OC Content Research Articles

Effects of land use change on organic carbon dynamics associated with soil aggregate fractions on the Loess Plateau, China

AbstractOrganic carbon (OC) sequestration through soil aggregation is an important aspect of land use change/conversion (LUCC) influencing the terrestrial ecosystem C cycle, although little is known on the changes in aggregate dynamics and their contributions to OC accumulation after LUCC in regions with serious soil erosion. Therefore, bulk soil samples under four land uses (farmland and three vegetated soils converted from farmland 42 years ago: Robinia pseudoacacia [RP42yr], Caragana korshinskii [CK42yr], and abandoned land [AL42yr]) in the Loess Plateau, China, was collected, separated into seven aggregate size fractions, and examined for OC content. Farmland conversion into AL42yr, CK42yr, and RP42yr increased macroaggregate (>2 mm) and mesoaggregate (2–0.25 mm) proportions, mean weight diameter, and geometric mean diameter but decreased microaggregates (0.25–0.053 mm) amount. Bulk soil and aggregates OC content and stock varied with soil depth and land use types but were usually highest in RP42yr. Mesoaggregates contained higher OC content and stock than other aggregates at 0‐ to 20‐cm depth under all land uses. Increases in the OC stocks of mesoaggregates accounted for 46% and 85% of the increase in bulk soil OC stocks at 0‐ to 20‐ and 20‐ to 40‐cm depth, respectively. Thus, soil OC accumulation after LUCC is mainly due to increased OC stock within mesoaggregates, which is further attributed to increased mesoaggregate proportions. Overall, vegetation restoration promotes the physical protection of OC by increasing soil aggregation, being a management option to enhance the C sequestration potential in ecological fragile regions.

Effect of tannery sludge amendments on the activity of soil enzymes and phytoremediation potential of two economically important cultivars of geranium (Pelargonium graveolens)

ABSTRACTA field experiment was conducted to observe the effect of TS amendments on soil enzymes and phytoremediation potential of two economically important cultivars of geranium. Different doses of TS were applied in soil to examine threshold limit of HMs where geranium cultivars can be grown successfully in contaminated sites. Treatment variation significantly affected pH, EC, OC, N, P, K and HM content in soil after 50 days of incubation. After harvest, both cultivars were examined to assess the impact of various treatments on their fresh herb, dry matter, essential oil yield and HM accumulation. C/G ratio close to 1 was observed at 50 tha−1 sludge treatment in both cultivars. Urease and β-glucosidase activities in soil were maximum at 50 tha−1 whereas dehydrogenase and phosphatase activities were maximum at 100 tha−1 in both cultivars. β-glucosidase, acid and alkaline phosphatase, urease and dehydrogenase activities were relatively high after 85 days over 45 days in both cultivars. Maximum metal uptake was found in roots of cv. Bourbon followed by leaves. Geranium was observed to be a good candidate for phytoremediation as it mitigates metal toxicity by root absorption and cv. Bourbon is better candidate for the same.

Fine Particulate Matter Source Profile of Typical Industries in Sichuan Province

An electrical low pressure impactor particle monitor was used to monitor typical industries in Sichuan Province, such as cement, glass, ceramic, brick-tile, coal-fired boiler, biomass boiler, power plant, and steel industry. Fine particulate matter source profiles of each industry were developed based on the laboratory analysis. The results showed that Si, Ca, and Mg were the major elements of building industry particulate matter emission. Sulfate emission from double sodium-calcium was higher than from other desulfurization technologies in the building industry. The main chemical components of PM2.5 from power plants were SO42-, Ca2+, NH4+, Mg, and Si, while OC, Al, Si, and Ca were the main chemical components of PM2.5 from coal-fired boilers. The content of OC was the most abundant in biomass briquette boiler particulate matter emissions, followed by K and EC. In term of the biomass fuel boiler PM2.5 source profile, OC, EC, and Cl- were the major chemical components. Ca was the largest component of PM2.5 from the steel industry, accounting for 18.11% of the total PM2.5 emission, followed by SO42-, Na+, and Fe.

The Types and The Amounts of Organic Matter Influence Carbon Dioxide Production in The Reclaimed-Mine Tropical Soils

The rate of carbon (C) mineralization plays an important role in environmental system as it determines the amount of carbon dioxide emit to the atmosphere and the amount of organic carbon stabilized by soil minerals. Therefore, assessing the influence of organic matter (OM) types on the C mineralization is essential to understanding mechanisms to reduce carbon dioxide production and to improve SOC contents in the reclaimed-mine tropical soils. In this study, four different types of OM (albizia, acacia, calopo and mixed-albizia-acacia-calopo) with 4 different rates: 0, 0.5, 1.0 and 1.5 of maximum capacity of soils to adsorb OM (Qmax) were added to a 3-years reclaimed-mine soil, and the C mineralization of added OM was quantified over a 90-day of incubation period. Results of the study revealed that the addition of albizia resulted in the C mineralization of 45.2% added OM, while the C mineralization of 58.1% added OM was observed when calopo was applied to the soil. Differences in the C mineralization with different types of OM was related to differences in the chemical composition of added OM. Addition of albizia at the rate of 0.5 Qmax produced the C mineralization of 38.7% added OM, while only 50.2% and 46.6% of added OM was mineralized when albizia was added to soils at rates of 1.0 and 1.5 Qmax, respectively. This study showed that the chemical composition of OM originated from vegetation may also be considered in the selection of vegetation types for mined-land reclamation in order to reduce carbon dioxide production and to increase the OC contents of the reclaimed-mine tropical soils.

Size Distribution and Carbon Component Characteristics of Atmospheric Particulate Matter from Motor Vehicles

Characterization of the size distribution and carbon components in particulates has become important for identifying the particulates in the atmosphere. The size distribution and carbon components of atmospheric particulate matter from motor vehicles in different regions were analyzed by using Micro-orifice uniform deposition impactors (MOUDI) and the organic carbon/elemental carbon (OC/EC) analyzer. With increasing particle size, the mass concentration of raw diesel/gasoline decreases. The highest mass concentration of particles collected near the chimney of an engine laboratory was observed for particle sizes ranging from 0.32-0.56 μm, while particles with sizes from 1.0-1.8 μm in the basement garage showed the most mass fractions. The OC1, OC2, and OC3 were the major parts of the OC contents in raw diesel particles. The EC2 was the main part of EC. The atmospheric particles collected in typical regions contained more OC3 and OC4. EC1 was the main part of EC in particles collected from the basement garage. The OC/EC ratios of raw diesel particles ranged from 0.92 to 2.50. The OC/EC ratios of particles collected near the chimney of an engine laboratory ranged from 1.40 to 2.53 and that of particles collected in the basement garage ranged from 2.36 to 4.82. Moreover, the OC/EC ratios in particles collected in the basement garage normally exceeded 2.0 and reached 4.82 at the largest size, which implies that many secondary particles were generated in the basement garage. The above-mentioned characteristics provide references that are beneficial for the identification of particulates in the atmosphere originating from motor vehicles.

Effect of crop rotation, fertilisation and tillage on main soil properties and its water extractable organic matter

The excessive use of fertilisers and frequent and deep tillage are not considered good agricultural practices because they increase production costs and reduce soil fertility. Water extractable organic matter (WEOM) is the fraction of soil organic matter responsible for nutrient transport and bioavailability. The aim of this work was to investigate the effect of a 2-year rotation of faba bean–wheat, cultivated for a decade, and the agricultural practices (conventional vs no tillage, and fertilisation vs no fertilisation) on selected soil parameters and WEOM quality. Results showed that the soil organic carbon (SOC) and the total nitrogen (TN) content increased after the wheat and faba bean, respectively. Plots managed with conventional tillage showed WEOM with higher OC content with respect to no-tillage plots. A higher WEOM OC content was observed also in the fertilised plots. The WEOM of fertilised and faba bean plots was derived from decomposition of native SOC, but the microbial community decomposition was the main origin of WEOM after wheat.

Concentrations of aliphatic and polycyclic aromatic hydrocarbons in ambient PM2.5 and PM10 particulates in Doha, Qatar

ABSTRACTOrganic carbon (OC), elemental carbon (EC), and 90 organic compounds (36 polycyclic aromatic hydrocarbons [PAHs], 25 n-alkane homologues, 17 hopanes, and 12 steranes) were concurrently quantified in atmospheric particulate matter of PM2.5 and PM10. The 24-hr PM samples were collected using Harvard Impactors at a suburban site in Doha, Qatar, from May to December 2015. The mass concentrations (mean ± standard deviation) of PM2.5 and PM10 were 40 ± 15 and 145 ± 70 µg m−3, respectively, exceeding the World Health Organization (WHO) air quality guidelines. Coarse particles comprised 70% of PM10. Total carbonaceous contents accounted for 14% of PM2.5 and 10% of PM10 particulate mass. The major fraction (90%) of EC was associated with the PM2.5. In contrast, 70% of OC content was found in the PM2.5–10 fraction. The secondary OC accounted for 60–68% of the total OC in both PM fractions, indicating photochemical conversions of organics are much active in the area due to higher air temperatures and solar radiations. Among the studied compounds, n-alkanes were the most abundant group, followed by PAHs, hopanes, and steranes. n-Alkanes from C25 to C35 prevailed with a predominance of odd carbon numbered congeners (C27–C31). High-molecular-weight PAHs (5–6 rings) also prevailed, within their class, with benzo[b + j]fluoranthene (Bb + jF) being the dominant member. PAHs were mainly (80%) associated with the PM2.5 fraction. Local vehicular and fugitive emissions were predominant during low-speed southeasterly winds from urban areas, while remote petrogenic/biogenic emissions were particularly significant under prevailing northwesterly wind conditions.Implications: An unprecedented study in Qatar established concentration profiles of EC, OC, and 90 organic compounds in PM2.5 and PM10. Multiple tracer organic compounds for each source can be used for convincing source apportionment. Particle concentrations exceeded WHO air quality guidelines for 82–96% of the time, revealing a severe problem of atmospheric PM in Doha. Dominance of EC and PAHs in fine particles signifies contributions from combustion sources. Dependence of pollutants concentrations on wind speed and direction suggests their significant temporal and spatial variability, indicating opportunities for improving the air quality by identifying sources of airborne contaminants.

Optimization of spray-drying process for concentrated orange juice

Response surface methodology was used to optimize spray-drying process for concentrated orange juice. Independent variables were: inlet air temperature (130–170 ºC) and maltodextrin 12DE content (60–75% wet basis (wb)). Responses variables were powder yield, moisture, and ascorbic acid retention. Moisture content was negatively affected by inlet air temperature, while ascorbic acid retention was directly related. Powder yield and ascorbic acid retention increased with the rise in maltodextrin content, while moisture content was negatively affected by maltodextrin content. Multiple response optimisation indicated that an inlet air temperature of 155 ºC and maltodextrin content of 74% wb were predicted to provide 77% powder yield, 3.7% wb moisture content, and 89% ascorbic acid retention.

Enhancing organic and inorganic carbon sequestration in calcareous soil by the combination of wheat straw and wood ash and/or lime.

Increasing organic carbon sequestration in agricultural soils is important for improving soil fertility and mitigating climate change. Wood ash is generally applied as a potassium fertilizer, but the effects of simultaneous incorporation of wood ash and crop straw on the turnover of soil organic carbon (SOC) and inorganic carbon (SIC) are not well understood. In this study, a 118-day lab incubation experiment was conducted using a calcareous soil (with 10 years of continuous maize cropping history) to study the effects of adding wheat straw, wood ash and lime. Our study showed that straw addition led to an increase in both SOC (19%) and SIC (3%). Wood ash and lime addition decreased CO2 emission by 182 and 1210 mg kg-1 and increased SIC by 125 and 1001 mg kg-1 during the incubation, respectively, which was due to supply of CaO from wood ash and lime. The increase of SOC content was 2.4% due to the addition of lime. In addition to straw addition enhanced straw-derived OC content, the addition of lime also increased straw-derived OC content by 34.5%. This study demonstrated that lime was more effective in reducing CO2 emission and and enhancing SOC than wood ash. In conclusion, adding lime to calcareous soil might be an effective method of enhancing carbon sequestration and slowing climate change.

Protection of extractable lipid and lignin: Differences in undisturbed and cultivated soils detected by molecular markers

Understanding formation of organo-mineral association is crucial for soil organic matter (SOM) stabilization. To remove reactive minerals from un-disturbed natural soil (NS) and two cultivated soils (dry-farming soil, TD, and terrace paddy soil, TP), a 10% HF/1M HCl treatment was applied. The mineral protection of different molecular SOM structures before and after cultivation was compared by using markers for lipid and lignin. The removal of reactive mineral increased the lipid extractability in TD and NS similarly, indicating that the cultivation did not reduce the mineral protection; this is attributable to fertilizer application and amorphous Fe oxide enrichment. In TP, the extent of lipid protection was lower than in TD, demonstrating that the protection depends on the type of cultivation. In contrast to lipids, lignin-derived phenols decreased over 80% after acid treatment. Furthermore, the ratios of acid to aldehyde in vanillyl ((Ad/Al)V) of TD and TP were much higher than in NS, indicating an increased oxidation of lignin in cultivated soils. During acid treatment, two distinct layers of soil particles were identified: an organic matter (OM)-enriched layer (LOM), and a non-reactive mineral-enriched layer (LNR) with hardly detectable OC content. However, up to 50% of lipids were detected in LNR, indicating that lipids did not selectively interact with reactive mineral particles. In TD and TP, (Ad/Al)V values were higher in LOM than in LNR, indicating a strong interaction of oxidized lignin in LOM. Therefore, the protection of lignin, especially highly oxidized lignin, can depend more on reactive minerals than lipid. Promoting the formation of organo-mineral complexes is the primary strategy for soil management, especially for highly oxidized OM.

High variability in iron-bound organic carbon among five boreal lake sediments

Being both stable carbon sinks and greenhouse gas sources, boreal lake sediments represent significant players in carbon (C) cycling. The release of dissolved organic carbon (DOC) into anoxic water is a widespread phenomenon in boreal lakes with impact on sediment C budgets. The association of OC with iron (Fe) is assumed to play an important role for this anoxic OC release via the dissimilatory reduction of Fe, but also to influence the stabilization of OC in sediments. To investigate the role of Fe–OC association for OC dynamics in different boreal lake sediments, we compared the content of Fe-bound OC [Fe–OC, defined as citrate bicarbonate dithionite (CBD) extractable OC] and the extent of reductive dissolution of solid-phase Fe and OC at anoxia. We found high among-lake variability in Fe–OC content, and while the amount of Fe–OC was high in three of the lakes (980–1920 µmol g−1), the overall contribution of Fe–OC to the sediment OC pool in all study lakes was not higher than 11%. No linkages between the amount of the Fe–OC pool and lake or sediment characteristics (e.g., pH, DOC concentration, sediment OC content, C:N ratio) could be identified. The observed release of OC from anoxic sediment may be derived from dissolution of Fe–OC in the lake sediments with high Fe–OC, but in other lake sediments, OC release during anoxia exceeded the sediment Fe–OC pool, indicating low contribution of reductive Fe dissolution to OC release from these lake sediments. The range of the investigated boreal lakes reflects the high variability in the size of the sediment Fe–OC pool (0–1920 µmol g−1) and CBD-extractable Fe (123–4050 µmol g−1), which was not mirrored in the extent of reductive dissolution of Fe (18.9–84.6 µmol g−1) and OC (1080–1700 µmol g−1) during anoxia, suggesting that Fe-bound OC may play a minor role for sediment OC release in boreal lakes. However, studies of redox-related OC cycling in boreal lake sediments should consider that the amount of Fe–OC can be high in some lakes.

Grass cultivation alters soil organic carbon fractions in a subtropical orchard of southern China

Understory management is evidently important for improving the ecological and economic effects of orchards, and grass maintenance in orchards is a potentially preferable floor management measure relative to clean tillage. It is widely accepted that grass maintenance increases soil organic carbon (SOC) content, but whether different SOC fractions respond consistently is less understood. To clarify the potential effects of grass maintenance on SOC fractions, three grass species, including a leguminous species (Stylosanthes guianensis cv. Reyan) and two gramineous species (Paspalum notatum Alain ex Flugge. and Pennisetum americanum x P. purpureum), were planted under young Litchi trees in a subtropical orchard of southern China for eight months using clean tillage as a control. The labile and non-labile SOC fractions and microbial C mineralization were investigated. Relative to the control, grass cultivation significantly increased or trended to increase the SOC content and this was mainly due to increases in the labile SOC fractions. The increased C lability and substrate supply support higher soil microbial biomass C, consequently accelerating the soil C mineralization process and resulting in a greater biologically mineralizable C pool. However, grass cultivation significantly decreased the non-readily oxidizable OC content, although it was relatively more chemically recalcitrant. Our results suggest that grass cultivation may favorably accelerate nutrient cycling in orchards due to higher labile C substrate availability and soil microbial biomass and activity. Nevertheless, grass cultivation could decrease SOC stabilization as indicated by the increased SOC lability in the grass-planting systems.

Deconvolving the Fate of Carbon in Coastal Sediments

AbstractCoastal oceans play a crucial role in the global carbon cycle, and are increasingly affected by anthropogenic forcing. Understanding carbon cycling in coastal environments is hindered by convoluted sources and myriad processes that vary over a range of spatial and temporal scales. In this study, we deconvolve the complex mosaic of organic carbon manifested in Chinese Marginal Sea (CMS) sediments using a novel numerical clustering algorithm based on 14C and total OC content. Results reveal five regions that encompass geographically distinct depositional settings. Complementary statistical analyses reveal contrasting region‐dependent controls on carbon dynamics and composition. Overall, clustering is shown to be highly effective in demarcating areas of distinct organic facies by disentangling intertwined organic geochemical patterns resulting from superimposed effects of OC provenance, reworking and deposition on a shelf region exhibiting pronounced spatial heterogeneity. This information will aid in constraining region‐specific budgets of carbon burial and carbon cycle processes.

English

Rate of mineralization for organic nutrient sources (ONS) depends on temperature, soil moisture, soil chemical, physical, biological properties as well as the chemical composition of the ONS. Erythrina abyssinica (EA), Erythrina brucei (EB) and Ensete ventricosum (EV) (ONS) were collected from Sidama and Wolaita, southern Ethiopia. Soil samples (0-20 cm) depths were collected from Cambisols and Luvisols areas. Physicochemical properties of the two soils were analyzed following standard analytical methods. For the greenhouse mineralization pot experiment, 21 treatments for each week were designed for EA, EB and EV in Luvisols and Cambisols. The treatments were arranged in a completely randomized design (CRD) with three replications. The incubation was carried out in green house for five consecutive weeks, the average TN contents of EA, EB and EV were 4.05, 3.35 and 2.56%, respectively. The pots were watered to field capacity every day or two. Each week, determination of OC and TN contents were conducted. The results of mineralization revealed that the TN concentration was highest in the first week and became low and constant at the third to fifth week. The same trend was followed by OC constant declining in both soil types. There was a reduction of C/N ratio in both soil types. The ONS had medium to high TN content and they decompose easily. Thus, the study reveals that these ONS can be used as alternative or supportive fast decomposing organic sources of fertilizers. Key words: C/N ratio, incubation, total nitrogen, organic carbon, organic nutrient sources.

Chemical Composition Characteristics of PM2.5 Emitted by Medium and Small Capacity Coal-fired Boilers in the Yangtze River Delta Region

Seven small and medium coal-fired boilers were selected to analyze the emission factors and chemical composition characteristics of PM2.5, and the efficiency of the dust collection unit in removing PM2.5, OC, and EC of different particle sizes. At the outlet of the dust collection unit, PM2.5 mass emission factor was around 0.047-0.283 g·kg-1 with an average of (0.146±0.081) g·kg-1. SO42- was the most abundant ionic component, followed by NH4+ and Ca2+. S was the most abundant among all the elements, followed by Al, Ca, and Fe. The contents of OC and EC fluctuated greatly, and the ratio of OC and EC produced by each boiler was greater than one. In the range of the measured particle sizes, the mass concentration of PM2.5 showed a singlet or bimodal distribution, and the peak value appeared at 0.07-0.12 μm and greater than 1 μm in bimodal distribution. The mass concentration of OC showed a bimodal or trimodal distribution, and the peak value appeared at 0.04 μm, 0.20-0.31 μm, and greater than 1 μm in trimodal distribution. The efficiencies of the dust collection unit in removing PM2.5, OC, and EC were 66%, 53%, and 23%, respectively.

Carbon sequestration in macroalgal mats of brackish-water habitats in Indian Sunderbans: Potential as renewable organic resource

Large influx of excess nutrients into sub-tropical brackish-water habitats is expected to radically affect the algal populations in the heavily populated Sunderbans brackish-water ecozone. Twelve selected brackish-water sites in the Indian Sunderbans were surveyed to investigate the growth performance of mat-forming dominant algal/cyanobacterial macrophytes and their potential for carbon (C) sequestration into hydrologic and pedologic pools. The mats were dominated by particular taxa at different seasons related to physico-chemical properties of the wetland habitats. Different environmental variables and biomass productivity parameters were measured on fortnightly basis to assess the carbon cycle related to dominant algal blooms of the study area. The dominating species at the twelve sites included seven genera (Spirogyra, Rhizoclonium, Ulva, Cladophora, Pithophora, Chaetomorpha) belonging to Chlorophyta, three genera (Polysiphonia, Gracilaria, Catenella) belonging to Rhodophyta and Lyngbya majuscula from cyanobacteria. Multivariate statistical methods indicated that nutrient availability, particularly dissolved P concentration and N:P ratio in the water column, along with salinity in the water column mainly affected biomass yield and C sequestration of mat-forming macrophytes and OC input into water column. However, OC contents of underlying muck proved to be very stable, though small influxes of OC occurred at each bloom. High biomass yields (34–3107 g/m2) of the dominant mat components accumulated enormous stocks of OC, very little of which reaches the pedologic pool. This transient biomass might be utilized as dietary supplements or biofuel feedstocks. Availability of important dietary fatty acids in Spirogyra punctulata, Gracilaria sp., Polysiphonia mollis, Rhizoclonium riparium, R. tortuosum, Pithophora oedogonia and Ulva lactuca was considered as suitability of these species as nutraceuticals. Fatty acid compositions of L. majuscula, Catenella repens, R. tortuosum and Cladophora crystallina were estimated to be applicable for producing biodiesel for usage in sub-tropical climates.

Sources, distributions, and burial efficiency of terrigenous organic matter in surface sediments from the Yellow River mouth, northeast China

Organic geochemical studies of surface sediments from Laizhou Bay, the Yellow River mouth, northeast China, were conducted to reveal the sources, distributions, and burial efficiency of terrigenous OC exported by the Yellow River. Bulk OC contents and δ13Corg values from 204 samples show that terrigenous OC mainly accumulates in two muddy patches, basically controlled by hydrodynamic conditions. Distributions and stable carbon isotopic compositions of individual n-alkanes from 45 samples suggest that short-chain n-alkanes, with even carbon-number predominance, are most likely microbial products from degradation of riverine fossil OC, whereas long-chain odd-numbered n-alkanes (n-C27, n-C29 and n-C31) and long-chain even-numbered n-alkanes (n-C26,n-C28 and n-C30) are representative of riverine soil OC and fossil OC, respectively. Integrated with previous reports of ∼100% burial efficiency of soil OC in the Yellow River mouth, concentration ratios of n-C27+29+31 to OC and n-C26+28+30 to n-C27+29+31 from the riverine particles to surface sediments in Laizhou Bay were constructed to indicate relative terrigenous OC contributions and fossil OC burial efficiency, respectively. The results suggest that the terrigenous OC contribution ranges from 14% to 57% in Laizhou Bay, with the highest values in the two muddy patches as well as in areas near the river mouth. The fossil OC burial efficiency ranges from 36% to 76%, with an TOC-weighted mean value of 42%. The 58% fossil OC lost during the transport and burial processes in the Yellow River mouth may provide a significant CO2 source.

Inhibition of radiocesium adsorption on 2:1 clay minerals under acidic soil environment: Effect of organic matter vs. hydroxy aluminum polymer

Radiocesium (RCs) is selectively adsorbed on interlayer sites of weathered micaceous minerals, which primarily controls the mobility of RCs in the soil environment. Pedogenesis under acidic condition (under wetter climate regime) implies that RCs adsorption sites may be covered with soil organic matter (OM) and/or intercalated with hydroxy-Al polymer (Al(OH)x). While these interactions well-known control RCs adsorption, the relative importance of the two processes is virtually unstudied in field environment. We hypothesized that Al(OH)x intercalation plays dominant role in the adsorption inhibition in both surface and subsurface soils because Al(OH)x has more direct effect on RCs access to frayed edge site (FES), the sites intermediate between an expansible and non-expansible interlayers. Soils from two forest soil profiles under temperate and tropical climate (Ono, Japan and Kinabalu, Malaysia) were sampled every 3cm from 0 to 30cm and sieved to isolate soil particles of ≤20μm diameters for the analysis of radiocesium interception potential (RIP) after a series of pretreatment. One subset was treated with H2O2 to remove OM. Another subset was further treated with hot sodium citrate to remove Al(OH)x after the H2O2 treatment. The changes in specific surface area (SSA) by the N2-BET method before and after the OM removal were determined to assess OM coverage on soil mineral surfaces. The contributions of OM removal to the total increase in RIP were surprisingly high (74.5–93.8%) in the uppermost soil layers (0–3cm), implying that (i) OM reduced the access of RCs to FES, and (ii) OM binding with Al (organo‑aluminum complexation) reduced Al(OH)x formation in the interlayers. Towards deeper layers, OM contribution progressively declined to 2.4–13.9% whereas the Al(OH)x effect increased up to 86.1–97.6% in both profiles. The highest OM coverage on mineral surface (83.7%) was observed in the uppermost soil layer of Ono series. The stepwise OM removal of this sample by a weaker oxidizing reagent (NaOCl) for 6, 12, 24, and 30h led to a gradual decline in OC content from 145gkg−1 to 67.2gkg−1. The OC losses were accompanied by a slight but progressive liberation in SSA from 8.3 to 12.2m2kg−1, indicating that a portion of the soil mineral surfaces became exposed. However, RIP did not largely increase after the NaOCl treatment up to 30h but remained quite low relative to the RIP value after the more complete OM removal by H2O2. These results indicate that the fraction of OM relatively resistant to chemical oxidation (presumably strongly bound to reactive portions of mineral surface) appeared to contribute to the inhibition of RCs adsorption on 2:1 interlayer sites. In conclusion, the ability of weathered micaceous minerals to retain RCs was largely reduced by two different mechanisms: OM coverage on the mineral surface (esp. at surface) and Al(OH)x interlayering (esp. at subsurface soil layers). Our results imply that long-term RCs dynamics may be strongly controlled by soil carbon level and thus ecosystem carbon balance (e.g., forest and grassland vs. bare and cropland) as well as the abundance and/or weathering degree of micaceous minerals.

Organic and inorganic contamination in sediments from Araçá Bay, São Sebastião, Brazil

The aim of this work is to verify the organic and inorganic contamination in Araçá Bay, which contains one of the last remnants of mangrove forest on the northern coast of São Paulo State, Brazil, to improve the environmental management of this area, which is part of the Marine Protected Area of the Northern Coast of São Paulo State (APAMLN) and the Environmental Protected Area of the Alcatrazes Municipality (APAMA). Surface sediments were analyzed to provide information on the levels, spatial trends and sources of trace elements, aliphatic hydrocarbons (AH), polycyclic aromatic hydrocarbons (PAH), and fecal steroids. Low levels of trace elements were observed, and the enrichment factors showed no evidence of contamination in the area. The highest concentrations of all organic contaminants were recorded in the samples collected in the external sublittoral stations, mainly in the São Sebastião Channel, which had the finest grain sizes and higher OC contents. With the exception of the samples collected in the inner part of the bay, most of the samples presented unresolved complex mixtures (UCM) of AH, which are indicators of petroleum and its derivative inputs. PAH concentrations were higher in the external stations, but the levels were below the limits of the sediment quality guidelines (SQG) recommended in Brazilian federal legislation on dredged sediments. The major sources of these compounds were from pyrolytic sources. Sewage contamination was detected mainly in the inner part of the bay, especially near the northern stream and the sewage outfall. The contaminant distributions were related to the hydrodynamics of the intertidal flat, with the most central dynamic areas presenting lower contaminant levels.

Impact of application of rock phosphate (RP) inoculated with phosphate solubilizing fungi (PSF) as a fertilizer on total nitrogen (TN), total organic carbon (TOC) and microbial count (MC) in clay soil

In this study the effect of four treatments of phosphate fertilizers (NS, RP, SP & RP inoculated with PSF (A. niger & A. fumigatus) using three doses (RD, 1/2 RD&2RD) on TN, OC and MC of Nile delta clay soil and its impact on some growth parameters of phasoleous vulgaris was monitored. The Results indicated that OC content of clay soil was positively affected by the amendment of soil with inoculated RP. Inoculation of RP with A.niger culture increased the OC content of the soil by 4.91%, 18.28%, 14.38% and 19.61% comparing to A.fumigatus, NS, RP and SP respectively. the highest soil organic carbon content obtained when soil was amended with inoculated RP in 1/2RD it increased by 1.02% and 7.232% comparing to the amendment of with RD and 2RD. RP inoculated with A.niger culture clay soil showed the highest TN content when amended with 2RD the presence of phasloeus vulgaris plant it was 19.19%. Different phosphate treatments affected MC in clay soil to reach the highest count when inoculated rock phosphate with the RD as a fertilizer it increased by5.66% & 20.75% case of A.fumigatus & A.niger respectively comparing to NS. The lowest count obtained when SP was used as a fertilizer, it decreased by 26.4% comparing to NS.