On Organic Carbon Research Articles

Single‐particle laser‐induced‐fluorescence spectra of biological and other organic‐carbon aerosols in the atmosphere: Measurements at New Haven, Connecticut, and Las Cruces, New Mexico

This study focuses on organic carbon (OC) aerosols, including natural biological aerosols, in the Earth's troposphere, and on laser‐induced fluorescence (LIF) spectral methods for studying these aerosols. LIF spectra of atmospheric OC and biological aerosols (having diameters greater than approximately 3 μm) measured at New Haven, Connecticut, and Las Cruces, New Mexico, are reported. A hierarchical clustering method was used to cluster approximately 90% of the single‐particle LIF spectra into 8–10 groups. Some of these groups have spectra that are similar to spectra of some important classes of atmospheric aerosol, such as humic/fulvic acids and humic‐like substances, bacteria, cellulose, marine aerosol, and polycyclic aromatic hydrocarbons (PAH). A comparison with previous measurements made at Adelphi, Maryland, reveals that the most highly populated clusters found at Adelphi, and some of the less populated ones, also appear in the LIF spectra at New Haven and Las Cruces, even though the regional climates at these locations is different (New England/Atlantic Coastal, for New Haven and Adelphi, and Chihuahuan Desert for Las Cruces), and the measurements were made in different seasons. The results are consistent with some (perhaps most) of the fluorors in OC and biological atmospheric aerosols being common to these three sites. On average, spectra characteristic of humic/fulvic acids and humic‐like substances (HULIS) comprise 28–43% of fluorescent particles at all three sites; whereas cellulose‐like spectra contribute only 1–3%.

The role of hydrology in annual organic carbon loads and terrestrial organic matter export from a midwestern agricultural watershed

Defining the control that hydrology exerts on organic carbon (OC) export at the watershed scale is important for understanding how the source and quantity of OC in streams and rivers is influenced by climate change or by landscape drainage. To this end, molecular (lignin phenol), stable carbon isotope, and dissolved organic carbon (DOC) data were collected over a range of flow conditions to examine the influence of hydrology on annual OC export from an 850 km 2 Midwestern United States agricultural watershed located in west central Indiana. In years 2002 and 2003, modeled annual DOC loads were 19.5 and 14.1 kg ha −1yr −1, while 71% and 85%, respectively, of the total annual OC was exported in flow events occurring during less than 20% of that time. These results highlight the importance of short-duration, high-discharge events (common in smaller watersheds) in controlling annual OC export. Based on reported increases in annual stream discharge coupled with current estimates of DOC export, annual DOC loads in this watershed may have increased by up to 40% over the past 50 years. Molecular (lignin phenol) characterization of quantity and relative degradation state of terrestrial OC shows as much temporal variability of lignin parameters (in high molecular weight dissolved organic carbon) in this one watershed as that demonstrated in previously published studies of dissolved organic matter in the Mississippi and Amazon Rivers. These results suggest that hydrologic variability is at least as important in determining the nature and extent of OC export as geographic variability. Moreover, molecular and bulk stable carbon isotope data from high molecular weight dissolved organic carbon and colloidal organic carbon showed that increased stream flow from the study watershed was responsible for increased export of agriculturally derived OC. When considered in the context of results from other studies that show the importance of flood events and in-stream processing of terrestrial organic carbon, our results show how hydrologic variability in smaller watersheds can reflect landscape-scale carbon dynamics in ways that cannot necessarily be measured at the outlets of large rivers due to multiple source signals and attenuated hydrology.

Cultivation effects on the distribution of organic carbon, total nitrogen and phosphorus in soils of the semiarid region of Argentinian Pampas

Cultivation of native land can reduce the quality of soil by decreasing topsoil contents of organic carbon, total nitrogen, and phosphorus in the semiarid Pampas of Argentina. The objective of this study was to analyze the changes produced by cultivation on organic carbon (OC), total nitrogen (TN) and phosphate (inorganic and organic fractions) in two aggregate sizes of three different semiarid soils of Argentina as a function of soil depth. The study was carried out on three soils (loamy Hapludoll, loamy Haplustoll and sandy loam Haplustoll), with two uses compared at each site. Generally, the Caldenal savanna-like ecosystem (native soil) and a cultivated counterpart with annual crops for more than 60 years (cultivated soil) were compared. Results showed that all soils had similar distribution patterns with depth of OC, TN, total inorganic phosphorus (Pi), organic phosphorus (Po) and available phosphorus (Pa) in the 100–2000 μm and < 100 μm aggregates of both the native and cultivated soils. Contents of OC, TN and Pi in the whole soil (< 2000 μm) decreased sharply with depth in native soils (OC: 50%, TN: 45% and Pi: 23%), but they had a more homogeneous distribution in cultivated soils. These tendencies were attributed to the stratification occurring in non-disturbed native soils and the mixing of the upper 20 cm in cultivated soils. Cultivation produced losses of OC (73%) and Po (64%) from the 100–2000 μm aggregates at both depths in the sandy loam Haplustoll, while it produced losses of TN (52%) and Pi (42%) from the < 100 μm aggregates in the upper 10 cm of the loamy Hapludoll. OC and Po losses of the sandy loam Haplustoll were probably produced by the mineralization of organic compounds, whereas TN and Pi losses of the loamy Hapludoll were produced by wind erosion and plant uptake. Larger relative decreases of OC and Po than TN in coarse aggregates (100–2000 μm) and Pi in fine aggregates (< 100 μm) with cultivation indicate that coarse aggregates are less stable than fine aggregates (< 100 μm), and therefore more sensitive to changes in soil quality due to changes in land use. We concluded that management practices that tend to improve the formation of large aggregates as no-till or permanent pastures should be used in coarse textured Haplustolls in order to prevent large OC and Po losses. Management practices that include soil plowing will produce a breakdown of coarse aggregates and will moderately decrease OC, Po, TN, Pa and Pi contents in loamy Haplustolls and Hapludolls. Nevertheless, the destruction of coarse aggregates will increase the risk of losses of these elements by wind erosion.

Effect of adsorption capacity of dissolved humic matter on leachability of dioxins from raw and treated fly ashes of municipal solid waste incinerators.

The purposes of this study are to obtain information on the leachability of dioxins depending on the samples, to confirm the effect of dissolved humic matter (DHM) on the leachability of dioxins, and to evaluate the suitability of the detoxification treatments specified by the Japanese government for the reduction of leachability of dioxins. In this study, the leachability of dioxins from raw and treated fly ash was evaluated by a 24-hour batch leaching test and by an extraction test repeated three times with DHM solution, whose concentration was determined to be 700 mg-OC/L as an initial concentration based on organic carbon (OC) from adsorption tests of DHM to fly ash. The leaching concentration from fly ash samples having high DHM adsorption capacity was low regardless of pH, and that from samples having relatively low adsorption capacity and high pH was largely increased. Therefore, it is expected that the leachability of dioxins from treated fly ashes would be reduced by avoiding high pH and enhancing the DHM adsorption capacity rather than by using the detoxification method specified. We also confirmed that increase of the leachability of HOPs due to DHM is not as large as known in condition that is composed of three phases of HOPs, DHM, and solid matrix.

Isotopic constraints of sedimentary inputs and organic carbon burial rates in the Saguenay Fjord, Quebec

The Saguenay Fjord (Quebec) has exceptionally high sedimentation rates resulting in up to 100 m-thick Holocene sequences filling some of its basins, partly due the frequent occurrence of rapidly deposited layers (landslides, seismic events, floods). In the present study, special attention is paid on the incidence of such events on organic carbon (OC) fluxes, sources and burial rates, using physical, sedimentological, geochemical and isotopic measurements on 4 sediment cores raised from the inner basin of the fjord and the adjacent Baie des Ha!Ha! In these cores, rapidly deposited layers (RDL) include notably a turbidite linked to a major earthquake in 1663, a landslide layer dating from 1971 (Saint-Jean-Vianney landslide), and a flood layer from 1996. Compared with background sediments, RDL are characterized by low OC contents (<1%), relatively high CaCO 3 contents (>2%), and low δ 13C values in OC (<−27‰). These geochemical properties indicate incorporation of reworked marine sediments from the Laflamme Sea, which occupied the area during postglacial times. δ 13C-OC values (−26.8±0.2‰) and C/N ratios (17.7±1.7) in the pre-industrial, pre-1663 fjord sediments, indicate that most sedimentary organic matter (OM) was then of terrigenous origin. Paper mill activity during the 20th century has resulted in OM fluxes growing almost exponentially until the mid-1960s, when major changes in industrial practices and the implementation of environmental regulations during the 1970s and later on, reduced the amount of industrial OM discharged into the fjord. This industrial OM shows an isotopic signature of −26.34±0.02‰ and C/N ratios >20, not unlike those of the regional terrestrial OM. OC burial rates since the 1663 earthquake varied between ∼20 and 290 gC m −2 yr −1. RDL seem to favour OC preservation in the fjord by reducing bioturbation and both oxic and anoxic OC degradation, and by contributing themselves to higher carbon burial rates. Therefore, transitional environments such as the Saguenay Fjord could represent significant long-term carbon sinks.

Organic Carbon Distributions in Shallow Soils of Pinyon‐Juniper Woodlands

AbstractProperties of soils associated with pinyon (Pinus edulis Engelm.)‐juniper (Juniperus spp.) communities of the western USA reflect a mosaic of canopy and interspace environments. This study was initiated to examine the influence of these contrasting environments on organic carbon (OC) distributions and associated soil properties of shallow soils in a pinyon‐juniper woodland of east‐central Utah. The mosaic of interspace and canopy environments results in a complex of soils with two distinct OC distribution patterns. In both interspace and canopy soils, color values and root distributions are related to measured OC. Tree roots are concentrated just above the lithic contact in transitional R/A and Cr/A horizons in all soils. Decay of this root material represents the dominant organic‐matter input to interspace soils, which are essentially devoid of vegetation and lack O horizons. As a result, OC increases with depth and the highest OC contents and darkest soil colors are found in R/A and Cr/A horizons of these soils. Canopy soils also have relatively high OC contents just above lithic contacts but contain maximum OC and darkest soil colors in A1 horizons underlying litter layers. All soils exhibit increases or irregular decreases in OC with depth and have similar distribution patterns for total N and NaHCO3‐extractable P. The OC distribution patterns result in inappropriate classification of some of these shallow upland soils as Fluvents according to the U.S. soil taxonomy.