Uncertainties and novel prospects in the study of the soil carbon dynamics

Establishment of the Kyoto Protocol has resulted in an effort to look towards living biomass and soils for carbon sequestration. In order for carbon credits to be meaningful, sustained carbon sequestration for decades or longer is required. It has been speculated that improved land management could result in sequestration of a substantial amount of carbon in soils within several decades and therefore can be an important option in reducing atmospheric CO2 concentration. However, evaluation of soil carbon sources and sinks is difficult because the dynamics of soil carbon storage and release is complex and still not well understood. There has been rapid development of quantitative techniques over the past two decades for measuring the component fluxes of the global carbon cycle and for studying the soil carbon cycle. Most significant development in the soil carbon cycle study is the application of accelerator mass spectrometry (AMS) in radiocarbon measurements. This has made it possible to unravel rates of carbon cycling in soils, by studying natural levels of radiocarbon in soil organic matter and soil CO2. Despite the advances in the study of the soil carbon cycle in the recent decades, tremendous uncertainties exist in the sizes and turnover times of soil carbon pools. The uncertainties result from lack of standard methods and incomplete understanding of soil organic carbon dynamics, compounded by natural variability in soil carbon and carbon isotopic content even within the same ecosystem. Many fundamental questions concerning the dynamics of the soil carbon cycle have yet to be answered. This paper reviews and synthesizes the isotopic approaches to the study of the soil carbon cycle. We will focus on uncertainties and limitations associated with these approaches and point out areas where more research is needed to improve our understanding of this important component of the global carbon cycle.     

Physicochemical soil parameters affecting sequestration and mycobacterial biodegradation of polycyclic aromatic hydrocarbons in soil

Six soils, obtained from grasslands and wooded areas in Northeastern Illinois, were physicochemically characterized. Measured parameters included total organic carbon (TOC) content, contents of humic acid, fulvic acid and humin, pore volume and pore size distribution, and chemical makeup of soil organic matter (determined using solid-state ¹³C-NMR). Moistened, gamma-sterilized soils were spiked with 200 ppm of either phenanthrene or pyrene (including ¹⁴C label); following 0, 40, or 120 days of aging, the contaminant-spiked soils were then inoculated with Mycobacterium austroafricanum strain GTI-23, and evolution of ¹⁴CO₂ was assessed over a 28-day period. Results for both phenanthrene and pyrene indicated that increased contact time led to increased sequestration and reduced biodegradation, and that TOC content was the most important parameter governing these processes. One soil, although only tested with phenanthrene, showed significantly lower-than-expected sequestration (higher-than-expected mineralization) after 40 days of aging, despite a very high TOC value (>24%). Because the level of sequestration in this soil was proportional to the others after 120 days of aging, this implies some difference in the temporal progression of sequestration in this soil, although not in its final result. The primary distinguishing feature of this soil was its considerably elevated fulvic acid content. Further experiments showed that addition of exogenous fulvic acid to a soil with very low endogenous humic acids/fulvic acids content greatly enhanced pyrene mineralization by M. austroafricanum. Extractabilities of 13 three- to six-ring coal tar PAHs in n-butanol from the six soils after 120 days of sequestration were strongly TOC-dependent; however, there was no discernible correlation between n-butanol extractability and mycobacterial PAH mineralization.     

Separation and capture of CO2 from large stationary sources and sequestration in geological formations--coalbeds and deep saline aquifers

The topic of global warming as a result of increased atmospheric CO2 concentration is arguably the most important environmental issue that the world faces today. It is a global problem that will need to be solved on a global level. The link between anthropogenic emissions of CO2 with increased atmospheric CO2 levels and, in turn, with increased global temperatures has been well established and accepted by the world. International organizations such as the United Nations Framework Convention on Climate Change (UNFCCC) and the Intergovernmental Panel on Climate Change (IPCC) have been formed to address this issue. Three options are being explored to stabilize atmospheric levels of greenhouse gases (GHGs) and global temperatures without severely and negatively impacting standard of living: (1) increasing energy efficiency, (2) switching to less carbon-intensive sources of energy, and (3) carbon sequestration. To be successful, all three options must be used in concert. The third option is the subject of this review. Specifically, this review will cover the capture and geologic sequestration of CO2 generated from large point sources, namely fossil-fuel-fired power gasification plants. Sequestration of CO2 in geological formations is necessary to meet the President's Global Climate Change Initiative target of an 18% reduction in GHG intensity by 2012. Further, the best strategy to stabilize the atmospheric concentration of CO2 results from a multifaceted approach where sequestration of CO2 into geological formations is combined with increased efficiency in electric power generation and utilization, increased conservation, increased use of lower carbon-intensity fuels, and increased use of nuclear energy and renewables. This review covers the separation and capture of CO2 from both flue gas and fuel gas using wet scrubbing technologies, dry regenerable sorbents, membranes, cryogenics, pressure and temperature swing adsorption, and other advanced concepts. Existing commercial CO2 capture facilities at electric power-generating stations based on the use of monoethanolamine are described, as is the Rectisol process used by Dakota Gasification to separate and capture CO2 from a coal gasifier. Two technologies for storage of the captured CO2 are reviewed--sequestration in deep unmineable coalbeds with concomitant recovery of CH4 and sequestration in deep saline aquifers. Key issues for both of these techniques include estimating the potential storage capacity, the storage integrity, and the physical and chemical processes that are initiated by injecting CO2 underground. Recent studies using computer modeling as well as laboratory and field experimentation are presented here. In addition, several projects have been initiated in which CO2 is injected into a deep coal seam or saline aquifer. The current status of several such projects is discussed. Included is a commercial-scale project in which a million tons of CO2 are injected annually into an aquifer under the North Sea in Norway. The review makes the case that this can all be accomplished safely with off-the-shelf technologies. However, substantial research and development must be performed to reduce the cost, decrease the risks, and increase the safety of sequestration technologies. This review also includes discussion of possible problems related to deep injection of CO2. There are safety concerns that need to be addressed because of the possibilities of leakage to the surface and induced seismic activity. These issues are presented along with a case study of a similar incident in the past. It is clear that monitoring and verification of storage will be a crucial part of all geological sequestration practices so that such problems may be avoided. Available techniques include direct measurement of CO2 and CH4 surface soil fluxes, the use of chemical tracers, and underground 4-D seismic monitoring. Ten new hypotheses were formulated to describe what happens when CO2 is pumped into a coal seam. These hypotheses provide significant insight into the fundamental chemical, physical, and thermodynamic phenomena that occur during coal seam sequestration of CO2.     

Soil carbon dynamics in cropland and rangeland

Most soils in the Midwestern USA have lost 30 to 50% of their original pool, or 25 to 40 Mg C/ha, upon conversion from natural to agricultural ecosystems. About 60 to 70% of the C thus depleted can be resequestered through adoption of recommended soil and crop management practices. These practices include conversion from plow till to no till, frequent use of winter cover crops in the rotation cycle, elimination of summer fallow, integrated nutrient management along with liberal use of biosolids and biological nitrogen fixation, precision farming to minimize losses and enhance fertilizer use efficiency, and use of improved varieties with ability to produce large root biomass with high content of lignin and suberin. The gross rate of soil organic carbon (SOC) sequestration ranges from 500 to 800 kg/ha/year in cold and humid regions and 100 to 300 kg/ha/year in dry and warm regions. The rate of SOC sequestration can be measured with procedures that are cost effective and credible at soil pedon level, landscape level, regional or national scale. In addition to SOC, there is also a large potential to sequester soil inorganic carbon (SIC) in arid and semi-arid regions. Soil C sequestration has numerous ancillary benefits. It is truly a win-win situation: extremely cost-effective, and a bridge to the future until alternative energy options take effect.     

Impact of soil movement on carbon sequestration in agricultural ecosystems

Recent modeling studies indicate that soil erosion and terrestrial sedimentation may establish ecosystem disequilibria that promote carbon (C) sequestration within the biosphere. Movement of upland eroded soil into wetland systems with high net primary productivity may represent the greatest increase in storage capacity potential for C sequestration. The capacity of wetland systems to capture sediments and build up areas of deposition has been documented as well as the ability of these ecosystems to store substantial amounts of C. The purpose of our work was to assess rates of sediment deposition and C storage in a wetland site adjacent to a small first-order stream that drains an agricultural area. The soils of the wetland site consist of a histosol buried by sediments from the agricultural area. Samples of deposited sediments in the riparian zone were collected in 5 cm increments and the concentration of 137Cs was used to determine the 1964 and 1954 deposition layers. Agricultural activity in the watershed has caused increased sediment deposition to the wetland. The recent upland sediment is highly enriched in organic matter indicating that large amounts of organic C have been sequestered within this zone of sediment deposition. Rates of sequestration are much higher than rates that have occurred over the pre-modern history of the wetland. These data indicate the increased sedimentation rates in the wetland ecosystem are associated with increased C sequestration rates.     

Emissions and risks associated with oxyfuel combustion: State of the science and critical data gaps

Oxyfuel combustion is a promising technology that may greatly facilitate carbon capture and sequestration by increasing the relative CO₂ content of the combustion emission stream. However, the potential effect of enhanced oxygen combustion conditions on emissions of criteria and hazardous air pollutants (e.g., acid gases, particulates, metals and organics) is not well studied. It is possible that combustion under oxyfuel conditions could produce emissions posing different risks than those currently being managed by the power industry (e.g., by changing the valence state of metals). The data available for addressing these concerns are quite limited and are typically derived from laboratory-scale or pilot-scale tests. A review of the available data does suggest that oxyfuel combustion may decrease the air emissions of some pollutants (e.g., SO₂, NOx, particulates) whereas data for other pollutants are too limited to draw any conclusions. The oxy-combustion systems that have been proposed to date do not have a conventional “stack” and combustion flue gas is treated in such a way that solid or liquid waste streams are the major outputs. Use of this technology will therefore shift emissions from air to solid or liquid waste streams, but the risk management implications of this potential change have yet to be assessed. Truly useful studies of the potential effects of oxyfuel combustion on power plant emissions will require construction of integrated systems containing a combustion system coupled to a CO₂ processing unit. Sampling and analysis to assess potential emission effects should be an essential part of integrated system tests.

Implications: Oxyfuel combustion may facilitate carbon capture and sequestration by increasing the relative CO₂ content of the combustion emission stream. However, the potential effect of enhanced oxygen combustion conditions on emissions of criteria and hazardous air pollutants has not been well studied. Combustion under oxyfuel conditions could produce emissions posing different risks than those currently being managed by the power industry. Therefore, before moving further with oxyfuel combustion as a new technology, it is appropriate to summarize the current understanding of potential emissions risk and to identify data gaps as priorities for future research.     

Redox potential characterization and soil greenhouse gas concentration across a hydrological gradient in a Gulf coast forest

Soil redox potential (Eh), concentrations of oxygen (O2) and three greenhouse gases (CO2, CH4, and N2O) were measured in the soil profile of a coastal forest at ridge, transition, and swamp across a hydrological gradient. The results delineated a distinct boundary in soil Eh and O2 concentration between the ridge and swamp with essentially no overlap between the two locations. Critical soil Eh to initiate significant CH4 production under this field conditions was about +300 mV, much higher than in the homogenous soils (about -150 mV). The strength of CH4 source to the atmosphere was strong for the swamp, minor for the transition, and negligible or even negative (consumption) for the ridge. Maximum N2O concentration in the soils was found at about Eh +250 mV, and the soil N2O emission was estimated to account for less than 4% for the ridge and transition, and almost negligible for the swamp in the cumulative global warming potential (GWP) of these three gases. The dynamic nature of this study site in response to water table fluctuations across a hydrological gradient makes it an ideal model of impact of future sea level rise to coastal ecosystems. Soil carbon (C) sequestration potential due to increasing soil water content upon sea level rise and subsidence in this coastal forest was likely limited and temporal, and at the expense of increasing soil CH4 production and emission.     

Carbon Sequestration Function of Check-Dams: A Case Study of the Loess Plateau in China

Check-dams are the most common structures for controlling soil erosion in the Loess Plateau. However, the effect of check-dams on carbon sequestration, along with sediment transport and deposition, has not been assessed over large areas. In this study, we evaluated the carbon sequestration function of check-dams in the Loess Plateau. The results indicate that there were approximately 11 000 check-dams distributed in the Loess Plateau, with an estimate of the amount of sediment of 21 × 10⁹ m³ and a soil organic carbon storage amount of 0.945 Pg. Our study reveals that check-dams in the Loess Plateau not only conserve soil and water but also sequester carbon.     

Feasibility of biochar application on a landfill final cover—a review on balancing ecology and shallow slope stability

Due to the increasing concerns on global warming, scarce land for agriculture, and contamination impacts on human health, biochar application is being considered as one of the possible measures for carbon sequestration, promoting higher crop yield and contamination remediation. Significant amount of researches focusing on these three aspects have been conducted during recent years. Biochar as a soil amendment is effective in promoting plant performance and sustainability, by enhancing nutrient bioavailability, contaminants immobilization, and microbial activities. The features of biochar in changing soil physical and biochemical properties are essential in affecting the sustainability of an ecosystem. Most studies showed positive results and considered biochar application as an effective and promising measure for above-mentioned interests. Bio-engineered man-made filled slope and landfill slope increasingly draw the attention of geologists and geotechnical engineers. With increasing number of filled slopes, sustainability, low maintenance, and stability are the major concerns. Biochar as a soil amendment changes the key factors and parameters in ecology (plant development, soil microbial community, nutrient/contaminant cycling, etc.) and slope engineering (soil weight, internal friction angle and cohesion, etc.). This paper reviews the studies on the production, physical and biochemical properties of biochar and suggests the potential areas requiring study in balancing ecology and man-made filled slope and landfill cover engineering. Biochar-amended soil should be considered as a new type of soil in terms of soil mechanics. Biochar performance depends on soil and biochar type which imposes challenges to generalize the research outcomes. Aging process and ecotoxicity studies of biochar are strongly required.     

Relationship between Urban and Rural Sulfate Levels

Abstract

The topic of global warming as a result of increased atmospheric CO₂ concentration is arguably the most important environmental issue that the world faces today. It is a global problem that will need to be solved on a global level. The link between anthropogenic emissions of CO₂ with increased atmospheric CO₂ levels and, in turn, with increased global temperatures has been well established and accepted by the world. International organizations such as the United Nations Framework Convention on Climate Change (UNFCCC) and the Intergovernmental Panel on Climate Change (IPCC) have been formed to address this issue. Three options are being explored to stabilize atmospheric levels of greenhouse gases (GHGs) and global temperatures without severely and negatively impacting standard of living: (1) increasing energy efficiency, (2) switching to less carbon-intensive sources of energy, and (3) carbon sequestration. To be successful, all three options must be used in concert. The third option is the subject of this review. Specifically, this review will cover the capture and geologic sequestration of CO₂ generated from large point sources, namely fossil-fuel-fired power gasification plants. Sequestration of CO₂ in geological formations is necessary to meet the President’s Global Climate Change Initiative target of an 18% reduction in GHG intensity by 2012. Further, the best strategy to stabilize the atmospheric concentration of CO₂ results from a multifaceted approach where sequestration of CO₂ into geological formations is combined with increased efficiency in electric power generation and utilization, increased conservation, increased use of lower carbonintensity fuels, and increased use of nuclear energy and renewables.

This review covers the separation and capture of CO₂ from both flue gas and fuel gas using wet scrubbing technologies, dry regenerable sorbents, membranes, cryogenics, pressure and temperature swing adsorption, and other advanced concepts. Existing commercial CO₂ capture facilities at electric power-generating stations based on the use of monoethanolamine are described, as is the Rectisol process used by Dakota Gasification to separate and capture CO₂ from a coal gasifier.

Two technologies for storage of the captured CO₂ are reviewed—sequestration in deep unmineable coalbeds with concomitant recovery of CH4 and sequestration in deep saline aquifers. Key issues for both of these techniques include estimating the potential storage capacity, the storage integrity, and the physical and chemical processes that are initiated by injecting CO₂ underground. Recent studies using computer modeling as well as laboratory and field experimentation are presented here. In addition, several projects have been initiated in which CO₂ is injected into a deep coal seam or saline aquifer. The current status of several such projects is discussed. Included is a commercial-scale project in which a million tons of CO₂ are injected annually into an aquifer under the North Sea in Norway. The review makes the case that this can all be accomplished safely with off-the-shelf technologies. However, substantial research and development must be performed to reduce the cost, decrease the risks, and increase the safety of sequestration technologies.

This review also includes discussion of possible problems related to deep injection of CO₂ . There are safety concerns that need to be addressed because of the possibilities of leakage to the surface and induced seismic activity. These issues are presented along with a case study of a similar incident in the past. It is clear that monitoring and verification of storage will be a crucial part of all geological sequestration practices so that such problems may be avoided. Available techniques include direct measurement of CO₂ and CH4 surface soil fluxes, the use of chemical tracers, and underground 4-D seismic monitoring.

Ten new hypotheses were formulated to describe what happens when CO₂ is pumped into a coal seam. These hypotheses provide significant insight into the fundamental chemical, physical, and thermodynamic phenomena that occur during coal seam sequestration of CO₂ .     

Measuring carbon in forests: current status and future challenges

To accurately and precisely measure the carbon in forests is gaining global attention as countries seek to comply with agreements under the UN Framework Convention on Climate Change. Established methods for measuring carbon in forests exist, and are best based on permanent sample plots laid out in a statistically sound design. Measurements on trees in these plots can be readily converted to aboveground biomass using either biomass expansion factors or allometric regression equations. A compilation of existing root biomass data for upland forests of the world generated a significant regression equation that can be used to predict root biomass based on aboveground biomass only. Methods for measuring coarse dead wood have been tested in many forest types, but the methods could be improved if a non-destructive tool for measuring the density of dead wood was developed. Future measurements of carbon storage in forests may rely more on remote sensing data, and new remote data collection technologies are in development.     

Soil quality and vulnerability in a Mediterranean natural ecosystem of Central Italy

Wet and dry atmospheric depositions and soil chemical and microbiological properties were determined in a Mediterranean natural ecosystem of Central Italy near Rome (Castelporziano Estate). The monitoring of depositions permitted us to quantify the exceedances of S and N compounds (expressed as eqH(+)ha(-1)year(-1)) over the critical loads of acidity. Critical loads, i.e. the quantity of a substance which a part of the environment can tolerate without adverse effects occurring, were determined adopting the level 0 methodology following the UN/ECE Convention on Long-range Transboundary Air Pollution. Deposition data were available for the period 1992-1997, and acidity exceedances were referred to the main vegetation types present in the area. Results showed that most part of the Estate has a medium degree of vulnerability to acidification, and the corresponding risk of acidification deriving from the exceedances of atmospheric deposition was rather low. The study of soil chemical and microbiological properties included mainly total soil organic carbon (SOC), microbial biomass-C, biomass-C/SOC, soil respiration, and metabolic quotient (qCO2). Soil organic C metabolism has been discussed on the basis of the results from eight sampling sites.     

Soil lead levels in a small town environment: a case study from Mt Pleasant, Michigan

Few studies are made on the potential soil Pb burden for a small city in rural environment. Data obtained by atomic absorption spectrophotometry suggest a somewhat weak significant positive relationship (r=0.27) between increased traffic volume and roadside soil Pb content. Median soil Pb levels along the most heavily travelled roads are 320 microg g(-1) while background concentrations are 200 microg g(-1). No significant relationship is found between predominant wind direction and soil Pb content. Zones where cars idle have only slightly elevated Pb levels. Older homes have soil Pb values exceeding 1000 microg g(-1); a significant positive relationship (r=0.59) exists between increasing soil Pb and home age. Schools, which are mainly located away from heavily travelled roads and typically of brick construction, have soil Pb concentrations at background levels. In general, the small city Pb burden is lower than in major urban areas. However, soils around older homes and in special locales, such as salvage yards, have Pb levels comparable to major urban areas.     

Effect of soil properties on bioavailability and extractability of phenanthrene and atrazine sequestered in soil

Sixteen soils with markedly different properties were analyzed to determine their porosity in the range of 7 nm-10 microm, cation-exchange capacity (CEC), surface area and clay mineralogy. The extent of sequestration of phenanthrene and atrazine has been shown to differ markedly among these soils. Correlations were sought between soil characteristics and four methods of measuring sequestration. Simple correlation analysis showed that some but not all measures of phenanthrene and atrazine sequestration were highly correlated with organic C content, nanoporosity or CEC but not other properties of the soils. Multiple linear-regression analysis suggested an interaction of organic C content with soil texture, CEC or surface area in determining the extent of atrazine or phenanthrene sequestration. We conclude that organic C content, CEC and other properties of soil may be useful predictors of sequestration of some compounds.     

The carbon-sequestration potential of municipal wastewater treatment

The lack of proper wastewater treatment results in production of CO(2) and CH(4) without the opportunity for carbon sequestration and energy recovery, with deleterious effects for global warming. Without extending wastewater treatment to all urban areas worldwide, CO(2) and CH(4) emissions associated with wastewater discharges could reach the equivalent of 1.91 x 10(5) t(CO2)d(-1) in 2025, with even more dramatic impact in the short-term. The carbon sequestration benefits of wastewater treatment have enormous potential, which adds an energy conservation incentive to upgrading existing facilities to complete wastewater treatment. The potential greenhouse gases discharges which can be converted to a net equivalent CO(2) credit can be as large as 1.91 x 10(5) t(CO2)d(-1) in 2025 by 2025. Biomass sequestration and biogas conversion energy recovery are the two main strategies for carbon sequestration and emission offset, respectively. The greatest potential for improvement is outside Europe and North America, which have largely completed treatment plant construction. Europe and North America can partially offset their CO(2) emissions and receive benefits through the carbon emission trading system, as established by the Kyoto protocol, by extending existing technologies or subsidizing wastewater treatment plant construction in urban areas lacking treatment. This strategy can help mitigate global warming, in addition to providing a sustainable solution for extending the health, environmental, and humanitarian benefits of proper sanitation.     

Level and distribution of DDT in surface soils from Tianjin, China

One hundred and eighty eight surface soil samples were collected from the Tianjin area to study the contamination of DDT and its metabolites. Measurements were taken for p,p'-DDE, p,p'-DDD, p,p'-DDT, o,p'-DDE, o,p'-DDD and o,p'-DDT for all samples. The results indicated that p,p'-DDT and p,p'-DDE were the predominant contaminant compounds in the surface soil samples, with mean concentrations of 27.5 and 18.8 ng g(-1) respectively. No significant differences in DDT concentrations were found between the soils from wastewater treated irrigated areas and other areas, suggesting that wastewater irrigation is not an important source of DDT in the area. However, the spatial distribution of soil DDTs levels in the area did correlate well with early direct application rates of pesticides. In addition, both pH level and organic carbon content are also known factors affecting the level of DDT and its metabolites. Although it was assumed that the use of these chemicals was banned in the early 1980s, the current concentration levels appear to be too high to be mere residuals after 20 years degradation.     

The effect of soil organic matter on fate of polycyclic aromatic hydrocarbons in soil: A microcosm study

A microcosm study was conducted to address the influences of air-soil partition and sequestration on the fate of polycyclic aromatic hydrocarbons (PAHs) in soil. Sterilized and unsterilized soils with soil organic carbon (SOC) content ranging from 0.23 to 7.06% were incubated in a chamber with six PAHs supplied through air. After 100 d of incubation when the system approached pseudo-steady state, the PAHs concentrations in the unsterilized soils still correlated with SOC significantly, while the association did not exist for those sterilized. The lower degradation rate in the soil with higher SOC was likely the major reason for the association between SOC and PAHs concentrations, while the decreased surface porosity likely suppressed such correlation for the sterilized samples. The results indicated that the sequestration was likely the major mechanism for the accumulation of PAHs in soils, while both of the soil porosity and PAHs properties had observed influences.     

Limitations on the role of incorporated organic matter in reducing pesticide leaching.

The use of organic amendments has been suggested as a method of controlling pesticide leaching through soils. The enarenados soils of the intensive horticulture of the Almeria province of southern Spain contain buried organic matter horizons above a soil layer amended with clay. This region is ideal for understanding the potential for and limitations of organic amendments in preventing pesticide pollution. This study measured the sorption and degradation potential of carbofuran in this soil system and the hydrological behaviour of the soil horizons. The sorption of carbofuran was controlled by the organic carbon content, the degradation was strongly pH-dependent and the acidic organic layer protected the sorbed carbofuran against degradation. Hydrologically, the soil system is dominated by ponding above an amended clay layer and by the presence of macropores that can transport water through this clay. A simple model is proposed on this basis and shows that although high levels of dissolved organic carbon can be released by buried organic horizons, the major control on re-release of sorbed pesticide is the potential for sorption hysteresis in this organic layer. A comparison of sorption and degradation data for carbamate insecticides used in the region with groundwater observations for these compounds shows that no amount of incorporated organic would protect against pollution from highly water-soluble compounds.     

Influence of soil and hydrocarbon properties on the solvent extraction of high-concentration weathered petroleum from contaminated soils

Petroleum ether was used to extract petroleum hydrocarbons from soils collected from six oil fields with different history of exploratory and contamination. It was capable of fast removing 76–94 % of the total petroleum hydrocarbons including 25 alkanes (C₁₁–C₃₅) and 16 US EPA priority polycyclic aromatic hydrocarbons from soils at room temperature. The partial least squares analysis indicated that the solvent extraction efficiencies were positively correlated with soil organic matter, cation exchange capacity, moisture, pH, and sand content of soils, while negative effects were observed in the properties reflecting the molecular size (e.g., molecular weight and number of carbon atoms) and hydrophobicity (e.g., water solubility, octanol–water partition coefficient, soil organic carbon partition coefficient) of hydrocarbons. The high concentration of weathered crude oil at the order of 10⁵ mg kg^?1 in this study was demonstrated adverse for solvent extraction by providing an obvious nonaqueous phase liquid phase for hydrocarbon sinking and increasing the sequestration of soluble hydrocarbons in the insoluble oil fractions during weathering. A full picture of the mass distribution and transport mechanism of petroleum contaminants in soils will ultimately require a variety of studies to gain insights into the dynamic interactions between environmental indicator hydrocarbons and their host oil matrix.     

Using forest health monitoring data to integrate above and below ground carbon information

The national Forest Health Monitoring (FHM) program conducted a remeasurement study in 1999 to evaluate the usefulness and feasibility of collecting data needed for investigating carbon budgets in forests. This study indicated that FHM data are adequate for detecting a 20% change over 10 years (2% change per year) in percent total carbon and carbon content (MgC/ha) when sampling by horizon, with greater than 80% probability that a change in carbon content will be determined when a change has truly occurred (P < or = 0.33). The data were also useful in producing estimates of forest floor and soil carbon stocks by depth that were somewhat lower than literature values used for comparison. The scale at which the data were collected lends itself to producing standing stock estimates needed for carbon budget development and carbon cycle modeling. The availability of site-specific forest mensuration data enables the exploration of above ground and below ground linkages.