All forest fire events generate some quantity of charcoal, which may persist in soils for hundreds to thousands of years. However, few studies have effectively evaluated the potential for charcoal to influence specific microbial communities or processes. To our knowledge, no studies have specifically addressed the effect of charcoal on ammonia-oxidizing bacteria (AOB) in forest soils. Controlled experiments have shown that charcoal amendment of fire-excluded temperate and boreal coniferous forest soil increases net nitrification, suggesting that charcoal plays a major role in maintaining nitrification for extended periods postfire. In this study, we examined the influence of fire history on gross nitrification, nitrification potential, and the nature and abundance of AOB. Soil cores were collected from sites in the Selway-Bitterroot wilderness area in northern Idaho that had been exposed twice (in 1910, 1934) or three times (1910, 1934, and 1992) in the last 94 yr, allowing us to contrast soils recently exposed to fire to those that experienced no recent fire (control). Charcoal content was determined in the O horizon by hand-separation and in the mineral soil by a chemical digestion procedure. Gross and net nitrification, and potential rates of nitrification were measured in mineral soil. Analysis of the AOB community was conducted using primer sets specific for the ammonia mono-oxygenase gene (amoA) or the 16S rRNA gene of AOB. Denaturing gradient gel electrophoresis was used to analyze the AOB community structure, while AOB abundance was determined by quantitative polymerase chain reaction. Recent (12-yr-old) wildfire resulted in greater charcoal contents and nitrification rates compared with sites without fire for 75 yr, and the more recent fire appeared to have directly influenced AOB abundance and community structure. We predicted and observed greater abundance of AOB in soils recently exposed to fire compared with control soils. Interestingly, sequence data revealed that Clusters 3 and 4, and not Cluster 2, of genus Nitrosospira dominated these forest soils, with a shift toward Cluster 3 in recently burned sites.

Federal efforts to establish reliable natural disinfection criteria for ground water supplies require the identification of appropriate indicator viruses to represent pathogenic viruses and an understanding of parameters affecting virus survival and transport in a variety of hydrogeologic settings. A high school septic system and the associated fecal waste‐impacted unconfined sand and gravel aquifer were instrumented to: (1) evaluate if the concentrations of enterovirus and coliphage in this system were sufficient to allow their use as indicator viruses; (2) establish viral transport rates, transport distances, and concentrations in a highly conductive cold water aquifer. Enteroviruses were found in only two of eight assays of the septic tank effluent (0.26 and 4.4 virus/L) and were below detection in eight ground water samples. Male‐specific and somatic coliphage were detectable in both the septic tank effluent (averaging 674,000 and 466,000 coliphage/L, respectively) and in the impacted underlying ground water, decreasing to detection limits beyond 38 m of the drainfield. Virus transport parameters in this aquifer were measured by seeding high numbers of MS2 and ØX174 coliphage into the ground water and documenting their transport over 17.4 m. A portion of the seeded virus traveled at least as fast as the bromide tracer (1 to 2.9 m/d). Proposed natural disinfection criteria would not be met in this aquifer using standard 30.5 m setback distances. In addition, the virus sorption processes and long survival times resulted in presence of viable seed virus for more than nine months.

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Ground water supplies contaminated with microbes cause more than 50% of the water-borne disease outbreaks in the United States. Proposed regulations suggest natural disinfection as a possible mechanism to treat microbe-impacted ground water under favorable conditions. However, the usefulness of current models employed to predict viral transport and natural attenuation rates is limited by the absence of field scale calibration data. At a remote floodplain aquifer in western Montana, the bacteriophages MS2, phiX174, and PRD1; attenuated poliovirus type-1 (CHAT strain); and bromide were seeded as a slug 21.5 m from a well pumping at a steady rate of 408 L/min. Over the 47-hour duration of the test, resulting in the exchange of 12 to 13 pore volumes, 77% of the bromide, 55% of the PRD1, 17% of the MS2, 7% of the phiX174, and 0.12% of the poliovirus masses were recovered at the pumping well. Virus transport behavior was controlled by mechanical dispersion, preferential flow, time-dependent nonreversible and reversible attachment, and apparent mass transfer to immobile domains within the sand and gravel dominated aquifer. The percentage of virus recovery appears correlated with reported viral isoelectric point (pI) values. Successful modeling of viral transport in coarse-grained aquifers will require separation of viral specific properties from reported lumped viral-transport system parameters.

A dynamic model that describes the biofiltration process for hydrogen sulfide removal from wastewater treatment plant air emissions was calibrated and validated using pilot-and full-scale biofilter data obtained from the Cedar Rapids (Iowa) Water Pollution Control Facilities. After calibration, the model was found to predict the dynamic effluent concentrations of the pilot-and full-scale biofilters well, with the measured data falling within 58 to 80% of the model output values. In addition, the model predicted the trend of the field data, even under field conditions of changing input concentration and at effluent concentrations below 1 ppm by volume. The model demonstrated that increasing gas residence time and temperature and decreasing influent concentration decreases effluent concentration. In addition, model simulations showed that a longer residence time is required to treat dynamic loading increases, indicating that biofilter design should account for the maximum influent concentration. These results can be used to help design and operate biofilters for controlling odorous and hazardous air emissions. Water Environ. Res., 74, 17 (2002).