Organic carbon concentrations in 3.5-billion-year-old lacustrine mudstones of Mars

Elemental carbon (EC) and organic carbon (OC) are major components of atmospheric PM2.5. In this article we represent the results of long-term measurements (8–12 years) of EC and OC at three different background sites in Finland: in a rural area (Virolahti) since the summer 2010, in a marine environment (Utö) since the summer 2011, and in a clean arctic environment (Pallas/Matorova) since 2014. The concentrations of OC and EC were measured with a semi-continuous organic and elemental carbon analyser (SC-OCEC) in all the sites. The yearly average concentrations of OC varied between 0.96–3.1, 0.76–1.6 and 0.30–0.69 μg m−3 at the rural (Virolahti), marine (Utö) and arctic (Pallas/Matorova) sites, respectively. Similarly, the corresponding yearly average concentrations of EC ranged between 0.095–0.48, 0.090–0.2 and 0.010–0.086 μg m−3 at those sites. A clear seasonal variation in OC and EC concentrations was observed at each measurement site. OC concentrations were highest during summertime whereas EC concentrations were highest in wintertime. The seasonality of OC was clearest at the Arctic site that had also the largest temperature variation and shortest growing season resulting in a sharp increase in OC concentrations from June to August. At all the measurement sites, OC concentrations gradually increased when the temperature rose over sub-zero temperatures whereas the daily average EC concentrations did not show as apparent temperature dependence as OC. Based on the cluster analysis, highest OC and EC concentrations, and the highest total load for EC (23–32%), at all the sites were detected with the air mass origin of southeast. In the marine environment, the effect of black carbon from ship plumes was investigated. The limit for ship fuel sulfur content changed during the measurement period (in January 2015), but it was not observed to influence the Optical EC concentrations. Overall, long-term, continuous measurements are crucial when the time trends in air quality and the effect of emission mitigation actions are investigated. In this study, a slight decrease in OC was observed at the Marine site, however, a decrease for EC was seen both at the rural and marine sites suggesting that the emission mitigation actions like EURO limits for light vehicles or improved after-treatment systems developed for industry and energy production have already decreased the background concentrations in rural areas.

The burial of organic carbon (OC) in marine sediments regulates CO2 content in the atmosphere. However, the OC sources and their effect on the OC preservation in sediments of the continental marginal sea remain elusive. Here, we survey the abundance, stable carbon and radiocarbon isotopes of OC, as well as mineral surface area and grain size in surface sediments from the shelf to the abyssal plain of the South China Sea. We found that the marine OC comprises the 63 ± 9% and 78 ± 14% of sedimentary OC off South China and Luzon, respectively. The petrogenic OC contributing to sedimentary OC in these sites is generally higher than that of soil OC (22 ± 10% vs. 12 ± 6%). The sedimentary OC off Taiwan is predominantly derived from petrogenic OC, accounting for 57 ± 10%, with remaining consisting of marine OC (36 ± 10%) and soil OC (6 ± 1%). High soil OC contents are found in fine sediments on the inner shelf off South China, and high petrogenic OC contents occur in fine sediments off Taiwan. Marine OC contents are high in fine sediments on the middle shelf and upper slope off South China, but low in coarse sediments on the outer shelf and upper slope, and fine sediments on the lower slope and abyssal plain. The OC sources, mineral surface area, and oxygen exposure time of OC together control the preservation of OC in sediments with their relative importance differing on varying depositional settings of this sea.

Proximity to inlet channel drives spatial variation in sediment carbon across a lagoonal seagrass meadow

有机碳和无机碳的流域输出是湖泊碳埋藏的重要驱动因子, 而喀斯特地区无机碳循环具有反应迅速且对人类活动影响敏感的特点. 在流域开发持续增强的背景下, 喀斯特地区湖泊有机碳和无机碳的来源、含量与埋藏通量可能会出现同步变化的协同模式. 本文以云南省石林喀斯特地区流域土地利用类型不同的两个中型湖泊(长湖、月湖)开展对比分析, 通过对沉积物钻孔的土壤侵蚀强度(磁化率)、流域外源输入(C∶N比值)、水动力(粒度)、营养盐(总氮、总磷)、藻类生产力(叶绿素色素)等代用指标的分析, 结合监测数据和历史资料重建了两个湖泊环境变化的近百年历史, 并定量识别了有机碳和无机碳埋藏响应流域开发的变化特征与协同模式. 沉积物磁化率和C∶N比值结果揭示了流域地表侵蚀和外源输入的阶段性特征, 同时总氮和总磷含量记录了长湖和月湖营养水平上升的长期模式. 在流域森林覆被较高(33.43%)的长湖中, 全岩和有机质C∶N比值分别与磁化率信号呈显著正相关(r=0.95和0.89, P＜0.001), 且与无机碳和有机碳含量呈显著负相关(r=-0.94, P＜0.001和r=-0.52, P=0.01), 反映了森林植被退化时流域碳输出的减少对沉积物碳含量的影响. 而在流域耕地覆被为主(60.98%)的月湖中, 全岩和有机质C∶N比值与磁化率信号呈显著负相关(r=-0.54, P＜0.01和r=-0.67, P＜0.001), 且全岩C∶N比值与无机碳含量(P=0.15)无显著关系, 反映了耕作强度的增加可能促进了水体富营养化和内源输入的增强. 在两个湖泊中, 营养水平的上升和内源生产力的增加促进了有机碳含量的快速增加. 进一步分析表明, 近百年来长湖有机碳与无机碳含量变化的同步性明显(r=0.54, P＜0.001)而在月湖中无显著关系(P=0.20, P>0.05). 两个湖泊中沉积通量的变化均与全岩C∶N比值呈显著正相关(r=0.48和0.45, P≤0.001), 且有机碳与无机碳埋藏通量均呈现同步变化的显著特征(r=0.72和0.85, P＜0.001). 其中长湖的无机碳埋藏通量显著高于有机碳埋藏通量, 而月湖的有机碳埋藏通量略高于无机碳埋藏通量, 反映了岩溶地区流域外源输入和水体富营养化的差异性驱动影响. 在流域开发增强的梯度下, 森林退化会降低流域碳输出的负荷, 而农业扩张和水体富营养化会促进藻类生长和内源有机碳的累积. 因此, 流域土地利用和水体营养水平对湖泊无机碳和有机碳埋藏变化的长期轨迹和协同模式产生了重要影响, 对喀斯特地区的碳库评估需要考虑无机碳循环的重要性.;Catchment-scale exports of organic and inorganic carbon plays an important role in affecting the lake sediment carbon burial. Inorganic carbon cycling in Karst landscapes is sensitive to human activities due to the rapid kinetics of carbonate dissolution. As with intensive watershed development, the source, content and burial loading of organic and inorganic carbon in Karst region may show a synchronous change. This study selected two medium-sized lakes (Lake Changhu and Lake Yuehu) with contrasting land uses patterns in the Shilin Karst area of central Yunnan for sediment surveys. With the proxies analyses for soil erosion (i.e. magnetic susceptibility (MS)), catchment allochthonous input (C∶N ratio), lake hydrology (particle size), nutrient levels (total phosphorus and nitrogen) and primary production (i.e. algal pigments), together with monitoring data and historical records, the history of limnological changes and catchment development over the last century for both lakes were reconstructed. Furthermore, long-term variation and synchronic pattern of sediment organic carbon (OC) and inorganic carbon (IC) burial in the context of catchment development were quantified. The sediment MS signal recorded the fluctuation in soil erosion intensity and a general pattern of long-term nutrient enrichment in both lakes. In Lake Changhu, with a higher land cover of forest (33.43%), the bulk and organic C∶N ratios were positively related with the MS signal (r=0.95 and 0.89, P < 0.001) but showed a negative relationship with sediment inorganic and organic carbon content (r=-0.94, P < 0.001 and -0.52, P=0.01), respectively, reflecting a significant impact of catchment carbon input. In Lake Yuehu, with a current land cover dominated by the cropland (60.98%), the bulk and organic C∶N ratios were negatively related with the MS signal (r=-0.54, P < 0.01 and -0.67, P < 0.001) and the bulk C∶N ratio showed no relationship with the sediment inorganic content (P=0.15), reflecting that the cropland expansion may have enhanced lake eutrophication and autochthonous input. In both lakes, nutrient enrichment and algal production enhanced the rapid OC accumulation. Additional analyses showed that there existed a significantly synchronous change between OC and IC content in Lake Changhu (r=0.54, P < 0.001) but not in Lake Yuehu (P=0.20, P>0.05). In both lakes, sediment loading was positively related with bulk C∶N ratio (r=0.48 and 0.45, P≤0.001), and there also existed a significantly synchronous change between OC and IC loadings (r=0.72 and 0.85, P < 0.001). Furthermore, the IC burial rate was significantly higher than that of OC in Lake Changhu, while IC consistently lower than OC in the nutrient-rich Lake Yuehu, reflecting differential forcing of vegetation degradation and lake eutrophication. With the intensive development in watershed, forest degradation can reduce the loading of catchment carbon export, while agricultural expansion and eutrophication would promote the growth of algae and the OC accumulation rate. Therefore, land use and lake nutrient levels can significantly impact the long-term trajectory and synchronic variation of sediment OC and IC burial. Thus, IC cycling should be considered in the regional assessment of carbon stock in karst areas.

Emission influences on air pollutant concentrations in New York state: II. PM2.5 organic and elemental carbon constituents

Large amounts of organic carbon (OC) and inorganic carbon (IC) are stored in coastal sediments. These carbon compounds play an important role in coping with global climate change. In this study, the surface sediments of four tidal flat sections in northern Jiangsu were analysed for their OC and IC contents, as well as changes in the physical and chemical properties of the sediments (particle size, pH, salinity (SAL), and N, P, and S contents). A partial least squares regression (PLSR) was conducted to explore the factors affecting OC and IC variations. According to the results, the OC and IC contents exhibited increasing trends when moving from the seaward to landward parts of the sections. The OC variations were large and IC variations were small in all four sections and the vegetation coverage contributes to the carbon content of tidal flat sediments. The PLSR analysis indicates that the main factors influencing OC and IC contents in the tidal flat system were particle size (sand, silt, and clay) and N content, while SAL had the least influence on OC and IC contents. The IC and OC contents are positively coupled, which may indicate that the nearshore vegetation has a greater contribution to OC, affects the coastal hydrodynamic conditions, and enhances the retention of IC. Additionally, the transformation of OC to IC also positively contributed to the coupling of their contents.

Spatial variations in geochemical characteristics of the modern Mackenzie Delta sedimentary system

Organic Carbon Geochemistry in the North-western Black Sea–Danube River System

Interpretation of particulate elemental and organic carbon concentrations at rural, urban and kerbside sites

Abstract. Knowledge of the sources of carbonaceous aerosol affecting air quality in Riyadh, Saudi Arabia, is limited but needed for the development of pollution control strategies. We conducted sampling of PM2.5 from April to September 2012 at various sites in the city and used a thermo-optical semi-continuous method to quantify the organic carbon (OC) and elemental carbon (EC) concentrations. The average OC and EC concentrations were 4.7 ± 4.4 and 2.1 ± 2.5 µg m−3, respectively, during this period. Both OC and EC concentrations had strong diurnal variations, with peaks at 06:00–08:00 LT and 20:00–22:00 LT, attributed to the combined effect of increased vehicle emissions during rush hour and the shallow boundary layer in the early morning and at night. This finding suggested a significant influence of local vehicular emissions on OC and EC. The OC ∕ EC ratio in primary emissions was estimated to be 1.01, close to documented values for diesel emissions. Estimated primary organic carbon (POC) and secondary organic carbon (SOC) concentrations were comparable, with average concentrations of 2.0 ± 2.4 and 2.8 ± 3.4 µg m−3, respectively. We also collected 24 h samples of PM10 onto quartz microfiber filters and analyzed these for an array of metals by inductively coupled plasma atomic emission spectroscopy (ICP-AES). Total OC was correlated with Ca (R2 of 0.63), suggesting that OC precursors and Ca may have similar sources, and the possibility that they underwent similar atmospheric processing. In addition to a ubiquitous dust source, Ca is emitted during desalting processes in the numerous refineries in the region and from cement kilns, suggesting these sources may also contribute to observed OC concentrations in Riyadh. Concentration weighted trajectory (CWT) analysis showed that high OC and EC concentrations were associated with air masses arriving from the Persian Gulf and the region around Baghdad, locations with high densities of oil fields and refineries as well as a large Saudi Arabian cement plant. We further applied positive matrix factorization to the aligned dataset of EC, OC, and metal concentrations (Al, Ca, Cu, Fe, K, Mg, Mn, Na, Ni, Pb, and V). Three factors were derived and were proposed to be associated with oil combustion, industrial emissions (Pb based), and a combined source from oil fields, cement production, and local vehicular emissions. The dominant OC and EC source was the combined source, contributing 3.9 µg m−3 (80 %) to observed OC and 1.9 µg m−3 (92 %) to observed EC.

Alluviation and sedimentation of the Yellow River are important factors influencing the surface soil structure and organic carbon content in its lower reaches. Selecting Kaifeng and Zhoukou as typical cases of the Yellow River flooding area, the field survey, soil sample collection, laboratory experiment and Geographic Information System (GIS) spatial analysis methods were applied to study the spatial distribution characteristics and change mechanism of organic carbon components at different soil depths. The results revealed that the soil total organic carbon (TOC), active organic carbon (AOC) and nonactive organic carbon (NOC) contents ranged from 0.05–30.03 g/kg, 0.01–8.86 g/kg and 0.02–23.36 g/kg, respectively. The TOC, AOC and NOC contents in the surface soil layer were obviously higher than those in the lower soil layer, and the sequence of the content and change range within a single layer was TOC>NOC>AOC. Geostatistical analysis indicated that the TOC, AOC and NOC contents were commonly influenced by structural and random factors, and the influence magnitudes of these two factors were similar. The overall spatial trends of TOC, AOC and NOC remained relatively consistent from the 0–20 cm layer to the 20–100 cm layer, and the transition between high- and low-value areas was obvious, while the spatial variance was high. The AOC and NOC contents and spatial distribution better reflected TOC spatial variation and carbon accumulation areas. The distribution and depth of the sediment, agricultural land-use type, cropping system, fertilization method, tillage process and cultivation history were the main factors impacting the spatial variation in the soil organic carbon (SOC) components. Therefore, increasing the organic matter content, straw return, applying organic manure, adding exogenous particulate matter and conservation tillage are effective measures to improve the soil quality and attain sustainable agricultural development in the alluvial/sedimentary zone of the Yellow River.

The present study was carried out to investigate the seasonal variation of organic carbon (OC) and elemental carbon (EC) in PM1 during 2018–2019 in the industrial area of Delhi, India. A cascade impactor was used to collect aerosol particles in four different size fractions (≥ PM10, PM2.5–10, PM2.5–1, ≤ PM1). The OC/EC analysis was performed by thermal/optical carbon analyzer (DRI 2001). The highest concentration of aerosol particles was observed in PM1 among four different size fractions (≥ PM10: 37.77 ± 16.07 µg/m3, PM2.5–10: 90.28 ± 41.84 µg/m3, PM2.5–1: 81.65 ± 43.85 µg/m3, and ≤ PM1: 151.75 ± 58.57 µg/m3). The annual average concentration of OC and EC in PM1 was found to be 34.12 ± 22.94 µg/m3 and 13.91 ± 11.45 µg/m3, respectively. Furthermore, a clear seasonal difference in the concentrations of OC and EC was observed. The highest OC and EC concentration were found during post-monsoon (OC: 59.58 ± 21.66 µg/m3) and winter season (EC: 23.90 ± 12.08 µg/m3), respectively. Although the lowest concentration of OC and EC was observed in the monsoon season (OC: 12.08 ± 6.98 µg/m3, EC: 3.88 ± 1.97 µg/m3). The annual average percentage contribution of OC and EC in PM1 was observed to be 22.48 and 9.16%, respectively. Total carbonaceous aerosol (TCA) accounted for 45.18% of PM1. The annual average OC/EC ratio was found to be 2.45, which indicates the secondary organic aerosol (SOA) formation. The OC/EC analysis reveals that OC2 and EC1 were dominant among eight carbon subfractions, which suggest a mixed source of emission. The higher value of inhalation dose of EC was observed during the winter season (309 µg), which can lead to a higher risk of cardiac and respiratory illness.

To study the characteristics of soil organic carbon （SOC） components and carbon pool management indicators of a Eucalyptus plantation after continuously simulating nitrogen deposition for five years and to explore the relationship between soil organic carbon components and soil environmental factors, it is helpful to understand the influence of nitrogen deposition on soil quality and SOC pool stability and provide a scientific basis for sustainable management of subtropical forest ecosystems and protection of the soil environment. In a long-term positioning test of simulating nitrogen deposition from 2018, four different treatments were selected： CK [0 kg·（hm2·a）-1], low nitrogen LN [50 kg·（hm2·a）-1], middle nitrogen MN [100 kg·（hm2·a）-1], and high nitrogen HN [150 kg·（hm2·a）-1]. The contents of SOC, light fraction organic carbon （LFOC）, heavy fraction organic carbon （HFOC）, easily oxidized organic carbon （EOC）, dissolved organic carbon （DOC）, particulate organic carbon （POC）, microbial biomass carbon （MBC）, soil physicochemical properties, carbon cycling-related enzyme activity, and carbon pool management indicators following the different treatments were measured. The results showed that： ① Compared to those in the control, the contents of SOC, DOC, EOC, POC, and MBC increased significantly with the increase in nitrogen deposition. By contrast, HFOC tended to decrease under the higher nitrogen deposition treatment. ② The input of nitrogen improved the carbon pool activity index and carbon pool management indicators significantly with the increase in nitrogen deposition levels. Nitrogen deposition enhanced the activities of sucrase, amylase, and dehydrogenase related to carbon cycling and improved soil carbon pool quality effectively. ③ The correlation and redundancy analysis between organic carbon components and soil environmental factors showed that soil pH, organic carbon content, and activated carbon components were negatively related. Physical and chemical indicators such as TN, AN, TK, AK, exchangeable ions, etc., all showed a significant or extremely significant positive correlation with organic carbon and its components, respectively. The soil physicochemical properties and carbon cycle-related enzymes promoted the increase in soil organic carbon and its component content to a certain extent. Soil exchange hydrogen, available potassium, total potassium, and amylase were the main environmental factors driving the changes in soil organic carbon composition and carbon pool management indicators. In conclusion, the continuous simulated nitrogen deposition for five years improved soil organic carbon, active organic carbon components, and carbon pool management indicators. This was beneficial to maintaining or improving the soil fertility of Eucalyptus plantations in mid-subtropical regions. However, there was a potential decrease in the content of heavy fractions of organic carbon and carbon storage under high nitrogen input levels [150 kg·（hm2·a）-1]. Long-term high nitrogen deposition may reduce the stability of soil organic carbon.

Legacy of plaggen agriculture: High soil organic carbon stocks as result from high carbon input and volume increase

Terrestrial organic carbon age and reactivity in the Yellow River fueling efficient preservation in marine sediments