CH4/CO2 ratios indicate highly efficient methane oxidation by a pumice landfill cover-soil

Landfills that generate too little biogas for economic energy recovery can potentially offset methane (CH₄) emissions through biological oxidation by methanotrophic bacteria in cover soils. This study reports on the CH₄ oxidation efficiency of a 10-year old landfill cap comprising a volcanic pumice soil. Surface CH₄ and CO₂ fluxes were measured using field chambers during three sampling intervals over winter and summer. Methane fluxes were temporally and spatially variable (?0.36 to 3044 mg CH₄ m^?2 h^?1); but were at least 15 times lower than typical literature CH₄ fluxes reported for older landfills in 45 of the 46 chambers tested. Exposure of soil from this landfill cover to variable CH₄ fluxes in laboratory microcosms revealed a very strong correlation between CH₄ oxidation efficiency and CH₄/CO₂ ratios, confirming the utility of this relationship for approximating CH₄ oxidation efficiency. CH₄/CO₂ ratios were applied to gas concentrations from the surface flux chambers and indicated a mean CH₄ oxidation efficiency of 72%. To examine CH₄ oxidation with soil depth, we collected 10 soil depth profiles at random locations across the landfill. Seven profiles exhibited CH₄ removal rates of 70–100% at depths <60 cm, supporting the high oxidation rates observed in the chambers. Based on a conservative 70% CH₄ oxidation efficiency occurring at the site, this cover soil is clearly offsetting far greater CH₄ quantities than the 10% default value currently adopted by the IPCC.     

Tillage and field scale controls on greenhouse gas emissions

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.     

The influence of sampling protocol on nonmethane hydrocarbon mixing ratios

The effect of sampling protocol on ambient air hydrocarbon mixing ratios was examined on eight sampling days in Los Angeles during 2007 and 2008. Four protocols, which were based on previously published multi-city urban hydrocarbon studies in the United States, were compared and differences were quantified. Whole air canister samples were collected and analyzed for nonmethane hydrocarbons (NMHCs). Differing sampling protocols resulted in large differences in mixing ratios, up to an order of magnitude, for certain NMHCs on the same sampling day. However, the magnitude of the variability between NMHC levels obtained by the four protocols was not consistent throughout the eight sampling days. It was found that sampling time, followed by sampling location, had the greatest influence on the magnitude of the mixing ratio. Ratios between hydrocarbons, often used in urban studies to gain information on emission sources, also varied depending on the protocol used. Comparison of absolute NMHC mixing ratios collected in urban environments using differing sampling protocols should be made with care.     

Assessment of the effects of nickel on benthic macroinvertebrates in the field

A field-based evaluation of the biological effects of potential nickel (Ni) exposures was conducted using monitoring data for benthic macroinvertebrates and water chemistry parameters for streams in England and Wales. Observed benthic community metrics were compared to expected community metrics under reference conditions using RIVPACS III+?software. In order to evaluate relationships between Ni concentrations and benthic community metrics, bioavailable Ni concentrations were also calculated for each site. A limiting effect from Ni on the 90th percentile of the maximum achievable ecological quality was derived at “bioavailable Ni” exposures of 10.3 μg l^?1. As snails have been identified as particularly sensitive to nickel exposure, snail abundance in the field in response to nickel exposure, relative to reference conditions, was also analysed. A “low effects” threshold for snail abundance based on an average of spring and autumn data was derived as 3.9 μg l^?1 bioavailable Ni. There was no apparent effect of Ni exposure on the abundance of Ephemeroptera (mayflies), Plecoptera (stoneflies) or Tricoptera (caddisflies) when expressed relative to a reference condition within the range of “bioavailable Ni” exposures observed within the dataset. Nickel exposure concentrations co-vary with the concentrations of other stressors in the dataset, and high concentrations of Ni are also associated with elevated concentrations of other contaminants.     

Cluster detection using Bayes factors from overparameterized cluster models

In this paper, we consider the use of a partition model to estimate regional disease rates and to detect spatial clusters. Formal inference regarding the number of partitions (or clusters) can be obtained with a reversible jump Markov chain Monte Carlo algorithm. As an alternative, we consider the ability of models with a fixed, but overly large, number of partitions to estimate regional disease rates and to provide informal inferences about the number and locations of clusters using local Bayes factors. We illustrate and compare these two approaches using data on leukemia incidence in upstate New York and data on breast cancer incidence in Wisconsin.     

METABOLIC RESPONSES OF AQUATIC BACTERIAL POPULATIONS TO SELECTED INSECTICIDES1

ABSTRACT: Indigenous bacterial populations from a fresh water reservoir were treated by adding five mg/1 Sevin or Malathion to the water at 23, 28, and 33 C. The degradation of Sevin was evidenced by the increased uptake of O₂ as measured by Warburg manometry. The principal degradation product of Sevin, 1-naphthol, appeared to stimulate metabolic activity of these populations to the same extent as the parent compound. The addition of Malathion to this system appeared, on the other hand, to suppress metabolic activity to some degree. Warburg manometry was shown to be a useful, rapid method for detecting effects of insecticides on aquatic microbial populations.     

Ants can sort their brood without a gaseous template

A fundamental issue of collective intelligence is whether the collective pattern or process is based on environmental information that explicitly codes for it or arises through self-organization of the individuals. Sometimes, these alternatives occur together. Adaptive systems may also be capable of utilizing different types of mechanism under different conditions. Sendova-Franks et al. (Anim Behav 68:1095–1106, 2004) demonstrated evidence for a self-organization mechanism of brood sorting in the ant Temnothorax albipennis, where the brood are sorted in a series of bands or concentric annuli that increase in size with distance from the colony centre. The work by Cox and Blanchard (J Theor Biol 204:223-238, 2000) suggests an alternative or complementary mechanism whereby the brood pattern is specified by the template of a CO₂ gradient. Here, we test for a gaseous template as a necessary condition for brood sorting. Under the experimental condition, we pumped the air out of the nest continuously to prevent the accumulation of any gaseous substances. We compared the brood pattern between the experimental and control conditions according to four characteristics: mean distance from centre, mean nearest-neighbour distance, shape and area. Under the experimental condition, the order of brood types according to the first two characteristics was the same as in the control. The area of the brood pattern was smaller, and its shape elongated under the experimental condition. As expected on the basis of these differences, mean distance from centre was greater and mean nearest-neighbour distance was smaller under the experimental condition (although not statistically significantly) and by the expected amount. We found evidence that ants avoid placing brood in the strongest airflow stream. This could explain the reduced area and elongated shape of the brood pattern under the experimental condition. We conclude that a gaseous template is not a necessary condition for brood sorting. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.