Composition Of Organic Carbon Research Articles

Influences of 13 Years New Conservation Management on Labile Soil Organic Carbon and Carbon Sequestration in Aggregates in Northeast China

New conservation management (NCM) for summer maize monocultures might cause changes in the organic carbon composition when compared with conventional tillage (CT). To investigate the difference, the soil organic carbon (SOC) under 13 years of NCM and CT was studied in Northeast China. The NCM involved the use of a 40 cm and 160 cm narrow-wide row (maize was planted in the narrow row in two lines) with straw retained, but with no tillage and change in ridge direction. SOC in different soil aggregate size classes and labile organic carbon fractions at 0–10 cm, 10–20 cm and 20–40 cm depths were evaluated. The results showed that there was no significant difference in SOC content at a 0–10 cm depth, with values ranging from 19.9 to 21.1 g·kg−1 between two management systems. The contents of microbial biomass carbon (MBC) and light fraction organic carbon (LFOC) were significantly higher in NCM than in CT in the upper 10 cm. Among the labile organic carbon fractions, the light fraction organic C (LFOC) was the most sensitive to management change. The portion of macroaggregates (>0.25 mm) was higher under NCM than under CT and decreased with the increase in soil depth. NCM improved the organic carbon storage in aggregates 1–0.5 mm and reduced the organic carbon storage in microaggregates. It was concluded that NCM would be an effective and useful management choice for the enhancement of soil C sequestration in maize field systems in Northeast China.

Isotopic evidence of environmental changes during the Devonian-Carboniferous transition in South China and its implications for the biotic crisis.

The Devonian-Carboniferous (D-C) transition coincides with the Hangenberg Crisis, carbon isotope anomalies, and the enhanced preservation of organic matter associated with marine redox fluctuations. The proposed driving factors for the biotic extinction include variations in the eustatic sea level, paleoclimate fluctuation, climatic conditions, redox conditions, and the configuration of ocean basins. To investigate this phenomenon and obtain information on the paleo-ocean environment of different depositional facies, we studied a shallow-water carbonate section developed in the periplatform slope facies on the southern margin of South China, which includes a well-preserved succession spanning the D-C boundary. The integrated chemostratigraphic trends reveal distinct excursions in the isotopic compositions of bulk nitrogen, carbonate carbon, organic carbon, and total sulfur. A distinct negative δ15 N excursion (~-3.1‰) is recorded throughout the Middle Si. praesulcata Zone and the Upper Si. praesulcata Zone, when the Hangenberg mass extinction occurred. We attribute the nitrogen cycle anomaly to enhanced microbial nitrogen fixation, which was likely a consequence of intensified seawater anoxia associated with increased denitrification, as well as upwelling of anoxic ammonium-bearing waters. Negative excursions in the δ13 Ccarb and δ13 Corg values were identified in the Middle Si. praesulcata Zone and likely resulted from intense deep ocean upwelling that amplified nutrient fluxes and delivered 13 C-depleted anoxic water masses. Decreased δ34 S values during the Middle Si. praesulcata Zone suggests an increasing contribution of water-column sulfate reduction under euxinic conditions. Contributions of organic matter produced by anaerobic metabolisms to the deposition of shallow carbonate in the Upper Si. praesulcata Zone is recorded by the nadir of δ13 Corg values associated with maximal △13 C. The integrated δ15 N-δ13 C-δ34 S data suggest that significant ocean-redox variation was recorded in South China during the D-C transition; and that this prominent fluctuation was likely associated with intense upwelling of deep anoxic waters. The temporal synchrony between the development of euxinia/anoxia and the Hangenberg Event indicates that the redox oscillation was a key factor triggering manifestations of the biodiversity crisis.

Effects of tillage on soil organic carbon and crop yield under straw return

No-tillage with straw mulch is an effective way to achieve soil sustainability. However, the specific redistributions of soil organic carbon composition, stocks, and crop yield remain unclear. The hypothesis that no-tillage had a minor effect on soil organic carbon stocks in 0–50 cm but decreased crop yield compared to plow-tillage under straw return was tested in this study. Soils properties from two decades of rice-wheat rotation field experiment were related to the yield of rice and wheat depending on tillage: 1) plow-tillage without straw return, 2) no-tillage with straw mulch, and 3) plow-tillage with straw return. No-tillage with straw mulch had the highest mean weight diameter of soil aggregates, the contents of macro-aggregates (>0.25 mm) organic carbon, particulate organic carbon (>53 µm), and soil organic carbon across tillage practices in 0–5 cm. However, it decreased the contents of macro-aggregates (>0.25 mm) organic carbon in 5–15 cm, the particulate organic carbon in 5–50 cm, and soil organic carbon in 5–30 cm compared to plow tillage with straw return due to less carbon input from roots and straw. Organic carbon stocks in micro-aggregates (<0.25 mm) and mineral-associated organic matter (<53 µm) did not vary between tillage practices. Hence the soil organic carbon stocks of plow tillage without straw return (48 Mg ha−1) were similar to that of no-tillage with straw mulch (51 Mg ha−1) but lower than that of plow tillage with straw return (57 Mg ha−1) in 0–50 cm. The mean annual yields of wheat and rice under no-tillage with straw mulch (14 t ha−1) were lower than that of plow tillage without straw return (15 t ha−1) and plow tillage with straw return (16 t ha−1). No-tillage-induced high soil bulk densities limited the rice yields. The yield losses of no-tillage with straw mulch were higher in rice than in wheat. The rice yield losses of no-tillage with straw mulch compared to plow tillage with straw return increased with experiment duration due to decreased available nitrogen in 7–14 cm and phosphorus contents in 0–14 cm over time. Conclusively, plow-tillage is more efficient for carbon sequestration and yield increase than no-tillage under straw return in rice-wheat farming by increasing carbon input in deep soils, soil available nutrients, and decreasing soil compactness.

Compositions and sources of sedimentary organic carbon on the tropical epicontinental sea

The deposition of fluvially derived terrestrial organic carbon (OC) together with marine OC in marine sediments has important implications for the global carbon cycle. However, dispersal extent and fates of terrestrial soil and petrogenic OC on the continental shelf have remained unclear and debated. Here, we present OC compositions and mineral properties of marine sediments from the Gulf of Thailand and the adjacent Mekong shelf, as well as river sediments from continents surrounding them in order to determine the provenance of sedimentary OC in this tropical epicontinental sea. We find that stable carbon isotope composition (δ13C) and radiocarbon activity (Δ14C) of sedimentary OC fall between those of marine OC and of river sediments, mainly composed of C3 plant-dominated pre-aged soil and petrogenic OC. Mixing model reveals that the OC in river sediments is predominantly sourced from pre-aged deep soils, accounting for 73 ± 5%, with the remaining consisting of modern surface soil (25 ± 6%) and bedrock (2 ± 1%). The sedimentary OC on the shelf is primarily derived from marine OC, accounting for 65 ± 15%, with terrestrial soil OC and petrogenic OC contributing 24 ± 14% and 10 ± 5%, respectively. The sources, degradation, and aging of OC and mineral surface area determine the spatial pattern of sedimentary OC compositions in the Gulf of Thailand and the Mekong shelf. The contents of marine, soil, and petrogenic OC decrease with increasing distance offshore, consistent with changes in spatial patterns of sedimentation rate of terrestrial materials and of marine primary production in the overlying water column. Extensive degradation of terrestrial OC and extremely low OC burial rate in this tropical epicontinental sea suggest a minor role on OC sequestration in marine sediments, but an important CO2 source to the atmosphere in the context of the global carbon cycle.

Contrasting controls of particulate organic carbon composition and age from riverine to coastal sediments of Eastern China Marginal Seas

Contrasting controls of particulate organic carbon composition and age from riverine to coastal sediments of Eastern China Marginal Seas

Root architectures differentiate the composition of organic carbon in bauxite residue during natural vegetation

Understanding plant root architectures induced changes in organic carbon accumulation and conversion is critical to predicting carbon cycling and screening appropriate plant species for ecological restoration on bauxite residue disposal areas. According to the ecological investigation of a weathered bauxite residue disposal area, three plants with different root architectures including Artemisia lavandulaefolia (A. lavandulaefolia), moss, and Zanthoxylum simulans (Z. simulans) were selected to investigate the rhizosphere effects on the composition and structure of organic carbon in bauxite residue. The physic-chemical properties, the contents and structure of different organic carbon fractions, and microbial communities of bauxite residue from rhizosphere and non-rhizosphere were analyzed. Plant growth decreased the saline-alkalinity, increased the contents of total organic carbon, particulate organic carbon and dissolved organic carbon, whilst enhancing the enzymatic activities of bauxite residue. Meanwhile, the rhizosphere effects had significant effects on the accumulation and stabilization of organic carbon in bauxite residue. A. lavandulaefolia had the strongest rhizosphere effects on the composition and structure of total organic carbon and dissolved organic carbon, whilst moss was more effective on the accumulation of particulate organic carbon in bauxite residue. Plant growth and root architecture changed the abundance of specific functional microorganisms and the complexity of microbial co-occurrence networks, thus elevating organic carbon levels in bauxite residue. During natural vegetation encroachment, rhizosphere exciting effects of the salt-tolerated plants could change the composition and structure of organic carbon fractions due to the comprehensive effectiveness of the improvement of physic-chemical properties and microbial communities. The findings improve our understanding of the responses of sequestration and stabilization of organic carbon pools to ecological restoration on bauxite residue disposal areas.

An approach for carbon content measurement in marine sediment: Application of organic and elemental carbon analyzer

Organic and Elemental Carbon (OEC) is widely applied in the atmospheric sciences for determining carbon content and distinguishing black carbon contents of aerosols, with an advantage that OEC-based approach can provide thermograms derived from carbonaceous material. It is potential to adopt the advantage to measure the content and composition of organic carbon (OC)% in marine sediments. Here, we utilized the OEC analyzer to measure the OC% in marine sediment based on the pyrolytic oxidation principle, and obtain the OC-derived carbon dioxide (CO2) thermograms. We examined marine sediments and reference materials to understand the stability and reproducibility of OC% measurements using our approach. The findings indicate that the OC% results (ranging from 1.44 to 1.59%, ave. 1.55 ± 0.03%, n = 64) based on this approach are accurate. In addition, CO2 concentration thermograms obtained by repeated measurements exhibit a strong reproducibility. Our approach can thus provide the concentrations of thermally-evolved CO2 with increasing heating temperature to deeply understand the reactivities of OC and the compositions in sediments. We suggest that the OEC-based OC% measurement is credible when samples preparation is well-performed (e.g., suitable sample mass and uniformly distributed loading). To sum up, we provide a means to accurately determine the OC% in marine sediments in terms of the ramped-pyrolysis principle.

Quantification of the sources of sedimentary organic carbon at methane seeps: A case study from the South China Sea

Large amounts of methane are stored along continental margins in the form of methane hydrate. Methane hydrate is sensitive to environmental change, resulting in the release of substantial quantities of methane upon its destabilization. In the marine subsurface, microorganisms consume most of the methane in the sulfate-methane transition zone and convert a certain amount of methane into organic matter. Burial of such organic matter deriving from methane oxidation represents a long-term carbon sink, therefore mitigating the effect of a prominent greenhouse gas on global warming. However, the controls on the formation and consumption of sedimentary organic matter at marine seeps remain poorly constrained, impeding accurate quantification of carbon burial at seeps and its role in the marine carbon cycle. To gain new insight on the effect of seeps on carbon burial, sediments from two seep sites of the South China Sea (Site F, Haiyang 4) and a nearby reference site (Jiulong canyon) were analyzed for total organic carbon contents (TOC), δ13CTOC and Δ14C values, total inorganic carbon contents (TIC) and δ13CTIC values, as well as organic nitrogen (N) contents. Depth distributions reveal that the TOC at seeps (Site F, 0.55% ± 0.08%, Haiyang 4, 0.67% ± 0.11%) is higher than in sediments not affected by seepage (Jiulong canyon, 0.50% ± 0.10%). The enrichment of total sulfur, high TIC, and negative δ13CTIC values in sediments from Site F and Haiyang 4 agrees with locally prominent sulfate-driven anaerobic oxidation of methane (AOM) and resultant precipitation of authigenic carbonate. At the two seep sites, the sediments are characterized by more negative δ13CTOC and Δ14C values and a lower TOC/N ratio, indicating a contribution of the microbial fixation of 13C-depleted methane to the local pool of sedimentary organic matter. A linear increase in 14C ages of organic carbon with sediment depth at the reference site indicates steady depositional conditions, whereas the 14C age of organic carbon at seeps is typified by contributions of methanotrophy-derived carbon. A Δ14C mass balance approach shows that carbon derived from fossil methane accounts for at least 10 to 20% of the organic carbon preserved in the sediments. By comparing seeps, hydrate-bearing sediments, modern coastal sediments, and Archaean rocks, it becomes apparent that the carbon stable isotope composition of organic carbon in seep sediments is mainly controlled by the rate of methane oxidation and marine primary productivity.

Geographic variation in organic carbon storage by seagrass beds

AbstractSince seagrasses are efficient sinks for marine organic carbon, there is growing interest in incorporating seagrass protection and restoration into climate mitigation schemes, that is, offering credit for accumulated carbon to offset carbon dioxide emissions. However, patterns and drivers of organic carbon storage by seagrasses are not well resolved, especially at scales relevant to management decisions. Here, we quantified geographic variation in standing stocks of sedimentary organic carbon (Mg Corg ha−1) associated with seagrasses along the northern Florida Gulf Coast using field surveys and sediment cores. We measured plant biomass, organic carbon, and sediment composition in each core. Using a multivariate modeling approach, we evaluated the relative importance of ecological, physical, oceanographic, and seascape drivers, developing the first spatially explicit predictions of seagrass‐associated carbon stocks for this region. Applying model predictions to confirmed seagrass beds and potential recovery areas, we also estimated the carbon storage value of potential seagrass conservation and restoration as the resulting stock enhancement value per hectare of seagrass (Δ Mg Corg ha−1). We found that organic carbon stored by seagrass sediments varied considerably across this region, with stocks significantly increasing with seagrass cover, proximity to oyster reefs, and distance from river outlets, highlighting potential synergies for coordinated management. We also found that current seagrass beds could offer nearly double the carbon storage value of potential recovery areas, emphasizing the importance of conservation as well as restoration. Our results have important implications for management, restoration, and understanding biogeographic patterns of seagrass ecosystem services.

Near equatorial paleoclimatic evolution and control on organic matter accumulation during the Cenomanian in the Abu Gharadig Basin, southern Tethys: Insights from palynology, organic petrography, and geochemistry

The beginning of the Late Cretaceous (Cenomanian) attested to a major marine transgression interrupted by sea level falls in north Africa, which led to significant environmental perturbation and widespread accumulation of organic matter-rich sediments. During this period, northern Egypt was located at the southern edge of the Tethys Ocean and deposition of thick siliciclastic alternations between shales, siltstones, and sandstones of the Bahariya Formation took place in the BED2 gas field of the Abu Gharadig Basin, north Western Desert. An integrated approach of palynofacies analysis and palynomorph composition, organic petrography, and geochemical analysis of total organic carbon (TOC)/Rock-Eval pyrolysis, carbonate content, XRD analysis, and clay mineralogy of thirty-nine cutting samples obtained from the lower-middle Cenomanian Bahariya Formation was conducted. This approach was used to characterize organic matter and possible occurrence of source rock intervals, paleoenvironmental and paleoclimatic conditions and their role in organic matter accumulation. Moderate to high proportions of pteridophyte and water fern spores and pollen grains of Araucariaceae (Araucariacites), Cheirolepidiaceae (mainly Classopollis), and Gnetalean (Elaterate pollen) and Afropollis versus the sparsely recorded xerophilous ephedroids (Ephedripites) indicate prevalent conditions of a warm and humid climate. This is consistent with clay mineral composition that is dominated mainly by kaolinite and smectite compared to low illite and the lack of chlorite, which indicated a predominantly warm-humid climate state. Palynofacies analysis showed two assemblages; the first one is dominated by phytoclasts and indicates gas-prone Type III kerogen and deposition in a fluvio-deltaic environment. The second palynofacies assemblage is characterized by moderate abundance of phytoclasts and AOM mostly of terrestrial origin, suggesting a mixed Type III/II kerogen and deposition in a marginal to shallow neritic shelf environment. The organic geochemical characterization showed relatively low average values of TOC, S2, and HI, indicating that the Bahariya Formation is characterized by Type III gas-prone kerogen. Thermal maturity of the Bahariya Formation ranges from immature to the early stage of the oil window. Additionally, organic matter characteristics of the Bahariya Formation are qualitatively and quantitatively similar to their equivalents from nearby basins. Low TOC contents are attributed to a high sedimentation rate and an increased terrestrial input of sand- and silt-sized fractions at shallow water column settings that controlled strong dilution and decomposition versus low burial efficiency of the organic matter.

Machine Learning Algorithms for Lithofacies Classification of the Gulong Shale from the Songliao Basin, China

Lithofacies identification and classification are critical for characterizing the hydrocarbon potential of unconventional resources. Although extensive applications of machine learning models in predicting lithofacies have been applied to conventional reservoir systems, the effectiveness of machine learning models in predicting clay-rich, lacustrine shale lithofacies has yet to be tackled. Here, we apply machine learning models to conventional well log data to automatically identify the shale lithofacies of Gulong Shale in the Songliao Basin. The shale lithofacies were classified into six types based on total organic carbon and mineral composition data from core analysis and geochemical logs. We compared the accuracy of Multilayer Perceptron (MLP), Support Vector Machine (SVM), Extreme Gradient Boosting (XGBoost), and Random Forest models. We mitigated the bias of imbalanced data by applying oversampling algorithms. Our results show that ensemble methods (XGBoost and Random Forest) have a better performance in shale lithofacies identification than the other models do, with accuracies of 0.868 and 0.884, respectively. The organic siliceous shale proposed to have the best hydrocarbon potential in Gulong Shale can be identified with F1 scores of 0.853 by XGBoost and 0.877 by Random Forest. Our study suggests that ensemble machine learning models can effectively identify the lithofacies of clay-rich shale from conventional well logs, providing insight into the sweet spot prediction of unconventional reservoirs. Further improvements in model performances can be achieved by adding domain knowledge and employing advanced well log data.

Secondary formation and source analysis of carbonaceous components in PM1 in a typical city, Southwest of China

Carbonaceous components are major components of PM1, which have a significant impact on climate change, air quality and human health. However, the secondary formation and source analysis of carbonaceous components in PM1 are still unclear. Therefore, in order to study the secondary formation and sources of carbonaceous components in PM1, PM1 samples were collected in Chengdu, a typical city located in southwest of China, from 2018 to 2019. The concentrations of organic carbon (OC), elemental carbon (EC) and isotopic compositions of carbon (δ13C) in PM1 were determined using a thermal/optical carbon analyzer and elemental analyzer-isotope ratio mass spectrometer. In addition, the δ13C values from relevant potential sources (C3 plants, C4 plants, vehicle exhaust and coal) were also determined. The results showed that the annual average concentrations of OC and EC in PM1 in Chengdu were 6.43 ± 3.30 μg·m−3 and 1.99 ± 0.98 μg·m−3, accounting for 13.83% and 4.28% of the PM1 mass concentration, respectively. The concentrations of OC in PM1 ranked in the order of winter > summer > spring > autumn, while the concentrations of EC varied in the order of winter > spring > autumn > summer. The concentrations of OC and EC in PM1 reached the maximum in winter, mainly due to the special meteorological conditions and significantly higher pollutant emissions. The correlations of OC and EC were higher in spring, autumn and winter, and lower in summer. It showed that OC and EC might have the same sources in spring, autumn and winter, while the sources of OC and EC were relatively complex in summer. The annual average concentration of secondary organic carbon (SOC) in PM1 was 2.23 ± 1.22 μg·m−3. The concentrations of SOC were higher in autumn and winter and lower in spring and summer. The special meteorological conditions and significantly higher pollutant emissions are important reasons for the higher SOC concentrations in winter. On the other hand, the low temperature in winter can also promote the formation of SOC. The results of carbon isotopic compositions indicated that the carbonaceous components in PM1 were mainly derived from vehicle exhaust (52.4%), C3 plants combustion (26.2%), coal burning (16.2%) and C4 plants combustion (5.2%). The findings help to deepen the understanding of the secondary formation and sources of carbonaceous components in PM1 and provide theoretical guidance for environmental management.

Habitats generated by the restoration of coal mining subsidence land differentially alter the content and composition of soil organic carbon.

The content and composition of soil organic carbon (SOC) can characterize soil carbon storage capacity, which varies significantly between habitats. Ecological restoration in coal mining subsidence land forms a variety of habitats, which are ideal to study the effects of habitats on SOC storage capacity. Based on the analysis of the content and composition of SOC in three habitats (farmland, wetland and lakeside grassland) generated by different restoration time of the farmland which was destroyed by coal mining subsidence, we found that farmland had the highest SOC storage capacity among the three habitats. Both dissolved organic carbon (DOC) and heavy fraction organic carbon (HFOC) exhibited higher concentrations in the farmland (20.29 mg/kg, 6.96 mg/g) than in the wetland (19.62 mg/kg, 2.47 mg/g) or lakeside grassland (5.68 mg/kg, 2.31 mg/g), and the concentrations increased significantly over time, owing to the higher content of nitrogen in the farmland. The wetland and lakeside grassland needed more time than the farmland to recover the SOC storage capacity. The findings illustrate that the SOC storage capacity of farmland destroyed by coal mining subsidence could be restored through ecological restoration and indicate that the recovery rate depends on the reconstructed habitat types, among which farmland shows great advantages mainly due to the nitrogen addition.

Deciphering the influence of soil and feed on the nutritional status of ruminants in rainfed areas using metagenomic analysis

The soil–plant-animal continuum is an emerging domain in biological research and hence, to ascertain this aspect, the present study was conducted in three agro-ecologically different areas in Andhra Pradesh and Telangana, India. The goal of this work was to explore the impact of feed type and geographical conditions on the growth dynamics of sheep feed with three different diets – sorghum stover (Vizag district), groundnut halums (Krishna district) and red gram chunni (Ranga Reddy district). Animals were fed these diets at night daily for 90 days after their routine daytime grazing. The study regions varied in altitude, annual rainfall and mean temperature. Soil analysis was performed in these regions to check for pH, mineral content, organic carbon and bacterial composition. Growth dynamics (average daily gain of 41.56–77.11 g per day) and feed conversion ratios (6.26–10.93) differed markedly (p < 0.05) among animals in the three regions. Metagenomics sampling of sheep ruminal fluid from sheep reared in the three distinct regions (and separate feed types) was carried out by sequencing 16S rRNA V3-V4 regions. Comparison of alpha diversity and operational taxonomic unit (OTU) richness showed remarkable variations in the Chao1, ACE, Shannon and Simpson indices. The results of this work reveal the relationship between feed type, geographical location and ruminal microflora composition. The presence of numerous genera and species differences were discovered in the three samples, and the presence of several methanogens was confirmed. In conclusion methane emissions from cattle and sheep may be mitigated by altering the feed type, which directly influences the ruminal and gut microflora composition. Further research is recommended in order to determine the optimal relationship between soil and feed and their impact on the nutritional status of ruminants in rainfed areas, taking into account various farming and agroclimatic conditions.

Phosphorus supply suppressed microbial necromass but stimulated plant lignin phenols accumulation in soils of alpine grassland on the Tibetan Plateau

Increased nitrogen (N) and phosphorus (P) inputs have fundamental effects on the soil organic carbon (SOC) composition and dynamics. However, the responses of plant- and microbial-derived SOC components to N and P addition in alpine grasslands are poorly understood. Based on a 10-year N and P addition experiment conducted in the alpine grassland of the Tibetan Plateau, we used amino sugars and lignin phenols as tracers for microbial necromass and plant lignin components, respectively, and explored their accumulation with the addition of N and P. We found that P and N + P addition (P supply) decreased microbial necromass, whereas N addition did not have a significant effect. In comparison, the P supply increased lignin phenols in the topsoil, but N addition decreased them in the subsoil. Among these factors, soil total P played a non-negligible role in controlling the accumulation of amino sugars and lignin phenols in soils. In addition, decreased ratios of fungi-to-bacteria necromass carbon and amino sugars to lignin phenols were observed with P supply. This implies that although the 10-year P supply did not change the SOC significantly, it may have eventually increased the SOC loss potential. Collectively, we attempted to elucidate the underlying mechanisms of long-term SOC sequestration, which has important implications for plant- and microbial-mediated carbon processes in the context of increasing N and P inputs.

Linking Seasonal Changes in Organic Matter Composition and Nutrients to Shifting Hydraulic Gradients in Coastal Urban Canals

AbstractThe capacity for coastal river networks to transport and transform dissolved organic matter (DOM) is widely accepted. However, climate‐induced shifts in stormwater runoff and tidal extension alter fresh and marine water source contributions, associated DOM, and processing rates of nutrients entering coastal canals. We investigate how time‐variable interactions among coastal water source contributions influence the concentrations of dissolved organic carbon (DOC), nutrients, and DOM composition in urban canals. We quantified the spatiotemporal variability of DOM quality and nutrient concentrations to determine contributions of tidal marine water, rainwater, stormwater runoff, and groundwater to three coastal urban canals of Miami, Florida (USA). We created a Bayesian Monte Carlo mixing model using measurements of fluorescent DOM (fDOM), DOC concentrations, δ18O and δ2H isotopic signatures, and chloride (Cl−). Fractional contributions of groundwater averaged 17% in the dry season and 26% at peak high tide during the subtropical wet season (September–November). The canal‐to‐marine head difference (CMHD) was a primary driver of groundwater contributions to coastal urban canals and monthly patterns of fDOM/DOC. High tide (&gt;1 m) and discharge events were found to connect canals to upstream sources of terrestrial DOM. Loading of terrestrially sourced DOC and DOM is pulsed to urban canals, shunted downstream and supplemented by microbially sourced DOM during the wet season at high tide. Overall, we demonstrate that a combined tracer approach with isotopes and fDOM can help identify groundwater contributions to coastal waterways and that autochthonous fDOM may prime the degradation of carbon or nutrients as the CMHD pushes inland.

Chemical Composition of Organic Carbon in Aggregate Density Fractions Under Cacao Agroforestry Systems in South Bahia, Brazil

Chemical Composition of Organic Carbon in Aggregate Density Fractions Under Cacao Agroforestry Systems in South Bahia, Brazil

Effects of Betula platyphylla invasion in North China on soil aggregate stability, soil organic carbon and active carbon composition of larch plantation

In order to better understand the changes of soil carbon sequestration capacity in forest after forest mixing, the effects of broadleaf tree invasion on soil aggregate stability and carbon sequestration were studied. In northern China, the pure Larix principis-rupprechtii plantations and the Larix principis-rupprechtii plantations invaded by Betula platyphylla at various degrees with the same site conditions were selected (Betula platyphylla had mixed degrees of 0.2 and 0.4). The distribution and stability of soil aggregates were analyzed, and soil organic carbon and active carbon components were determined. The distribution of soil macroaggregates (> 0.25 mm) increased with the increase in the mixed degree of Betula platyphylla. The mixture of Betula platyphylla could effectively increased SOC, EOC, DOC and MBC of the original soil and soil aggregates of different diameter classes. The invasion of Betula platyphylla had a positive indirect impact on soil carbon sequestration by affecting the soil physical and chemical properties and the aggregate stability. The invasion of Betula platyphylla had significant positive effects on soil aggregate stability, erosion resistance and soil nutrient status in Larix principis-rupprechtii plantation. Maybe the selection of suitable broadleaf mixed species can improve the soil quality and soil organic carbon sequestration of the Larix principis-rupprechtii plantation in this area.

Altered Organic Matter Chemical Functional Groups and Bacterial Community Composition Promote Crop Yield under Integrated Soil–Crop Management System

Sustainable agricultural production is essential to ensure an adequate food supply, and optimal farm management is critical to improve soil quality and the sustainability of agroecosystems. Integrated soil–crop management based on crop models and nutrient management designs has proven useful in increasing yields. However, studies on its effects on the chemical composition of soil organic carbon (SOC) and microbial community composition, as well as their linkage with crop yield, are lacking. Here, we investigated the changes in SOC content, its chemical functional groups, and bacterial communities, as well as their association with crop yield under different farmland management based on four farmland management field trials over 12 years (i.e., FP: farmer practice; IP: improved farmer practice; HY: high-yield system; and ISSM: integrated soil–crop system management). The crop yield increased by 4.1–9.4% and SOC content increased by 15–87% in ISSM compared to other farmland management systems. The increased proportion of Methoxy C and O-alkyl C functional groups with a low ratio of Alkyl C/O-alkyl C, but high Aliphatic C/Aromatic C in ISSM hints toward slow SOC decomposition and high soil C quality. The relative abundances of r-strategists (e.g., Firmicutes, Myxobacteria, and Bacteroidetes) was highest under the ISSM. Co-occurrence network analysis revealed highly complex bacterial communities under ISSM, with greater positive links with labile SOC functional groups. The soil fertility index was the main factor fueling crop yields, as it increased with the relative abundance of r-strategists and SOC content. Our results indicated that crop yield advantages in ISSM were linked to the high C quality and shifts in bacterial composition toward r-strategists by mediating nutrient cycling and soil fertility, thereby contributing to sustainability in cropping systems.

Production and Characterization of Wild Sugarcane (Saccharum spontaneum L.) Biochar for Atrazine Adsorption in Aqueous Media

Wild sugarcane (Saccharum spontaneum L.) is an invasive plant species in the Central American region. Due to its low nutrient and water requirements, it can grow fast and displace native species. Therefore, its biomass is considered a waste to prevent the further distribution of the specie. This study investigates the production and characterization of wild sugarcane biochar to provide a use for its waste. The produced biochar was used for atrazine adsorption in aqueous solutions to provide a possible application of this biochar near the water bodies that were often detected to be contaminated with atrazine. The biochar was produced via top-lit updraft gasification with airflow rates between 8 to 20 L/min, achieving yields ranging from 22.9 to 27.5%. Batch experiments revealed that biochar made at 12 L/min presented the best removal efficiency (37.71–100%) and the maximum adsorption capacity (qm = 0.42 mg/g). Langmuir (R2 = 0.94–0.96) and Freundlich (R2 = 0.89–0.97) described the experimental data appropriately. Fourier transform infrared spectroscopy suggested that atrazine removal in wild sugarcane biochar could be mainly due to carboxylic functional groups. In addition, the biochar organic carbon composition contributed to a higher removal capacity in biochar produced at different airflow rates.