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Fly Ash Characteristics and Carbon Sequestration Potential
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Soil respiration under flooded conditions is considered to be very small compared with aerobic soil respiration of soil organic matter. However, anaerobic decomposition of soil plays a key role in carbon cycling in flooded ecosystems. On the other hand, coal-ash wastes, such as fly ash and bottom ash, are known to function as a soil amendment for mitigating emission and enhancing carbon sequestration in up land soils. In this study, we investigated bottom ash as a soil amendment for mitigating emission, and thus enhancing carbon sequestration under anaerobic conditions. We observed that amendment of bottom ash without external organic source led to significant reduction in emission rate and in total cumulative emission flux over the incubation period, which was proportional to the amount of bottom ash applied. We also found that soil microbial biomass increased in response to application of bottom ash. These results suggest that bottom ash can be utilized to store as a stable soil organic carbon in flooded ecosystems, as in aerobic situations.
Disposal of high amount of coal combustion by-products, such as fly ash and bottom ash, is of a great concern to the country, due to the huge treatment cost and land requirement. On the other hand, those coal-ash wastes are considered to have desirable characteristics that may improve physical, chemical, and biological properties of soils. Especially, compared with fly ash, bottom ash has a larger particle size, porous surface area, and usable amount of micronutrients. In the present study, we examined bottom as a soil amendment for mitigating emission and enhancing carbon sequestration in soils fertilized with organic matter (hairy vetch, green barely, and oil cake fertilizer). Through laboratory incubation, released from the soil was quantitatively and periodically monitored with an enforced-aeration and high-temperature respirometer. We observed that amendment of bottom ash led to a marked reduction in emission rate and cumulative amount of released, which was generally proportional to the amount of bottom ash applied. We also found that the temporal patterns of emission and C sequestration effects were partially dependent on the relative of proportion labile carbon and C/N ratio of the organic matter. Our results strongly suggest that amendment of bottom ash has potential benefits for fixing labile carbon as more stable soil organic matter, unless the bottom ash contains toxic levels of heavy metals or other contaminants.
Soil quality research has focused on intensively managed agricultural and forest soils, but the concept and importance of soil quality is also pertinent to reclaimed mine soils and other disturbed ecosystems. Adding organic amendments has been used as a means for ameliorating mine soils and improving their quality, but the long-term effects of amendments on soil quality are not known. In 1982, a mined site was amended with seven different surface treatments: a control (nothing added), 30 cm of native soil, 112 Mg ha -1 sawdust, and municipal sewage sludge (SS) at rates of 22, 56, 112, and 224 Mg ha -1. Four replicates of each treatment were installed as a randomized complete block design. Each plot was split and planted with pitch x loblolly pine hybrid (Pinus rigida x taeda) trees and Kentucky-31 tall fescue (Festuca arundinacea Schreb.). During the 16-yr period, organic matter content, total organic N, N mineralization potential, aggregate stability, and other physical and chemical properties were measured as mine soil quality indicators. The comparative ability of these organic amendments to positively affect organic matter content, total N, and other parameters was most apparent and pronounced after 5 yr. However, after 16 yr, soil organic matter (SOM) content and total N appeared to be equilibrating at ≈10 000 and 750 kg ha -1, respectively. Organic matter inputs by vegetation alone across the 16-yr period in the control plots resulted in organic matter and N mineralization potential values comparable to levels in the organically-amended plots, indicating the overriding importance of vegetation in the soil recovery process. After 16 yr, there appears to be no lasting soil quality improvements due to addition of organic amendments to this mine soil. Amendments improved short-term production, but their cost of transport and application may be difficult to justify based on long-term soil quality improvement.
The exchange of carbon dioxide between the atmosphere, biosphere and pedosphere is an important consideration when assessing agricultural and environmental management or policy decisions and their relationship to climate change. Field experimentation is the best way to gather data, but experimental data are specific to the management, soils and climate that represent the research site. Inadequate field data exist to address all management options across all soil types and climates. We have used the Intergovernmental Panel on Climate Change inventory approach to estimate changes in soil carbon storage resulting from various land use and management options. We generate a regional assessment of the relative impact of implementing changes in agricultural management on soil carbon storage. For each agricultural region of the United States, we present an estimated annual change in soil carbon storage for each management option. Results should prove especially useful in evaluating management options and tradeoffs.
Soils are an effective sink for carbon storage and immobilization through biomass productivity and enhancement of soil organic carbon (SOC) pool. The SOC sink capacity depends on land use and management. Degraded lands lose large amounts of C through SOC decomposition, erosion, and leaching. Thus, restoration of disturbed and degraded mine lands can lead to increase in biomass productivity, improved soil quality and SOC enhancement and sequestration. Reclamation of mined lands is an aggrading process and offers significant potential to sequester C. A chronosequence study consisting of 0-, 5-, 10-, 15-, 20- and 25-year-old reclaimed mine soils in Ohio was initiated to assess the rate of C sequestration by pasture and forest establishment. Undisturbed pasture and forest were used as controls. The SOC pool of reclaimed pasture sites increased from 15·3 Mg ha−1 to 44·4 Mg ha−1 for 0–15 cm depth and from 10·8 Mg ha−1 to 18·3 Mg ha−1 for 15–30 cm depth over the period of 25 years. The SOC pool of reclaimed forest sites increased from 12·7 Mg ha−1 to 45·3 Mg ha−1 for 0–15 cm depth and from 9·1 Mg ha−1 to 13·6 Mg ha−1 for 15–30 cm depth over the same time period. The SOC pool of the pasture site stabilized earlier than that of the forest site which had not yet attained equilibrium. The SOC sequestered in 0–30 cm depth over 25 years was 36·7 Mg ha−1 for pasture and 37·1 Mg ha−1 for forest. Copyright © 2000 John Wiley & Sons, Ltd.
Application of alkaline fly ash to acid soils is related to beneficial effects, such as increase of pH to a desired level and nutrient supply to plants, and to possible adverse effects, such as enrichment of soils with substances toxic to plants and animals (e.g. B, Mo, Se) and increase of salinity to undesirable levels. Therefore, use of alkaline fly ash as a beneficial amendment of acid soils needs to be evaluated with respect to phytotoxic and environmental impacts. Samples of alkaline fly ash, from two different sources, were added to two Red Mediterranean acid soils at rates equal to 5, 20 and 50 g kg−1 soil, and changes, relative to the untreated soil, of soil pH, salinity, B and P levels were measured. Ryegrass (Lolium perenne L.) was grown in pots containing fly ash–soil mixtures for 300 days, and dry biomass yield and cumulative plant uptake of B and P were calculated. Soil application of fly ash at these rates increased the pH, up to about 8, and the electrical conductivity of the saturation extract, up to about 2.5 dS m−1, in both soils. Available soil P (0.5 M NaHCO3 extractable) was unaffected by fly ash application. Water soluble B remained less than 1 mg litre−1 in the saturation extract, and hot water extractable B was less than 1 mg kg−1 soil. Dry biomass yield of ryegrass and cumulative plant uptake of B and P increased significantly with fly ash application. Therefore, fly ashes with low B and salt content can be used as liming agents in acid soils at rates not exceeding the 40 Mg/ha. Potential environmental impacts must also considered.
Coal combustion by-products may offer significant benefits if used properly to neutralize soil acidity, but unintended release of trace components must be considered. A study was conducted with two objectives: (i) To compare the efficacy of two different preparations of fly ash with that of conventional ag lime for their ability to raise soil pH and reduce exchangeable Al; and (ii) to determine if the Al applied in fly ash produces detrimental changes in soil properties following subsequent acidification. Either fly ash in one of two forms, or conventional ag lime, was applied to three acid soils (Anselmo loam, Valentine sandy loam, and Holdrege sandy loam) in a pot study at rates equal to 0.5, 1.0, and 1.5 times the soils' lime requirements. Soils were equilibrated in triplicate at approximately 33 kPa water potential in the greenhouse for 315 days (liming phase), during which pH and exchangeable aluminum (Al) were measured. The soils were then acidified under similar conditions for 439 days (acidification phase) by adding dilute acid solution to simulate management-induced acidification, and pH and exchangeable Al were then measured again. Both fly ashes and ag lime were effective in raising soil pH by up to 1.2 units and in reducing exchangeable Al by up to 5.6 mg kg-1. Two-way interactions involving soil, liming material, and rate of application produced different results for combinations of these factors. All amendments helped the soils resist subsequent acidification compared with zero-rate treatments but differed based on the 3-way combinations of soil, liming material, and rate of application. We concluded that overliming (as indicated by exceeding the target pH of 6.5) is a problem with all liming materials on the coarsest soils, suggesting that lime calibration should be re-examined. The fly ash materials seem to contribute to soil exchangeable Al after acidification, but this contribution is inconsequential if soil pH values are maintained at agronomic optima.
Concern for the potential global change consequences of increasing atmospheric CO has prompted interest in the 2 development of mechanisms to reduce or stabilize atmospheric CO . During the next several decades, a program 2 focused on terrestrial sequestration processes could make a significant contribution to abating CO increases. The 2 reclamation of degraded lands, such as mine-spoil sites, highway rights-of-way, and poorly managed lands, represents an opportunity to couple C sequestration with the use of fossil-fuel and energy by-products and other waste material, such as biosolids and organic wastes from human and animal sewage treatment facilities, to improve soil quality. Degraded lands are often characterized by acidic pH, low levels of key nutrients, poor soil structure, and limited moisture-retention capacity. Much is known about the methods to improve these soils, but the cost of implementation is often a limiting factor. However, the additional financial and environmental benefits of C sequestration may change the economics of land reclamation activities. The addition of energy-related by-products can address the adverse conditions of these degraded lands through a variety of mechanisms, such as enhancing plant growth and capturing of organic C in long-lived soil C pools. This review examines the use of fossil-fuel combustion by-products and organic amendments to enhance C sequestration and identifies the key gaps in information that still must be addressed before these methods can be implemented on an environmentally meaningful scale.
The soil is a natural resource, non renewable in the short term or very difficult to renew and expensive either to reclaim or to improve following erosion, physical degradation or chemical pollution. The increasing pressure on land and water resources, leading to degradation and pollution of those resources, and a reduced productive capacity calls for a system which can store detailed information on natural resources of all kinds in such a way that these data can be accessed, combined and analyzed from the point of view of potential use, in relation to food requirements, environmental impact and conservation. Such a system is a prerequisite for policy formulation, development planning at all levels, efficient use of both internal and external resources, and for implementation of development programmes.
During the past several years, the use of animals for toxicity testing has come under critical surveillance. For ethical and economic reasons, various techniques have been developed and proposed as potential alternatives for some of the whole animal toxicity assays. One assay proposed as an alternative to animal testing is the luminescent bacteria toxicity test (LBT), provided under the trade name of Microtox. The sensitivity and specificity of the LBT was compared with two commonly used toxicity tests--the L-929 Minimal Eàgle's Medium (MEM) elution cytotoxicity test and the Draize test. Cytotoxicity and LBT test data from 709 medical device and biomaterial extracts were compared using a positive/negative ranking system which provided a measurement of false positive and false negative results. These data were compiled from nine separate laboratories producing or using a wide variety of biomaterials and medical device products. The LBT was more sensitive than the tissue culture assay and displayed few false negatives. LBT EC50 values were compared with eye irritancy categories for a group of 34 chemicals and 27 personal care products. As with tissue culture, the LBT was more sensitive and produced minimal false negatives. The data from this study indicate the LBT has potential as a rapid, simple method to screen biomaterials and personal care products for toxicity and irritancy.