Composition Of Organic Carbon Research Articles

Environmental and hydrologic controls on sediment and organic carbon export from a subalpine catchment: insights from a time series

Abstract. Studies engaging in tracking headwater carbon signatures downstream remain sparse, despite their importance for constraining transfer and transformation pathways of organic carbon (OC) and developing regional-scale perspectives on mechanisms influencing the balance between remineralization and carbon export. Based on a 40-month time series, we investigate the dependence of hydrology and seasonality on the discharge of sediment and OC in a small (350 km2) Swiss subalpine watershed (Sihl River basin). We analyze concentrations and isotopic compositions (δ13C, F14C) of particulate OC and use dual-isotope mixing and machine learning frameworks to characterize and estimate source contributions, transport pathways, and export fluxes. The majority of transferred OC is sourced from plant biomass and soil material. The relative amount of bedrock-derived (petrogenic) OC, abundant in headwater streams, progressively decreases downstream in response to a lack of source material and efficient overprinting with biospheric OC, illustrating rapid organic matter alteration over short distances. Large variations in OC isotopic compositions observed during baseflow conditions converge and form a homogenous mixture enriched in OC and characterized by higher POC-F14C values following precipitation-driven events. Particulate OC isotopic data and model results suggest that storms facilitate surface runoff and the inundation of riparian zones, resulting in the entrainment of loose plant-derived debris and surficial soil material. Although particle transport in the Sihl River basin is mainly driven by hydrology, subtle changes in bedrock erosivity, slope angle, and floodplain extent likely have profound effects on the POC composition, age, and export yields.

Finding a VOICE in the Southern Hemisphere: A new record of global organic carbon?

Variations in the carbon isotopic composition of carbonate and organic carbon (δ13Ccarb and δ13Corg) are generally used to record perturbations in the global carbon cycle, which are in turn closely linked to changes in climate. However, because of climate gradients on Earth, assignment of the “global” signal in ancient records is not straightforward. Here, we report the δ13C values of organic material in the Upper Jurassic to Lower Cretaceous sedimentary record of the Vaca Muerta Formation, situated in the Neuquén Basin, Argentina, which show similar patterns to those observed in several northern latitude basins. This record of δ13C values in the organic material differs from those measured in the early Atlantic Ocean, a record previously considered to be representative of the global values of organic carbon. As a result of the global synchronicity observed in the δ13C values of organic material from both northern and southern latitudes, we suggest that these patterns may represent the global record of δ13C values in organic material rather than those measured in the proto−Atlantic Ocean. The δ13C values of the organic components show a slight initial decrease of ∼2‰ in the early Tithonian (149−145 Ma) and then another decrease of ∼2‰ before reaching a minimum of −30.29‰ in the late Tithonian (145−143 Ma), followed by a gradual increasing trend throughout the Berriasian (143.1−137.7 Ma). The early Valanginian (137.7−135.5 Ma) was marked by a more substantial increase in δ13C values up to −23.46‰. These changes mirror those seen in Northern Hemisphere locations during the Late Jurassic and Early Cretaceous, where this perturbation has been termed the Volgian isotopic carbon excursion (VOICE). This difference in the Late Jurassic and Early Cretaceous δ13C values between the early Atlantic Ocean and the Neuquén Basin is interpreted to be the result of the climate gradient at the time, which was characterized by more humid conditions in high latitudes compared to dry conditions in the Atlantic Ocean basin.

Controls on the stratigraphic distribution of organic carbon in ancient deep-marine levees

Modern deep-marine levees have been shown to be an important reservoir of the world's total buried organic carbon; however, few studies have attempted to assess this in ancient systems. Deep-marine levees are extensive features that experience high rates of sedimentation, making them ideal sites for significant carbon burial, and therefore examining the distribution of organic material in ancient levee deposits could provide insight into paleoenvironmental conditions and the evolution of ancient ocean and climate systems. In this study, a 350-m-thick succession of mudstone-dominated levee deposits of the Windermere Supergroup in British Columbia, Canada, was stratigraphically logged in centimeter-scale detail and samples taken with 4–10 m spacing. X-ray fluorescence (XRF) and total organic carbon (TOC), were conducted to evaluate the elemental composition and distribution of organic carbon to evaluate trends in paleoenvironmental conditions such as primary productivity, ocean redox, weathering intensity, and detrital flux. TOC ranges from <0.2% to 15.55% (corrected for the effects of metamorphism). Organic-rich strata, taken to be ≥ 1% TOC, are principally confined to a single 60 m-thick stratigraphic interval, and typically occur as anomalously thick, mud-rich sandstone turbidites, with organic matter occurring mostly as micro-scale carbon sorbed onto the surface of clay grains. In this same interval, trends in XRF data indicate an increase in primary productivity, weathering intensity, and detrital influx, and a decrease in ocean oxygenation levels. These data suggest that intense continental weathering, high terrigenous input, elevated sea level, and relatively low oxygenation conditions all act to enhance organic matter production, accumulation, and preservation. However, although all these components contributed to increased organic production, accumulation, and preservation on their own, the results of this study suggest that it is the temporal coincidence of all of them in a “perfect storm” that is required for significant organic carbon enrichment.

Assessing shellfish farming-mediated benthic impacts based on organic carbon flux simulation and composition of macrofaunal community

Marine benthic environments serve as the ultimate sink for sediment organic matter (SOM), but shellfish farming can potentially disturb the natural sink of seston, altering ecosystem functioning. Understanding the potential disturbance of a shellfish farm and its ecological effects is therefore important for a responsible management of shellfish-mediated marine ecosystem. In this study, the variations in benthic organic carbon flux of a bottom-based Manila clam (Ruditapes philippinarum) farm in Laizhou Bay, China were estimated by using a carbon flux model coupled with hydrodynamic and individual growth models. SOM and macrofaunal community were monitored for 3 years to investigate their changes to the carbon fluxes. Model simulations illustrated that the carbon flux in an area of 247 km2 was altered due to seston depletion and biodeposition, which caused decrease and increase in SOM in different areas, respectively. Cluster analysis based on taxonomic composition of macrofaunal community divided the sites into four groups, which corresponded with predicted changes of carbon flux. Increased carbon flux caused higher disturbance level (indicated by AMBI) to the macrofaunal community but increased species richness, abundance, and Shannon-Wiener index, suggesting the community was both disturbed and benefited from clam farming. This study confirmed that the benthic organic carbon flux is a key factor causing differences in SOM and macrofaunal community outside the farm, and thus can be used as an efficient method for estimating the benthic impacts of shellfish farming both in and outside the farming area.

Seasonal Variation of Aerosol Composition and Sources of Water-Soluble Organic Carbon in an Eastern City of China

The mitigation of aerosol pollution is a great challenge in many cities in China, due to the complex sources and formation mechanism of particulate matter (PM) in different seasons. To understand the particular features of pollution in China and formulate different targeted policies, aerosol samples of PM2.5 were collected from January to October of 2018 in Longyou. The temporal profile of the meteorological parameters and the concentrations of water-soluble inorganic ions (WSIs) and organic matter (OM) were characterized. An Aerodyne High-Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-TOF-AMS) was also applied to further analyze the composition of water-soluble organic carbon (WSOC). The sources of WSOC were resolved by positive matrix factorization (PMF) analysis. The origin of air parcels and potential sources of WSOC were analyzed using a backward trajectory and potential source contribution function (PSCF). Winds from the northeast dominated each sampling period, and the relative humidity did not show a significant difference. The results showed that the proportion of OM in PM2.5 was the highest in summer and decreased in spring, autumn, and winter in turn. Four organic aerosol (OA) factors, including a hydrocarbon-like factor, a coal combustion factor, and two oxygenated OA factors, were identified in the WSOC by means of PMF analysis. The hydrocarbon-like OA (HOA) contributed the majority of the WSOC in summer, while the contribution of the coal-combustion OA (CCOA) increased significantly in winter, suggesting the presence of different sources of WSOC in different seasons. The air parcels from the north of China and Zhejiang province contributed to the CCOA in winter, while those from the marine regions in the south and southeast of China mainly contributed to the HOA during spring and summer. The weighted PSCF (WPSCF) analysis showed that the regions of east Zhejiang province were the main contributors, which means that local and regional emissions were the most probable source areas of WSOC. It implied that not only were the emissions control of both local and regional emissions important but also that the transport of pollutants needed to be sufficiently well accounted for to ensure the successful implementation of air pollution mitigation in Longyou.

Численное моделирование первичной биопродуктивности пелагических экосистем палеозоя

The article considers an approach to the reconstruction of the bioproductivity of Palaeozoic pelagic ecosystems based on the numeric modelling of the carbon isotope fractionation. The model uses information on the carbon dioxide content in atmosphere, water temperature, and carbon isotopic composition of carbonates and conodont elements. The developed model is tested on the material from the Upper Devonian — Lower Carboniferous of the northern Cis-Urals (successions of carbonate platform and slope of intrashelf depression). It allows reconstructing of the primary productivity of the Palaeozoic pelagic ecosystems and their dynamics on the basis of limited data. The results of the modelling are considered as rather qualitative than quantitative. The carbon isotope composition of total organic carbon was used for controlling the quality of the model.

Composition, distribution, and source of organic carbon in surface sediments of Erhai Lake, China

Lake sediment is an important organic carbon (OC) sink. Nevertheless, few studies have been conducted on sediment organic carbon (SOC) in lakes, and the effects of environmental variables on SOC pools remain poorly understood. We combined physicochemical and spectroscopic analyses to investigate the composition, distribution, and source of OC in surface sediments of Erhai Lake, southwest China, and explored the relationships between environmental variables and its SOC pool. The SOC pool consists of relatively high proportions of labile organic carbon fractions, mainly from algal production, which are rapidly decomposed and exhibit high turnover rates. The relative content of humus carbon ranges from 13.5 % to 20.5 %, with fulvic acid carbon predominating (average 52.95 %), indicating weak humification and a relatively active humus carbon pool. The dissolved organic matter in water column and sediments of Erhai Lake is largely influenced by endogenous production, with a great contribution from phytoplankton. Surface sediments contained more protein-like components than overlying waters (80.0 % vs. 63.0 %), attributed mainly to abundant algal deposition and intense bacterial metabolism. Among environmental variables, sediment chlorophyll a showed the strongest relationship with the SOC pool, and was associated with rapid decomposition and promotion of the humification process, which supported the conclusion that algae had an important influence on the SOC pool. The SOC pool in the southern region of the lake is mainly contributed by algae, other microorganisms, and sewage, exhibiting a greater potential to release organic matters into the water column. The center and northern SOC pools show relatively stable characteristics and stronger OC sink capacity, mainly because of the input of terrestrial refractory organic matters from runoff. Our data shed light on the OC storage mechanisms in the surface sediments of Erhai Lake and provide theoretical bases for enhancing the OC sink of sediments in the lake.

Fertilization makes strong associations between organic carbon composition and microbial properties in paddy soil

Fertilization changes the soil organic carbon (SOC) composition, affecting the carbon cycle of paddy soil. Understanding the mechanisms of physical fraction and chemical composition of SOC responding to fertilization can help regulate the nutrient release and carbon sequestration. However, it is unclear whether these changes in SOC composition to fertilization are consistent and how these are regulated by biotic and abiotic properties. Therefore, a positioning experiment in a rice field was conducted with a total of nine treatments. Chemical fertilizers (0, 337.5, and 675 kg ha−1; C0, C50, and C100, respectively) and fungal residue (0, 10,000, and 20,000 kg ha−1; F0, F50, and F100, respectively) were applied to evaluated (i) changes in the physical fraction and chemical composition of SOC, (ii) changes in soil properties, microbial biomass and community, and (iii) establish relationships among soil properties, microbial community, microbial biomass, and SOC composition. Our results showed that the application of fungal residue exhibited more significant effects on SOC physical fractions than those with the chemical fertilizers. Furthermore, the chemical composition of SOC was more respond to the application of chemical fertilizers than fungal residue. The partial least squares path model indicated that soil properties mainly affected the mineral-associated organic carbon (MAOC) by microbial biomass. In addition, bacterial diversity played an important role in improving the accumulation of MAOC. The SOC chemical composition was mediated by fungal community composition and bacterial diversity. In conclusion, fungal residue application affected SOC physical fraction by increasing soil properties, microbial biomass, and bacterial diversity. Chemical fertilizers application mainly mediated the chemical composition of SOC by altering fungal community composition and decreasing bacterial diversity.

Atmospheric biogenic volatile organic compounds in the Alaskan Arctic tundra: constraints from measurements at Toolik Field Station.

The Arctic is a climatically sensitive region that has experienced warming at almost 3 times the global average rate in recent decades, leading to an increase in Arctic greenness and a greater abundance of plants that emit biogenic volatile organic compounds (BVOCs). These changes in atmospheric emissions are expected to significantly modify the overall oxidative chemistry of the region and lead to changes in VOC composition and abundance, with implications for atmospheric processes. Nonetheless, observations needed to constrain our current understanding of these issues in this critical environment are sparse. This work presents novel atmospheric in situ proton-transfer-reaction time-of-flight mass spectrometry (PTR-ToF-MS) measurements of VOCs at Toolik Field Station (TFS; 68°38' N, 149°36' W), in the Alaskan Arctic tundra during May-June 2019. We employ a custom nested grid version of the GEOS-Chem chemical transport model (CTM), driven with MEGANv2.1 (Model of Emissions of Gases and Aerosols from Nature version 2.1) biogenic emissions for Alaska at 0.25° × 0.3125° resolution, to interpret the observations in terms of their constraints on BVOC emissions, total reactive organic carbon (ROC) composition, and calculated OH reactivity (OHr) in this environment. We find total ambient mole fraction of 78 identified VOCs to be 6.3 ± 0.4 ppbv (10.8 ± 0.5 ppbC), with overwhelming (> 80 %) contributions are from short-chain oxygenated VOCs (OVOCs) including methanol, acetone and formaldehyde. Isoprene was the most abundant terpene identified. GEOS-Chem captures the observed isoprene (and its oxidation products), acetone and acetaldehyde abundances within the combined model and observation uncertainties (±25 %), but underestimates other OVOCs including methanol, formaldehyde, formic acid and acetic acid by a factor of 3 to 12. The negative model bias for methanol is attributed to underestimated biogenic methanol emissions for the Alaskan tundra in MEGANv2.1. Observed formaldehyde mole fractions increase exponentially with air temperature, likely reflecting its biogenic precursors and pointing to a systematic model underprediction of its secondary production. The median campaign-calculated OHr from VOCs measured at TFS was 0.7 s-1, roughly 5 % of the values typically reported in lower-latitude forested ecosystems. Ten species account for over 80 % of the calculated VOC OHr, with formaldehyde, isoprene and acetaldehyde together accounting for nearly half of the total. Simulated OHr based on median-modeled VOCs included in GEOS-Chem averages 0.5 s-1 and is dominated by isoprene (30 %) and monoterpenes (17 %). The data presented here serve as a critical evaluation of our knowledge of BVOCs and ROC budgets in high-latitude environments and represent a foundation for investigating and interpreting future warming-driven changes in VOC emissions in the Alaskan Arctic tundra.

Interactions of the Westerlies and Asian Summer Monsoon Since the Last Deglaciation in the Northeastern Qinghai‐Tibet Plateau

AbstractThe Asian summer monsoon (ASM), controlled by tropical ocean‐atmosphere systems, and the westerlies, directly linked to high‐latitude climates, interact in mid‐latitude East Asia. Located at a climate junction, the northeastern Qinghai‐Tibetan Plateau (QTP) is a sensitive zone for the interaction of the westerlies and ASM. In the current work, we present a new loess data set from the northeastern QTP since the last deglaciation, including grain size, stable isotope (δ13Corg and δ18Ocarb), total organic carbon, total nitrogen, magnetic susceptibility, and mineral composition. The PMIP3‐CMIP5 multi‐model ensemble and TraCE‐21ka transient simulation are used synthetically to analyze climate mechanisms. All proxies suggest instable glacial climate and stable interglacial climate in the northeastern QTP. The coarser grain size during the last deglaciation compared with the Holocene reflects intensified westerlies controlled by the weakening of Atlantic Meridional Overturning Circulation and existing ice sheets. More positive δ18Ocarb values during abrupt cooling events [Heinrich event 1 (H1) and the Younger Dryas (YD)] indicate the effect of a weakened monsoon triggered by the low‐latitude solar insolation and sea surface temperature. Therefore, the anti‐phase pattern between the ASM and westerlies is the primary reason for differences in climate stability. Moreover, low temperature favors the predomination of C3 plants and the development of permafrost, leading to more negative δ13Corg values and fine grain size during the H1 and YD. Taken together, the anti‐phase relationship between the westerlies and ASM emphasizes the complicated dynamic characteristics of atmospheric systems in the mid‐latitudes and the challenges for future predictions.

Changes in soil microbial metabolic activity following long‐term forest succession on the central Loess Plateau, China

AbstractForest succession can alter terrestrial ecosystem processes and potentially impact subsurface carbon dynamics. However, the effects of long‐term forest succession on soil microbial metabolic activity remain unclear. This study investigated a long‐term forest succession approximately ~160 years after farmland abandonment on the central Loess Plateau, China, to explore the changes in soil microbial metabolism following the forest succession. Among them, the soil basal respiration (BR), microbial quotient (qMB), and metabolic quotient (qCO2) were studied. The results showed that the BR and qCO2 were increased following forest succession, whereas the qMB showed the opposite trend. Forest succession also increased the activities of β‐1,4‐glucosidase (BG) and β‐D‐cellobiosidase (CBH). The increase of BR and qCO2 and the decrease of qMB occurred in the early stage (&lt;60 years). However, the increase of BG and CBH mainly occurred in the later period (&gt;100 years). Soil microbial metabolic activity was closely related to litter biomass, dissolved organic carbon, fungal, and bacterial community composition. In conclusion, long‐term forest succession changes soil microbial community structure and promotes soil organic carbon accumulation, while the increase of soil respiration and metabolism promotes the release of carbon element following forest succession, thus reducing soil microbial carbon utilization efficiency.

Effects of biological soil crusts on soil labile organic carbon of patchy alpine meadows in the Source Zone of the Yellow River, West China

Biological soil crusts (BSCs) play an important ecological role in the biogeochemical cycles, but there is limited knowledge about their effects on the composition of soil labile organic carbon (LOC) in the soil of patchy alpine meadow. In patchy alpine meadow with different altitudes, the different LOC compartments, vegetation, soil properties and C-hydrolase activity of active patches (with plateau pika), inactive patches (without plateau pika), restored patches, BSCs patches, and healthy alpine meadow were analyzed to assess the effects of BSCs on LOC. The key influence pathway of eco-environmental factors of LOC was determined by the structural equation model (SEM). The results showed that the BSCs at the altitude of 3570 m increased dissolved organic carbon (DOC), easily oxidized organic carbon (EOC) and microbial carbon (MBC) by 293%, 73% and 36%, respectively, compared with active patches in the 0–2 cm layer, which was significantly higher than those of inactive patches and recovered patches. There was no significant difference among DOC, EOC and MBC in different patches at the altitude of 4224 m. The MBC content of active patches decreased, but other patches and healthy alpine meadow showed a Λ- shaped change with altitude. The contents of soil total nitrogen and organic matter of BSCs patches were generally higher than those of active and inactive patches at three different altitudes. Structural equation model results showed that at the altitude of 3570 m, total nitrogen had a strong positive correlation with DOC, with a path coefficient of 0.677. There was a direct negative relationship between soil organic matter and DOC (path coefficient = −0.278) at the altitude of 4013 m. At the altitude of 4224 m, there was no direct correlation among soil nutrient, C-hydrolase activity, and soil LOC. Therefore, BSCs mainly promote the accumulation and recovery of LOC by increasing the soil total nitrogen content in different patches at different altitudes, which are beneficial to the restorations of LOC, total nitrogen and soil organic matter. Hence, they should be considered as key factors in the processes of restoring patchy alpine meadows.

Contrasting particle fluxes and composition in a submarine canyon affected by natural sediment transport events and bottom trawling

Submarine canyons are important conduits of sediment and organic matter to deep-sea environments, mainly during high-energy natural events such as storms, river floods, or dense shelf water cascading, but also due to human activities such as bottom trawling. The contributions of natural and trawling-induced sediment and organic matter inputs into Palamós Canyon (NW Mediterranean) were assessed from three instrumented moorings deployed in the axis and northern flank of the canyon covering the trawling closure (February) and the trawling season (March-December) of 2017. During the trawling closure, large sediment fluxes with high contents of labile marine organic matter content were registered in the canyon axis, associated to storm resuspension on the shelf that coincided with dense shelf water cascading and high surface water productivity. Although no major natural sediment transport events occurred during the following spring and summer months, near-daily trawling-induced sediment gravity flows were recorded in the northern flank mooring, placed directly below a fishing ground, which sometimes reached the canyon axis. Compositionally, the organic matter transferred by trawling resuspension was impoverished in the most labile biomarkers (fatty acids, amino acids, and dicarboxylic acids) and had a high degree of degradation, which was similar to surficial sediment from the adjacent fishing ground. Trawling resuspended particles masked the transfer of organic matter enriched in labile biomarkers that naturally occur during the quiescent summer months. Overall, bottom trawling enhances the magnitude of particle fluxes while modifying its organic carbon composition, increasing the re-exposure and transfer of degraded organic carbon and potentially affecting benthic communities that rely on the arrival of fresh organic matter.

Dynamics and internal links of dissolved carbon in a karst river system: Implications for composition, origin and fate

Dissolved carbon (DC) deciphers biotic and abiotic processes in aquatic ecosystems, representing a critical component of global carbon cycling. However, underlying drivers of riverine DC dynamics and internal links have yet to be studied. Here, we investigated fluvial physicochemical characteristics, dissolved inorganic carbon (DIC) species, carbon dioxide (CO2) exchange, dissolved organic carbon (DOC) compositions and properties in a karst river system Qijiang, Southwest China. Carbonate dissolution combined with photosynthetic uptake could explain dynamics of DIC species. Carbon sequestration caused low-magnitude of partial pressure of aqueous CO2 (pCO2, 620.3 ± 1028.7 μatm) and water-air CO2 flux (F, 154.3 ± 772.6 mmol/m2/d), yielding an annual CO2 emission of 0.079 Tg CO2/y. Relatively high biological index (BIX, 0.77–0.96 on average) but low humification index (HIX, 0.67–0.78 on average) indicated notable autochthonous processes. Humic-like component was the predominant DOC, accounting for 39.0%-75.2% with a mean of 57.2% ± 6.17%. Meanwhile, tryptophan-like component (5.84% ± 2.31%) was also identified as collective DOC by parallel factor analysis (PARAFAC) across samples. Biological metabolism established internal linkages between DIC and DOC in the karst river system. Our findings highlighted biological process as a determinant for DC cycling in karst aquatic ecosystems.

Long-term partial substitution of chemical nitrogen fertilizer with organic fertilizers increased SOC stability by mediating soil C mineralization and enzyme activities in a rubber plantation of Hainan Island, China

The partial substitution of chemical nitrogen (N) fertilizer with organic fertilizers is widely used to maintain soil fertility and enhance crop yield, although its effects on soil organic carbon (SOC) composition, mineralization and stability are not fully understood. For this study, a 12-year field experiment was conducted in a rubber plantation field of Hainan Island, China. Three fertilizer treatments included no fertilizer application as control (CK), chemical fertilizer application (NPK), and half of the chemical N fertilizer plus manure application equivalent to half of chemical N fertilizer (NPKM). We determined the soil physicochemical properties, four labile SOC compositions (microbial biomass carbon (MBC), light fraction organic carbon (LFOC), dissolved organic carbon, dissolved organic carbon extracted by hot water (HOC), particulate organic carbon (POC)), four C-associated soil enzymes (β-1, 4-glucosidase (BG), polyphenol oxidase (POX), catalase (CAT) and cellulase), and SOC mineralization (from a 46-day aerobic incubation experiment) in two soil layers (topsoil layer (0–10 cm) and subsoil layer (10–20 cm)). Compared with NPK, NPKM significantly increased soil pH, total nitrogen, total phosphorus, available phosphorus and potassium, NH4+-N, and NO3−-N contents, and SOC, LFOC, POC, HOC, and MBC concentrations. NPKM had higher cumulative CO2 production but lower SOC mineralization potential (Cp) than NPK, although the difference was not significant. In both soil layers, NPKM significantly increased POX activity, but decreased BG and CAT activities. Soil pH can regulate enzyme activities and synthesis in acidic soil in a tropical region with a significantly positive correlation with POX activity. Compared with NPK, the relatively lower Cp/SOC and higher carbon quality index (CQI) indicated higher SOC stability (Cp/SOC) in NPKM. The redundancy analysis results revealed that the dominant factors affecting SOC stability were NH4+-N, pH, POC and MBC in NPK, and available phosphorus, BG, and pH in NPKM. In the three fertilization treatments, the POX was the dominant factor affecting the CQI. Conclusively, half of the chemical N fertilizer plus half of the manure application could facilitate SOC stability by mediating soil C mineralization and enzyme activities in the rubber plantation of Hainan Island, China.

Aggregate-associated carbon compositions explain the variation of carbon sequestration in soils after long-term planting of different tea varieties

Strategies to increase carbon (C) sequestration in tea plantation soils are pertinent to mitigating global climate change, but little is known about the variation in C sequestration in soils planted with different tea varieties. In the current study, we collected 0–20 and 20–40 cm layer soil samples from a tea plantation planted with four tea varieties (Chuancha No.3 (CC3), Chuanmu No. 217 (CM217), Chuannong Huangyazao (CN), and C. sinensis ‘Fuding Dabaicha’ (FD)). Soil organic carbon (SOC) stock and composition in the bulk soil and aggregate fractions, as well as the SOC stability index (SI), were investigated. Both SOC stock and composition in the bulk soil or aggregate fractions were variable among the soils after planting different tea varieties. Overall, the highest SOC stock (0–40 cm) was observed in FD soil, followed by CN, CC3, and CM217 soil. This difference was dominated by the SOC stock associated with macroaggregates, and the highest macroaggregate-associated SOC stock was detected in FD soil in both soil layers. Moreover, FD soil showed the highest proportion of macroaggregates in both soil layers, accumulated the greatest recalcitrant organic carbon (ROC) and further contributed to the highest SI values of SOC associated with most aggregate fractions. In contrast, CN topsoil (0–20 cm) accumulated the greatest labile organic carbon (LOC) in most aggregate fractions, which had a positive correlation with the amount of C return by pruning litter. Ultimately, long-term planting of FD promoted macroaggregate formation, and ROC accumulation in aggregates greatly contributed to maintaining high C sequestration in the tea plantation soils and showed a high potential for future C budgets; in contrast, the tea plantation soil planted with CN could be a potential C source because of high C return.

East Siberian Sea: Interannual heterogeneity of the suspended particulate matter and its biogeochemical signature

The East Siberian Sea (ESS) is the largest, shallowest and most icebound Arctic marginal sea. It receives substantial input of terrigenous material and climate-vulnerable old organic carbon from both coastal erosion and rivers draining the extensive permafrost-covered watersheds. This study focuses on the interannual variability and spatial distribution of suspended particulate matter (SPM) in the surface and bottom waters of the ESS during the ice-free period in 2000, 2003, 2004, 2005 and 2008. We report on the composition and variability of particulate organic carbon (POC), total nitrogen (TN), POC/TN ratios, carbon and nitrogen isotopes (δ13C, δ15N) and provide estimates of the contribution of terrestrial organic carbon (terrOC) based on the δ13C isotopic values.The results show that interannual SPM distribution and elemental-isotopic characteristics of POC differ significantly between the western biogeochemical province (WBP; West of 165oE) and the eastern biogeochemical province (EBP; East of 165oE) of the ESS. The SPM mean concentration in the WBP is almost an order of magnitude higher than in the EBP. From west-to-east of the ESS, SPM tends to become more depleted in δ15N, while the δ13C becomes isotopically heavier. This trend can be explained by a shift in organic matter sources from terrigenous origin (erosion of the coastal ice complex and riverine POC) to becoming dominantly from marine plankton.The maximum contribution of terrOC to POC reached 99% in parts of the WBP, but accounts for as low as 1% in parts of the EBP. At the same time, the type of atmospheric circulation and its associated regime of both water circulation and ice transport control a displacement of the semi-stable biogeochemical border between WBP and EBP to the east or to the west if compared to its long-term average position near 165oE. Our multi-year investigation provides a robust observational basis for better understanding of the transport and fate of terrigenous material upon entering the ESS shelf waters. Our results also provide deeper insights into the interaction in the land-shelf sea system of the largest shelf sea system of the World Ocean, the East Siberian Arctic Shelf system.

Fine particles and pyrogenic carbon fractions regulate PAH partitioning and burial in a eutrophic shallow lake

Aquatic particles and organic carbon (OC) regulate the occurrence and transport of hydrophobic organic contaminants such as polycyclic aromatic hydrocarbons (PAHs) in water-suspended particle-sediment interfaces. Conventional studies on the mechanisms regulating the relationships between PAHs and total particles/OC have ignored micro-scale regulatory factors such as particle size and OC composition. Field research in the eutrophic shallow Lake Taihu, China, revealed that the fine particle fractions 2.7–10 μm in diameter had stronger PAH adsorption capacity and significantly regulated PAH particle size distribution and water-particle partitioning. Selective PAH biodegradation by planktonic microorganisms probably significantly weakened the capacity of the coarse fractions to regulate PAHs. OC fragments at different temperature gradients had markedly different influences on the particle size distribution of PAHs. High-temperature pyrogenic OC fractions (part of black carbon) were the principal OC regulatory factors for medium-to high-molecular-weight PAHs. However, the OC fragments did not directly affect the particle distribution of low-molecular-weight PAHs. During particle deposition and burial, microbial PAH utilization and efficiency probably regulated the burial potential of various hydrophobic PAH species. Biodegradation of relatively less hydrophobic PAHs with octanol-water partition coefficients (log Kow) < 5.8 showed an increasing trend with decreasing PAH hydrophobicity. Biological pump action of the relatively higher hydrophobic PAH species (log Kow > 5.8) showed a decreasing trend with increasing PAH hydrophobicity. The discoveries of the present work further clarified the mechanisms of PAH partitioning and burial in a eutrophic shallow lake and collectively provides a valuable reference for modeling the transport and dispersal mechanisms of hydrophobic, particle-bound organic contaminants in other aquatic ecosystems.

Soil Fertility Improvement and Carbon Sequestration through Exogenous Organic Matter and Biostimulant Application

One of the main tasks in the search for environmentally friendly crop-growing methods is to increase soil fertility by improving its physical, chemical and biological parameters. The aim of this study was to determine the effect that the long-term annual application of different types of soil fertility agents (exogenous organic matter: 1. manure, 2. straw in combination with nitrogen fertilization and liming and 3. the addition of biostimulants) had on organic matter properties, including humic acid (HAs) properties. The research was carried out on the basis of soil samples from a ten-year pot experiment which was set up as single-factor pot experiment with four replications. PVC pots with perforated bottoms were filled with soil samples taken from the tilled layer of an arable field where winter wheat was grown in monoculture. The pots were exposed directly to the weather and were left without vegetation. The soil samples were assayed for the content of total organic carbon (TOC), total nitrogen and fractional composition of humus. HAs were extracted with the Schnitzer method and analyzed for the elemental composition, spectrometric parameters in the FT-IR and UV-VIS range and hydrophilic and hydrophobic properties. In addition, EPR spectra were produced. The results showed that the content of organic matter compared to soil without additives increased with the use of manure and the use of straw in the CaO variant and in the form of a mulch. The content of dissolved organic carbon (DOC) ranged from 124.6 to 286.1 mg kg−1 and had strong positive correlation with TOC content. The values of the ratio of carbon content in humic acids to carbon content in fulvic acids (CHAs/CFAs) ranged from 0.71 to 0.99. The use of a biostimulator—with or without the addition of straw—increased carbon sequestration in humic acid molecules, as well as their oxidation level and their share of hydrophobic fractions with the longest retention time. Thus, the addition of UGmax intensifies humification processes, leading to the formation of stable humic acid molecules.

C4 vegetation characteristics in the monsoon rainforest of the Pearl River delta during the MIS 2 period

The impact of abrupt climate change during glacial periods on terrestrial ecosystems are widely acknowledged by paleoecology and paleoclimate communities as key issues in the ongoing debate on geographical distribution and patterns of genetic diversity of species. However, the C4 plant expansion in subtropical South China at the mouth of the Pearl River during the glaciated Marine Isotope Stage 2 (MIS 2) in response to millennial-scale climate changes is largely unknown. In this study we present results of the isotopic composition of sediment organic carbon (δ13CTOC) obtained from a high-resolution fluvial sequence from the Pearl River delta plain in southern China to show millennial-scale C3/C4 ecosystem changes during the MIS 2 interval. Three major C4 grassland expansions and declines of the monsoon rainforest landscape are identified during the MIS 2 period. Our results reveal that during MIS 2 δ13CTOC values shifted profoundly from about −29 ‰ to enriched values of up to −17 ‰ three times and we interpret these as due to episodic expansions of the C4 plants to form a mixed C3/C4 plant ecosystem with the collapse of a pure C3 monsoon rainforest community in this region. These drastic expansions of C4 ecological systems occurred at 24.8–24 ka, 23.8–21 ka, and 18–15.6 ka cal BP intervals, equivalent to well-known Heinrich Stadial (HS) 2, Last Glacial Maximum (LGM), and HS1 super-cold Northern Hemisphere intervals. We found that these drastic changes of plant ecosystems closely tracked the monsoon records during the significant weakening of Asian Summer Monsoon Intervals (WSMIs) of the MIS 2 period.