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481.
Komilis DP 《Waste management (New York, N.Y.)》2006,26(1):82-91
Six municipal solid waste (MSW) and yard waste components (food waste, mixed paper, yard waste, leaves, branches, grass clippings) were aerobically decomposed to measure the extent of decomposition under near optimal conditions. Decomposition was characterized by at least two principal stages, for most components, as was indicated by the carbon dioxide production rates. An aerobic biodegradation conceptual model is presented here based on the principle that solids hydrolysis is the rate-limiting step during solid waste composting. The mineralizable solid carbon of each solid waste component was assumed to comprise the readily, the moderately and the slowly (or refractory) hydrolysable carbons, each hydrolyzing at different rates to aqueous (water soluble) carbon. Aqueous carbon mineralizes to CO2 at rapid rates that are not rate-limiting to the process. Solids hydrolysis rate constants were calculated after fitting the experimentally determined carbon dioxide production rate data to model results. Hydrolysis rates for the readily hydrolysable carbon in all components ranged from approximately 0.06 to 0.1 d(-1); hydrolysis rates for the moderately hydrolysable carbon ranged from 0.005 to 0.06 d(-1). Leaves, branches and grass clippings did not have a readily hydrolysable carbon fraction, whilst the leaves and branches had the largest slowly hydrolysable carbon fractions (70%, 82%, respectively, of the total solid organic carbon). Grass and yard waste did not contain slowly hydrolysable carbon fractions. Food waste had the largest readily hydrolysable carbon fraction and produced the highest amount of CO2 among all substrates. Moderately hydrolysable solid carbon fractions ranged from 16% to 90% of the total solid organic carbon for all substrates used. 相似文献
482.
J. Hejzlar K. Šámalová P. Boers B. Kronvang 《Water, Air, & Soil Pollution: Focus》2006,6(5-6):487-494
Steady-state models for the prediction of P retention coefficient (R) in lakes were evaluated using data from 93 natural lakes and 119 reservoirs situated in the temperate zone. Most of the
already existing models predicted R relatively successfully in lakes while it was seriously under-estimated in reservoirs. A statistical analysis indicated the
main causes of differences in R between lakes and reservoirs: (a) distinct relationships between P sedimentation coefficient, depth, and water residence
time; (b) existence of significant inflow–outflow P concentration gradients in reservoirs. Two new models of different complexity
were developed for estimating R in reservoirs: , where τ is water residence time (year), was derived from the Vollenweider/Larsen and Mercier model by adding a calibrated parameter
accounting for spatial P non-homogeneity in the water body, and is applicable for reservoirs but not lakes, and , where [Pin] is volume-weighted P concentration in all inputs to the water body (μg l−1), was obtained by re-calibrating the OECD general equation, and is generally applicable for both lakes and reservoirs. These
optimised models yield unbiased estimates over a large range of reservoir types. 相似文献
483.
Tzialla CE Veresoglou DS Papakosta D Mamolos AP 《Journal of environmental management》2006,80(1):90-98
Soil physicochemical characteristics, total aboveground biomass, number of species and relative abundance of groups and individual species were measured along a moisture gradient in a pasture, flooded in part during winter through early summer, adjacent to Pamvotis lake in Ioannina, Greece. Soil and vegetation measurements were conducted in 39 quadrats arranged in four zones perpendicular to the moisture gradient. The zone closest to the lake, recently separated from the lake, became part of the pasture and its soil texture was quite different from that of the other zones with a substrate containing 91% sand. Except for pH, this zone had the lowest values in the other five soil physicochemical characteristics measured (organic matter, total and extracted inorganic nitrogen, Olsen extracted phosphorus and extractable potassium); in the other zones organic matter, total nitrogen, phosphorus and potassium tended to increase from the driest to the wettest zone. Total aboveground biomass, ranging from 280 to 840 gm-2, is high for herbaceous pastures in the conditions of Mediterranean climate and it was not related to distance from the lake's shoreline, although the highest values were measured at intermediate distances, or to any of the various soil characteristics measured. Also, the number of species/0.25 m2 was not related to any of the various soil characteristics, but it was highest at the intermediate distances from the lake's shoreline. Species composition varied along the moisture gradient. Forbs as well as annual grasses and legumes declined in abundance from the driest to the wettest places; the reverse was the case for sedges and perennial grasses and legumes. These results indicate that the soil moisture gradient was the principal factor affecting soil characteristics and plant species composition. Since most species were recorded in all the four zones of the pasture, indicating that these can tolerate all variations in abiotic conditions of pasture, the vegetation zonation seems to be influenced by competition. Each functional group of species tends to dominate in a particular range of the soil moisture gradient where it is better suited and tends to exclude competitively other species. Management practices (mowing and grazing) affect the kinds of processes which maintain the observed community structure either by preventing the establishment of later successional species, like reeds and woody species, or by moderating the shoot competition, especially in the wetter zones, and thus permitting the creeping species to grow successfully. 相似文献
484.
Sanphoti N Towprayoon S Chaiprasert P Nopharatana A 《Journal of environmental management》2006,81(1):27-35
In order to increase methane production efficiency, leachate recirculation is applied in landfills to increase moisture content and circulate organic matter back into the landfill cell. In the case of tropical landfills, where high temperature and evaporation occurs, leachate recirculation may not be enough to maintain the moisture content, therefore supplemental water addition into the cell is an option that could help stabilize moisture levels as well as stimulate biological activity. The objectives of this study were to determine the effects of leachate recirculation and supplemental water addition on municipal solid waste decomposition and methane production in three anaerobic digestion reactors. Anaerobic digestion with leachate recirculation and supplemental water addition showed the highest performance in terms of cumulative methane production and the stabilization period time required. It produced an accumulated methane production of 54.87 l/kg dry weight of MSW at an average rate of 0.58 l/kg dry weight/d and reached the stabilization phase on day 180. The leachate recirculation reactor provided 17.04 l/kg dry weight at a rate of 0.14l/kg dry weight/d and reached the stabilization phase on day 290. The control reactor provided 9.02 l/kg dry weight at a rate of 0.10 l/kg dry weight/d, and reached the stabilization phase on day 270. Increasing the organic loading rate (OLR) after the waste had reached the stabilization phase made it possible to increase the methane content of the gas, the methane production rate, and the COD removal. Comparison of the reactors' efficiencies at maximum OLR (5 kgCOD/m(3)/d) in terms of the methane production rate showed that the reactor using leachate recirculation with supplemental water addition still gave the highest performance (1.56 l/kg dry weight/d), whereas the leachate recirculation reactor and the control reactor provided 0.69 l/kg dry weight/d and 0.43 l/kg dry weight/d, respectively. However, when considering methane composition (average 63.09%) and COD removal (average 90.60%), slight differences were found among these three reactors. 相似文献
485.
Employing in-depth, elite interviews, this empirical research contributes to understanding the dynamics among policy windows,
policy change, and organizational learning. First, although much of the research on agenda setting—how issues attract enough
attention that action is taken to address them—has been conducted at the national scale, this work explores the subnational,
regional scale. With decentralization, regional-scale environmental decision-making has become increasingly important. Second,
this research highlights the role of policy windows and instances of related organizational learning identified by natural
resources managers. Having practitioners identify focusing events contrasts with the more typical approach of the researcher
identifying a particular focusing event or events to investigate. A focusing event is a sudden, exceptional experience that,
because of how it leads to harm or exposes the prospect for great devastation, is perceived as the impetus for policy change. 相似文献
486.
The extensive literature on environmental justice has, by now, well defined the essential ingredients of cumulative risk,
namely, incompatible land uses and vulnerability. Most problematic is the case when risk is produced by a large aggregation
of small sources of air toxics. In this article, we test these notions in an area of Southern California, Southeast Los Angeles
(SELA), which has come to be known as Asthmatown. Developing a rapid risk mapping protocol, we scan the neighborhood for small
potential sources of air toxics and find, literally, hundreds of small point sources within a 2-mile radius, interspersed
with residences. We also map the estimated cancer risks and noncancer hazard indices across the landscape. We find that, indeed,
such large aggregations of even small, nondominant sources of air toxics can produce markedly elevated levels of risk. In
this study, the risk profiles show additional cancer risks of up to 800 in a million and noncancer hazard indices of up to
200 in SELA due to the agglomeration of small point sources. This is significant (for example, estimates of the average regional
point-source-related cancer risk range from 125 to 200 in a million). Most importantly, if we were to talk about the risk
contour as if they were geological structures, we would observe not only a handful of distinct peaks, but a general “mountain
range” running all throughout the study area, which underscores the ubiquity of risk in SELA. Just as cumulative risk has
deeply embedded itself into the fabric of the place, so, too, must intervention seek to embed strategies into the institutions
and practices of SELA. This has implications for advocacy, as seen in a recently initiated participatory action research project
aimed at building health research capacities into the community in keeping with an ethic of care. 相似文献
487.
What is soil organic matter worth? 总被引:3,自引:0,他引:3
The conservation and restoration of soil organic matter are often advocated because of the generally beneficial effects on soil attributes for plant growth and crop production. More recently, organic matter has become important as a terrestrial sink and store for C and N. We have attempted to derive a monetary value of soil organic matter for crop production and storage functions in three contrasting New Zealand soil orders (Gley, Melanic, and Granular Soils). Soil chemical and physical characteristics of real-life examples of three pairs of matched soils with low organic matter contents (after long-term continuous cropping for vegetables or maize) or high organic matter content (continuous pasture) were used as input data for a pasture (grass-clover) production model. The differences in pasture dry matter yields (non-irrigated) were calculated for three climate scenarios (wet, dry, and average years) and the yields converted to an equivalent weight and financial value of milk solids. We also estimated the hypothetical value of the C and N sequestered during the recovery phase of the low organic matter content soils assuming trading with C and N credits. For all three soil orders, and for the three climate scenarios, pasture dry matter yields were decreased in the soils with lower organic matter contents. The extra organic matter in the high C soils was estimated to be worth NZ$27 to NZ$150 ha(-1) yr(-1) in terms of increased milk solids production. The decreased yields from the previously cropped soils were predicted to persist for 36 to 125 yr, but with declining effect as organic matter gradually recovered, giving an accumulated loss in pastoral production worth around NZ$518 to NZ$1239 ha(-1). This was 42 to 73 times lower than the hypothetical value of the organic matter as a sequestering agent for C and N, which varied between NZ$22,963 to NZ$90,849 depending on the soil, region, discount rates, and values used for carbon and nitrogen credits. 相似文献
488.
Manure water-extractable phosphorus (WEP) data are used in indices and models to assess P transport in runoff. Methods to measure WEP vary widely, often without understanding the effect on how much P is extracted. We conducted water extractions on five dairy, swine, and poultry manures to assess single and sequential extractions, drying manures, solution to solid (cm3 g(-1)) extraction ratios, and P determination method. We found little difference in WEP of single or sequential extractions. Increasing extraction ratio from 10:1 to 250:1 resulted in more WEP recovered, but in a diminishing fashion so that ratios of 200:1 and 250:1 were not significantly different. Patterns of increased WEP with extraction ratio varied with manure type, presence of bedding material, and drying treatment. Fresh and air-dried manures had similar patterns, but differed substantially from oven-dried (90 degrees C) manures. The differential effect of oven-drying on WEP was greatest for dairy and poultry manure, and less for swine manure. We analyzed water extracts colorimetrically before and after digestion, to examine the potential effect of P determination by inductively coupled plasma (ICP) spectroscopy. Digested extracts always contained more P. For manures with bedding, drying decreased the difference in P measured before and after digestion. The opposite was true for manures without bedding. Results highlight the influence of methodology on manure WEP measurement and caution needed when comparing data across studies using different WEP methods. Overall, our results point to a need for a standard manure water extraction method. 相似文献
489.
Tillage and field scale controls on greenhouse gas emissions 总被引:3,自引:0,他引:3
There is a lack of understanding of how associations among soil properties and management-induced changes control the variability of greenhouse gas (GHG) emissions from soil. We performed a laboratory investigation to quantify relationships between GHG emissions and soil indicators in an irrigated agricultural field under standard tillage (ST) and a field recently converted (2 yr) to no-tillage (NT). Soil cores (15-cm depth) were incubated at 25 degrees C at field moisture content and 75% water holding capacity. Principal component analysis (PCA) identified that most of the variation of the measured soil properties was related to differences in soil C and N and soil water conditions under ST, but soil texture and bulk density under NT. This trend became more apparent after irrigation. However, principal component regression (PCR) suggested that soil physical properties or total C and N were less important in controlling GHG emissions across tillage systems. The CO2 flux was more strongly determined by microbial biomass under ST and inorganic N content under NT than soil physical properties. Similarly, N2O and CH4 fluxes were predominantly controlled by NO3- content and labile C and N availability in both ST and NT soils at field moisture content, and NH4+ content after irrigation. Our study indicates that the field-scale variability of GHG emissions is controlled primarily by biochemical parameters rather than physical parameters. Differences in the availability and type of C and N sources for microbial activity as affected by tillage and irrigation develop different levels and combinations of field-scale controls on GHG emissions. 相似文献
490.
White JC Parrish ZD Gent MP Iannucci-Berger W Eitzer BD Isleyen M Mattina MI 《Journal of environmental quality》2006,35(4):992-1000
Field experiments were conducted to optimize the phytoextraction of weathered p,p'-DDE (p,p'-dichlorodiphenyldichloroethylene) by Cucurbita subspecies. The effects of two soil amendments, mycorrhizae or a biosurfactant, on p,p'-DDE accumulation was determined. Also, p,p'-DDE uptake was assessed during plant growth (12, 26, 38, and 62 d), and cultivars that accumulate weathered p,p'-DDE were intercropped with cultivars known not to have that ability. Cucurbita pepo L. ssp. pepo accumulated large amounts of the contaminant, having stem bioconcentration factors, amounts of p,p'-DDE translocated, and contaminant phytoextraction that were 14, 9.9, and 5.0 times greater than C. pepo L. ssp. ovifera (L.) D.S. Decker, respectively. During 62 d, the stem BCF (bioconcentration factor) for p,p'-DDE in subspecies pepo remained constant and the total amount of contaminant accumulated was correlated with plant biomass (r(2) = 0.86). For subspecies ovifera, the stem BCF was highest at 12 d (1.5) but decreased to 0.39 by 62 d, and p,p'-DDE removal was not correlated with plant biomass. Mycorrhizal inoculation increased p,p'-DDE accumulation by both subspecies by an average 4.4 times. For subspecies pepo, mycorrhizae increased the percentage of contaminant extracted from 0.72 to 2.1%. Biosurfactant amendment also enhanced contaminant accumulation by both subspecies, although treatment reduced subspecies ovifera biomass by 60%. The biosurfactant had no effect on the biomass of subspecies pepo, increased the average contaminant concentration by 3.6-fold, and doubled the overall amount of p,p'-DDE removed from the soil. Soil amendments that enhance the mobility of weathered persistent organic pollutants will significantly increase the amount of contaminant phytoextraction by Cucurbita pepo. 相似文献