Variability Of Organic Carbon Research Articles

Spatial and Temporal Variations in Soil Organic Carbon in Northwestern China via Comparisons of Different Methods

Soil organic carbon (SOC) is a crucial component for investigating carbon cycling and global climate change. Accurate data exhibiting the temporal and spatial distributions of SOC are very important for determining the soil carbon sequestration potential and formulating climate strategies. An important scheme of mapping SOC is to establish a link between environmental factors and SOC via different methods. The Shiyang River Basin is the third largest inland river basin in the Hexi Corridor, which has closed geographical conditions and a relatively independent carbon cycle system, making it an ideal area for carbon cycle research in arid areas. In this study, 65 SOC samples were collected and 21 environmental factors were assessed from 2011 to 2021 in the Shiyang River Basin. The linear regression (LR) method and two machine learning methods, i.e., support vector machine regression (SVR) and random forest (RF), are applied to estimate the spatial distribution of SOC. RF is slightly better than SVR because of its advantages in the comparison of classification. When latitude, slope, and the normalized vegetation index (NDVI) are used as predictor variables, the best SOC performance is shown. Compared with the Harmonized World Soil Database (HWSD), the optimal scheme improved the accuracy of the SOC significantly. Finally, the spatial distribution of SOC tended to increase, with a total increase of 135.94 g/kg across the whole basin. The northwestern part of the middle basin decreased by 2.82% because of industrial activities. The SOC in Minqin County increased by approximately 62.77% from 2011 to 2021. Thus, the variability of the spatial SOC increased. This study provides a theoretical basis for the spatial and temporal distributions of SOC in inland river basins. In addition, this study can also provide effective and scientific suggestions for carbon projects, offer a key scientific basis for understanding the carbon cycle, and support global climate change adaptation and mitigation strategies.

Temperature seasonality regulates organic carbon burial in lake

Organic carbon burial (OCB) in lakes, a critical component of the global carbon cycle, surpasses that in oceans, yet its response to global warming and associated feedbacks remains poorly understood. Using a well-dated biomarker sequence from the southern Tibetan Plateau and a comprehensive analysis of Holocene total organic carbon variations in lakes across the region, here we demonstrate that lake OCB significantly declined throughout the Holocene, closely linked to changes in temperature seasonality. Process-based land surface model simulations clarified the key impact of temperature seasonality on OCB in lakes: increased seasonality in the early Holocene saw warmer summers enhancing ecosystem productivity and organic matter deposition, while cooler winters improved organic matter preservation. The Tibetan Plateau’s heightened sensitivity to climate and ecosystem dynamics amplifies these effects. With declining temperature seasonality, we predict a significant slowdown or reduction in OCB across these lake sediments, leading to carbon emissions and amplified global warming.

Source Identification of Organic Carbon in Mountainous Reservoirs Sediments Using Stable Isotopes and n‐Alkanes

AbstractThis study focuses on the sources of organic carbon (OC) in surface sediments of reservoirs in the mountainous regions, as well as their dynamics and contribution mechanisms in the carbon cycle. Spatial variations in organic carbon, n‐alkanes, δ13C, and δ15N were analyzed, and a Bayesian isotope mixing model was applied to quantify the relative contributions of different OC sources. The results indicate that the concentration range of organic carbon in sediments is 0.88%–3.72%. The average concentration of long‐chain n‐alkanes is 3.69 μg/g, accounting for 71.4%, indicating that the main source of organic carbon is allochthonous organic carbon. In addition, the Bayesian mixture model results of carbon and nitrogen isotopes also indicate that allochthonous organic carbon is the main contributor. Specifically, sewage (33.1%), C₃ plants (27.1%), and soil organic carbon (19.9%) were identified as the dominant sources. This research highlights the influence of human activities, such as urbanization and agriculture, on OC dynamics and underscores the role of reservoirs in regulating OC transport. The findings provide critical insights into the mechanisms of OC sequestration in agricultural watersheds and offer valuable guidance for water resource management and ecological protection strategies in mountainous environments.

Impact of cascade reservoir on the sources of organic matter in sediments of Lancang river.

The construction of dams to intercept natural rivers constitutes the most severe human activity influencing the underlying surface. This study focuses on four cascade reservoirs of the Lancang River and explores their impact on the migration of organic matter in sediments. The research reveals significant spatial variations in total organic carbon (TOC) and total nitrogen concentrations in the sediments of the four reservoirs. The carbon and nitrogen isotopes indicate that terrigenous organic matter is the main source of TOC in the sediments, contributing an average of 66.80%. Endogenous algal-derived organic matter is the second significant source, contributing between 14.30% and 32.91%. The sources contributed from upstream organic matter are the lowest, ranging from 6.36% to 15.33%. Our study demonstrates that the construction of cascade reservoirs may significantly alter the processes of material sources in the river basin ecosystem, particularly in the large reservoir which increased more endogenous algal-derived organic matter.

Spatial Variation and Stock Estimation of Soil Organic Carbon in Cropland in the Black Soil Region of Northeast China

Soil organic carbon (SOC) sequestration in cropland is not only instrumental in combating climate change, but it also significantly enhances soil fertility. It is imperative to precisely and accurately quantify the SOC sequestration potential and assess the relative significance of various multiple explanatory factors in a timely manner. We studied 555 soil samples from the cropland topsoil (0–15 cm) across the black soil region in Northeast China between the years 2021 and 2022, and we identified 16 significant impact factors using one-way ANOVA and Pearson correlation coefficient analysis. In addition, the Random Forest (RF) model outperformed the Cubist model in predicting the spatial distribution of SOC contents. The predicted ranges of SOC contents span from 5.24 to 43.93 g/kg, with the average SOC content using the RF model standing at 17.24 g/kg in Northeast China. Stepwise regression and structural equation modeling revealed climate and topography as key factors affecting SOC distribution. The SOC density in the study area varied from 0.51 to 9.11 kg/m2, averaging 3.30 kg/m2, with a total SOC stock of 1226.64 Tg. The SOC sequestration potential in the study area was estimated at 3057.65 Tg by the categorical maximum method, with a remaining sequestration capacity of 1831.01 Tg. The study area has great potential for SOC sequestration. We hope to transform the theoretical value of SOC sequestration potential into actual SOC sequestration capacity by promoting sustainable agriculture and additional strategies. Our findings provide insights into the global soil conditions, SOC storage capacities, and effective SOC management strategies.

Organic petrology and geochemistry of the late Neogene Shizigou Formation in the Qaidam Basin, China: Characteristics of a prospective microbial gas source rock

The discovery of natural gas trapped in the late Neogene Shizigou Formation in the Yikeyawuru anticline indicates the potential for additional microbial gas reservoirs outside of the primary exploration targets for microbial gas in the younger, i.e., the Pleistocene sediments of the Qaidam Basin. In this study, a detailed investigation is presented on the bulk geochemistry and organic petrography of the potential microbial source rocks as well as on molecular organic geochemistry of the solvent extracts obtained from the late Neogene Shizigou Formation of the Yiliping Depression. The objectives are to elucidate i) the depositional environment, ii) biological sources of organic matter (OM), and iii) biodegradation levels in these microbial gas source rocks.The samples from the well situated at the center of the Yiliping Depression (the H 1 well) exhibit minor variations in total organic carbon (TOC) and total sulfur contents, whereas the samples from the well located at the margin of the depression (the Y 3 well) show large variations in these values. All these samples are presently thermally immature. The kerogen of the TOC-rich Y 3 well samples is mainly composed of mixed types II–III kerogen and characterized by a complex maceral composition (i.e., a mixture of large fragments of huminite, semifusinite, fusinite, resinite/fluorinite, lamalginite, and liptodetrinite). In contrast, samples from the H 1 well contain typically type III kerogen with a less complex maceral composition consisting of huminite, lamalginite, and liptodetrinite. The molecular data illustrates that the OM is predominantly derived from bacterial and algal biomass as well as aquatic higher plants (primarily in the Y 3 well samples), while angiosperms are the primary source of the subordinate terrestrial OM in the samples. The marginal area is characterized by salinity levels akin to normal marine conditions with bottom-water paleoredox conditions ranging from dyoxic (samples with high TOC content) to oxic, whereas the central area developed a mesosaline environment with oxic bottom-water conditions prevailing. In contrast to the primary microbial gas producing layer, the Pleistocene Qigequan Formation, the late Neogene Shizigou Formation exhibits a higher contribution of emergent macrophytes but a reduced abundance of lower aquatic organisms in the OM as well as a higher salinity level in the water column. Despite the late Neogene Shizigou Formation demonstrating a lower potential for hydrocarbon generation and a lower degree of biodegradation of OM than the Qigequan Formation, it still shows generally favorable geological and geochemical conditions that are conducive to the development of microbial gas reservoirs, which is underscored by the biodegradation levels between 3 and 4 for the studied samples.

Variation in Soil Moisture Content and Soil Organic Carbon in Different Agroforestry Practices in Moshi Rural District, Northern Tanzania

Agroforestry has been widely practiced in the northern highlands of Tanzania because of its prominent effects in reducing soil losses, maintaining soil moisture contents (SMCs), and improving land-use efficiency and farmer’s livelihood. We tested the hypothesis that variations of soil moisture contents in 0-20 cm and 20-40 cm depths from various agroforestry Practices differ significantly in intensified small-scale agroforestry systems. The relationship between SMCs and soil organic carbon was also evaluated. Soil samples were collected from 10 x 10 m2 plot in three points along the diagonal of the quadrat using soil auger. SMCs were determined by gravimetric method and expressed as SMC%. SOC was determined by Walkley and Black method and expressed as SOC %. The variation in SMCs% among the different agroforestry Practices were statistically determined by ANOVA in R software while the correlation between SMCs and SOC were statistically determined by Pearson product-moment analysis. Variation of SMCs was statistically insignificant (p>0.05) among surveyed sites. SMCs increased significantly (p<0.05) with increasing soil depth from 0-40 cm depth in all agroforestry Practices except in the mixed intercropping agroforestry practice (MAP). At 0-20 cm and 20-40 cm, SMCs differed significantly among agroforestry Practices (P = 0.071) and (P = 0.003), respectively. Coffee Intercropping Agroforestry Practice (CIAP) had higher (P<0.05) SMCs at 0-20 cm depth compared to BAP and MWPAP. But, at 20-40 cm depth, soil moisture contents in CIAP differed significantly (P<0.05) with SMCs all AFPs. SMCs showed a positively significant (P<0.05) relationship with SOC within 0-20 cm and 20-40 cm depths. The current study confirms that different agroforestry practices have different influence on the amount and vertical distribution of soil moisture. Therefore, management practices in agroforestry systems should aim to encourage the use of practices which ensure a stable amount of moisture contents in the soil

Assessing spatiotemporal variations of soil organic carbon and its vulnerability to climate change: A bottom-up machine learning approach

Soil organic carbon (SOC) is a crucial component of the terrestrial carbon cycle and essential for agricultural productivity. Quantifying its sensitivity to future climate change is vital for sustaining agricultural practices and mitigating greenhouse gas emissions. However, this remains a challenge as long-term SOC data are scarce and substantial uncertainties regarding future climate scenarios. This study presents a bottom-up machine learning framework to assess the spatiotemporal variations of SOC and its vulnerability to climate change in the Jinghe River Basin, a typical loess hilly and gully watershed. Firstly, the long-term (2000–2023) dynamics of SOC was estimated by integrating in-situ measurements with machine learning techniques. Results show that the high SOC values are primarily distributed in the farmland of the mountain-loess transition zone, while the low-value areas are mainly found in the loess region. During the study period, the SOC content exhibited a slight increasing trend with a rate of 0.02 ​g ​kg−1 ​yr−1 (p ​= ​0.449). The vulnerability of farmland surface SOC to future climate change was then evaluated by combining a robust machine learning model with the bottom-up framework. To this end, the study explored a wide range of possible future climates to identify critical climate thresholds and their spatial variation across the basin’s farmlands. Based on this analysis, this research found that the farmland in the northern basin is generally more susceptible to changing climate with even marginal rises in temperature could lead to severe loss in SOC. These results highlight the need for proactive climate adaptation strategies to safeguard SOC in vulnerable agricultural landscapes, ensuring soil health and resilience in the face of climate change.

Global Distributions of Reactive Iron and Aluminum Influence the Spatial Variation of Soil Organic Carbon.

Organic carbon persistence in soils is predominantly controlled by physical accessibility rather than by its biochemical recalcitrance. Understanding the regulation of soil iron (Fe) and aluminum (Al) (hydr)oxides, playing a dominant role in mineral protection, on soil organic carbon (SOC) would increase the reliable projections of the feedback of terrestrial ecosystems to global warming. Here, we conducted a continental-scale survey in China (341 sites) and a global synthesis (6786 observations) to reveal the global distributions of Fe/Al (hydr)oxides and their effects on SOC storage in terrestrial ecosystems. We generated the first global maps of soil Fe/Al (hydr)oxides with high accuracy (with R2 more than 0.74). The variance decomposition analysis showed that Fe/Al (hydr)oxides explained the most proportion of variance for topsoil (0-30 cm) and subsoil (30-100 cm) SOC. Therefore, soil Fe/Al (hydr)oxides play a stronger role in explaining the spatial variation of SOC than well-studied climate, edaphic, vegetated, and soil depth factors in both topsoil and subsoil. Collectively, the planetary-scale significance of soil Fe/Al (hydr)oxides for SOC highlights that soil Fe/Al (hydr)oxides should be incorporated into Earth System Models to reduce the uncertainty in predicting SOC dynamics.

Differential Spatiotemporal Patterns of Major Ions and Dissolved Organic Carbon Variations from Non-Permafrost to Permafrost Arctic Basins: Insights from the Severnaya Dvina, Pechora and Taz Rivers

The Arctic river basins, among the most sensitive regions to climate warming, are experiencing rapid temperature rise and permafrost thawing that profoundly affect their hydrological and hydrochemical systems. However, our understanding of chemical export from Arctic basins to oceans remains limited due to scarce data, particularly in permafrost-dominated regions. This study examines the spatiotemporal variations and seasonal dynamics of major ions (Na+, K+, Mg2+, Ca2+, Cl−, SO42−) and dissolved organic carbon (DOC) concentrations across three river basins with varying permafrost extents: the Severnaya Dvina (2006–2008, 2012–2014), the Pechora (2016–2019) and the Taz Rivers (2016–2020). All the data were sourced from published Chemical Geological researches and were taken from Mendeley and PANGAEA datasets. Our results showed that DOC concentrations ranged from 1.75 to 26.40 mg/L, with the Severnaya Dvina River exhibiting the highest levels of DOC concentrations, alongside significantly elevated ion concentrations compared to the other two basins. A positive correlation was observed between DOC concentrations and river discharge, with peaks during the spring flood and summer baseflow due to leaching processes. The Severnaya Dvina and Pechora Rivers exhibited the highest DOC values during the spring flood, reaching 26.40 mg/L and 8.07 mg/L, respectively. In contrast, the Taz River had the highest runoff during the spring flood season, but the DOC concentration reached its highest value of 11.69 mg/L in the summer. Specifically, a 1% increase in river discharge corresponded to a 1.25% rise in DOC concentrations in the Severnaya Dvina River and a 1.04% increase in the Pechora River, while there was no significant correlation between runoff and DOC concentrations in the Taz River. Major ion concentrations demonstrated a negative correlation with river discharge, remaining relatively high during winter low-flow period. A robust power-law relationship between river discharge and concentration of DOC and major ions was observed, with distinct variations across the three river basins depending on permafrost extent. The Pechora and Taz Rivers, characterized by extensive permafrost, exhibited increasing trends in river discharge and DOC concentrations, accompanied by decreasing major ion concentrations, whereas the non-permafrost-dominated Severnaya Dvina River basin showed the opposite pattern. The Taz River, with the most extensive permafrost, also displayed a delayed DOC peak and more complex seasonal ion concentration patterns. These findings highlight the importance of varying permafrost extents and their implications for water quality and environmental protection in these vulnerable regions.

Evaluating the impacts of area closure on soil properties in south central highland of Ethiopia

Soil degradation affects its quality and productivity of the land. To control soil degradation, various soil and water conservation (SWC) measures, including area closure are implemented. Understanding the impacts of SWC measures could support planning and implementation of land management practices. This study aimed to investigate impacts of area closure on soil properties in south central highland of Ethiopia. To acquire the necessary data, we conducted interviews with 80 households. Furthermore, nine years old area closure with physical soil and water conservation (AC-SWC), open grazing with physical SWC (OG-SWC), and open grazing without physical SWC (OG) were identified and each divided into upper, middle, and lower slope positions. In each slope position, 3 sample plots were established at 25–50 m intervals. A total of 27 composite samples and other 27 core samples for bulk density (3 treatments∗3 slope position∗3 replications) were collected and analyzed for soil properties. The data were analyzed using descriptive statistics and one-way ANOVA. The results showed that about 98 % of the respondents perceived that area closure would be an effective way to restore degraded land. Majority of the farmers (86 %) believed that area closure could reduce soil erosion and replenish soil fertility and thus, is beneficial in improving land productivity. Soil test results revealed that AC-SWC had significantly greater (P < 0.05) clay fractions, pH, available potassium, and available phosphorus than OG-SWC and OG. Variations of soil organic carbon (SOC) and total nitrogen (TN) were more pronounced. The SOC in AC-SWC was 83 % and 314 % greater than OG-SWC and OG, respectively. In the AC-SWC, TN was three and seven times higher than that of OG-SWC and OG, respectively. This could be due to vegetation restoration that reduces erosion, and enhances organic matter, moisture, and nutrient. The SOC, TN, pH, available potassium, and clay were significantly greater (P < 0.05) at lower slope position than upper in all forms of land management, which could be due to deposition at downslope. About 12 % and 11 % variations of clay fractions and SOC were, respectively, observed in between upper and lower slope positions at AC-SWC, but they varied by 25 % and 57 %, respectively, in OG. These imply area closure has had a beneficial effect on soil properties even on sloping land. AC-SWC is an important option to integrate in land management for rehabilitation of degraded soil.

Distribution characteristics of soil active organic carbon at different elevations and its effects on microbial communities in southeast Tibet.

Global mountain ecosystems have garnered significant attention due to their rich biodiversity and crucial ecological functions; however, there is a dearth of research on the variations in soil active organic carbon across altitudinal gradients and their impacts on microbial communities. In this study, soil samples at an altitude of 3,800 m to 4,400 m were collected from Sejira Mountain in the southeast Tibet, and soil active organic carbon components, soil microbial community diversity, composition and structure distribution and their relationships were systematically analyzed. The results revealed a non-linear relationship between the elevation and the contents of soil organic carbon (SOC) and easily oxidized organic carbon (ROC), with an initial increase followed by a subsequent decrease, reaching their peak at an altitude of 4,200 m. The Shannon diversity of bacteria exhibited a significant decrease with increasing altitude, whereas no significant change was observed in the diversity of fungi. The bacterial community primarily comprised Acidobacteria, Proteobacteria, Chloroflexi, and Actinobacteriota. Among them, the relative abundance of Proteobacteria exhibited a negative correlation with increasing altitude, whereas Actinobacteriota demonstrated a positive correlation with elevation. The fungal communities primarily consisted of Basidiomycota, Ascomycota, and Mortierellomycota, with Ascomycota prevailing at lower altitudes and Basidiomycota dominating at higher altitudes. The diversity and composition of bacterial communities were primarily influenced by altitude, SOC, ROC, and POC (particulate organic carbon). Soil carbon-to-nitrogen ratio (C/N), dissolved organic carbon (DOC), and available phosphorus (AP) emerged as key factors influencing fungal community diversity, while POC played a pivotal role in shaping the composition and structure of the fungal community. In conclusion, we believe that soil active organic carbon components had a greater impact on the bacterial community in the primary forest ecosystem in southeast Tibet with the elevation gradient increasing, which provided a theoretical basis for further understanding of the relationship between the microbial community and soil carbon cycle in the plateau mountain ecosystem under the background of climate change.

Pre-ozonation coupled with forward osmosis with fertilizer as draw solution for simultaneous wastewater treatment and agricultural irrigation

Membrane-based processes have emerged as effective solutions for treating tannery wastewater. Persistent membrane fouling remains a significant obstacle to long-term operational sustainability, and residual pollutants often persist in the treated effluent. To address these challenges, we investigated an integrated ozone-forward osmosis (O3-FO) process, with a focus on evaluating the efficacy of pre-ozonation in alleviating membrane fouling, as well as exploring the possibilities of this integrated process for the reuse of tannery wastewater. Fertilizer, specifically 2 M Ca(NO3)2, served as the draw solution (DS) in this process. The findings reveal that the integrated system demonstrated remarkable pollutant retention capabilities. Notably, no metal was detected in the fertilizer. Therefore, the integrated process not only dilutes the fertilizer but also minimizes the risk of heavy metal contamination to both crops and soil. Furthermore, pre-ozonation effectively mitigated membrane fouling, resulting in an increase in membrane flux with a maximum increase of 20.98 % at 0.6 L/min. Orthogonal partial least squares-discriminant analysis (OPLS-DA) revealed pre-ozonation has the most significant impact on four parameters: water flux (Jw), chemical oxygen demand (COD), fouling resistance (Rf) and oxidation reduction potential (ORP). Meanwhile, ammonium nitrogen (NH4-N) variation, dissolved organic carbon (DOC) variation and ORP played an important role in the four systems. Multi-criteria decision analysis (MCDA) showed that the 0.2 L/min O3-FO system achieved the highest score (0.66), followed by 0.6 L/min (0.53), 0.4 L/min (0.41) and 0 L/min (0.29). This research offers a theoretical framework for the synergistic integration of advanced oxidation and membrane technology in the treatment of industrial wastewater.

Temporal and Spatial Variations of Soil Organic Carbon and the Influencing Factors in Shaanxi Province in Recent 30 Years

Soil organic carbon （SOC） variation is a significant indicator for the soil quality dynamic and global carbon cycle. Therefore, it is necessary to study the regional temporal and spatial distribution of SOC pool and the influencing factors. In this study, a total of 540 soil data and environmental variables were collected from Shaanxi Province during a 30-year period from 1985 to 2015, and univariate analysis of variance and path analysis were used to explore the temporal and spatial distribution characteristics of SOC content and the influencing factors of SOC change. The results showed that the SOC contents of Shaanxi Province in both 1985 and 2015 were the highest in central Shaanxi, followed by those in southern Shaanxi, and they were significantly higher than those in northern Shaanxi. From 1985 to 2015, the increase in SOC in southern Shaanxi was the highest （21.28%）, and that in central Shaanxi was 15.33%. The content of SOC in northern Shaanxi was decreased by 10.23%, caused by significant decrements in the bottom horizons of 60-80 cm and 80-100 cm. Compared with that in 1985, the increases in SOC content in the 0-100 cm soil profile （with every 20 cm as a horizon） ranged from 3.21% to 29.39% in 2015. The increase in SOC content of skeletal soils was largest, followed by that of alluvial soils. Correlation analysis and path analysis showed that SOC content was positively correlated with altitude, average annual precipitation, normalized vegetation index, and total nitrogen content and was in significant negative correlation with curvature, bulk density, and pH. Total nitrogen content was the main controlling factor affecting SOC content. The results of the study can provide reference for future carbon management measures in the region.

Salinity increases under sea level rise strengthens the chemical protection of SOC in subtropical tidal marshes

The rise in sea levels due to global warming could significantly impact the soil organic carbon (SOC) pool in coastal tidal marshes by altering soil salinity and flooding conditions. However, the effects of these factors on SOC protection in coastal tidal marshes are not fully understood. In this study, we employed a space-for-time approach to investigate the variations in soil active carbon components and mineral-associated organic carbon under different salinity gradients (freshwater and brackish) and flooding frequencies (high and low tidal flats).The soil organic carbon (SOC) and easily oxidizable organic carbon (EOC) contents at the low-flooding frequency sites were higher than those at the high-flooding frequency sites. The dissolved organic carbon (DOC) content was higher at the high-salinity sites compared to the low-salinity sites, while the soil microbial biomass carbon (MBC) content was higher at the low-salinity sites than at the high-salinity sites. The EOC/SOC and DOC/SOC ratios were greater at the high-salinity sites than at the low-salinity sites, whereas the MBC/SOC ratios were higher at the low-salinity sites than at the high-salinity sites. Iron (Fe) and aluminum (Al) mineral-associated organic carbon [Fe(Al)-OC] and calcium-associated organic carbon (Ca-OC) contents were higher at the high-salinity sites compared to the low-salinity sites, and at the low-flooding frequency sites compared to the high-flooding frequency sites.Meanwhile, Fe(Al)-OC was the dominant fraction among mineral-associated organic carbon at all sites. The dominant phyla of bacterial community included Proteobacteria (49.31 %–66.36 %), Firmicutes (2.67 %–28.44 %), Chloroflexi (3.81 %–9.54 %), and Acidobacteria (4.28 %–7.02 %). In addition, Desulfobacca, a sulfate-reducing bacterium, promoted the formation of mineral-associated organic carbon.Random forest analysis showed that SOC and DOC were key factors in promoting mineral-associated organic carbon formation. Partial least squares path modeling (PLS-PM) indicated that sea level rise affects DOC content by altering soil physicochemical properties, promoting the formation of mineral-associated organic carbon.In summary, while soil organic carbon activity increases, the chemical association of minerals with organic carbon is becoming increasingly crucial for the protection of organic carbon under rising salinity conditions driven by sea level rise.

Estimation of top soil properties by Sentinel-2 imaging

ABSTRACT This study evaluated the feasibility of using free multispectral remote sensing data from Sentinel-2A satellites to predict soil properties in Northern Karnataka, India. Sentinel-2A images were downloaded for selected sites, covering Vertisol, Ultisol, and Alfisol soils. Multiple linear regression (MLR) models incorporated four Sentinel-2 bands and six spectral indices (NDVI, GNDVI, SAVI, TVI, EVI, and BI) as independent variables, with soil properties as dependent variables. Surface samples (0–15 cm depth) were collected from March to May 2022. The analysis showed significant correlations between individual bands and soil properties, with variations in Organic Carbon (OC) compared to sand, silt, clay, and pH. Sand positively correlated with all spectral indices, while silt, clay, and pH were negatively correlated. The red and Near-Infrared (NIR) bands showed a non-significant relationship with OC. No significant correlation was found between EVI and the soil properties. Strong regression coefficients were observed between Sentinel-2 predictions and laboratory measurements: sand (r² = 0.63), silt (r² = 0.73), clay (r² = 0.59), and pH (r² = 0.59). These results demonstrate the potential of Sentinel-2 data for predicting soil properties, offering a valuable tool for managing unsampled agricultural fields.

Fate of soil organic carbon in estuarine mangroves: Evidences from stable isotopes and lignin biomarkers

Coastal wetlands are increasingly recognized for their role in climate change mitigation, particularly through the sequestration of soil organic carbon (SOC). Despite widespread acknowledgement of their importance, the variation in organic carbon (OC) sources among different estuarine mangrove wetlands, and how these sources interact with environmental factors, is not fully elucidated. This research focuses on the role of estuarine mangrove wetlands in climate change mitigation through SOC sequestration. It explores the distribution, sources, and decomposition of SOC in a wetland with four mangrove communities along a tidal gradient. These include a tidal flat, a Sonneratia apetala forest, a mixed S. apetala and Kandelia obovata forest, and a K. obovata forest. The study employs biogenic element analysis (C, N, lignin phenols) and natural stable carbon isotope ratios (δ13C and δ15N) to assess SOC. Key findings show a decrease in SOC and total nitrogen (TN) from the upstream K. obovata forest to the downstream tidal flat. A stable isotope mixing model reveals a diminishing mangrove-derived OC contribution in topsoil (0–40 cm), estimated at 62 % in the K. obovata forest, 45 % in the central region, and 24 % in tidal flats. Soil profiles suggest microbial decomposition as the main isotope fractionation mechanism, with lignin analysis indicating woody angiosperms as the primary OC source. These findings enhance understanding of OC origins and decomposition in coastal wetlands and inform “blue carbon” management, highlighting the terrestrial-estuary continuum's significance.

Greater variation of soil organic carbon in limestone- than shale-based soil along soil depth in a subtropical coniferous forest within a karst faulted basin of China

Lithology strongly influences soil microbial traits and edaphic factors and in turn soil organic carbon (SOC) dynamics. However, the effect of lithology on microbial traits, edaphic factors and resulting SOC physical fractions variation along soil depth remains inadequately understood in karst faulted basin of China. This understanding is critical for improving SOC stability. By separating SOC into labile particulate organic carbon (POC) and stable mineral-associated organic carbon (MAOC) over karst limestone and non-karst shale soil in a subtropical coniferous forest, we aimed to assess potential regulatory mechanisms underlying lithology-associated SOC stability variations across soil depth by integrating soil nutrients, mineralogical characteristics, and microbial traits. We found that SOC and its fractions were higher in limestone than in shale soil, which implying vegetation restoration effects on SOC and its fractions partly depending on lithology. Additionally, we found that the effects of soil depth on SOC and its fractions were greater in limestone soils than shale soils, and the ratios of MAOC to SOC (MAOC:SOC) and MAOC to POC (MAOC:POC) show a opposite trend in response to soil depth between two the lithologies. Variation partitioning and random forest analyses revealed that among multiple factors, the variation of SOC stability assessed via MAOC:SOC was mainly explained by microbial traits than soil nutrients and mineral properties. Contrast to soil depth, structural equation modeling analyses showed that lithology was the primary factor controlling the SOC stability when microbial traits, soil nutrients and mineralogical characteristics were controlled as conditional variables. Overall, these results highlight the crucial role of lithology in regulating the SOC stability along soil depth, which improve our understanding and management of soil carbon (C) pool in karst faulted basin of southwest China.

Assessment of the Impact of Sulphur Levels on Soil Chemical Properties in S-de icient Sandy Loam Soil of Amritsar

Limited understanding of how varying sulphur levels affect soil chemical properties in S-deicient sandy loam soil speciically found in Amritsar. A pot experiment was conducted on mustard cv. RLC 3 and broccoli cv. Palam Samridhi in a factorial completely randomized design with three replications. Four levels of sulphur were applied to the soil, and plants were harvested 30 and 60 days after germination. The study aimed to investigate the impact of sulphur levels on soil chemical properties. The results showed that the value of soil pH was reduced signiicantly with an increase in the S level. The highest soil pH (8.12) was recorded where no sulphur-1 was applied, whereas the least (7.65) was found in 60 mg S kg soil treatment. There was no signiicant variation in electrical conductivity and soil organic carbon during the study. Soil available sulphur increased linearly with a simultaneous increase in levels -1 -1 of sulphur resulting in a maximum value (12.75 mg kg ) at 60 mg S kg soil treatment, compared to no sulphur application (4.31 mg-1 -1 kg ). Notably, soil properties signiicantly improved with the application of 60 mg S kg soil, particularly under mustard followed by broccoli crop.

Hydrology, vegetation, and soil properties as key drivers of soil organic carbon in coastal wetlands: A high-resolution study

Coastal wetlands are important blue carbon ecosystems that play a significant role in the global carbon cycle. However, there is insufficient understanding of the variations in soil organic carbon (SOC) stocks and the mechanisms driving these ecosystems. Here we analyze a comprehensive multi-source dataset of SOC in topsoil (0–20 cm) and subsoil (20–100 cm) across 31 coastal wetlands in China to identify the factors influencing their distribution. Structural equation models (SEMs) reveal that hydrology has the greatest overall effect on SOC in both soil layers, followed by vegetation, soil properties, and climate. Notably, the mechanisms driving SOC density differ between the two layers. In topsoil, vegetation type and productivity directly impact carbon density as primary sources of carbon input, while hydrology, primarily through seawater salinity, exerts the largest indirect influence. Conversely, in subsoil, hydrology has the strongest direct effect on SOC, with seawater salinity also influencing SOC indirectly through soil and vegetation mediation. Soil properties, particularly pH, negatively affect carbon accumulation, while climate influences SOC indirectly via its effects on vegetation and soil, with a diminishing impact at greater depths. Using Random Forest, we generate high-resolution maps (90 m × 90 m) of topsoil and subsoil carbon density (R2 of 0.53 and 0.62, respectively), providing the most detailed spatial distribution of SOC in Chinese coastal wetlands to date. Based on these maps, we estimate that SOC storage to a depth of 1 m in Chinese coastal wetlands totals 74.58 ± 3.85 Tg C, with subsoil carbon storage being 2.5 times greater than that in topsoil. These findings provide important insights into mechanism on driving spatial pattern of blue carbon and effective ways to assess carbon status on a national scale, thus contributing to the advancement of global blue carbon monitoring and management.