Showing papers on "Organic matter published in 1989"

δ13C Measurements as Indicators of Carbon Flow in Marine and Freshwater Ecosystems

Abstract: Stable isotope ratios provide clues about the origins and transformations of organic matter. A few key reactions control the isotopic composition of most organic matter. Isotopic variations introduced by these reactions are often passed on with little change so that isotopic measurements can indicate natural pathways and flows “downstream” from these key reactions. When chemical and metabolic processes scramble the information content of molecules, isotopic compositions are often preserved. This realization has prompted increasing use of stable isotope analyses as a tool for understanding complex ecological processes.

Texture, climate, and cultivation effects on soil organic matter content in U.S. grassland soils

Abstract: Soil organic C content, a major source of system stability in agroecosystems, is controlled by many factors that have complex interactions. The purpose of this study was to evaluate the major controls over soil organic carbon content, and to predict regional patterns of carbon in range and cultivated soils. We obtained pedon and climate data for 500 rangeland and 300 cultivated soils in the U.S. Central Plains Grasslands, and statistically analyzed relationships between C and soil texture and climate. Regression models of the regional soils database indicated that organic C increased with precipitation and clay content, and decreased with temperature. Analysis of cultivated and rangeland soils indicated that C losses due to cultivation increased with precipitation, and that relative organic C losses are lowest in clay soils. Application of the regression models to a regional climate database showed potential soil organic matter losses to be highest in the northeastern section of the Central Plains Grasslands, decreasing generally from east to west. These statistical data analyses can be combined with more mechanistic models to evaluate controls of soil organic matter formation and turnover, and the implications for regional management. S ORGANIC MATTER is a major component of biogeochemical cycles of the major nutrient elements, and the quantity and quality of soil organic matter both reflect and control primary productivity. The amount of soil organic matter represents the balance of primary productivity and decomposition and as such is a sensitive and integrated measure of change in ecosystem function. Understanding the processes that control soil organic matter dynamics and their I.C. Burke, CM. Yonker, W.J. Parton, C.V. Cole and D.S. Schimel, Natural Resource Ecology Lab., Colorado State Univ., Fort Collins, CO 80523; and K. Flach, Agronomy Dep., Colorado State Univ., Fort Collins, CO 80523. Received 20 June 1988. 'Corresponding author. Published in Soil Sci. Soc. Am. J. 53:800-805 (1989). response to management is essential for informed use of agricultural land. Jenny (1980) describes four sets of state factors responsible for the formation of soil organic matter, and illustrates the influence of parent material, time, climate, and biota as individual controls over soil properties. Controls over soil organic matter properties may have complex interactions; separate analysis of such controls may limit useful predictions. Parton et al. (1988) illustrate the use of a mechanistic model in evaluating simultaneously changing controls. Although such models can be highly successful, field data are necessary to validate predictions across complex gradients. It is widely recognized that cultivation of grassland soils leads to depletion of soil organic matter (Alway, 1909; Russel, 1929; Hide and Metzger, 1939; Haas et al., 1957; and many others). Soil organic C losses of as much as 50% have been documented in the U.S. Central Plains Grasslands (Haas et al., 1957), with losses strongly dependent on management regime and regional location. The extent of soil organic matter depletion has been shown to depend upon the same variables as those controlling soil organic matter formation: climate (Haas et al., 1957; Honeycutt, 1986; Cole et al., 1989), soil texture (Tiessen et al., 1982; Schimel et al., 1985a), landscape position (Schimel et al., 1985a,b; Honeycutt, 1986; Yonker et al., 1988), and management regime (Janzen, 1987; Cole et al., 1988). An integrated assessment of soil organic matter losses across the U.S. Central Grasslands requires analysis of soils with varying temperature, precipitation, and soil physical properties. The objectives of this paper were threefold: (i) to establish quantitative relationships between native soil organic matter levels in the Central Plains Grasslands and key driving variables: precipitation, temperature, and soil texture; (ii) to develop predictions of cultivation induced soil organic carbon loss as a function BURKE ET AL.: TEXTURE, CLIMATE, AND CULTIVATION EFFECTS ON U.S. GRASSLAND SOILS 801 of climate and soil texture; and (iii) to use these predictions to map potential soil organic C depletion.

Carbon and nitrogen dynamics along the decay continuum: Plant litter to soil organic matter

Abstract: Decay processes in an ecosystem can be thought of as a continuum beginning with the input of plant litter and leading to the formation of soil organic matter. As an example of this continuum, we review a 77-month study of the decay of red pine (Pinus resinosa Ait.) needle litter. We tracked the changes in C chemistry and the N pool in red pine (Pinus resinosa Ait.) needle litter during the 77-month period using standard chemical techniques and stable isotope analyses of C and N.

Mechanisms of dissolved organic carbon adsorption on soil

Abstract: (…) In this study, the sources of DOC adsorption on two proposed waste-site soils are defined, and the chemical mechanisms operative during the adsorption process are specified. Adsorption isotherms for the two soils determined at constant pH, ionic strength (I), and temperature indicated that DOC adsorption increased with increasing soil profile depth. Different adsorption capacities were exhibited by the two soils, however, which was related to their contrasting indigenous organic matter contents and mineralogies. (…)

Microbially Mediated Increases in Plant-Available Phosphorus

Abstract: Publisher Summary This chapter elaborates the microbially mediated increases in plant-available phosphorus (P). The importance of microorganisms in soil nutrient cycling and their role in plant nutrition has been realized for a long time. Their active part in the decomposition and mineralization of organic matter and release of nutrients is crucial to sustaining the plant productivity. The concentration of total P in soils ranges from 0.02 to 0.5% and averages approximately 0.05%, the variation being largely because of differences in weathering intensity and parent material composition. The uptake of P from relatively insoluble sources can be affected by the type of plant growing in the soil. The effect of mycorrhizae on plant P uptake and the effect of soil P on mycorrhizae were among the first aspects of these symbioses studied. Under soil conditions, potential benefits of adding P-solubilizing (PS) organisms would depend on several factors, one of the most important being the activity of the PS microbial population already in the soil. In almost all cases, the major sources of PS isolates have been soils. The mechanism of action of PS microorganisms is also elaborated.

Carbon isotopes in soils and palaeosols as ecology and palaeoecology indicators

Abstract: THERE are few quantitative techniques in use today for palaeoecological reconstruction in terrestrial depositional systems. One approach to such reconstructions is to estimate the proportion of C3 to C4 plants once present at a site using carbon isotopes from palaeosol carbonates1–3. Until now, this has been hampered by an inadequate understanding of the relationship between the carbon isotopic composition of modern soil carbonate and coexisting organic matter. Here we have found that the two systematically differ by 14–16% in undisturbed modern soils. This difference is compatible with isotopic equilibrium between gaseous CO2, and aqueous and solid carbonate species in a soil system controlled by diffusive mass transfer of soil CO2 derived from irreversible oxidation of soil organic matter. Organic matter and pedogenic carbonate from palaeosols of Pleistocene to late Miocene age in Pakistan also differ by 14–16%,. This indicates that diagenesis has not altered the original isotopic composition of either phase, thus confirming their use in palaeoecological reconstruction.

Organic-Inorganic Interactions and Sandstone Diagenesis

Abstract: The maturation of organic material in hydrocarbon source rocks and inorganic diagenetic reactions in reservoir sandstones are a natural consequence when a prism of sedimentary rocks is buried. We can predict the distribution of porosity and permeability enhancement in potential hydrocarbon reservoirs by integrating the reaction processes characterizing the progressive diagenesis of a reservoir/source rock system. A variety of observations suggests that the organic solvents needed to increase aluminosilicate and carbonate solubilities in sandstones can be generated either by thermal or oxidative cracking of carbonylic or phenolic groups from kerogen in adjacent source rocks. For example, nuclear magnetic resonance (NMR) spectra of kerogen show that peripheral carbonylic and phenolic groups are released from the kerogen molecule before liquid hydrocarbons are generated. Experimental data indicate these water-soluble organic species can significantly affect the stability of both carbonates and aluminosilicates. Water-soluble organic acid anions (carboxylic) have been observed in oil-field waters in concentrations up to 10,000 ppm, and they commonly dominate the alkalinity in the fluid phase from 80° to 120°C. We can model the integration of organic and inorganic diagenetic reactions by constructing a series of potential reaction pathways with increasing temperature for a system that includes aluminosilicates, carbonates, organic chelate species (carboxylic and phenolic), and CO2. The important chemical divides in these diagenetic flow diagrams are dependent on temperature, the nature of the pH buffer (carbonate species or organic acid anion species), and the relationship between organic acid anions and PCO2 (P = partial pressure). Forward predictive capabilities result when this general diagenetic model is placed in a time-temperature framework. The detailed organic and inorganic geochemistry and the general thermal scenario used in the time-temperature ana ysis must be basin specific. Casting the diagenetic history of a sandstone into this type of process-oriented model helps us move from a descriptive mode to a predictive mode of analysis. Two types of information result: (1) general optimum conditions for porosity and permeability enhancement in sandstones are delineated and (2) specifically, the degree and potential for porosity and permeability enhancement are determined. Predictive models have been developed for several tectonic settings, including rift or pull-apart basins and intermontane or Laramide basins. From these reconstructions, we can forward-predict the porosity-enhancing potential of a diagenetic system based on an understanding of the reaction process in a time-temperature framework.

Pre-biotic organic matter from comets and asteroids

Abstract: Several authors have suggested that comets or carbonaceous asteroids contributed large amounts of organic matter to the primitive Earth, and thus possibly played a vital role in the origin of life. But organic matter cannot survive the extremely high temperatures (>10(4) K) reached on impact, which atomize the projectile and break all chemical bonds. Only fragments small enough to be gently decelerated by the atmosphere--principally meteors of 10(-12)-10(-6) g--can deliver their organic matter intact. The amount of such 'soft-landed' organic carbon can be estimated from data for the infall rate of meteoritic matter. At present rates, only approximately 0.006 g cm-2 intact organic carbon would accumulate in 10(8) yr, but at the higher rates of approximately 4 x 10(9) yr ago, about 20 g cm-2 may have accumulated in the few hundred million years between the last cataclysmic impact and the beginning of life. It may have included some biologically important compounds that did not form by abiotic synthesis on Earth.

The post-Paleozoic chronology and mechanism of 13C depletion in primary marine organic matter.

Abstract: Carbon-isotopic compositions of geoporphyrins have been measured from marine sediments of Mesozoic and Cenozoic age in order to elucidate the timing and extent of depletion of 13C in marine primary producers. These results indicate that the difference in isotopic composition of coeval marine carbonates and marine primary photosynthate was approximately 5 to 7 permil greater during the Mesozoic and early Cenozoic than at present. In contrast to the isotopic record of marine primary producers, isotopic compositions of terrestrial organic materials have remained approximately constant for this same interval of time. This difference in the isotopic records of marine and terrestrial organic matter is considered in terms of the mechanisms controlling the isotopic fractionation associated with photosynthetic fixation of carbon. We show that the decreased isotopic fractionation between marine carbonates and organic matter from the Early to mid-Cenozoic may record variations in the abundance of atmospheric CO2.

Determination of atmospheric soot carbon with a simple thermal method

Abstract: The dark component of carbonaceous aerosols is often referred to as “soot carbon”. Soot consists of pure elemental carbon along with highly polymerized organic matter. An accurate discrimination between the soot carbon and the other components of carbonaceous aerosols is difficult to obtain by thermal analytical processes. Here, we report an optimization of a 2-step thermal method focused on the soot carbon determination of atmospheric particles. The organic material which does not absorb visible light is removed from the collection substrate under a pure oxygen flow during a precombustion step which has been carefully optimized in terms of temperature (340°C) and duration (2 h). The remaining carbon content is determined by coulometric titration of the CO 2 evolved from the combustion of the samples. The method has been tested quantitatively for analytical artefacts (e.g., “soot” production due to the charring of organics; soot losses during the preheating step) by using various standards such as pure graphite, pure organic and natural biogenic compounds and replicates of ambient air samples collected in urban, rural and forested areas in France. The results obtained so far indicate that this approach satisfactorily distinguishes between organic and soot carbon and allows reliable soot carbon determination at the μg level in atmospheric samples from a wide variety of environments. This study confirms that soot carbon is not composed primarily of elemental carbon. It appears to be a variable mixture of highly condensed organic compounds. These compounds may be either combustion-derived material or the result of low-temperature gas-to-particle conversion processes. DOI: 10.1111/j.1600-0889.1989.tb00316.x

Dynamics of Soil Organic Matter in Tropical Ecosystems

Abstract: Organic inputs to the soil must be considered separate from soil organic matter (SOM) to understand properly the physical, chemical, and biologi­ cal processes involved in the sustainability of tropical agroecosystems. Present management of organic inputs is largely empirical and qualita­ tive. A better understanding of the role ot organic inputs on the processes involved in litter decomposition, nutrient cycling, and soil aggregation is needed. The management of organic inputs should be as predictable as that of inorganic inputs, such as fertilizers and lime. The application of or­ ganic inputs should promote the synchrony of nutrient release w;th plant growth demands. Predictive parameters are needed to approach synchrony. Research on decomposition of organic inputs should be con­ ducted in various agroecosystems. Very little is known about the role of root litter in tropical agroecosystems. Six research imperatives are iden­ tified for tropical agroecosystems: (1)quantify the biomass and nutrient content of aboveground organic inputs: (2)develop predictive parameters for nutrient release patterns, or quality, of organic inputs; (3) investigate the effect of piacement of organic inputs on nutrient Organic Input Management in Tropical Agroecosystems 125 availability; (4) quantify production and nutrient releaie by roots, identify resource quality parameters (see Chapter 4) that describe root decom­ position, and determine the relative importance of roots as sources of nutrients: (5) investigate the effects of quality and placement of organic in­ puts on soil physical properties; and (6) understand how organic inputs are transformed into functional SOM pools in soils differing in texture, mineralogy, and moisture and temperature regimes. We need reliable field methods ior measuring root production and decomposition, transfer from organic inputs into SOM fractions, and transfer processes among SOM pools. The diversity of tropical species and farming systems provides ample combinations of crops and organic inputs for improving tropical agroecosystems. Agroecosystems differ from natural ecosystems in that large amounts of biomass and nutrients are removed as crops. Nutrient outputs via crop harvests far exceed the other nutrient loss pathways combined. This is shown in Table 1 where asummary of annual crop nutrient budget studies from temperate-region countries is presented. A long-standing principle of sound agriculture is to replace the nutrienis lost via crop harvests by adding either inorganic or organic fertilizers. Aside from adding nutrients, organic additions improve soil physical properties and help maintain soil organic matter content, all of which positively affect plant productivity (Allison, 1973). Organic inputs to the soil consist of aboveand belowground litter, crop residues, mulches, green manures, animal manures, and sewage. Some of these inputs are grown and recycled on site " Tablo 1. Summary of nutrient inputs and outputs (kg hayr") of 18 crop production systems from the United Statos, United Kingdom, Netherlands, France, Israel, and Japan. (Mean and standard deviations calculated from data of Frissel, 1978.) Nutrient inouts or outouts Nitrogen Phosohorus Potassium Inputs Inorganic fertilizer 156 t 189 39 "t38 119 = 188 Nfixation 19 ±: 39 Other 13 ±: 13 0.4 t 0.8 9 13 Total 188 ± 75 39 "t39 127 t 176 Outputs -arvest removal 103 t 86 16 ±16 91 ±t 13 Denitrification 20 224a Leacflng 38b nd nd Total 127 ±: 95 16 = 6 91 ± 13 Balance 60 "93 24 ±30 37 = 77 a. Mean of 10 out ot 18 data sets reportir,j denitrification. b. Mean of 3 out of 18 data sets reporting leaching. nd = not determined. 126 Dynamics of SOM in Tropical Ecosystems (internal to the system), while others are brought in from other sites, thu, constituting an cetrnal source of nutrients and orezanic C. Organic inputs are distinct from soil organic matter (SONM), which can be defincd as organic material of biological oricin that has undergone partial or complete transformation in the soil and is located below the soil surface. In much of the literature, organi.: 'puts and SOM arc lumped together as "organic matter," creating considerable con-fusion %4hcnattempting to evaluate and manage the role of organic :nputs c mpared to that of sod organic matter. We proposc, therefore, to discourai'c using the term organicmatterand encourage the use of organic inputs and soti ,rgantc matter ISOM). Although early acriculturc depcnded heavily on organic inputs, the emphasis shiftcd to inorganic fertilizcrs as they became abundant and economi­ cally practical. Today, because agricultural development in much of the tropics is largely limited by economic constraints, emphasis must again be placed on use of organic inputs along 'ith chcmic:;l fertilizers. This paper briefly reviews Figure 1. Conceptual model cf ra;cr -ccls and transfers of soil organic matter. Numbers indicate focus of research 'mperatives (see text conclusions).

Determination of organic matter content in arid-zone soils using a simple loss-on-ignition method

Abstract: A simple and rapid procedure for the determination of organic matter content in mineral soils by loss‐on‐ignition without pretreatment was studied. Attention was given to the possible effect of inorganic compounds abundant in mineral soils on the estimation of organic matter content by this method. Both fast heating (DTA‐TGA type) studies and prolonged heating procedures were employed on natural and “synthetic”; soils. The results were compared to those obtained by the dichromate wet‐oxidation method widely used in soil laboratories for organic matter determination. In a group of 91 soils collected from various mineral soils in Israel, and having OM contents between 0.09 and 13.23%, a correlation coefficient of 0.972 was obtained for the linear regression between organic matter content measured by the proposed method and organic carbon measured by the dichromate wet‐oxidation method.

Organic matter of the troposphere - V: Application of molecular marker analysis to biogenic emissions into the troposphere for source reconciliations.

Abstract: Organic matter in tropospheric aerosols is derived from two major sources and is admixed depending on the geographic area. These sources are biogenic detritus and anthropogenic emissions. The biogenic materials in the solvent-extractable organic matter are comprised predominantly of higher plant waxes, with lesser amounts of resin and microbial detritus and the anthropogenic components are primarily vehicular emissions (e.g. oils, soot, etc.) and input from combustion (e.g. charcoal, thermally-altered biogenic matter, etc.). Both biogenic detritus and anthropogenic emissions contain organic compounds (C12−C40+), which can be identified with unique and distinguishable distribution patterns. Molecular composition analysis has been applied to such extracts after suitable chemical separation into subfractions (i.e. hydrocarbons, ketones, aldehydes, carboxylic acids, alcohols, and wax esters). Both homologous compound series and specific natural products (e.g. phytosterols, terpenes, etc.) are identified as molecular markers. Aerosols from rural and remote areas in the western United States, South America, Nigeria and Australia have been analyzed and all contained predominantly plant waxes. The loadings of hydrocarbons ranged approximately from 10–1400 ng/m3 of air, of fatty acids from 10–450 ng/m3 and of fatty alcohols from 10–1650 ng/m3. These higher molecular weight lipids primarily from flora comprise a major component of the organic carbon in rural and remote aerosols. They are thus important indicators for regional biogenic sources in the global cycling of organic carbon.

Influence of macroclimate on soil microbial biomass

Abstract: Soils from 12 agricultural long-term experimental fields located in contrasting climatic regions were used to assess the influence of macroclimate on soil microbial biomass (Cmicr). Cmicr was measured using the substrate-induced respiration technique. When Cmicr was calculated on the basis of soil dry mass (mg Cmicr g−1 soil d.m.), only poor correlations with climatic variables were found. However, when Cmicr was calculated based on organic carbon (mg Cmicr g−1 Corg), close relationships with climatic variables were found. Especially, integrative climatic variables which reflected not only the temperature regime but also the moisture conditions, were found to be good predictors of the Cmicr-to-Corg ratio. The best predictor was the precipitation-evaporation quotient which accounted for 68% of the variance. With a stepwise, multiple-linear regression procedure, the clay content and pH of the soils were found to account for another 2 and 3% of the variance, respectively. Parts of the remaining variance could be accounted for by differences in fertilization, crops, tillage practices or residue returns. The Cmicr-to-Corg ratio of monocultures was significantly lower than that of crop rotations, and so was that of mineral fertilized compared to organically manured plots. The organic matter content of the soils studied were at or near the equilibrium level. An equilibrium function for the Cmicr-to-Corg ratio was calculated: y = 18.18+ 108.3-e−6.728x, where x = precipitation/ evaporation. Deviation from this equilibrium line would indicate that a certain soil is losing or accumulating organic matter.

Effect of chemical forms of cadmium, zinc, and lead in polluted soils on their uptake by cabbage plants

Abstract: Seven soils which had been polluted with heavy metals from a zinc smelter were sequentially extracted so that Cd, Zn, and Pb could be partitioned into five operationally defined chemical fractions: exchangeable, bound to carbonate, bound to Fe−Mn oxide, bound to organic matter, and residual. Cabbage was planted in the soils to examine the effects of concentration and chemical form of the metals in soil on their uptake. The exchangeable fraction contained 55, 13, and 6%, and carbonate fraction 11, 10, and 6% of the total Cd, Zn, and Pb, respectively. The highest amount of Zn (42%) was detected in residual, and Pb (43%) in organic fraction. Metal levels in plant were in accord with their levels in soil. Heavy metals in exchangeable and carbonate forms strongly controlled their uptake more than the total content in soil. Proportion of metal uptake to their amount in the soils was Cd>Zn>Pb agreeing with soluble sequence of the elements in soil. The uptake rate of exchangeable+carbonate forms was the same for the three elements (0.76, 1.01, and 0.98% of Cd, Zn, and Pb, respectively).

Role of debris dams in the structure and functioning of low-gradient headwater streams

Abstract: The importance of debris dams to organic matter dynamics and the mac- roinvertebrate community of two low-gradient, headwater streams on the Coastal Plain of Virginia was examined through sampling of natural dams and by experimental manipu- lation of dam abundance. Buzzards Branch had permanent flow and a sand substrate; Colliers Creek had intermittent flow and an organic substrate. Dam abundance varied from 8 to 13 dams/100 m of stream length and covered only 1-3% of channel surface. Annual mean storage of organic matter (ash-free dry mass; particles >0.15 mm) in debris dams was 922 g/m2 and 3356 g/m2 in Colliers Creek and Buzzards Branch, respectively. Wood > 16 mm constituted 73-80% and fine particulate organic matter (FPOM; particles 0.15-1 mm) < 1% of total organic matter in the streams. Dams stored 21% and 85% of the coarse particulate organic matter (CPOM) on the channel surface in Colliers Creek and Buzzards Branch, respectively. Storage was highly seasonal, with highest concentrations following autumnal leaf fall and only 5-17% of December storage present in February. Dams were net exporters of large amounts of small particles of CPOM and FPOM. Macroinvertebrate density and biomass in dams was correlated with changes in organic matter storage both over seasons and between streams. Annual mean densities were 8915 individuals and 22 302 individuals/, and biomass was 0.3 g/m2 and 3.2 g/m2, in Colliers Creek and Buzzards Branch, respectively. Densities were at least 10 times, and biomass 5 times, as great in dams as on sediment. Increasing the abundance of dams increased organic matter storage, macroinvertebrate abundance, and the relative contribution of shredders to biomass, both in dams and on sediment. Increasing dam abundance also increased retention of leaves during base and especially storm flow. Widespread removal of riparian vegetation throughout the south- eastern Coastal Plain, resulting in a decrease in the number of dams in streams, no doubt has altered the ecological characteristics of these streams relative to historical, pristine conditions. In particular, the transport of both energy and nutrients to downstream riverine areas likely is greater, and production of higher consumer levels probably is lower under present conditions.

C-Isotope stratigraphy, a monitor of paleoenvironmental change: A case study from the early cretaceous

Abstract: Today's disturbance of the global carbon cycle induced by anthropogenic processes has raised new interest in the history of the global carbon cycle and its relationship to climate and other geochemical cycles. Carbon-isotope stratigraphy proves to be most useful as a monitor of the history of the carbon-cycle during the last 200 million years. In the introductory paragraphs of this review the mode of functioning of the global carbon-cycle is summarized and the connection between carbon-cycle and carbon isotope geochemistry is documented. A case study on the disturbance of the global carbon cycle during the Aptian-Albian is presented. The disturbance of the carbon cycle lasting up to millions of years is recorded in the carbon-isotope stratigraphy of pelagic sediments. It is superimposed on high frequency sedimentological cycles, related to climate and oceanographic cycles of 20, 40 or 100 ky duration. The data reviewed suggest that the change in the global carbon system was linked to a global acceleration of geochemical cycles triggered by a long-term change in atmospheric CO2 controlled by the rate of sea-floor formation and by volcanic activity. Increased accumulation rates of terrestrial material and terrestrial organic matter in marine sediments may be used as an indicator of an intensified hydrological cycling resulting in higher water-discharge rates. An intensification of the Aptian-Albian water cycle is further reflected in continental sediments monitoring a period of elevated humidity. An increase in water discharge rates should have affected the transfer rate of dissolved nutrients from continents to oceans. Elevated concentrations of phosphorus may have led to an increase in Aptian-Albian oceanic productivity enhancing the transfer of marine organic matter from the oceanic into the sedimentary reservoir. Increased productivity, increased bulk sedimentation rates and poorly oxygenated deep-water led to increased preservation of marine and terrestrial organic matter in marine sediments. The accelerated output of marine organic carbon from the oceanic reservoir is ultimately registered in the positive carbon-isotope excursion of the marine carbonate carbon-isotope stratigraphy.

Organic contaminants in Welsh soils: polynuclear aromatic hydrocarbons

Abstract: Soil samples from 49 locations in Wales have been analyzed for 14 polynuclear aromatic hydrocarbons (PAHs) by HPLC with UV and fluorescence detection to define the normal or typical range of PAHs in surface soils (0–5 cm). The ΣPAH (defined as the sum of 14 PAH compounds sought) values vary by over 3 orders of magnitude. In general, soils show a constant qualitative mixture of PAH components but marked differences in absolute values along the remote-rural-urban gradient. Soil organic matter content has some controlling influence over soil ΣPAH values, but other soil properties (percent clay, bulk density) do not. In general, soils naturally rich in organic matter, such as peat bogs or deciduous and coniferous woodland soils, contain higher ΣPAH concentrations. SIMCA pattern recognition studies have been used to examine patterns in the samples and the variables. Principal component analysis supported the classification of “remote/rural” and “urban” soil samples based on the pattern of PAH; the distinction between remote/rural and urban is made at 600 μg of ΣPAH kg-1. The data are discussed further in the context of factors controlling soil PAH patterns.

Solid-state Carbon-13 Nuclear Magnetic Resonance and Infrared Spectroscopy of Composted Organic Matter

Abstract: Use of stabilized composts as horticultural container media has been a fruitful and desirable alternative in utilization of agricultural wastes. We prepared compost from cattle manure and investigated the products at various stages of the composting process. The objectives of this work were to measure, quantify and correlate changes in the organic constituents of separated cattle manure (CSM—the solid fraction obtained by centrifugal separators from a slurry of cattle manure) during composting by using both chemical and spectroscopical analytical methods. This research should provide the information necessary for the establishment of maturity indexes for CSM. Carbon-13 NMR spectra acquired with Cross-Polarization Magic Angle Spinning (CPMAS) and infrared spectra measured with a Fourier-Transform InfraRed spectrophotometer (FTIR) were applied to bulk CSM samples without extraction. Both methods confirmed the presence of appreciable amounts of carbohydrates throughout the composting process. During the process the level of carbohydrates decreased while levels of alkyl C, aromatic C, and carboxyl groups increased. The higher rate of decomposition of the carbohydrates resulted in the accumulation of modified lignin. Changes in FTIR absorbance ratios of several distinct peaks were linearly and significantly correlated with various parameters of compost maturity. Crude fiber analyses showed lower concentrations of soluble organic matter, hemicellulose and cellulose while that of lignin increased. Cation exchange capacity increased from 63 to 181 cmol/kg OM, and humic substances content increased markedly from 38 to 71% of the organic matter, while the C/N ratio decreased from 27.1:1 to 8.7:1 during the 147-d composting process. The proposed spectrometric procedures using CPMAS ¹³C-NMR and FTIR measurements directly on decomposing organic matter without extraction, provide information exhibiting significant correlations with more conventional chemical parameters of compost maturity. Contribution from the Seagram Center for Soil and Water Sciences.

Influence of sorghum residues and tillage on soil organic matter and soil microbial biomass in an australian vertisol

Abstract: Short- and medium-term changes in soil organic matter content following a change in soil management or land use are often difficult to measure because they occur slowly against a large background of soil organic matter which can have considerable spatial variability. Results from an experiment with grain sorghum (Sorghum bicolor L.) on a vertisol in sub-tropical Australia demonstrate the usefulness of two techniques for detecting trends in surface soil organic matter before they can be assessed by conventional methods. Firstly, using soil microbial biomass C as a sensitive indicator of changes in soil organic matter. Secondly, by using initial values of soil organic C or total N, measured before imposition of treatments, as a covariate in an analysis of variance. The combination of these techniques provided the most sensitive approach for detecting changes. The above-ground residues of sorghum (41 dry matter ha−1) were either retained or removed from plots that received conventional or zero tillage for 6 yr. Averaged over tillage treatments, soil organic C in the surface 0–10 cm layer was 8% greater in the residue-retained than in the residue-removed treatment, a difference equivalent to 16% of the C added as residues. The trend to increased soil total N was not significant. Residue retention caused larger percentage increases in microbial biomass C, measured by the chloroform fumigation-incubation method, than in total organic C and total N. The increase in biomass C was 12%, biomass N 23% and biomass P 45%, equivalent to 0.7% of the C, 7% of the N and 32% of the P added in residues. Residue retention decreased the biomass C-to-P ratio from 48 to 35, but these values were still much wider than those previously measured in U.K. soils. Residue retention increased respiration by about 45% (measured by CO2 evolution during a 30-day incubation) but had little effect on biomass C-to-N ratio or mineralization of N. Averaged over the two residue management treatments, soil organic C in the surface 10 cm layer was 7% greater under zero tillage than under conventional tillage. The corresponding increase in biomass C was 14–21%, but there were no differences in biomass N or biomass P. CO2 evolution and specific respiration by the biomass (μ g CO2-C evolved g−1 biomass C day−1) were less in zero-tilled than in conventionally tilled soils. The combined effects of residue retention and zero tillage caused increases of 15% in surface soil organic C, 18% in soil total N and 31% in biomass C.

Fluxes of Cu, Zn, Pb, Cd, Cr, and Ni in temperate forest ecosystems

Abstract: The literature on the fluxes of six heavy metals in temperate forest ecosystems is reviewed. Special attention is given to wet and dry deposition and internal flux, to metal budgets for ecosystems and soils, to concentrations in aqueous compartments of the ecosystem and to speciation in soil solutions. Metal fluxes are discussed in relation to pollution load, soil type, tree species and land use. The mobility of Cu and Pb is strongly dependent on the solubility of organic matter. These metals are commonly accumulated in forest soils. Zinc, Cd and Ni are greatly influenced by soil acidity and are often lost in considerable amounts from acidified soils. Chromium is often at balance in forest ecosystems. Implications for metal solubility and budgets in forest soils are discussed in connection with an increase in soil acidification.

Priming effect of some organic additions to 14C-labelled soil.

Abstract: Small amounts of organic substances or finely-ground plant material were added to soil containing 14C-labelled organic matter. The rates of CO2 and 14CO2 production were measured with an i.r. spectrometer and a liquid scintillation counter, respectively. The extra 14CO2 (primed C) that evolved during decomposition most probably originated from conversions in the (microbial) biomass. We suggest that priming according to the original definition, viz., an acceleration of the decomposition of (stable) soil organic matter (humus), did not exist or was negligible in our experiments. Extra 14CO2 was produced after unlabelled glutamate was added to washed suspensions of 14C-labelled biomass in perlite. The amount of 14CO2 varied with the amount of biomass. The difference between the priming (extra 14CO2 production) caused by glucose (small and lasting only 2–3 days) and that caused by glutamate and aspartate (relatively large and lasting 30–40 days) was very pronounced. After decomposition, glucose, cellulose, wheat straw and sewage sludge left more carbon in the soil than was lost due to priming, so that there was a positive net effect. The two amino acids, glutamate and aspartate, however, had slightly negative net effects. The phenomena observed are probably the result of an accelerated turnover of biomass-carbon. The extra loss of 14C during the priming period was less than the original amount of 14C present in the biomass.