Mean Organic Carbon Research Articles

Both nutrients and macrophytes regulate organic carbon burial: Insights from high-resolution spatiotemporal records of a large shallow lake (Baiyangdian) in eastern China

Both ecological regime shifts and carbon cycling in lakes have been the subject of global debates in recent years. However, the direct linkage between them is poorly understood. Lake Baiyangdian, a representative large shallow lake with the coexistence of a macrophyte-dominated area (MDA) and an algae-dominated area (ADA) in eastern China, allowing better understanding of the relationship between regime shifts and organic carbon (OC) burial in lakes. On the basis of Bayesian isotopic mixing modelling of C/N ratios and δ13C values, the sediment OC is primarily of autochthonous origin. The mean OC burial rate (OCBR) was 39 g C m−2 yr−1 before eutrophication occurred in 1990 and increased approximately 2.7-fold to 106 g C m−2 yr−1 after eutrophication. Partial least squares path modelling revealed that this change can be largely attributed to enhanced primary productivity and rapid burial as a result of intensified human perturbation. In terms of spatial patterns, the OCBR was greater in the MDA than in the ADA, which may be related to the different burial and mineralization processes of debris from macrophytes and algae. It then deduced that a decrease in the OCBR and an increase in the mineralization rate might have occurred after a shift from a macrophyte-dominated state to an algae-dominated state. Our findings highlight that eutrophication generally increases OC burial by enhancing lake primary productivity. However, once nutrient levels reach a critical range, lake ecosystems may shift from a macrophyte-dominated state to an algae-dominated state, which can lead to a significant reduction in the carbon burial capacity of lakes. Therefore, more attention should be given to avoiding shifts in eutrophic lakes, as such shifts can alter carbon cycling.

Vegetation composition and organic carbon content along right-of-ways on Interstate Highway 35 in Bexar County, Texas

Roadside habitat through major urban areas may offer remnant examples of natural grasslands. These habitats may be subjected to frequent as mowing and exposure to automobile emissions and runoff. This study was conducted on interstate highway right-of-ways in San Antonio, Texas, U.S.A. We compared the vegetation species and diversity, and the organic carbon of leaf litter, plants, and soils. Two non-native grasses accounted for 50.9% cover, while all native forbs and grasses accounted for only 9.8% cover. The mean biomass of non-native grasses was 4.5 times greater than that of all native species. Organic carbon content of leaf litter, plants, and soils was variable among the study sites, possibly due to management practices and a drought that occurred during the study. The mean organic carbon content in the upper 20 cm soil was 5.0 kg·C/m2 and organic carbon content was greater in the upper 10 cm than organic carbon in the 10.1 to 20 cm portion. Cynodon dactylon and Bouteloua curtipendula exhibited the greatest photosynthesis efficiency indicating these grasses are more adaptable to hot summer temperatures found in Central Texas. The organic carbon content along a major interstate was 13793 kg·C/ha for leaf litter, vegetation, and the upper 20 cm of the soil. We conclude that interstate highways provide habitat for some native species, but the vegetation along right-of-ways is dominated by two non-native grasses. It appears unlikely that roadside habitat can be restored to resemble native grasslands without large scale and costly restoration efforts.

Carbon Reduction Associated with Sediment Reworking through Burrows of the Thalassinid Mud Shrimp Laomedia sp. (Crustacea: Laomediidae) from Korean Intertidal Sediments

This study evaluated the biotic and abiotic factors influencing the sediment reworking rate (SRR) of Laomedia sp. through in situ measurements and assessed the organic carbon reduction by comparing carbon concentrations between particles collected from the water column and reworked sediments. The SRR was significantly correlated with the duration of submergence at high elevation, whereas it showed a stronger correlation with mound height than with the duration of submergence at low elevation. The organic carbon content of suspended particles was reduced by 68% by the sediment reworking of Laomedia sp., with a mean organic carbon reduction of 0.01 gC ind.−1 d−1. This reduction resulted from particle selection by the inhabitant and by accumulation along the burrow walls. The estimated annual organic carbon reduction associated with the sediment reworking was 12.8 gC m−2 yr−1. The transport of organic carbon from the burrows into the water column was comparatively high relative to other species. These findings suggest that Laomedia sp. plays a significant role in enhancing the carbon cycle as an important bioturbator, with its burrows acting as carbon sinks by trapping organic carbon in intertidal sediments. Therefore, bioturbation by macroinvertebrates should be considered when evaluating carbon sequestration in intertidal sediments.

Effect of Different Multipurpose Tree Species on Physico-chemical Properties of Loamy Sand Soil Under Rainfed Conditions

A field experiment was conducted at Agroforestry Research Station, Sardarkrushinagar Dantiwada Agricultural University, Sardarkrushinagar, during 2019-20. The soils of the experimental field was low in organic carbon (0.24 per cent), available nitrogen (143.50 kg N/ha) and DTPA extractable iron (3.18 mg/kg), medium in available phosphorus (Olsen’s P 48.90 kg P2O5/ha), available potash (180.00 kg K2O/ha), manganese (7.8 mg/kg) and zinc (0.79 mg/kg) and high in copper content (0.61 mg/kg). An experiment consisting of six years old Agroforestry tree plantation which consisted of five multipurpose tree species (MPTs) viz., Tectona grandis, Eucalyptus camaldulensis, Gmelina arborea, Casuriana equstifolia and Melia azadiracht were designed in CRD with four replications. The experiment consisting of 96 trees per species with a plot size of 24 m × 16 m under 4 m × 4 m tree spacing. Among the above six tree species significantly the lowest BD (1.56 Mg/m3), higher WHC (27.87 per cent) and soil porosity (38.03 per cent) was recorded under Casuarinas equisetifolia tree species. Similarly the maximum mean organic carbon (0.445 per cent), available N (165.17 kg/ha), available K2O (196.26 kg/ha) and DTPA extractable iron (4.22 mg/kg) and copper (1.05 mg/kg) content were noted under Casuarina equisetifolia tree species. Whereas, the mean maximum available P2O5 (57.92 kg/ha) was noted under Tectona grandis. The mean maximum DTPA extractable manganese (8.34 mg/kg) and zinc (0.925 mg/kg) was noted under Eucalyptus camaldulensis and Melia azadiracht tree species, respectively.

Aggregate stability and carbon and N dymamics in macroaggregate size fractions with different soil texture

Soil nutrient cycling, the distribution of soil aggregates, and their stability are directly influenced by soil texture. Different sizes of soil aggregates provide microhabitats for microorganisms and therefore influence soil carbon (C) and nitrogen (N) mineralization. The purpose of the present study was to assess the aggregate stability and dynamics of carbon and nitrogen in macroaggregate size fractions (1-8 mm) with different clay content from meadow soils. Surface soil samples (0-15 cm) were collected from 4- to 5-year-old forage crops. Four macroaggregate size classes were isolated by dry sieving and analyzed for their mass proportions: fine macroaggregates (FM) (less than 1 mm), medium-fine macroaggregates (MFM) (1-2 mm), medium-coarse macroaggregates (MCM) (2-4 mm), and large-coarse macroaggregates (LCM) (4-8 mm). The dry mean weight diameter (MWD), organic carbon (OC), total nitrogen (TN), carbon and nitrogen of microbial biomass (C-MB, N-MB) were determined. CO2 emission and net nitrogen mineralized (NM) were measured after 14 weeks of incubation. The amounts of FM were significantly lower than those of intermediate macroaggregates (MCM and MFM) and decreased markedly with increasing clay content within soil macroaggregates. In general, the amounts of macroaggregate size fractions were lowest in soils with high clay content. MWD exhibited a significant correlation with particle size distribution, OC, and MB-C. OC, TN, MB-C, and MB-N contents within macroaggregates increased with decreasing macroaggregate size and increasing clay content of macroaggregate fractions. The CO2 emission and NM content increased with increasing macroaggregate size, indicating higher organic C and N mineralization activity in larger macroaggregates. Mineralization of OC was lowest in macroaggregate fractions with the highest clay content. We conclude that clay content can increase the protection of microbial biomass in meadow soils. Small macroaggregates tend to contain more recalcitrant organic matter compared to larger macroaggregates.

Heavy metals in surface sediments of Lake Patria wetland, southern Italy, and environmental risk

The study investigated the presence of heavy metals in the surface sediments of one of the most important wetlands in south Italy, Lake Patria, and the related environmental risk. Surface sediments were analyzed for particle size and shape, total organic carbon and As, Cd, Cr, Cu, Fe, Hg, Ni, Pb and Zn levels. Mean total organic carbon was high, 3.1 %, with a peak of 5.9 % near the input of freshwater channel whereas sediments appeared to be mainly composed of sand and/or gravel and significantly polluted by metals especially Cr, Cu and Zn. Data from heavy metals spatial distribution, Pearson correlation, principal component analysis and geochemical indices suggested dominant anthropogenic source for most metals. Mean Igeo values of Cr, Cu and Ni were in the range of 4.6–7.3 of strongly polluted class while their relative mean enrichment factors were largely exceeding the threshold of the anthropic pollution, 1.5. A very high pollution situation was also outlined when considering the Cf indices, with Cr, Cu and Ni possessing mean values from an order of magnitude of ten to hundred times higher the very high polluted class, 6 ≤ Cf. On the overall, the integrated indices of modified contamination degree, pollution load and ecological risk revealed a serious pollution scenario. The mean comprehensive ecological hazard index was fivefold the most critical limit, ≥600, in almost all the lagoon and especially in the locations close to channel.

Evaluating the Soil Quality Indicators in Various Yield Zones of Pulses in Tamil Nadu, India

Background: In recent years, there is growing demand for pulses in Tamil Nadu and the government has implemented various schemes and programmes to promote cultivation. However, the evaluation and categorization of soils for pulse production is crucial in determining the suitability of land for pulse cultivation and offer improvement through the adoption of improved crop management practices. Methods: A systematic soil quality assessment survey was taken up during 2020-2022 in the major pulse growing blocks of Virudhunagar district viz., Sattur, Aruppukottai and Thiruchuli based on past ten years yield data and it was classified into three categories viz., low yielding ( less than 400 kg ha-1), medium (400 to 700 kg ha-1) and high yielding ( greater than 700 kg ha-1) categories. Three hundred samples were collected from these zones. Results: The positive effects of soil physical, chemical, and biological qualities on the yield of pulse crops were justified through the yield data of the high yielding zone which ranged from 769 to 989 kg ha-1 with an average pulse yield of 880 kg ha-1. This may be attributed to more favourable soil physical environment in terms of soil texture (sandy clay loam), higher mean percentage of water stable aggregates (51%) and a favourable pH of 7.52. These parameters coupled with lower bulk density (1.23 Mgm-3), optimum infiltration rate (1.76 cm hr-1) and maximum mean organic carbon status (1.38 mg kg-1) contributed to higher range of soil cation exchange capacity (28.7 to 47.2 cmol p+ kg-1). In addition, the presence of avilable nitrogen and phosphorus, potassium, sulphur and availability of mean micronutrient contents viz., DTPA iron and DTPA zinc resulted in better quality of these soils contributing to maximum pulse productivity in this zone. Soil respiration rate with mean respiration rate of 4.48 mg CO2 kg-1 d-1 in high yield category compared to that of 2.34 mg CO2 kg-1 d-1 in low yield category, which is well correlated with better soil organic matter content in the former than the latter group of soil. Therefore, this study formulates a clear understanding of the variations in soil quality parameters for adopting efficient nutrient management practices towards obtaining maximum productivity of pulse crops.

Mean Particle Size, Organic Carbon, and Porewater Salinity Distribution of Surface Sediments Using a Dataset from the Hwangdo Tidal Flat, Taean, Western Korea

Mean Particle Size, Organic Carbon, and Porewater Salinity Distribution of Surface Sediments Using a Dataset from the Hwangdo Tidal Flat, Taean, Western Korea

A case-crossover study of ST-elevation myocardial infarction and organic carbon and source-specific PM2.5 concentrations in Monroe County, New York.

Previous work reported increased rates of cardiovascular hospitalizations associated with increased source-specific PM2.5 concentrations in New York State, despite decreased PM2.5 concentrations. We also found increased rates of ST elevation myocardial infarction (STEMI) associated with short-term increases in concentrations of ultrafine particles and other traffic-related pollutants in the 2014-2016 period, but not during 2017-2019 in Rochester. Changes in PM2.5 composition and sources resulting from air quality policies (e.g., Tier 3 light-duty vehicles) may explain the differences. Thus, this study aimed to estimate whether rates of STEMI were associated with organic carbon and source-specific PM2.5 concentrations. Using STEMI patients treated at the University of Rochester Medical Center, compositional and source-apportioned PM2.5 concentrations measured in Rochester, a time-stratified case-crossover design, and conditional logistic regression models, we estimated the rate of STEMI associated with increases in mean primary organic carbon (POC), secondary organic carbon (SOC), and source-specific PM2.5 concentrations on lag days 0, 0-3, and 0-6 during 2014-2019. The associations of an increased rate of STEMI with interquartile range (IQR) increases in spark-ignition emissions (GAS) and diesel (DIE) concentrations in the previous few days were not found from 2014 to 2019. However, IQR increases in GAS concentrations were associated with an increased rate of STEMI on the same day in the 2014-2016 period (Rate ratio [RR] = 1.69; 95% CI = 0.98, 2.94; 1.73 μg/m3). In addition, each IQR increase in mean SOC concentration in the previous 6 days was associated with an increased rate of STEMI, despite imprecision (RR = 1.14; 95% CI = 0.89, 1.45; 0.42 μg/m3). Increased SOC concentrations may be associated with increased rates of STEMI, while there seems to be a declining trend in adverse effects of GAS on triggering of STEMI. These changes could be attributed to changes in PM2.5 composition and sources following the Tier 3 vehicle introduction.

Unexpected high alkyl carbon contents in organic matter-rich sandy agricultural soils of Northwest Central Europe

Carbon sequestration in Plaggic Anthrosols is most often investigated by bulk soil carbon inventories, without considering the form in which the carbon is stored (e.g., particulate or mineral-associated organic matter (OM), its capacity, or its chemical composition). Here, we focus on the unusual high organic carbon (OC) accumulation in sandy Plaggic Anthrosols and adjacent reference soils under agricultural use. In these soils, the mineral fraction ≤20 µm which is commonly assumed to be the major factor for OC stabilization, are very low in mass proportion. Soil organic matter (SOM) physical fractionation was done to evaluate the quantity and quality of OC in the topsoil (Ap horizon). For the fraction ≤20 µm (medium and fine silt-, and clay-sized particles), we measured the concentration of OC and calculated its OC storage capacity and contribution. The OC of the fraction ≤20 µm was radiocarbon-dated and analyzed for its chemical composition by solid-state 13C NMR spectroscopy. The highly sandy (∼90 % sand and coarse silt) soils showed an accumulation of OC much higher than the conventionally calculated saturation level controlled by the proportion of the fraction ≤20 µm. Unexpectedly, Plaggic Anthrosols and the respective reference soils showed similar fractional OC concentrations, radiocarbon ages, and OM composition. The isolated fraction ≤20 µm contained, on average, 81 % of the total soil OC in only 9 % of the corresponding soil mass. All soil fractions ≤20 µm are characterized by a high mean OC concentration in the topsoil (reference soils: 226 ± 66.5 mg OC g−1, Plaggic Anthrosols: 202 ± 59.0 mg OC g−1) with a C/N ratio of 15 on average for both soils. The OM composition of the fraction ≤20 µm was specifically rich in alkyl-C, with unusually low proportions of O-alkyl-C and low contents of aryl-C. The radiocarbon concentration (F14C) indicated that topsoil OM of the ≤20 µm fraction is stored for long time periods with high mean conventional radiocarbon ages (14C) not only for Plaggic Anthrosols (F14C: 0.92 ± 0.04; 14C: 639 yBP) but also for the reference soils (F14C: 0.93 ± 0.04; 14C: 575 yBP) and received low inputs of OC derived from recent photosynthesis. Our data indicate the existence of specific SOM accumulation processes in the investigated sandy agricultural soils, resulting particularly large SOM stocks which cannot be explained by mechanistic association of OM with mineral surfaces. It is not clear, if this inherited OM is stable under present-day soil and management conditions.

Cover crops do not increase soil organic carbon stocks as much as has been claimed: What is the way forward?

When compared to virgin land (forest and grassland), croplands store significantly lower amounts of organic carbon (OC), mainly as a result of soil tillage, and decreased plant inputs to the soil over the whole year. Doubts have been expressed over how much reduced and zero tillage agriculture can increase OC in soils when the whole soil profile is considered. Consequently, cover-crops that are grown in-between crops instead of leaving soils bare appear as the "last man standing" in our quest to enhance cropland OC stocks. Despite the claim by numerous meta-analyses of a mean carbon sequestration rate by cover crops to be as high as 0.32 ± 0.08 ton C ha-1 year-1 , the present analysis showed that all of the 37 existing field studies worldwide only sampled to a depth of 30 cm or less and did not compare treatments on the basis of equivalent soil mass. Thirteen studies presented information on OC content only and not on OC stocks, had inappropriate controls (n = 14), had durations of 3 years or lower (n = 5), considered only one to two data points per treatment (n = 4), or used cover crops as cash crops (i.e., grown longer that in-between two crops) instead of catch crops (n = 2), which in all cases constitutes shortcomings. Of the remaining six trials, four showed non-significant trends, one study displayed a negative impact of cover crops, and one study displayed a positive impact, resulting in a mean OC storage of 0.03 ton ha-1 year-1 . Models and policies should urgently adapt to such new figure. Finally, more is to be done not only to improve the design of cover-crop studies for reaching sound conclusions but also to understand the underlying reasons of the low efficiency of cover crops for improved carbon sequestration into soils, with possible strategies being suggested.

An Improved Framework for Estimating Organic Carbon Content of Mangrove Soils Using loss-on-ignition and Coastal Environmental Setting

The use of loss on ignition (LOI) measurements of soil organic matter (SOM) to estimate soil organic carbon (OC) content is a decades-old practice. While there are limitations and uncertainties to this approach, it continues to be necessary for many coastal wetlands researchers and conservation practitioners without access to an elemental analyzer. Multiple measurement, reporting, and verification (MRV) standards recognize the need (and uncertainty) for using this method. However, no framework exists to explain the substantial differences among equations that relate SOM to OC; consequently, equation selection can be a haphazard process leading to widely divergent and inaccurate estimates. To address this lack of clarity, we used a dataset of 1,246 soil samples from 17 mangrove regions in North, Central, and South America, and calculated SOM to OC conversion equations for six unique types of coastal environmental setting. A framework is provided for understanding differences and selecting an equation based on a study region’s SOM content and whether mineral sediments are primarily terrigenous or carbonate in origin. This approach identifies the positive dependence of conversion equation slopes on regional mean SOM content and indicates a distinction between carbonate settings with mean (± 1 S.E.) OC:SOM of 0.47 (0.002) and terrigenous settings with mean OC:SOM of 0.32 (0.018). This framework, focusing on unique coastal environmental settings, is a reminder of the global variability in mangrove soil OC content and encourages continued investigation of broadscale factors that contribute to soil formation and change in blue carbon settings.

Trace element contamination in soils surrounding the open-cast coal mines of eastern Raniganj basin, India.

Trace element pollution of soils surrounding coal-mining areas affects the health of local communities. The increasing coal-mining and associated activities in the Raniganj basin (east India) have led to increased soil concentration of certain trace elements. To quantify the elevated trace element (TE) concentrations in the soil surrounding coal-mining areas, 83 surface soil, coal, and shale samples were collected from open-cast mining areas of the eastern Raniganj basin. The soils present are sandy silt, silty sand, and silty in nature, but almost no clay. They are acidic (pH = 4.3) to slightly alkaline (pH = 7.9) with a mean electrical conductivity (EC) of 340.45µS/cm and a mean total organic carbon (TOC) of 1.80%. The northern and western parts of the study area were found to be highly polluted by certain metallic trace elements. The relevant environmental indices, geoaccumulation index (Igeo), contamination factors (CF), enrichment factors (EF), and pollution load index (PLI) were calculated and assessed. Analysis revealed that Cr was highly enriched in these soil samples, followed by Pb, Co, Cu, Cd, Fe, Ni, Mn, Zn, As, and Al. Geostatistical analyses (correlation coefficients and principal component analysis) indicated that the occurrence of some trace elements (Al, Cd, Co, Cu, Fe, Mn, Ni, and Zn) is most likely linked to the various coal-mining operations in the study area. However, the anomalous Cr and Pb distributions are likely influenced by other anthropogenic, mainly industrial, inputs besides coal mining. These results justify the adoption of rigorous soil monitoring programs in the vicinity of coal-mining areas, to identify pollution hotspots and to develop strategies to reduce or mitigate such environmentally damaging pollution.

Spatial Distribution of Soil Nutrient Status of Biswanath District, Assam, North East India

Rice-based cropping system is a key for food security in Assam. However, the productivity of such systems has declined continuously due to deterioration in soil fertility owing mainly to faulty agricultural practices. The study was carried out to study the nutrient status of soils of the Biswanath district of Assam in the year 2021. A total of 200 no of geo-reference surface (up to 30 cm) soil samples were collected. The coefficient of variation (CV) was used for the interpretation of the variability of the indicators. Available phosphorous, available potassium DTPA-iron, DTPA-manganese, DTPA-zinc, and DTPA-copper were identified to be the most variable soil indicators (CV > 35%). Electrical conductivity, organic carbon, available nitrogen, and cation exchange capacity, were found as the moderately variable parameters (CV 15–35%). The least variation (CV < 15) was found pH. The mean pH, electrical conductivity and organic carbon were 5.23, 0.54 ds/m, and 0.81 percent respectively. The cation exchange capacity of the soil varied from 4.40 to 11.60 cmol(p+)/kg with the mean value of 6.74cmol(p+) /kg. The available nitrogen, available potassium and available phosphorus were 380.01kg /ha, 169.00 kg/ha and 38.01 kg/ha. The district's respective DTPA-Fe, DTPA-Cu, DTPA-Mn, and DTPA-Zn levels were found to be 83.34 mg/kg, 2.59 mg/kg, 22.25 mg/kg, and 0.79 mg/kg. The spatial distribution of each parameter was presented on the GIS platform for easy availability through IDW method of interpolation.

Towards an improved representation of carbonaceous aerosols over the Indian monsoon region in a regional climate model: RegCM

Abstract. Mitigation of carbonaceous aerosol emissions is expected to provide climate and health co-benefits. The accurate representation of carbonaceous aerosols in climate models is critical for reducing uncertainties in their climate feedback. In this regard, emission fluxes and aerosol life cycle processes are the two primary sources of uncertainties. Here, we demonstrate that the incorporation of a dynamic ageing scheme and emission estimates that are updated for the local sources improves the representation of carbonaceous aerosols over the Indian monsoon region in a regional climate model, RegCM, compared with its default configuration. The respective mean black carbon (BC) and organic carbon (OC) surface concentrations in 2010 are estimated to be 4.25 and 10.35 µg m−3 over the Indo-Gangetic Plain (IGP) in the augmented model. The BC column burden over the polluted IGP is found to be 2.47 mg m−2, 69.95 % higher than in the default model configuration and much closer to available observations. The anthropogenic aerosol optical depth (AOD) increases by more than 19 % over the IGP due to the model enhancement, also leading to a better agreement with observed AOD. The respective top-of-the-atmosphere, surface, and atmospheric anthropogenic aerosol short-wave radiative forcing are estimated at −0.3, −9.3, and 9.0 W m−2 over the IGP and −0.89, −5.33, and 4.44 W m−2 over Peninsular India (PI). Our results suggest that the combined effect of two modifications leads to maximum improvements in the model performance in regions where emissions play a dominant role.

Temporal variation and source identification of carbonaceous aerosols in Monrovia, Liberia

This study examined the atmospheric Black Carbon (BC) and Organic Carbon (OC) data for two years from January 2019 to December 2020 in Monrovia, Liberia. This study is the first of its kind in Monrovia, Liberia and the Mano River Union region. The objective is to evaluate the temporal variation in BC and OC over Monrovia and locate the probable local and regional source locations contributing to BC and OC therein. We also presented here the relationship of BC and OC with meteorological parameters. The highest BC (∼1.4 µg m−3) and OC (∼14 µg m−3) concentrations were observed in January 2019 and 2020. A clear seasonal effect was found in both years, with high mean BC (∼4.9 µg m−3) and OC (∼10 µg m−3) during the dry season (November to April). Diurnal variation suggested high BC and OC during 5:00–7:00 AM, 12 noon, 2:00 PM, and 4:00–7:00 PM. Long-range transportation and local emission sources were studied using Conditional Bivariate Probability Function (CBPF), and Concentration Weighted Trajectory (CWT). CBPF indicated that higher BC and OC concentrations were experienced when the wind was blowing from the South (at >2 ms−1) and North-West (1–2 ms−1) where a lot of shipping activities are carried out. CWT for BC showed that the air mass passes over Senegal through Guinea Bissau via the Atlantic Ocean while for OC, on the Atlantic Ocean and Freeport of Monrovia, indicating shipping emissions as probable sources. The results of this study can help policymakers devise appropriate strategies to control the BC and OC emissions over Monrovia, Liberia.

Tracking sources of PM10 emissions and deposition in the industrial city of Ostrava, Czech Republic: A carbonaceous δ13C-based approach

The sources of airborne particulate matter (PM10) emissions in Ostrava, Czech Republic, were investigated. Emphasis was placed on their organic carbon (OC) and elemental carbon (EC) contents, and their carbon stable isotope composition, δ13C. Emission sources were identified using OC-δ13C and concentration values. To track the extent of long-term deposition, these sources were also identified using the black carbon (BC) δ13C values of soil samples. At all sampling sites, wind flow is predominantly (65–80%) bidirectional in either SW-NE or NE-SW trajectories. Source apportionment along these dominant airflow trajectories was calculated from an isotopic 13C mass balance, and according to differences in the OC content and δ13C values of PM10. Determined emission sources are: (i) combustion of Silesian hard coal (δ13C = −24.5‰); (ii) local Ostrava coal combustion (δ13C = −25.5 to −26‰), automotive emissions (δ13C = −26.5‰), and biogenic particles (δ13C = −28 to −28.5‰). Winter emissions (mean OC concentrations from 12 to 25 μg m−3) originated mostly from coal combustion (80%) in domestic and industrial point sources. Differences were ascribed to automotive emissions. Ostrava is located near the Czech-Polish border, transboundary emissions are transported under a southbound wind flow that transported from 40 to 80% of the collected PM10. Summer emissions were lower (mean OC concentration from 6 to 8 μg m−3). Automotive emissions accounted for up to 40%, whilst biogenic production accounted for 60%. Absence of 13C isotope data of secondary OC (SOC 1.2–1.5 μg m−3) increases uncertainty in our source apportionment in summer; when SOC could comprise >20% of total OC. Contribution of SOC to the winter-measured OC is much lower (5–10%), and has no significant effect on mass balances. The upper soil layer analyses revealed long-term deposition of the same emissions sources. We conclude that the stable δ13C isotope values of OC and EC are useful for discriminating against local sources of PM10 pollution in relatively small urban areas, containing discrete polluting sources. Such a simplified approach can be easily standardized and implemented to manage regulatory compliances in the increasingly commoditized carbon offset market.

Impact of topsoil mining for unfired mudbricks on soil quality in eastern KwaZulu‐Natal, South Africa

AbstractTopsoil mining associated with informal mud brick making is common in rural villages of South Africa. The impact of topsoil mining on soil quality, however has not been investigated. This study therefore assessed the impact of topsoil mining associated with unfired mud bricks on selected soil quality indicators in two villages of KwaZulu‐Natal, South Africa. First, local miners were interviewed to ascertain information related to topsoil mining, brickfield site identification and soil suitability for mud bricks. Two brickfields per village mined for ≤5 and > 20 years, respectively were used in this study. Experiment consisted of three treatments, that is, unmined, mined and recovering lands replicated three times. Nine soil samples were collected (0–10 cm) from each site (three composite samples per treatment) with corresponding bulk density samples taken at 0–5 cm using core rings. The average topsoil mining depth was 30 cm. Interviews revealed that isidaka (poorly drained sandy clay) and isibomvu (red soil) are preferred over ubumba (clayey) soils. Topsoil mining increased silt fraction across all studied brickfields with an average of 45.2% in mined compared with 30.6% in unmined treatments. The response of clay fractions was variable across villages and mining time. Mining significantly decreased mean weight diameter, exchangeable bases, organic carbon, and nitrogen content and stocks and porosity while it increased bulk density. Results show that topsoil mining for mud brick making results in poor soil physical quality, nutrient availability and carbon storage with implications for land degradation in mud brickfields.

Carbonaceous aerosol transport from the Indo-Gangetic Plain to the Himalayas: Carbon isotope evidence and light absorption characteristics

The Indo-Gangetic Plain (IGP) is a major regional and global emitter of atmospheric pollutants, which adversely affect surrounding areas such as the Himalayas. We present a comprehensive dataset on carbonaceous aerosol (CA) composition, radiocarbon (Δ14C) -based source apportionment, and light absorption of total suspended particle (TSP) samples collected over a 3-year period from high-altitude Jomsom in the central Himalayas. The 3-year mean TSP, organic carbon (OC), and elemental carbon (EC) concentrations were 92.0 ± 28.6, 9.74 ± 6.31, and 2.02 ± 1.35 μg m−3, respectively, with the highest concentrations observed during the pre-monsoon season, followed by the post-monsoon, winter, and monsoon seasons. The Δ14C analysis revealed that the contribution of fossil fuel combustion (ffossil) to EC was 47.9% ± 11.5%, which is consistent with observations in urban and remote regions in South Asia and attests that EC likely arrives in Jomsom from upwind IGP sources via long-range transport. In addition, the lowest ffossil (38.7% ± 13.3%) was observed in winter, indicating large contributions in this season from local biomass burning. The mass absorption cross-section of EC (MACEC: 8.27 ± 1.76 m2/g) and water-soluble organic carbon (MACWSOC: 0.98 ± 0.45 m2/g) were slightly higher and lower than those reported in urban regions, respectively, indicating that CA undergo an aging process. Organic aerosol coating during transport and variation of biomass burning probably led to the seasonal variation in MAC of two components. Overall, WSOC contributed considerably to the light absorption (11.1% ± 4.23%) of EC. The findings suggest that to protect glaciers of the Himalayas from pollution-related melting, it is essential to mitigate emissions from the IGP.

Response of leaf stoichiometry of Potentilla anserina to elevation in China's Qilian Mountains.

Plants adapt to changes in elevation by regulating their leaf ecological stoichiometry. Potentilla anserina L. that grows rapidly under poor or even bare soil conditions has become an important ground cover plant for ecological restoration. However, its leaf ecological stoichiometry has been given little attention, resulting in an insufficient understanding of its environmental adaptability and growth strategies. The objective of this study was to compare the leaf stoichiometry of P. anserina at different elevations (2,400, 2,600, 2,800, 3,000, 3,200, 3,500, and 3,800 m) in the middle eastern part of Qilian Mountains. With an increase in elevation, leaf carbon concentration [(C)leaf] significantly decreased, with the maximum value of 446.04 g·kg−1 (2,400 m) and the minimum value of 396.78 g·kg−1 (3,500 m). Leaf nitrogen concentration [(N)leaf] also increased with an increase in elevation, and its maximum and minimum values were 37.57 g·kg−1 (3,500 m) and 23.71 g·kg−1 (2,800 m), respectively. Leaf phosphorus concentration [(P)leaf] was the highest (2.79 g·kg−1) at 2,400 m and the lowest (0.91 g·kg−1) at 2,800 m. The [C]leaf/[N]leaf decreased with an increase in elevation, while [N]leaf/[P]leaf showed an opposite trend. The mean annual temperature, mean annual precipitation, soil pH, organic carbon, nitrogen, and phosphorus at different elevations mainly affected [C]leaf, [N]leaf, and [P]leaf. The growth of P. anserina in the study area was mainly limited by P, and this limitation was stronger with increased elevation. Progressively reducing P loss at high elevation is of great significance to the survival of P. anserina in this specific region.