTP. The experiment set up the turning treatments once every 2 d (CT2) or once every 4 d (CT4) after crushing pretreatment. A protocol of no crushing and turning once every 4 d was used as the control (CK). The results showed that compared with CK, CT2 could increase the organic matter degradation rate by 22.5 %, increase the humus content and germination index by 18.9 % and 14.3 %, while CT4 had no obvious effect. CT2 can effectively promote the elimination of tetracycline and β-lactam antibiotics and increase their elimination rate by 7.9–19.3 %. CT2 increased the abundance functional genes involved in carbohydrate metabolism, amino acid metabolism, energy metabolism, cellulolysis, xylanolysis, and chitinolysis of bacteria, and increased the functional genes abundance of carbohydrates, proteins, lipids, and nucleotide metabolism in fungi. Furthermore, several functional enzymes, such as protease and cellulase showed the highest activity in CT2. In conclusion, crushing pretreatment and turning once every two days have the best composting effect.

Marine sediment nitrogen isotopes and their implications for the nitrogen cycle in the sulfate-methane transition zone

IntroductionRecent work has proposed that the nitrogen isotopes in marine sediments can be impacted by anaerobic oxidation of methane (AOM), since nitrogen uptake by anaerobic methanotrophic archaea (ANME) modifies the nitrogen isotope compositions of bulk sediment. Thus, unraveling the AOM-driven nitrogen cycle in the sulfate-methane transition zone (SMTZ) becomes significant. Additional study of the nitrogen cycle between sediment and interstitial water in SMTZ is needed.MethodsTo better understand the nitrogen cycle in the SMTZ, we analyzed NH4+ concentrations of interstitial water and nitrogen isotopes of sediment in the core GC10 from the southwestern Taiwan Basin in the South China Sea.ResultsThe defined SMTZ is located at 560–830 cmbsf, based on methane and sulfate concentrations, as well as TS/TOC ratios, δ13CTIC and δ34S values. In the SMTZ, the NH4+ concentration decreases, the δ15NTN shows a negative excursion, δ15Ndecarb displays a positive excursion.DiscussionsNH4+ concentration decrease is interpreted by sulfate-reducing ammonium oxidation (SRAO). The δ15NTN shows negative excursion, which is most likely interpreted to N2 (δ15N=0‰) released from SRAO that was fixed into marine sediment via ANME nitrogen fixation. The δ15Ndecarb shows a negative correlation with NH4+ concentrations, indicating that it was controlled by organic matter decomposition. In the SMTZ, the methane competes with organic matter for becoming the substrate of sulfate reduction bacteria, which possibly decreases the organic matter degradation rate and causes δ15Ndecarb relative positive excursion. Although δ15Ndecarb is controlled by organic matter degradation, δ15NTN still reveals a negative excursion in the SMTZ. This likely indicates that nitrogen uptake by ANME/AOM microbial consortiums mainly modifies the nitrogen isotope of soluble nitrogen in the SMTZ.ConclusionsThis study indicates unique geochemistry processes in SMTZ will modify nitrogen characteristics in sediment/interstitial water, and the latter can serve as a proxy for AOM.

Estimation of organic matter degradation rate and accumulation in soil using 15N-labeled cattle manure compost

Estimation of organic matter degradation rate and accumulation in soil using ¹⁵N-labeled cattle manure compost

Preservation of Organic Matter in Aqueous Deposits and Soils Across the Mars‐Analog Qaidam Basin, NW China: Implications for Biosignature Detection on Mars

AbstractA variety of aqueous deposits and soils from gullies, fluvial channels, mountain slopes, alluvial fans, playas, polygons, and yardangs have been found on Mars. However, the occurrence of sedimentary organic matter (SOM) in these landscapes under hyperarid and strongly radiative conditions has yet to be fully assessed. With various desiccated landforms analogous to those on Mars, the Qaidam Basin in northwestern China is considered a promising hyperarid Martian analog. Here, aqueous deposits and soils from nine landforms across the extremely dry northwestern Qaidam and from four landforms across the dry southeastern Qaidam were sampled and investigated. Our results reveal that landform and moisture are important controls on organic carbon distribution across the Qaidam Basin, while sedimentary origin has a dominant effect in the extremely dry northwestern Qaidam. Combined with previous studies, low organic carbon contents of soils in the extremely dry northwestern Qaidam suggest possibly low rates of microbial carbon input and of organic carbon degradation in Mars‐like environments. High organic carbon contents of aqueous deposits together with increasing trends along rivers indicate preservation of relic SOM and possibly slow degradation rates of organic matter as compared to their exposure timescale. Moreover, soils from the distal alluvial fan are found to favor the concentration of pedogenic organic carbon as compared to those from other landforms in the dry southeastern Qaidam and from all landforms in the extremely dry northwest. This suggests that subsoils in the distal fans are promising candidate targets for biosignature detection on Mars.