Black Carbon Input Research Articles

POLYCYCLIC AROMATIC HYDROCARBONS AS INDICATORS OF SOIL POLLUTION IN THE ZONE AFFECTED BY THE TRANSPORT COMMUNICATIONS OF THE GORLOVO ANTHRACITE DEPOSIT

The areas adjacent to open coal mining facilities are affected by different kinds of anthropogenic impact, including dust pollution. To reveal the extent of technogenic impact, the parameters characterising the content and composition of 19 priority polycyclic aromatic hydrocarbons (PAHs) in chernozem soils adjacent to the haul road of the Gorlovo anthracite deposit (the Novosibirsk Region) were assessed. It is shown that the maximum total concentration of PAHs (>1000 ng/g) is reached at the distance of 100 m from the source, while the levels higher than the background are detected at a distance of 1000 m. The effect of dominating wind direction and the presence of tree belt were determined to affect the total PAH content in soil but leave their group composition unchanged at a distance of 2000 m from the road. At the same time, the individual composition of PAHs in soils changes with an increase in the distance from the pollution source. The concentration of benz(α)pyrene and total PAH content, calculated for benz(α)pyrene toxic equivalents, were determined in the soils of territories adjacent to the road and compared with the current standards in force in the Russian Federation (sanitary rules and regulations). Statistical processing of the results, performed by the principal component analysis, shows that the input of black carbon in the form of anthracite coal dust into soil is most adequately represented by polyarene ratio PHE/(PHE + CHR), where PHE is phenanthrene, and CHR is chrysene. However, the threshold of technogenic load (<0.8), that was previously established for objects in which anthracite is the main source of PAHs, requires confirmation for black soils.

Black carbon derived from pyrolysis of maize straw and polystyrene microplastics affects soil biodiversity

Understanding the environmental correlation of microbial community under external stimulation is significant for ecological restoration. However, few studies focused on the response of soil biodiversity induced by black carbon (BC) derived from pyrolysis of straw and microplastics (MPs) due to their widespread existence in natural environment. In this study, polystyrene MPs (PS) and maize straw with different mass ratios were used as raw materials to prepare BC by pyrolysis. The surface morphology, chemical composition and sequential variations of different functional groups of BC were systematically analyzed. The leachate from BC was identified by three-dimensional excitation emission matrice (3D-EEM). The corresponding results showed that yield, value of O/C and N element content of BC decreased with more PS. The changed C content and oxygen-containing functional groups occurred. The order of functional groups of BC formed by co-pyrolysis was: C=C > C-O > C-H > Si-O-Si. The main component of leaching from BC was humic-like and fulvic-like acid. Simultaneously, the input of exogenous BC into soil affected abundance, composition and metabolic pathways of microorganisms. The study helps to understand environmental implication of BC which was pyrolyzed from maize straw and MPs, providing an idea for improving biogeochemical cycle process in soil.

Assessing the quantum yield spectrum of photochemically produced reactive intermediates from black carbon of various sources and properties

Black carbon (BC) is ubiquitous in sunlit waters and atomosphere. Recent studies revealed that under sunlight irradiation BC is photoactive on producing photochemically produced reactive intermediates (PPRIs), a group of key species in accelerating earth's surface biogeochemical processes and pollutant dynamics. Nevertheless, reported PPRIs productions from BC exhibit large inconsistency and the intrinsic capacities of BC in producing PPRIs remain poorly characterized. This work provided a wavelength-dependent quantum yields (QYs) assessment of four environmentally-relevant PPRIs (excited triplet state BC (3BC*), singlet oxygen (1O2), hydrogen peroxide (H2O2), and hydroxyl radical (·OH)) from various BC. The QYs of all investigated PPRIs exhibit high dependence on incident light wavelength. For instance, the QYs of 1O2 dramatically decreased from 4.4% to 0.4% with light wavelength increasing from 375 to 490 nm and decreased to 0 above 490 nm. Suprisingly, PPRIs QYs only varied by 2.0–2.5-fold among BC prepared from different biomasses (i.e., pine needle, shell, straw, and wood), while the pyrolysis temperature and size of BC demonstrate higher impacts on the PPRIs QYs by up to 30.3- and 7.1-fold variations, respectively. Analyses on the physicochemical properties of BC demonstrate that QYs of 3BC* and 1O2 were linked to the optical properties of BC, while the QYs of H2O2 and ·OH were determined by multiple factors including the surface redox characteristics. Further, PPRIs productions from BC follow similar paths and efficiencies compared to those from natural organic matter. The revealed QYs of BC-derived PPRIs establish a key basis for evaluating PPRIs-mediated element cycles and pollutant transformation in natural waters, which are becoming increasingly important in the context of higher BC input from more frequent wildfires and artificial sources.

The black carbon cycle and its role in the Earth system

Black carbon (BC) is produced by incomplete combustion of biomass by wildfires and burning of fossil fuels. BC is environmentally persistent over centuries to millennia, sequestering carbon in marine and terrestrial environments. However, its production, storage and dynamics, and therefore its role in the broader carbon cycling during global change, are poorly understood. In this Review, we discuss BC cycling across the land-to-ocean continuum. Wildfires are the main source of BC, producing 128 ± 84 teragrams per year. Negative climate–BC feedbacks could arise as wildfire increases with anthropogenic warming, producing more BC, which in turn will sequester carbon, but the magnitude of these effects are unknown. Most BC is stored in terrestrial systems with some transported to the ocean via rivers and the atmosphere. However, the oceanic BC budget is not balanced, with known BC removal fluxes exceeding BC inputs. We demonstrate these observed inconsistencies using a simple ocean box model, which highlights key areas of future research. Measurements of BC mineralization and export rates along the land-to-ocean continuum and quantification of previously unexplored sources of oceanic BC are needed to close the global BC budget. Black carbon is produced by wildfire and fossil fuel burning, and persists in the environment over centuries to millennia. This Review describes black carbon sources and budgets, discusses its transport along the land-to-ocean continuum and highlights its enigmatic cycling in the ocean.

Anthropogenic fire fingerprints in Late Pleistocene and Holocene sediments of Sodmein Cave, Egypt

Sodmein Cave in Egypt is an exceptional archive for the study of past human behavior and anthropogenic fire history. Stratified remains of human occupation were excavated, ranging from the Middle Stone Age to the Neolithic. Hearths were repeatedly detected throughout the stratigraphy, with the lowest Pleistocene level having particularly large fire pits. This study is the first to apply a black carbon (BC) method on sediments bearing archaeology from the last 120,000 years. The method oxidizes BC to benzene polycarboxylic acids (BPCA) as a proxy for fire residue input. We detected significant changes in BC amounts throughout the stratigraphy; the highest contents in the form of two distinctive peaks were found in samples corresponding to the beginning of the Late Pleistocene (3.3 and 2.2 g BC kg−1, respectively), indicating frequent burning. In the overlying layers, BC remained low (on average: 0.2 g BC kg−1) until the beginning of the Holocene, when contents increased, and human influence became visible again (1.7 g BC kg−1). Also, BPCA composition as a proxy for changes in fire temperature changed significantly over the stratigraphy. In the Pleistocene, residues of hotter fires were predominantly found, while the Holocene was characterised by a change to low-temperature fires. Variations in BC input and source are in agreement with the archaeological results, demonstrating the varying intensities and recurrence of human visits to the shelter during the last 120,000 years, but also show the potential to resolve different phases of human occupation more finely, when the archaeological findings are accompanied by geochemical BC analyses.

Semi-enclosed bays serve as hotspots for black carbon burial: A case study in Jiaozhou Bay, western Yellow Sea

The provenance of black carbon (BC) and its role in affecting contaminant cycling in both the atmosphere and aquatic environments have been extensively studied. However, the fate and cycling dynamics of BC, particularly in marine environments, are poorly understood. Herein, soot BC was determined in the semi-enclosed Jiaozhou Bay to examine the seasonal variability, residence timescale in seawater, and settling flux to sediments, together with particle-reactive 234Th. Soot BC ranged from 0.39 to 4.26 μmol-C L−1. On average, spring produced the highest value of 1.88 ± 0.31 μmol-C L−1, followed by winter (1.59 ± 0.18 μmol-C L−1), summer (0.94 ± 0.09 μmol-C L−1), and autumn (0.90 ± 0.09 μmol-C L−1). The seasonality of soot BC was similar to the activity concentration of particulate 234Th (i.e., 234ThP). The close relationships between soot BC and 234ThP (p < 0.01) provide the basis for the application of 234Th to trace the fate of soot BC. Based on the 234Th deficit with respect to 238U, the residence times of soot BC were estimated to be 41 ± 6 d and 36 ± 5 d for May–August and August–November, respectively. The shorter residence times of soot BC than that of seawater indicated that soot BC delivered to Jiaozhou Bay settled in the local sediments. Furthermore, soot BC concentrations were higher in the inflow seawater from the Yellow Sea than the outflow water from Jiaozhou Bay, implying a net input of soot BC from the Yellow Sea to Jiaozhou Bay. The soot BC fluxes were 0.266 ± 0.035 mmol-C m−2 d−1 and 0.0472 ± 0.0065 mmol-C m−2 d−1 for May–August and August–November, respectively. From the bay-scale perspective, Jiaozhou Bay had buried 0.101 ± 0.010 Gg of soot BC each year. These results indicate that the semi-enclosed Jiaozhou Bay acts as an effective trap for soot BC and particle-reactive contaminants.

Tracing Riverine Particulate Black Carbon Sources in Xijiang River Basin: Insight from Stable Isotopic Composition and Bayesian Mixing Model

Rivers transport abundant terrestrial carbon into the ocean, constituting a fundamental channel between terrestrial carbon pools and oceanic carbon pools. The black carbon (BC) derived from biomass and fossil fuel combustion is an important component of the riverine organic carbon flux. A recent study estimated that approximately 17 ~ 37 Tg C of BC was delivered in suspended particle phase by rivers per year. The particulate black carbon (PBC) in river systems has rarely been investigated and its controlling factors have remained largely unknown. The stable isotopic compositions of PBC in Xijiang River during the wet season are reported in this study. We found that the PBC/particulate organic carbon (POC) ratio in Xijiang River was slightly higher than that of other rivers, which may be a result of the mobility difference between POC and PBC, aerosol BC input and riverine biogenic effect. We found that the isotopic compositions of PBC depleted 13C compared with those of POC and dissolved organic carbon (DOC). This divergence may be derived from the fractionation during soil organic matter production and biomass burning or fossil fuel combustion BC particles input with different isotopic compositions. The MixSIAR model indicated that most of the PBC in the study area was derived from fossil fuel combustion (~80%), the contribution of C4 plants burning was limited. Our result highlights that in the watershed without wildfire impact, the aeolian transport and deposition of the particles from fuel oil, coal combustion, and vehicle exhaust could significantly affect the BC flux in rivers.

Leachable soil black carbon after biochar application

Black carbon (BC) enters soil via deposition of emissions and nowadays also via application of biochar. Recent studies indicate that a yet not quantified part of BC is lost from soil by leaching, which implies that BC exists in water-transportable form (so-called water-extractable BC; WEBC). We aim at quantifying the amount of WEBC in soil and at elucidating whether it relates to biochar application. The composition of WEBC was further tested to evaluate the degree of BC weathering over time after application, hypothesizing that BC degrades into smaller polyaromatic units. We analysed total BC and WEBC in topsoil (0–10 cm) of a field trial with application of 0, 4.5, and 9 Mg biochar ha−1 using the benzene polycarboxylic acid method. To see if there is a temporal relation between BC input and WEBC formation, we took samples directly after biochar application and three years later. Bulk BC and also WEBC concentrations increased with increasing biochar application rates. In contrast, WEBC portions of bulk BC decreased with increasing amount of applied biochar. On average, we found between 7.56 ± 2.50 and 12.56 ± 1.34 mg WEBC per kg agricultural soil, making up 0.6–1.84% of bulk BC. Over time, no loss or accumulation of either component was observed. However, we found that the composition of WEBC differed from bulk BC; i.e. WEBC consisted of less condensed aromatic structures than bulk BC indicating that de-condensation processes are involved in the formation of leachable BC.

Historical Black Carbon Reconstruction from the Lake Sediments of the Himalayan-Tibetan Plateau.

Black carbon (BC) is one of the major drivers of climate change, and its measurement in different environment is crucial for the better understanding of long-term trends in the Himalayan-Tibetan Plateau (HTP) as climate warming has intensified in the region. We present the measurement of BC concentration from six lake sediments in the HTP to reconstruct historical BC deposition since the pre-industrial era. Our results show an increasing trend of BC concurrent with increased anthropogenic emission patterns after the commencement of the industrialization era during the 1950s. Also, sedimentation rates and glacier melt strengthening influenced the total input of BC into the lake. Source identification, based on the char and soot composition of BC, suggests biomass-burning emissions as a major contributor to BC, which is further corroborated by open-fire occurrence events in the region. The increasing BC trend continues to recent years, indicating increasing BC emissions, mainly from South Asia.

Biogeochemical Impacts of a Black Carbon Wet Deposition Event in Halong Bay, Vietnam

Black carbon (BC) is emitted to the atmosphere during biomass, biofuel and fossil fuel combustion, and leaves the atmosphere via dry or wet deposition on land and on the ocean. On a global scale, wet deposition accounts for about 80% of the total atmospheric BC inputs to the ocean. The input of BC particles to the ocean can enrich surface waters with carbon and associated elements, and owing to high porosity and surface-active properties, BC can alter biogeochemical cycles by sorbing dissolved compounds and promoting aggregation. The rain-mediated input of BC to the ocean and its consequences on nutrient concentrations and particle dynamics were studied in Halong Bay, Vietnam, during a 24 h cycle impacted by short and heavy rainfall events. This study suggests that once introduced in the surface ocean via wet deposition, BC sorbs dissolved organic matter (DOM) and stimulates aggregation processes. The observed wet deposition events were characterized by sudden and pulsed inputs of BC particles that created a thin layer of sinking surface-active aggregates, acting as a net-like scavenger for DOM, nutrients (especially phosphate), and small particles. In addition, the wet deposition events coincided with an enrichment of nutrients in the surface microlayer, with an excess input of nitrogen relative to phosphorus leading to an increase of the molar N:P ratio from 24:1 to 37:1. In the underlying water, the molar N:P ratio also increased (i.e., from 39:1 to 64:1), and this can be attributed to the preferential scavenging of dissolved P-compounds on sinking BC-aggregates.

Large-river dominated black carbon flux and budget: A case study of the estuarine-inner shelf of East China Sea, China

Mobilization of terrestrial-derived and recalcitrant black carbon (BC), including char and soot, from land to ocean exerts a significant influence on the global carbon cycle. This study elaborated the occurrence and spatial distributions of BC, char, and soot concentrations, as well as their burial fluxes, in the estuarine-inner shelf surface sediments of the East China Sea (ECS), an epicontinental sea adjacent to Chinese high-intensity BC emission source regions. Using a combination of BC measurements in the Yangtze River water and coastal ECS aerosol samples, a preliminary BC budget was concurrently constrained. The spatial distribution of char concentrations resembled largely that of BC, but differed significantly from that of soot, indicating that char and soot exhibited different geochemical behaviors. In contrast to concentrations, BC, char, and soot burial fluxes exhibited highly consistent spatial patterns, and all declined as the distance from the coastline increased. For the coastal ECS, riverine discharge dominated (~92%) the total BC input, with the Yangtze River alone accounting for as high as ~72%. The area-integrated sedimentary BC sink flux (630 ± 728 Gg/yr) in the coastal ECS was equivalent to the total BC influx (670 ± 153 Gg/yr), which coincided well with the regional sediment budget. This suggested that the terrestrial-derived and recalcitrant BC could be regarded as an alternative geochemical proxy for tracing the sediment source-to-sink processes in this region. Comparisons between BC and co-generated polycyclic aromatic hydrocarbons (PAHs) budgets in the coastal ECS revealed similarities in their input pathways, but dramatic differences in their ultimate fates. Despite these, the ECS estuarine-inner shelf could serve as a major sink of these terrestrial-based materials in the global ocean.

Carbon concentration and isotope composition of black carbon in the topsoil of the central and southeastern Qinghai-Tibetan Plateau, and their environmental significance

The carbon concentration and carbon isotope of black carbon (BC) have been widely used to reconstruct fire history and vegetation change. In order to establish the relationship between BC, contemporary vegetation and climate at the high altitudes of the Qinghai-Tibetan Plateau (QTP), we investigated the carbon concentration and carbon isotope composition of BC and soil organic carbon (SOC) (%BC, %SOC, δ13CBC and δ13CSOC) in 29 topsoil samples from the central and southeastern QTP. In general, the %SOC and %BC of topsoil show generally similar variations, indicating a common controlling factor for SOC and BC production, i.e., vegetation. The relatively small BC/SOC ratios fall in the range of BC/OC for pyrogenic particles from biomass burning, indicating a minor contribution of BC from fossil fuel combustion. The δ13CSOC of topsoil can effectively indicate local vegetation in the QTP. The δ13CBC and δ13CSOC are positively correlated, whereas the δ13CBC values are more negative than those of δ13CSOC. This could due to fire season and fractionation processes during post-deposition, but not carbon isotope fractionation during combustion or exogenous BC input. Therefore, BC in topsoil of the QTP mainly records ‘local’ environmental information, and the δ13CBC can be used in paleovegetation reconstruction in combination with the local climate.

Sources and burial fluxes of soot black carbon in sediments on the Mackenzie, Chukchi, and Bering Shelves

Black carbon (BC) has been recognized as a climate forcing and a major component in the global carbon budget. However, studies on BC in the Arctic Ocean remain scarce. We report here variations in the abundance, sources and burial fluxes of sedimentary soot black carbon (soot-BC) in the western Arctic Ocean. The soot-BC contents averaged 1.6 ± 0.3, 0.46 ± 0.04 and 0.56 ± 0.10 mg-C g−1 on the Mackenzie, Chukchi and Bering Shelves, respectively, accounting for 16.6%, 10.2% and 10.4% of the total organic carbon in surface sediment. Temporally, contents of soot-BC remained fairly stable before 1910, but increased rapidly after the 1970s on the Mackenzie Shelf, indicating enhanced source input related to warming. Comparable δ13C signatures of soot-BC (− 24.95‰ to − 24.57‰) to C3 plants pointed to a major biomass source of soot-BC to the Beaufort Sea. Soot-BC showed similar temporal patterns with large fluctuations in the Chukchi/Bering shelf regions, implying the same source terms for soot-BC in these areas. Two events with elevated soot-BC corresponded to a simultaneous increase in biomass combustion and fossil fuel (coal and oil) consumption in Asia. The similar temporal variability in sedimentary soot-BC between the Arctic shelves and Asian lakes and the comparable δ13C values manifested that anthropogenic emission from East Asia was an important source of soot-BC in the western Arctic and subarctic regions. The burial fluxes of soot-BC, estimated from both 137Cs- and 210Pb-derived sedimentation rates, were 2.43 ± 0.42 g-C m−2 yr−1 on the Mackenzie Shelf, representing an efficient soot-BC sink. Soot-BC showed an increase in buried fluxes from 0.56 ± 0.02 g-C m−2 yr−1 during 1963–1986 to 0.88 ± 0.05 g-C m−2 yr−1 after 1986 on the Chukchi Shelf, and from 1.00 ± 0.18 g-C m−2 yr−1 to 2.58 ± 1.70 g-C m−2 yr−1 on the Bering Shelf, which were consistent with recent anthropogenically enhanced BC input observed especially in Asia. Overall, the three Arctic shelves could bury more than 3000 Gg soot-BC each year, attesting to an important role of the Arctic and subarctic shelves in global BC budget and carbon cycle.

Seasonal dynamics of atmospheric and river inputs of black carbon, and impacts on biogeochemical cycles in Halong Bay, Vietnam

Emissions of black carbon (BC), a product of incomplete combustion of fossil fuels, biofuels and biomass, are high in the Asia-Pacific region, yet input pathways and rates to the ocean are not well constrained. Atmospheric and riverine inputs of BC in Halong Bay (Vietnam), a hotspot of atmospheric BC, were studied at monthly intervals during one year. Climate in Halong Bay is governed by the monsoon regime, characterized by a northeast winter monsoon (dry season) and southeast summer monsoon (wet season). During the dry season, atmospheric BC concentrations averaged twice those observed during the wet season. In the sea surface microlayer (SML) and underlying water (ULW), concentrations of particulate BC (PBC) averaged 539 and 11 µmol C L–1, respectively. Dissolved BC (DBC) concentrations averaged 2.6 µmol C L–1 in both the SML and ULW. Seasonal variations indicated that PBC concentration in the SML was controlled by atmospheric deposition during the dry season, while riverine inputs controlled both PBC and DBC concentrations in ULW during the wet season. Spatiotemporal variations of PBC and DBC during the wet season suggest that river runoff was efficient in transporting PBC that had accumulated on land during the dry season, and in mobilizing and transporting DBC to the ocean. The annual river flux of PBC was about 3.8 times higher than that of DBC. The monsoon regime controls BC input to Halong Bay by favoring dry deposition of BC originating from the north during the dry season, and wet deposition and river runoff during the wet season. High PBC concentrations seem to enhance the transfer of organic carbon from dissolved to particulate phase by adsorbing dissolved organic carbon and stimulating aggregation. Such processes may impact the availability and biogeochemical cycling of other dissolved substances, including nutrients, for the coastal marine ecosystem.

Does Black Carbon Contribute to Eutrophication in Large Lakes?

Eutrophication is a major ecological crisis in water bodies. This is mainly driven by anthropogenic activities in the catchment that incorporate various nutrients. Input of nutrients can also be driven by atmospheric deposition, which has a large footprint that goes beyond local point source(s). In particular, black carbon (BC) can be a carrier of various nutrients and increase primary productivity in lakes. We need to monitor the input of BC in large water bodies to fully understand its role in driving primary productivity and change in trophic status.

Distribution and preservation of black carbon in the East China Sea sediments: Perspectives on carbon cycling at continental margins

We determined the concentrations and radiocarbon (14C) compositions of black carbon (BC) in the sediments of the East China Sea (ECS). The BC concentrations, which were in the range of 0.30–1.52mg/g, accounted for 12–65% of the total organic carbon (TOC). The distribution of BC in ECS sediments was controlled by factors such as grain size, distance from the coast, and deposition rate. Radiocarbon measurements of BC yielded ages of 6350–10,440 years before present (BP), suggesting that the percentage of BC derived from biomass combustion was in the range of 29–48%. The BC burial flux in sediments of the ECS was estimated to be ∼1.39×106t/yr, which was similar to burial fluxes reported for shelf sediments in other areas. However, the magnitude of the total BC sink was far greater than that of any other shelf regions studied to date, indicating the global importance of BC accumulation in the ECS, and the magnitude of BC input from large rivers (e.g., the Changjiang). The riverine delivery of BC to the ECS (73%) was far greater than that of atmospheric flux (27%). Further study of the BC cycle and the interactions of BC with other organic compounds in marginal seas was required to better understand the role of BC in the global carbon cycle.

Molecular chemistry in humic Ferralsols from Brazilian Cerrado and forest biomes indicates a major contribution from black carbon in the subsoil

Soil organic matter (OM) stability plays an important role in the global carbon cycle. The molecular characterisation of soil OM may contribute to an understanding of the feedback mechanisms between soil OM and climate. Umbric Ferralsols with humic properties (humic Ferralsols) are characterised by a thick dark carbon-rich A horizon, and co-occur next to Umbric Ferralsols without humic characteristics. They are concentrated in south-eastern Brazil which suggests an environmental control. In order to understand OM stability in these soils, humic Ferralsols from three Brazilian biomes were studied, including Cerrado (savanna), subtropical forest and tropical forest. The studied soils were developed on several geological substrates, including basalt, gneiss, chamokites, phyllite and tertiary sediments. The molecular composition of the free light fraction (FLF), occluded light fraction (OLF) and 0.1M NaOH extractable OM of samples from topsoil and subsoil from eight profiles was examined using analytical pyrolysis (pyrolysis-GC/MS). The light fraction reflects litter and charcoal, obtained by density fractionation before (FLF) and after (OLF) ultrasonic disruption; the NaOH extractable fraction (humic acid+fulvic acid) reflects more decomposed material. The chemical differences among soils from different Brazilian biomes were much smaller than the vertical gradient within each profile. The results showed that, within the light fractions, the content of which varied between 2% and 22% of the total carbon content (Ct), black carbon (BC) derived pyrolysis products showed a higher abundance in the topsoil. In the extractable OM, which varied between 46% and 88% of Ct, BC derived pyrolysis products showed a higher abundance in the subsoil. This suggests a continuous input of BC and an increase in the degree of decomposition with depth. Pyrolysis products associated with BC contributed up to 10% to the extractable pyrolysable fraction in the subsoil. The results suggest that degradation of charcoal, which is translocated to the subsoil by macroscopic soil organisms, results in a relative high contribution from naphthalene, 2-ethenylnaphthalene, phenanthrene, benzene, dibenzofuran and benzonitrile (subsoil) compared to (other) polyaromatic hydrocarbons (PAHs; C1-, C2- and C3-naphthalenes and fluorene) in relatively fresh charcoal (topsoil). The results highlight the importance of the subsoil in studies of the long term effects of fire on soil OM and suggest that BC is an important factor that underlies carbon stability in humic Ferralsols.

Atmospheric black carbon deposition and characterization of biomass burning tracers in a northern temperate forest

Aerosol black carbon (BC) is considered the second largest contributor to global warming after CO2, and is known to increase the atmosphere's temperature, decrease the albedo in snow/ice, and influence the properties and distribution of clouds. BC is thought to have a long mean residence time in soils, and its apparent stability may represent a significant stable sink for atmospheric CO2. Despite recent efforts to quantify BC in the environment, the quantification of BC deposition rates from the atmosphere to terrestrial ecosystems remains scarse. To better understand the contribution of atmospheric BC inputs to soils via dry deposition and its dominant emission sources, atmospheric fine particle (PM2.5) were collected at the University of Michigan Biological Station from July to September in 2010 and 2011. PM2.5 samples were analyzed for organic C, BC, and molecular markers including particulate sugars, carboxylic acids, n-alkanes, polycyclic aromatic hydrocarbons, and cholestane. Average atmospheric BC concentrations in northern Michigan were 0.048 ± 0.06 μg m−3 in summer 2010, and 0.049 ± 0.064 μg m−3 in summer 2011. Based on atmospheric concentrations, particulate deposition calculations, and documented soil BC, we conclude that atmospheric deposition is unlikely to comprise a significant input pathway for BC in northern forest ecosystem. The major organic tracers identified in fine particulates (e.g. levoglucosan and docosanoic acid) suggest that ambient PM2.5 concentrations were mainly influenced by biomass burning and epicuticular plant waxes. These results provide baseline data needed for future assessments of atmospheric BC in rural temperate forests.

Black carbon accrual during 2000 years of paddy-rice and non-paddy cropping in the Yangtze River Delta, China

Rice straw burning has accompanied paddy management for millennia, introducing black carbon (BC) into soil as the residue of incomplete combustion. This study examined the contribution of BC to soil organic matter and the rate at which it accumulates in paddy soils as a result of prolonged paddy management. Soil depth profiles were sampled along a chronosequence of 0-2000 years of rice-wheat rotation systems and adjacent non-paddy systems (50-700 years) in the Bay of Hangzhou (Zhejiang province, China). The soil BC content and its degree of condensation were assessed using benzene-polycarboxylic acids (BPCAs) as geochemical markers. The results showed that despite regular long term BC input, BC only contributed 7-11% of total soil organic carbon (SOC) in the topsoil horizons. Nevertheless, along with SOC, paddy soils accumulated BC with increasing duration of management until 297 years to reach a steady-state of 13 t BC ha(-1). This was 1.8 times more than in non-paddy soils. The fate of BC in paddy soils (0-1 m) could be modeled revealing an average annual input of 44 kg ha(-1) yr(-1), and a mean residence time of 303 years. The subsoils contributed at least 50% to overall BC stocks, which likely derived from periods prior to land embankment and episodic burial of ancient topsoil, as also indicated by BPCA pattern changes. We conclude that there is a significant but limited accumulation of C in charred forms upon prolonged paddy management. The final contribution of BC to total SOC in paddy soils was similar to that in other aerobic ecosystems of the world.

Contrasting temporal trends and relationships of total organic carbon, black carbon, and polycyclic aromatic hydrocarbons in rural low-altitude and remote high-altitude lakes

Historical records of total organic carbon (TOC), black carbon (BC), and polycyclic aromatic hydrocarbons (PAHs) were reconstructed in dated sediment cores from four nearby lakes in central Switzerland. In the sub-Alpine Lake Thun, located at 558 m a.s.l., the proximity to anthropogenic emission sources is reflected in higher input of BC and PAHs into sediments with fluxes only slightly decreasing during the last decades. PAH/BC ratios are relatively high and correlation between levels of total PAHs and BC is almost inexistent in Lake Thun, probably due to the presence of less condensed forms of the BC spectrum (char BC) that is underestimated with the chemothermal oxidation method applied in this study. The sediment profiles of TOC, BC, and PAHs are noticeably different in the mountain lakes located around 2000 m a.s.l. In Lake Engstlen, the PAH/BC ratios, as well as the correlation between PAHs and BC, point towards appreciable amounts of predominantly light soot particles. Light soot particles have higher mobility and can, therefore, be efficiently transported to this remote site. The proglacial Lake Oberaar is shown to be a receptor of BC and PAHs released by the fast melting adjacent glacier acting as a secondary source for these conservative species temporarily stored in the glacier ice. Finally, Lake Stein is in strong contrast to all other lakes. High flux of BC into Lake Stein, combined with constant temporal evolutions of BC and PAHs, and in particular BC/TOC ratios approaching 100% are all strong indications for a geogenic presence of graphite in its catchment area.