Distribution Of Organic Carbon Research Articles

Satellite-Derived Dissolved Organic Carbon Distribution and Variability in an Interconnected Estuary off the Southeastern U.S

Satellite-Derived Dissolved Organic Carbon Distribution and Variability in an Interconnected Estuary off the Southeastern U.S

Spatiotemporal distribution of sedimentary chloropigments and organic carbon in a shelf sea ecosystem, with a focus on the cold water mass

The Yellow Sea is one of the most thoroughly studied shelf seas in the northwestern Pacific. However, many aspects of the northern Yellow Sea sediments remain poorly understood. Sedimentary chloropigments and total organic carbon (TOC) are crucial components that indicate benthic primary productivity and ecosystem functioning in the marginal sea system. The present study investigated the temporal and spatial variations of sediment chloroplastic pigments (Chl-a and Pha-a) and TOC contents in relation to seasons and the northern Yellow Sea Cold Water Mass (NYSCWM). Decadal trends were also examined using linear regression on time-series data from 12 cruises conducted over a nine-year period (2006–2014). The correlations between sedimentary Chorophy-a (Chl-a), Pheophorbide-a (Pha-a), TOC, and their ratios with other abiotic and biotic factors were analyzed to detect any effects of the NYSCWM on the spatiotemporal distribution of sediment Chl-a, Pha-a, TOC contents, as well as the ecological relevance of their ratios as indicators of food quality (freshness) in the benthic system. The NYSCWM substantially influences the spatial and seasonal distribution of sedimentary Chl-a, Pha-a, and TOC contents. High values of Pha-a, TOC, and the ratios of Pha-a/(Chl-a + Pha-a) and TOC/Chl-a were often observed in the central region of the NYSCWM, where Chl-a showed clear seasonal fluctuations while Pha-a and TOC remained relatively constant. While sedimentary TOC appears to negatively mirror the spatial pattern of primary productivity in the water column, the spatial pattern of sedimentary Chl-a in relation to NYSCWM is less evident. However, the contents of Pha-a and TOC in the central NYSCWM sediments were higher than those at surrounding NYSCWM stations. Surface sediment Pha-a/(Chl-a + Pha-a) ratio was negatively correlated with meiofauna abundance and biomass and positively correlated with nematode/copepod ratio. This finding indicates that the quality of sediment organic matter is important to meiofauna. Conversely, the lower organic degradation rate at the lower bottom temperature of the NYSCWM may explain the observed higher Pha-a and TOC contents in its central area. Time-series data collected over nine years at the NYSCWM stations showed a decreasing trend for Chl-a, while TOC and the ratio of Pha-a/(Chl-a + Pha-a) exhibited increasing tendencies. This trend may imply a reduced quality of food supply to the benthic food web in the shelf sea system, along with degraded ecosystem functioning and service under the impacts of global change and anthropogenic disturbances.

Distribution and Preservation of Total Organic Carbon and Total Inorganic Carbon in Pipahai Lake over the Past Century

Carbon burial patterns in lakes and their dynamic changes significantly impact terrestrial carbon sink fluxes and global carbon budgets. In this study, multi-indicator analysis of sediment core samples (P1, P2, and P3) from Pipahai Lake was conducted. Integrating the chronological sequences of 210Pb and 137Cs, we identified the historical changes and spatial characteristics of total organic carbon (TOC) and inorganic carbon (TIC) burial in Pipahai Lake since 1884. The results show that the TOC content was higher than that of the TIC. They exhibited an increasing trend with decreasing depth. Linear regression results indicated that the variation of TOC is less directly affected by precipitation (R = 0.39) and temperature (R = 0.58), while temperature may have a greater impact on TOC. From 1884 to 1995, nutrients were not the primary factor influencing changes in TOC. The synchronous variation in TIC and TOC contents reflects a higher contribution of external inputs to carbon burial in the Pipahai Lake basin. After 1996, nutrients may have begun to affect variations in TOC. The TOC primarily originates from distal aeolian transport or autochthonous sources, though human activity has played a role in its evolution. The TIC content is controlled by the TOC content and autochthonous sources. This study will contribute to the understanding of the carbon cycling dynamics and their influencing mechanisms in a high-altitude lake ecosystem.

Seafloor sediment characterization improves estimates of organic carbon standing stocks: an example from the Eastern Shore Islands, Nova Scotia, Canada

Abstract. Continental shelf sediments contain some of the largest stocks of organic carbon (OC) on Earth and play a vital role in influencing the global carbon cycle. Quantifying how much OC is stored in shelf sediments and determining its residence time is key to assessing how the ocean carbon cycle will be altered by climate change and possibly human activities. Spatial variations in terrestrial carbon stocks are well studied and mapped at high resolutions, but our knowledge of the distribution of marine OC in different seafloor settings is still very limited, particularly in dynamic and spatially variable shelf environments. This lack of knowledge reduces our ability to understand and predict how much and for how long the ocean sequesters CO2. In this study, we use high-resolution multibeam echosounder (MBES) data from the Eastern Shore Islands offshore Nova Scotia (Canada), combined with OC measurements from discrete samples, to assess the distribution of OC content in seafloor sediments. We derive four different spatial estimates of organic carbon stock: (i) OC density estimates scaled to the entire study region assuming a homogenous seafloor, (ii) interpolation of OC density estimates using empirical Bayesian kriging, (iii) OC density estimates scaled to areas of soft substrate estimated using a high-resolution classified substrate map, and (iv) empirical Bayesian regression kriging of OC density within areas of estimated soft sediment only. These four distinct spatial models yielded dramatically different estimates of standing stock of OC in our study area of 223 km2: 80 901, 58 406, 16 437 and 6475 t of OC, respectively. Our study demonstrates that high-resolution mapping is critically important for improved estimates of OC stocks on continental shelves and for the identification of carbon hotspots that need to be considered in seabed management and climate mitigation strategies.

Spatial distribution characteristics and influencing factors of soil organic carbon based on the geographically weighted regression model.

Quantifying the effects of environmental factors on soil organic carbon and spatial distribution is fundamental to soil quality regulation, restoration, and response to climate change. The present study aims to explore the spatial distribution characteristics of the soil organic carbon (SOC) contents in Anhui Province, China, based on national soil data. In addition, we used the geographically weighted regression (GWR) model to quantify the influence degrees of environmental factors on the soil organic carbon density (SOCD). The results showed that the spatial distribution of SOCD in Anhui Province in both 1985 and 2018 was characterized by high in the south and low in the north. The GWR model prediction results of the 0-30cm SOCD showed local coefficients of determination (local R2) ranging from 0.21 to 0.96 and 0.14 to 0.96 in 1985 and 2018, respectively. Therefore, the predicted results were effective in evaluating the overall spatial distribution of the SOCD in Anhui Province. The regression coefficients of the normalized difference vegetation index (NDVI) and air temperature ranged from - 0.39 to 5.67 and - 0.17 to 3.11, respectively, demonstrating their strong controlling effects on the spatiotemporal variations in the 0-30cm SOCD in Anhui Province.

Assessing the distribution of soil organic carbon under three plant species across coastal sabkhas: A comparative analysis

Assessing the distribution of soil organic carbon under three plant species across coastal sabkhas: A comparative analysis

How human activities reshape carbon burial in estuarine sediment systems: Evidence from the Yangtze Estuary

Estuaries are critical zones for understanding the dynamics of organic carbon (OC) burial, particularly in the context of human intervention, yet detailed information remains limited. This study presents comprehensive field observations aimed at assessing the spatial and temporal variations in sedimentary OC sources, composition, and distribution within the Yangtze Estuary. By employing a three-endmember estimation, we determined the contributions of fluvial, marine, and salt marsh plants to OC in the mouth bar as 52 ± 6 %, 28 ± 12 %, and 20 ± 9 %, respectively. To address the complexities introduced by human activities and dispersal processes, we utilized a PCA-MC four-endmember model, which revealed that redispersal terrigenous organic matter from the outer estuary, categorized as “marine origin”, accounted for 26 ± 10 % re-deposited within the estuary. During the construction of the Deep Channel Navigation Project (DCNP), we observed a shift in terrigenous OC deposition from the North Passage (NP) to the South Passage (SP), along with an increased contribution from salt marsh plants. Post-DCNP completion, sedimentary OC compositions exhibited significant differences between the NP and SP, with the SP enriched in fresh terrigenous OC and the NP showing degraded signals due to dredging activities and source discrimination. Human interventions not only altered the estuarine geomorphology and hydrodynamics but also impacted OC burial and sequestration by modifying sources and compositions. This study highlights the transition of estuarine regions from carbon sinks to potential sources, underscoring the necessity for a comprehensive understanding of carbon cycle dynamics in Anthropocene-influenced estuarine environments.

Spatial variation of soil carbon, nitrogen, and phosphorus in the Caatinga dry forest

Soil nutrients are crucial for understanding the impact of global changes on terrestrial ecosystems. Carbon (C), nitrogen (N), and phosphorus (P) are required in specific quantities by plants and are related to soil fertility. In the Caatinga, one of the world’s largest and most diverse tropical dry forests, there have been limited studies investigating the factors that contribute to the spatial distribution of organic carbon (OC), N, and P in the soil and, even fewer, those that explored the use of Machine learning (ML) modeling. In this research, we aim to predict the spatial distribution of these properties at depths ranging from 0 to 20 cm in the Caatinga biome and assess the predictive capability of environmental and geographic variables. We used the Random Forest model in Google Earth Engine to forecast maps with a spatial resolution of 30 m. The best result was obtained for predicting P [Lin's concordance correlation coefficient (LCCC) of 0.32 and R2 of 0.25], followed by OC (LCCC of 0.25 and R2 of 0.17), N (LCCC of 0.21 and R2 of 0.12) and C/N ratio (LCCC of 0.14 and R2 of 0.10). The final maps exhibited a consistent spatial pattern, with OC, N, and C/N ratio showing correlation with climatic covariates (air and soil temperature in the first 15 cm deep), topographic data (altitude), and geographic regions (longitude and latitude). The variation in P content was primarily influenced by parent material. We highlight the relevance of ecotones, which recorded the highest average levels of C and N and C/N, demonstrating the importance of these areas for the maintenance and dynamics of these ecosystems.

Soil profile distribution of organic, inorganic, and labile carbon and nitrogen fractions vary in semi‐arid drylands under long‐term conservation tillage systems

AbstractChanges in soil carbon (C) and nutrients considerably influence soil health and agricultural sustainability. However, how agricultural management affects C and N allocation among various soil organic matter pools and their linkages with soil health are not clear for arid and semi‐arid regions. This study aimed to evaluate the soil profile distribution of selected C and N fractions and associated soil health properties in conventional tillage (CT), no‐tillage (NT), and strip tillage (ST) fields and quantify the relationship of labile and inorganic C and N fractions to soil organic carbon (SOC) sequestration in semi‐arid dryland cropping systems. Crop rotation was a 4‐year cycle of corn (Zea mays L.)—sorghum (Sorghum bicolor L. Moench)—winter wheat (Triticum aestivum L.)—fallow across all tillage systems. Soil samples were collected from 0–20, 20–40, and 40–60 cm depths of each plot in July 2022, after 9 years of plot establishment, and analysed for potentially mineralizable carbon (PMC), microbial biomass carbon (MBC), SOC, soil inorganic (SIC), soil total carbon (STC), soil inorganic nitrogen (SIN), total labile nitrogen (TLN), total organic nitrogen (SON), and labile organic nitrogen (LON) and other soil health indicators. The results indicate that PMC was 31% more and LON was 23% more in NT than in CT, whilst ST resulted in lower pH and had only 10%, 9%, and 24% more SON, STN, and LON, respectively, than CT in 0–60 cm profile. The SIC stock was negatively correlated with MBC, PMC, SON, STN, LON, TLN, and SIN, whilst positively correlated with depth, STC, and pH. After 9 years of conservation tillage, whilst depth‐wise distribution varied among tillage systems, soil C sequestration rate was negative in the 0–60 cm profile under both NT and ST compared with CT, mainly owing to more SIC accumulation in deeper depth of conventional system. These results show the complexity of soil C and N allocation under different tillage systems, with NT and ST supporting greater C and N storage in the surface soil and CT supporting more C and N storage in the deeper depth. Soil biological activity indicators appear to drive surface SOC accumulation, whilst soil pH and N availability influenced SIC accumulation in lower depths.

Climate and Soil Geochemistry Influence the Soil Organic Carbon Content in Drylands of the Songliao Plain, Northeast China

AbstractThe understanding of the spatial distribution of soil organic carbon (SOC) and its influencing factors is crucial for comprehending the global carbon cycle. However, the impact of soil geochemical and climatic conditions on SOC remains limited, particularly in dryland farming areas. In this study, we aimed to enhance the understanding of the factors influencing the distribution of SOC in the drylands of the Songliao Plain, Northeast China. A dataset comprising 35,188 measured soil samples was used to map the SOC distribution in the region. Multiple linear regression (MLR) and random forest models (RFM) were employed to assess the importance of driving indicators for SOC. We also carried out partial correlation and path analyses to further investigate the relationship between climate and geochemistry. The SOC content in dryland soils of the Songliao Plain ranged from 0.05% to 11.63%, with a mean value of 1.47% ± 0.90%. There was a notable increasing trend in SOC content from the southwest to the northeast regions. The results of MLR and RFM revealed that temperature was the most critical factor, demonstrating a significant negative correlation with SOC content. Additionally, iron oxide was the most important soil geochemical indicator affecting SOC variability. Our research further suggested that climate may exert an indirect influence on SOC concentrations through its effect on geochemical properties of soil. These insights highlight the importance of considering both the direct and indirect impact of climate in predicting the SOC under future climate change.

Patterns and causes of soil heavy metals and carbon stock in green spaces along an urbanization gradient

The surge in urbanization has correspondingly given rise to exacerbated carbon footprint and burgeoning heavy metal (HM) contamination, constituting a critical impediment to the realization of environmentally sustainable urban development pathways. Therefore, it is highly essential to investigate the impacts of urbanization process on soil carbon, heavy metals (HMs), as well as their interrelationships. Employing remote sensing and land use data within a 45 km radius in Chongqing, this study selected 31 sites to assess the variation in urban green spaces (UGSs) carbon sequestration capabilities and associated HM pollution risks across differing urbanization levels. Results showed that urbanization dynamics and land use history play a more decisive role than current anthropogenic management in shaping the distribution of soil carbon and HMs within urban environments. The average soil organic carbon (SOC) distribution of UGSs is 8.47 mg ha−1 (1.50–24.20 mg ha−1), concurrent with moderate HM pollution showing Ni: 32.03–33.50 mg kg−1, Pb: 27.93–29.65 mg kg−1, Cu: 26.97–41.20 mg kg−1, while Cd exhibits the most severe pollution range of 0.23–0.30 mg kg−1. The rate of urbanization significantly influences SOC stocks, exhibiting an increase when the urbanization rate is below 70.79 % and a decrease upon surpassing this threshold. The concentration of HMs is predominantly determined by the historical usage of the land, with a marked escalation correlating with the duration of land utilization history. These relationships were quantitatively modeled through the application of fitted linear functions. The structural equation model demonstrated that UGSs operating without anthropogenic disturbance tend towards degradation, indicating that temporary homeostasis might be sustained via the addition of N and P nutrients and pH modulation. In conclusion, we formulate an Urban Green Spaces Development Hypothesis that aims to shed light on the multifaceted challenges encountered by cities amidst varying degrees of urbanization and, concurrently, to probe potential ameliorative strategies.

Assessment of the capability of Landsat-8 satellite imagery for predicting soil organic carbon distribution

Soil organic carbon (SOC) is an important component of soil and plays a crucial role in addressing climate change. As a key component of soil organic matter, SOC directly impacts soil fertility, water retention, nutrient cycling, and overall soil health. The determination of SOC concentrations in soil often relies on costly physical sampling and chemical analysis. The aim of this research was to build a predictive model of SOC using satellite imagery of Landsat 8 OLI/TIRS over an agricultural area (Oued El Alleug) in the north of Algeria. The statistical correlations between the spectral bands (B2 and B6) and chemically measured SOC concentrations showed that it is possible to predict spatially the SOC concentrations. The results also showed that the topographic variables are not determinant in the spatial prediction of SOC concentrations. The predicted model showed an acceptable performance with a coefficient of determination (R2) = 0.7 and a root mean square error (RMSE) = 7.08 g/kg during the validation phase. The results of this study are important, as they will facilitate decision-making in soil conservation practices and enhance land management, especially in areas facing increasing agricultural and environmental pressures.

Developing a digital mapping of soil organic carbon on a national scale using Sentinel-2 and hybrid models at varying spatial resolutions

Mapping the spatial distribution of soil organic carbon (SOC) is crucial for monitoring soil health, understanding ecosystem functions, and contributing to global carbon cycling. However, few studies have directly compared the influence of hybrid models and individual models with varying spatial resolutions on SOC prediction at a national scale. In this study, by combining remote sensing data, we utilized the LUCAS 2018 soil dataset to evaluate the potential capacities of hybrid models for predicting SOC content at different spatial resolutions in Germany. The hybrid models PLSRK and RFK consisted of partial least square regression (PLSR) with residual original kriging (OK) models, and random forest (RF) models with residual OK models, respectively. Individual PLSR and RF models were used as reference models. All these models were applied to estimate SOC content at 10 m, 50 m, 100 m, and 200 m spatial resolutions. Sentinel-2 bands, band indices, and topography variables were as predictors. The results revealed that hybrid models had a more accurate prediction of SOC content with higher explanations and lower prediction errors compared with individual models. The RFK model at the spatial resolution of 100 m was the fittest model with R2 = 0.416, RMSE = 0.545, and RPIQ = 1.647, which enhanced 3.74% of explanation compared with the performance of RF model. The results also showed that hybrid models at a relatively coarse resolution (100 m) had better accuracy instead of those at high spatial resolution (10 m, 50 m). Sentinel-2 remote sensing data showed significant predictive capabilities for estimating SOC content. The predicted spatial distribution of SOC content revealed that the high SOC concentrated in the northwest grassland, central and southwestern mountains, and the Alps in Germany. Our study provided a benchmark SOC map in Germany for monitoring the changes resulting from land use and climate impacts, and we illustrated the accuracy of hybrid models and the effects of spatial resolutions on SOC predictions at a national scale.

Change in Land Use Affects Soil Organic Carbon Dynamics and Distribution in Tropical Systems

Anthropogenic land cover change is directly responsible for the deforestation and degradation of tropical forests. In this context, assessing soil organic carbon (SOC) stocks is key to understanding the impact of anthropogenic activities on SOC so that we can implement management practices that effectively reduce emissions or promote carbon sequestration. Our objective was to assess the effect of land-use change on the dynamics and distribution of SOC in three systems (agriculture, pasture and agroforestry) after 40 years of deforestation in a tropical dry forest in the central–eastern region of Honduras. For this purpose, the bulk density, percentage of coarse fragments (>2 mm) and soil organic carbon content were determined at three depths (0.00–0.10 m, 0.10–0.20 m and 0.20–0.30 m). The results showed an increase in bulk density for all new uses, although soil compaction had not yet occurred. In terms of total soil organic carbon (TOC) stocks, deforestation caused a decrease from 17% to 48% in agricultural and agroforestry soils, respectively; on the other hand, grasslands did not show significant differences compared to tropical dry forest, suggesting that they have a high potential as carbon sinks in deforested tropical areas. However, this did not imply a better state of the system, as the greatest increases in bulk density were found in pastures.

Soil carbon stocks and nutrient stratification in a volcanically active coffee-dominated landscape in south-central Guatemala

The volcanoclastic mountains of Central America offer elevations ideal for coffee production. Both vulcanism and land use can have significant impacts on soil formation and properties. We evaluated how the interactive impacts of soil formation and coffee-dominated land use modulate soil storage and vertical distribution of organic carbon and nutrient elements in a volcanically active landscape dominated by coffee agriculture in south-central Guatemala. Thirty-seven pedons under coffee production (n = 29), forest cover (n = 5) and pasture (n = 3) were characterized and classified, and concentrations and stocks of organic carbon and macronutrient and micronutrient elements were quantified across genetic horizons. Additionally, soil organic carbon (SOC) stock values calculated using the fixed depth (FD) and equivalent soil mass (ESM) methodologies were compared. The active stratovolcano in the region had a strong effect on the development of andic properties and soil horizon burial, with thirty-one pedons classified as Andisols, three as Inceptisols and three as Entisols. Land use management practices and soil horizon burial by deposition of volcanic material were partly reflected in the vertical distribution of SOC concentrations and stocks. The vertical distribution of macronutrients was generally more sensitive to land use than the vertical distribution micronutrients, which could potentially reflect differences in inputs via fertilizers and vegetation cover and in outputs with biomass harvest. Soil organic carbon stocks were similar when calculated by FD and ESM, reflecting relatively consistent depth-wise bulk density. These results demonstrate that in volcanically active landscapes, land use should be considered in concert with soil-forming factors to comprehensively understand organic carbon and nutrient element storage in soils.

Heavy metals distribution and their ecological risk in the surface sediments of Haizhou Bay, China

A comprehensive analysis of heavy metal concentrations, sources, and pollution status was conducted on thirty surface sediment samples collected from Haizhou Bay, China in 2020. The spatial distributions of Cu, Pb, Zn, Cr, Cd, and total organic carbon (TOC) were found to be analogous. Noteworthy, sporadic pollution effects from Cu, Cr, and As were detected, although heavy metal concentrations remained below the probable effect level (PEL). A suite of analytical methods, including Pearson's correlation coefficient, geoaccumulation index, sediment quality guidelines, potential ecological risk index, and principal component analysis, was employed to elucidate the sources and assess the pollution risks. The results indicated that Hg emerged as the predominant heavy metal pollutant in Haizhou Bay sediments, with several stations showing high pollution levels that require attention. Other heavy metals were mainly of natural origin, indicating no significant pollution in the study area.

Exploring the West African forest island phenomenon: scientific insights gained, successes achieved and capacities strengthened.

Anthropogenic activities around local villages in mesic savanna landscapes of West Africa have resulted in soil improvement and forest establishment outside their climatic zones. Such unique 'forest islands' have been reported to provide ecosystem services including biodiversity conservation. However, the science underpinning their formations is limitedly studied. In 2015 and with funding support from the Royal Society-DFID (now FCDO), we set out to investigate the biogeochemistry of the forest islands in comparison with adjacent natural savanna and farmlands across 11 locations in Burkina Faso, Ghana and Nigeria. Our results showed that the forest islands do not differ significantly from the adjoining ecosystems in soil mineralogy implying that their formation was anthropogenically driven. We observed greater soil organic carbon and nutrient distributions in the forest islands, which also had more stable macro (>500 μm) and meso-aggregates (500-250 μm) than the adjoining agricultural lands. We found that soil micro-aggregate (250-53 μm) stability was climate (precipitation) driven in the West African ecosystems while meso- and macro-aggregate stability was land-use driven. In one of the unique forest islands we studied in the Mole National Park of Ghana, we found its mineral-associated organic carbon over 40% greater than the adjoining natural savanna with potential implications for the achievement of the global initiative of the '4p1000' in West Africa. We conclude that the North-South-South research collaboration has established clearly, the science underlying the age-long West African forest island phenomenon and has, among many successes, led to capacity building of young scientists driving cutting-edge research in climate change adaptation and food systems transformation in the sub-region.

Spodosol development and soil organic carbon distribution along a lithosequence in perhumid coastal temperate rainforest

AbstractA dense concentration of old‐growth forest and a wet, cold climate promote mineral weathering and leaching in coastal temperate rainforest soils. Our objective was to assess soil development and soil organic carbon (SOC) distribution across 18 soil profiles in remote, upland terrain of southeast Alaska where pedon data are sparse. We made soil morphological observations, collected samples, and completed laboratory analyses to measure SOC content, pH, and particle size distribution. The survey of upland backslope soils included north‐ and south‐facing hillslopes derived from three lithologies (slate, metavolcanic, and phyllite). The soils across all sites were very gravelly (51.8 ± 20.4% coarse fragments), acidic (mineral soil pH 4.85 ± 0.45), and moderately deep (96.56 ± 37.80 cm); thin, broken E horizons were underlain by thick, carbon‐rich spodic horizons. Soil development was relatively consistent as demonstrated by the Profile Development Index with values from 15 to 26 and Podzolization Index values spanning 8 to 14. A mean pedon SOC stock of 198.02 ± 81.42 Mg C ha−1 (n = 18) was calculated using data collected for all upland organic and mineral soils from our work. The accumulation of SOC was similar among soils formed from contrasting lithologies with averages of 182 ± 15.70 Mg C ha−1 for slate, 188 ± 53.80 Mg C ha−1 for metavolcanic, and 218 ± 124 Mg C ha−1 for phyllite. Our work contributes to soil morphological observations, laboratory data, and SOC stock estimates required to better constrain and model pedogenic processes and SOC stock in remote forests where data sets are limited.

Effects of fertile islands on soil organic carbon density and labile organic carbon distribution in elm (Ulmus macrocarpa Hance)-dominated sparse wood grasslands in southeastern Inner Mongolia, China

In semi-arid savanna grasslands, the sparse distribution of trees often forms what are commonly known as fertile islands. However, the effect of these trees on soil organic carbon (SOC), microbial biomass carbon (MBC), and dissolved organic carbon (DOC), remains poorly understood. In this study, the spatial distribution patterns of SOC, MBC, and DOC were investigated across soil profiles (0–5, 5–10, 10–30, 30–50, and 50–100 cm) at three distances from the tree trunk in an elm-dominated savanna ecosystem in Northeast China. Our results suggest that SOC, MBC, and DOC were significantly influenced by both the distance from the tree and the soil depth. The research provides evidence that elm trees can form fertile island effects, thereby enhancing the contents of SOC and labile organic carbon fractions.

Spatiotemporal distribution patterns of iron, manganese, and arsenic within the river infiltration zone and the potential geochemical activity at key interfaces

The river infiltration zone is a mixed area of surface water and groundwater under the riverbed and along the riverbank, which is greatly affected by river infiltration. Currently, there is a lack of understanding regarding the migration and transformation processes of Fe, Mn, and As, along with their correlation with organic carbon in the river infiltration zone affected by riverbed scouring and siltation processes. In this study, based on techniques such as pore water sampling and the Tessier sequential extraction, the spatiotemporal variations in Fe, Mn, and As concentrations and possible geochemical processes at the riverbed sediment–water interface and along the river infiltration flow path were revealed. The results indicated that the potential geochemical activity of Fe, Mn, and As and the distribution of organic carbon in the riverbed sediment responded to riverbed scouring–siltation processes. Compared to the high water level period, the potential geochemical activity of Fe, Mn, As, and organic carbon in the riverbed sediment generally exhibited an upward trend during the low water level period, indicating more intense Fe and Mn biogeochemical reactions. During river infiltration, the labile organic carbon (LOC) was preferentially utilized, and with increasing depth, the sedimentary organic carbon (SOC) continuously transformed into LOC and dissolved organic carbon (DOC). Affected by riverbed scouring processes, the transition time from oxidizing to reducing conditions in the pore water increased, and the Fe, Mn, and As reduction zones moved deeper and farther from the riverbank, resulting in a significant expansion of the groundwater pollution area. The reductive dissolution of iron and manganese oxides/hydroxides and the oxidation of organic matter–bound Fe, Mn, and As were the main biogeochemical processes contributing to the release of Fe, Mn, and As in the river infiltration zone. These research results have crucial theoretical significance and practical application value for the sustainable utilization of groundwater resources and the remediation of groundwater pollution.