Patterns Of Organic Carbon Research Articles

Influence of Prosopis cineraria based agroforestry system on soil attributes in rainfed arid western Rajasthan

The experiment was conducted at Agricultural Research Station (SKN Agriculture University) Fatehpur-Shekhawati, Sikar (Rajasthan) during 2016-2019 to find out the distribution pattern of soil pH, EC, OC and available nutrients (N, P, K and S) under Prosopis cineraria (khejri) based agroforestry system in comparison to the sole cropping system. The results envisaged that soil pH was lower in P. cineraria-based agroforestry system (7.80) than sole cropping-based system (7.85) at 0 to 15 cm soil depth and the corresponding values were 7.99 and 8.02 at 15 to 30 cm soil depth. No significant difference was observed in electrical conductivity (EC) between the systems and cropping pattern at both the soil depths, except cropping pattern at 0 to 15 cm soil depth. Organic carbon (OC) content increased significantly in P. cineraria-based agroforestry system in comparison to the sole cropping system at both soil depths. However, the interaction between systems and crops was found significant only at 0 to 15 cm soil depth. Available nitrogen content (kg/ha) was significantly higher (97.90 and 79.55) in P. cineraria-based agroforestry system in comparison to the sole cropping system (83.09 and 58.24) at both the soil depth, respectively. Available phosphorus content (kg/ha) in soil was significantly higher (15.58 and 10.89) in P. cineraria-based agroforestry system in comparison to the sole cropping system (12.94 and 9.84) at both the soil depth. Available potassium content (kg/ha) was also found to be significantly higher in P. cineraria-based agroforestry systems (283.77 and 256.87) in comparison to sole cropping systems (271.71 and 247.80) at different soil depths, respectively. The available sulfur content was also found to be significantly higher in P. cineraria-based agroforestry system. The study indicated that P. cineraria trees improved soil conditions beneath their canopies in comparison to the sole crop.

Spatiotemporal variability of organic carbon in streams and rivers of the Northern Hemisphere cryosphere

The earth's cryosphere is the outpost of climatic warming, which leads to rapid changes of organic carbon (OC) transport from terrestrial to aquatic ecosystems. OC in the cryosphere rivers plays vital roles in the carbon cycle and river ecosystem health. Yet, we still lack a comprehensive assessment of the spatiotemporal patterns of riverine OC across the Northern Hemisphere cryosphere. Here, we compiled OC concentration, radiocarbon (14C), and the specific ultraviolet absorbance (SUVA) of dissolved OC (DOC) at 254 nm data from 1007 unique sites, extracted from 138 published literature between 1972 and 2022. Overall, the average DOC and particulate OC (POC) concentrations are 6.34 and 2.61 mg C L−1, respectively, with the average age of DOC and POC being ~1100 and ~4300 years BP, respectively, indicating the release of aged carbon pools. Seasonal variations in DOC and POC concentrations, Δ14C-DOC and SUVA254 were observed, with distinct spatial variations closely linked to specific watershed characteristics. We found permafrost-impacted watersheds displayed significantly higher DOC concentrations, younger OC ages but lower POC concentrations compared to glacier-impacted watersheds. Meanwhile, in boreal forest watersheds, DOC is the most concentrated and youngest in varied ecoregions. Additionally, in permafrost regions characterized by higher permafrost extent, ground ice content, or lowlands with thick overburden cover, riverine DOC is more concentrated and aromatic. We estimated that specific OC fluxes in glacier rivers are higher than that in permafrost rivers (4.77 and 1.86 g C m−2 yr−1, respectively). Our results highlight the complex and variable spatiotemporal patterns of riverine OC in the northern cryosphere, which are essential for assessing the impact of OC on the global carbon cycle and climate warming.

Phosphorus stocks and pools in eroding streambank soils

Phosphorus (P) in streambank soils can directly enter waterbodies via streambank erosion. How much and what form of P is entailed by this terrestrial-aquatic transfer has implications for the degree and timespans of downstream water quality impacts. Quantifying the bioavailability and spatial distribution of soil P species in streambanks is needed to comprehensively assess the fate of P eroded into streams and their potential risk to downstream water quality. This study quantitatively evaluated the abundance and speciation of P in streambank profiles of Polecat Creek, IL, USA using sequential (Hedley) P fractionation. The HCl extractable fraction, interpreted as Ca-P and insoluble in water, was the dominant form of P accounting for 12–73% of total P (14–344 g m−2) with higher stocks in C horizons (131 ± 26 g m−2) than the overlying B (36 ± 7.6 g m−2) and A (41 ± 12 g m−2) horizons. Ca-P was strongly positively correlated with soil pH and inorganic carbon (IC) content, demonstrating the influence of apatite-rich loess parent material of this region in driving P speciation. Organic P (Org-P) accounted for 1–33% of total P (0.1–104 g m−2) with significantly higher stocks in A horizon (39 ± 5 g m−2) than B (11 ± 7 g m−2) and C (22 ± 7 g m−2) horizons, concomitant with the pattern of organic carbon (OC) and reflective of strong biological (riparian vegetation) controls on this pool of potentially mineralizable P. Subsurface increases in Org-P occurred for buried A horizons in banks created by alluvial depositions indicated the strong influence of fluvial processes on streambank P distribution and speciation. Fe/Al-P accounted for 1–21% of total P stocks and was generally enriched in the surface A (50 ± 30 mg kg−1) and B (35 ± 39 mg kg−1) horizons. The most immediately bioavailable pool, exchangeable P (Exc-P), was the smallest across streambanks, constituting < 10% of total P and largely relegated to A horizon (1.2–20.4 g m−2). This proof of concept offers valuable information about the variation of P stocks and speciation by genetic horizons in streambanks.

Patterns of organic carbon and nitrogen stocks in soil particle-size fractions along an aridity gradient in Northern China’s deserts

Clay and silt fractions (<53 μm in particle size) play a critical role in soil organic carbon (SOC) storage and are used to characterize SOC storage in terrestrial ecosystems. However, there is unclarity about SOC content and stock in soil particle-size fractions in deserts where the soil is immature. In this study, we investigated the composition of soil particles and the stocks of SOC and N in two particle-size fractions of 0–53 μm and 0–100 μm at the top (0–30 cm) and deeper (30–50 cm) layers along an aridity gradient. The very fine sand (53–100 μm in particle size) was the major component of bulk soil. The C and N stocks in the top 50 cm of soil decreased linearly with increasing aridity, from 63.5 MgC ha−1 to 4.1 MgC ha−1 and from 4.6 MgN ha−1 to 0.8 MgN ha−1, respectively. Organic C content in two soil particle-size fractions and their contribution to bulk SOC decreased linearly with increasing aridity. Organic C content in < 100 μm soil particle-size fraction accounted for 57.8 %-99.2 % of bulk SOC, and it was only 0.6 %-24.2 % in the < 53 μm fraction. SOC stock was estimated by < 100 μm soil particle-size fractions compared with clay and silt (<53 μm). Organic C content in two soil particle-size fractions was higher in the alpine and steppe deserts than in the Gobi and sandy deserts; it was significantly higher at 0–30 cm than at 30–50 cm for all deserts. Vegetation cover was the first predictor for the organic C content in two soil particle-size fractions and their contribution to bulk SOC, addressing the direct contribution of plant-derived C inputs to soil particle-size fraction. Our study provides strong empirical evidence that organic C and N in deserts are better estimated by soil particles < 100 μm rather than clay and silt-sized fraction (<53 μm in particle size).

Soil carbon–nitrogen coupled accumulation following the natural vegetation restoration of abandoned farmlands in a karst rocky desertification region

Vegetation restoration on abandoned farmlands is one of the typical methods for accumulating soil organic carbon (OC) and total nitrogen (TN). However, the coupling of soil OC and N accumulation following vegetation restoration remain poorly known in karst rocky desertification regions in Southwest China. Four natural vegetation restoration lands, namely, grassland, shrubland, secondary forest I, and secondary forest II, were chosen with farmland as a reference. Soil samples were collected to determine the soil aggregates, soil OC and TN accumulation, soil inorganic N content, and soil N transformation rates. The amount of different soil aggregates fractions and stability of soil aggregates, levels of soil OC and TN in whole soil and aggregates, levels of soil inorganic N, and soil N transformation rates were considerably increased by vegetation restoration following farmland abandonment. The increases in total soil OC and TN stocks mainly contributed to the increase of OC and TN stocks in large aggregates. The soil C:N ratios and amount of exchangeable calcium were the important factors associated with soil OC and TN accumulation. Soil net N mineralization and nitrification rates were similar to the patterns of soil OC or TN concentrations in grassland to secondary forest. Soil substrate controlled soil N transformation rates along vegetation restoration. Our results suggested that abandoning farmlands for natural vegetation restoration can improve the soil structure, facilitate the coupled accumulation of soil C and N, and enhance soil N transformation rates and N availability, but the coupling accumulation of soil C and N may be limited by soil N in the early stages of vegetation restoration.

Online measurement of carbonaceous aerosols in suburban Shanghai during winter over a three-year period: Temporal variations, meteorological effects, and sources

Carbonaceous aerosols have adverse effects on both human health and the climate. To understand the temporal variations and sources of carbonaceous aerosols, organic carbon (OC) and elemental carbon (EC) were measured hourly in suburban Shanghai in 2015–2017 during winter. The average OC concentrations were 7.34 ± 4.51 μgC/m3 in 2015, 7.16 ± 4.43 μgC/m3 in 2016, and 6.4 ± 3.22 μgC/m3 in 2017. The EC concentrations decreased significantly each year, with average concentrations of 3.82 ± 2.43, 2.91 ± 2.28, and 2.46 ± 1.88 μgC/m3, respectively, which caused the OC/EC ratio to increase from 2015 to 2017. Although the meteorological conditions differed each winter, there was a similar pattern of OC and EC diurnal variations, with concentrations peaking at 08:00 and 20:00, largely due to rush-hour vehicle emissions. A downward trend of EC/CO and EC/NO2 (mass ratios) but steady CO and NO2 concentrations from 2015 to 2017 revealed that the characteristics of primary vehicle emissions changed, and that less EC was emitted. Secondary organic carbon (SOC) and primary organic carbon (POC) were estimated with the minimum R2 (MRS) method. The hiemal SOC/OC values in suburban Shanghai were 19.2 ± 18.6% in 2015, 31.1 ± 18.6% in 2016, and 51.0 ± 21.4% in 2017, exhibiting an increasing trend. As the PM2.5 concentration increased (from 0 to 50 μg/m3 to 100–300 μg/m3), a decreasing SOC/OC ratio (from 43.6 ± 23.9% to 21.8 ± 17.7%) was observed over the three years, showing that primary emissions were the main contributors to carbonaceous aerosols on haze days. Case analysis of haze events further demonstrated that the primary sources of OC and EC were vehicle emissions. The contributions of biomass burning and coal combustion to carbonaceous aerosols became less important over the study period. This study highlights the importance of controlling vehicle emissions to reduce carbonaceous aerosol concentrations in the suburbs of the Chinese megacity, Shanghai.

Conversion of organic carbon from decayed native and invasive plant litter in Jiuduansha wetland and its implications for SOC formation and sequestration

It is still controversial which type of plant litter is conducive to soil organic carbon (SOC) formation. Here we are to explore the conversion of organic carbon (OC) from decayed plant litter in soil and its influence on final SOC sequestration. In situ investigation combined with laboratory soil incubation experiments were conducted in mixing zones dominated by halophytes of Phragmites communis and Spartina alterniflora in the Jiuduansha wetland of the Yangtze River estuary to investigate differences in conversion patterns of OC from two decayed plant litters of different characteristics using traditional physicochemical indicators and stable isotope tracing. Additionally, the mechanism of biotransformation was investigated through analysis of soil microbial community structure. Due to the higher content of lignin and cellulose in P. communis litter, the associated soil microbial community was more conducive to the formation of soil humus (HS). By contrast, more easily decomposable S. alterniflora litter induced its related soil microbial community more amenable to mineralization. Consequently, OC from decayed S. alterniflora litter remained in soil for less time than that from decayed P. communis, and the lost OC was more readily converted into CO2. OC from decayed P. communis was degraded very slowly during the early stage of conversion (November), and its longer duration in soil was favorable for HS formation. Analysis of the conversion of intermediates derived from different types of decayed plants can provide insight into plant litter input and SOC formation, and indicate the whereabouts of lost OC. From the perspective of plant biomass and conversion of plant litter-derived OC, P. communis is more conducive to soil carbon sequestration than S. alterniflora.

Soil texture determines the distribution of aggregate-associated carbon, nitrogen and phosphorous under two contrasting land use types in the Loess Plateau

Organic carbon (OC) and nutrient dynamics are closely related to soil texture, but how texture influences the distribution of OC and nutrients in aggregates in various land use types has not been examined. This knowledge gap precludes our mechanistic understanding of soil biogeochemical cycles at large spatial scales. Herein we compared the contents and stoichiometric ratios of OC and nutrients in both bulk soils and aggregates in cropland and woodland across a clay content gradient (7–31%) in the Loess Plateau. The soil metrics that were measured included the proportions of water-stable aggregates, and the contents of OC, nitrogen (N) and phosphorous (P) in bulk soils and each aggregate fraction. The stoichiometric ratios of carbon (C), N and P were calculated. The relationships between soil metrics and clay content were analyzed. We hypothesize that OC, N and P in aggregates increase with clay content, and these relationships are independent of land use types. In partial support of these hypotheses, the proportion of macroaggregates and the contents of OC, N and P in bulk soils and most aggregate fractions linearly increased with clay content. The slopes of these linear relationships were not affected by land use type. The C/N ratio were minimally affected, while the C/P and N/P ratios in both bulk soils and aggregates increased with clay content, and these relationships changed with land use type. Proportion of macroaggregates, contents of OC and N, and ratios of C/N, C/P and N/P were significantly higher in woodland than in cropland across or within sites. Furthermore, the distribution patterns of OC, N and P contents, and C/P and N/P ratios among aggregates varied with site and land use type. These suggested that soil texture determines the distribution of OC, N and P and their stoichiometric ratios within soil aggregates in the Loess Plateau of China, and most of these determining relationships were independent from land use types.

Organic carbon patterns and budgets in the Long Island Sound estuary

AbstractA multi‐year observational time series was evaluated across the 150 km central axis of the U.S. east coast's Long Island Sound (LIS) estuary, in three distinct regions. Fluxes were calculated at the boundaries of the regions using observations coupled to a hydrodynamic model and applied to a mass balance to assess organic carbon (OC) export from LIS. For all years, during stratified summer periods, LIS was a net exporter of OC to the continental shelf. LIS annual net carbon export however, varied with river flow. The heterotrophic or autotrophic nature of LIS also shifted inter‐annually. During the mass balance analysis period (2009–2012), LIS ranged between net OC import from the continental shelf and heterotrophy in the lowest river flow year (2012) and net export of OC and autotrophy in the highest flow year (2011). Analysis suggests that LIS switches from net OC import to export when the annual river inputs exceed 19 km3 yr−1. Applying these thresholds to the annual river flow record suggests that net import occurred in 15% of the last 20 years and that LIS usually is a net exporter of OC (85%). Annually averaged LIS carbon export values based on river flow conditions over the last 20 yr are estimated at 56 ± 64 × 106 kg yr−1. Analysis also suggests that LIS shifts from net heterotrophic to net autotrophic when annual river flow exceeds 26 km3 yr−1 (35% of the last 20 yr). Net heterotrophic conditions are most common, representing 65% of the last 20 yr.

Improving organic aerosol treatments in CESM/CAM5: Development, application, and evaluation.

New treatments for organic aerosol (OA) formation have been added to a modified version of the CESM/CAM5 model (CESM‐NCSU). These treatments include a volatility basis set treatment for the simulation of primary and secondary organic aerosols (SOAs), a simplified treatment for organic aerosol (OA) formation from glyoxal, and a parameterization representing the impact of new particle formation (NPF) of organic gases and sulfuric acid. With the inclusion of these new treatments, the concentration of oxygenated organic aerosol increases by 0.33 µg m−3 and that of primary organic aerosol (POA) decreases by 0.22 µg m−3 on global average. The decrease in POA leads to a reduction in the OA direct effect, while the increased OOA increases the OA indirect effects. Simulations with the new OA treatments show considerable improvement in simulated SOA, oxygenated organic aerosol (OOA), organic carbon (OC), total carbon (TC), and total organic aerosol (TOA), but degradation in the performance of HOA. In simulations of the current climate period, despite some deviations from observations, CESM‐NCSU with the new OA treatments significantly improves the magnitude, spatial pattern, seasonal pattern of OC and TC, as well as, the speciation of TOA between POA and OOA. Sensitivity analysis reveals that the inclusion of the organic NPF treatment impacts the OA indirect effects by enhancing cloud properties. The simulated OA level and its impact on the climate system are most sensitive to choices in the enthalpy of vaporization and wet deposition of SVOCs, indicating that accurate representations of these parameters are critical for accurate OA‐climate simulations.

Chemical characteristics and deposition fluxes of dust-carbon mixed coarse aerosols at three sites of Delhi, NCR

The present paper reports chemistry and fluxes of dust-carbon mixed coarse particles. For the purpose of this study, different carbonaceous fractions i.e. organic carbon ((OC), elemental carbon (EC) and carbonate carbon (CC) of atmospheric dust and their respective local soils were quantified at three sites of National Capital Region (NCR) of Delhi viz. Jawaharlal Nehru University campus (JNU), Connaught Place (CP) and Vishali area of Ghaziabad (GB). It has been observed that the OC and EC levels were approximately five to nine times higher in urban atmospheric dust than their corresponding soils, whereas CC levels were about three times higher than the corresponding soils. Average dustfall fluxes were significantly different at all the sites due to their different land-use patterns. At urban background site (JNU), the dust flux was lowest (172 mg/m2/day) followed by CP, a commercial site, (192 mg/m2/day) and GB, an industrial/residential area, (302 mg/m2/day). Similar to the dustfall pattern, the mean values of OC, EC and CC deposition fluxes were also observed to be lowest at JNU (9.2, 0.8 and 1.0 mg/m2/day, respectively) as compared to CP (12.2, 1.2 and 1.3 mg/m2/day, respectively) and GB sites (11.1, 1.1 and 1.4 mg/m2/day, respectively). Interestingly, unlike fine mode, different correlation pattern of OC and EC in coarse mode dust aerosols at three sites has suggested their independent deposition processes and source contribution. Fluxes of major water soluble inorganic ions (Na+, NH4+, K+, Ca2+, Mg2+, F−, Cl−, NO3− and SO42−) were also determined. Ca2+, Cl− and SO42− were found to be the major ionic species of water soluble fraction of the urban dust at all the sites. These interactions are corroborated by the morphology of the mixed aerosols. High levels of measured chemical species and their spatial distribution revealed close correspondence with the local emissions from transport, industries, biomass burning, road dust and construction activities etc.

Preferential burial of permafrost‐derived organic carbon in Siberian‐Arctic shelf waters

AbstractThe rapidly changing East Siberian Arctic Shelf (ESAS) receives large amounts of terrestrial organic carbon (OC) from coastal erosion and Russian‐Arctic rivers. Climate warming increases thawing of coastal Ice Complex Deposits (ICD) and can change both the amount of released OC, as well as its propensity to be converted to greenhouse gases (fueling further global warming) or to be buried in coastal sediments. This study aimed to unravel the susceptibility to degradation, and transport and dispersal patterns of OC delivered to the ESAS. Bulk and molecular radiocarbon analyses on surface particulate matter (PM), sinking PM and underlying surface sediments illustrate the active release of old OC from coastal permafrost. Molecular tracers for recalcitrant soil OC showed ages of 3.4–13 14C‐ky in surface PM and 5.5–18 14C‐ky in surface sediments. The age difference of these markers between surface PM and surface sediments is larger (i) in regions with low OC accumulation rates, suggesting a weaker exchange between water column and sediments, and (ii) with increasing distance from the Lena River, suggesting preferential settling of fluvially derived old OC nearshore. A dual‐carbon end‐member mixing model showed that (i) contemporary terrestrial OC is dispersed mainly by horizontal transport while being subject to active degradation, (ii) marine OC is most affected by vertical transport and also actively degraded in the water column, and (iii) OC from ICD settles rapidly and dominates surface sediments. Preferential burial of ICD‐OC released into ESAS coastal waters might therefore lower the suggested carbon cycle climate feedback from thawing ICD permafrost.

The characteristics and origins of carbonaceous aerosol at a rural site of PRD in summer of 2006

Abstract. Both organic carbon (OC) and elemental carbon (EC) were measured during PRIDE-PRD 2006 summer campaign by using a semi-continuous thermal-optical carbon analyzer at a rural site, Back Garden (BG), which is located 50 km to the northwest of Guangzhou City. Together with the online EC/OC analyzer, various kinds of instruments related to aerosol chemical properties were employed here, which provided a good opportunity to check data quality. The concentrations of OC correlated well with the mass of organic matter (OM) and water soluble organic carbon (WSOC), implying the reliability of the data measured in this campaign. The average OC concentrations in fine particle for three typical periods during the campaign (local emission influence, typhoon and precipitation and normal days) were 28.1 μgC m−3, 4.0 μgC m−3 and 5.7 μgC m−3, respectively; and EC were 11.6 μgC m−3, 1.8 μgC m−3, and 3.3 μgC m−3, respectively. The diurnal patterns of EC and OC during the campaign were higher at night and in early morning than daytime, which was probably caused by the primary emission and accumulation in the occurrence of low boundary layer. Compared with the constant diurnal enhancement ratios of EC, the enhancement ratio of OC (OC versus (CO-CObackground)) kept in a relative high level in the afternoon, with a similar diurnal profile to oxygenated organic aerosol (OOA), due to the strong photochemical formation of OC. Here, a modified EC tracer method was used to estimate the formation of secondary organic carbon (SOC). These results showed that the average SOC concentration (normal days) at BG site was about 2.0 ± 2.3 μgC m−3, and the SOC fraction in OC could reach up to 80% with the average of 47%. The modified approach in this study proved to be effective and reliable for SOC estimation based on good correlations between estimated SOC versus OOA or WSOC, and estimated POC versus hydrocarbon-like organic aerosol (HOA).

Temporal variation in organic carbon spiraling in Midwestern agricultural streams

Inland freshwaters transform and retain up to half of the carbon that enters from the terrestrial environment and have recently been recognized as important components of regional and global carbon budgets. However, the importance of small streams to these carbon budgets is not well understood due to the lack of globally-distributed data, especially from streams draining agricultural landscapes. We quantified organic carbon pools and heterotrophic metabolism seasonally in 6 low-order streams draining row-crop fields in northwestern Indiana, USA, and used these data to examine patterns in organic carbon spiraling lengths (SOC; km), downstream velocities (VOC; m/d), and turnover rates (KOC; day−1). There were seasonal differences in SOC, with the longest spiraling lengths in winter (range: 7.7–54.4 km) and the shortest in early and late summer (range: 0.2–9.0 km). This seasonal pattern in SOC was primarily driven by differences in discharge, suggesting that hydrology tightly controls the fate of organic carbon in these streams. KOC did not differ seasonally, and variability (range: 0.0007–0.0193 day−1) was controlled by differences in stream water soluble reactive phosphorus concentrations. Compared to previous studies conducted primarily in forested streams, agricultural streams tended to be less retentive of organic carbon. These systems function predominantly as conduits transporting organic carbon to downstream ecosystems, except during low, stable-flow periods (i.e., late summer) when agricultural streams can be as retentive of organic carbon as forested headwaters. High organic carbon retention in the late summer has implications for coupled carbon and nitrogen cycling (i.e., denitrification), which may play an important role in removing nitrate from stream water during periods of low flow.

Temporal and spatial patterns of organic carbon are linked to egg deposition by beach spawning horseshoe crabs (Limulus polyphemus)

The spring spawning by the American horseshoe crab (Limulus polyphemus L.) results in temporally and spatially discrete inputs of eggs onto sandy beaches in Delaware Bay, USA. We tested the hypothesis that seasonal patterns of sediment organic carbon on Delaware Bay beaches is linked to this pulsed input of horseshoe crab eggs. At a location with minimal horseshoe crab spawning activity (Higbee Beach), there was little seasonal variation in sediment organic carbon, no distinction between organic carbon levels as a function of shoreline position or sediment depth, and no significant correlation between the abundance of crab eggs and percent organic carbon. Conversely, at a prime horseshoe crab spawning habitat (North Beach), organic carbon levels were seasonally pulsed and were correlated with egg abundance. Moreover, the strongest evidence of seasonality was seen at the middle foreshore location at the 15–20 cm depth, consistent with the highest input of horseshoe crab eggs. Although some of the organic carbon contributed by horseshoe crab eggs in May–June leaves the beach in the form of hatched larvae later in the year, there is a net input of organic carbon to the system in the form of unfertilized and/or dead eggs, egg membranes, and embryonic molts. We suggest that the inputs of eggs from horseshoe crabs and other beach spawning animals, such as grunion and capelin, make significant contributions to the energy budget of sandy beaches.

Impact of open crop residual burning on air quality over Central Eastern China during the Mount Tai Experiment 2006 (MTX2006)

Abstract. The impact of open crop residual burning (OCRB) on O3, CO, black carbon (BC) and organic carbon (OC) concentrations over Central Eastern China (CEC; 30–40° N, 111–120° E), during the Mount Tai Experiment in 2006 (MTX2006) was evaluated using a regional chemical transport model, the Models–3 Community Multiscale Air Quality Modeling System (CMAQ). To investigate these pollutants during MTX2006 in June 2006, daily gridded OCRB emissions were developed based on a bottom-up methodology using land cover and hotspot information from satellites. This model system involving daily emissions captured monthly–averages of observed concentrations and day-to-day variations in the patterns of O3, CO, BC and OC at the summit of Mount Tai (36° N, 117° E, 1534 m a.s.l., Shandong Province of the People's Republic of China) with high correlation coefficients between the model and observations ranging from 0.55 to 0.69. These results were significantly improved from those using annual biomass burning emissions. For monthly-averaged O3, the simulated concentration of 80.8 ppbv was close to the observed concentration (81.3 ppbv). The MTX2006 period was roughly divided into two parts: 1) polluted days with heavy OCRB in the first half of June; and 2) cleaner days with negligible field burning in the latter half of June. Additionally, the first half of June was characterized by two high-pollution episodes during 5–7 and 12–13 June, separated by a relatively cleaner intermediate period during 8–10 June. In the first high-pollution episode, the model captured the high O3, CO, BC and OC concentrations at the summit of Mount Tai, which were associated with OCRB over southern CEC and subsequent northward transport. For this episode, the impacts of OCRB emissions on pollutant concentrations were 26% (O3), 62% (CO), 79% (BC) and 80% (OC) at the summit of Mount Tai. The daily OCRB emissions were an essential factor in the evaluation of these pollutants during MTX2006. These emissions have a large impact not only on primary pollutants but also on secondary pollutants, such as O3, in the first half of June over northeastern Asia. The model reproduced reasonably well the variation of these pollutants in MTX2006, but underestimated daily averages of both CO and BC by a factor of 2, when using emission data from almost solely anthropogenic fuel sources in the latter half of the observation period when field burning can be neglected.

A 1600 year multiproxy record of paleoclimatic change from varved sediments in Lake Xiaolongwan, northeastern China

A multiproxy record from Lake Xiaolongwan, northeastern China, reveals distinct stratigraphical patterns in organic carbon, total nitrogen, organic carbon isotope, nitrogen isotope, clastic content and dinocyst concentration, over the past 1600 years. High atomic C/N ratios in the sediment suggest that a large amount of organic matter in the sediments is derived from vascular plants and soil in the catchment. Based on the good agreement between cyclical variations of δ13Corg in the sediments and the spring drought index from historical documents, we interpret that the variation of δ13Corg in the sediments is an indicator of humidity or precipitation in the study area. Several notable drought periods with heavier δ13Corg occurred during AD 490–570, AD 780–990, AD 1360–1450, AD 1590–1670 and the last 150 years. These century‐scale drought episodes correspond to solar activity. It suggests that solar forcing plays an important role for the δ13Corg variation in the sediments through driving the changes in humidity/vapor pressure deficit. Dinocyst concentration is high during most of the Medieval Warm Period, and low during the European Dark Age and the Little Ice Age. The increase in dinocyst concentration is generally synchronous with decrease of δ15N value. The δ15N values in the studied lake are most likely influenced by the duration and intensification of lake overturn, which regulates the amount of depleted δ15N nutrients (dissolved organic nitrogen and ammonium) and dinoflagellate blooms.

Seasonal and diurnal variations of organic carbon in PM2.5 in Beijing and the estimation of secondary organic carbon

Organic carbon (OC) and elemental carbon (EC) in PM2.5 were measured hourly with a semicontinuous thermal‐optical analyzer in Beijing, China, during four seasons from November 2005 to October 2006. The average OC concentrations measured at Peking University (PKU) site in urban Beijing were 20 ± 19, 12 ± 7, 10 ± 5, and 18 ± 11 μgC/m3 in winter, spring, summer, and autumn, respectively. Distinct seasonal and diurnal patterns of OC were observed, and their concentrations were significantly influenced by the seasonal and diurnal changes in sources, emission rates, and mesoscale meteorology. The impacts of meteorological parameters such as wind and precipitation on OC and EC concentrations are also discussed. OC and EC concentrations were found to be well correlated in winter, spring, and autumn, indicating their common origins, while their correlation was poorer in summer, especially in the afternoon, indicating that the influence of secondary organic carbon (SOC) was significant for this period. SOC concentrations were estimated by using the EC‐tracer method as about 2.6 ± 3.1, 2.8 ± 2.4, 4.5 ± 2.9, and 4.1 ± 4.0 μgC/m3, accounting for 19%, 27%, 45%, and 23% of total organic carbon in winter, spring, summer, and autumn, respectively. This result showed that the relative contribution of SOC to OC in PM2.5 at this urban location was only comparable to that of primary organic carbon (POC) to OC in summer, while in the other three seasons, OC was dominated by POC.

Modeling Tillage‐Induced Redistribution of Soil Mass and Its Constituents within Different Landscapes

Tillage is a driving force of soil movement in cultivated fields. Soil constituents, together with the mass of soil, are redistributed across landscapes by tillage. The pattern of tillage‐induced soil constituent redistribution is determined by the pattern of tillage erosion (tillage‐induced soil mass loss or gain) and the dispersivity of translocation. In this study, we used a convoluting procedure and developed a Tillage Translocation Model (TillTM) to simulate the tillage translocation process and to demonstrate tillage‐induced soil mass and soil organic carbon (OC) (as an example of soil constituents) redistributions across four hypothetical landscapes subjected to different tillage patterns (directions) and over different lengths of tillage period. We determined that the local tillage‐erosion rate is mainly dependent on topography and that the effects of tillage pattern and the length of tillage period are relatively minor. The redistribution of OC content in the till layer is mainly determined by the number, location, and size of soil loss positions in the landscape, as well as the soil loss rates at these positions. Net loss of OC content occurs in the till layer and this loss increases with time. In contrast, an increase of OC content in the sublayer occurs at soil accumulation positions. The model was validated against field data collected at a site near Cyrus, MN. The patterns of OC and inorganic C redistribution can be adequately estimated by TillTM. There are discrepancies, however, between the model‐estimated values and the field measurements due to the limitations and uncertainties associated with the model. The results clearly showed that tillage translocation causes the vertical redistribution of soil constituents across the landscape, which implies that tillage translocation is one of the driving forces behind the spatial variability of soil properties and properties that impact biophysical processes.

Characteristics of elemental carbon and organic carbon in PM 10 during spring and autumn in Chongqing, China

PM 10 (particulate matter with aerodynamic diameter less than 10 μm) samples were collected simultaneously at nine urban sites and one urban background site during two intensive observation campaigns in 2006. Concentrations of elemental carbon (EC) and organic carbon (OC) in PM 10 were analyzed using an element analyzer. The characteristics regarding spatial and seasonal distribution patterns of OC and EC concentrations and their contributions to PM 10 mass, as well as correlation between OC and EC, were investigated in detail. The average OC and EC concentrations for urban sites were 57.5 ± 20.8 and 8.3 ± 3.9 μg/m 3, respectively, both being around three times higher than those for urban background site. As a whole, EC concentrations did not show distinct seasonal variations, though OC concentrations were generally higher in autumn than in spring. For urban sites, total carbonaceous aerosol (TCA) accounted for 33.2% in spring and 35.0% in autumn of PM 10 mass. The OC and EC concentrations were found significantly correlated to each other both in spring and in autumn, implying the existence of similar emission sources such as coal combustion. The OC/EC ratios generally exceeded 2.0, indicating the presence of secondary organic carbon (SOC), whose estimated concentration for urban Chongqing was 26.7 and 39.4 μg/m 3, accounting for 48.9 and 61.9% of the total OC observed in the samples, in spring and in autumn, respectively.