Accounting for the depth distribution of 137Cs in on-line mobile gamma spectrometry through primary and forward-scattered photons

Stationary and mobile field gamma spectrometry is a useful tool for rapid estimation of environmental radioactivity inventories on and in the ground. A weak point however, is that the depth distribution of the activity in the ground must be known in order to calculate the true activity per unit area or unit mass from an observed photon fluence rate. A promising method for converting incoming spectral data into both true activity content and depth distribution in real time is the peak-to-valley method, which is based on an analysis of the ratio between count rates from primary and forward-scattered photons. In this study the peak-to-valley method was adapted to car-borne mobile gamma spectrometry, where the depth distribution of (137)Cs is fitted to a Lorenz function. Results from field experiments with a large HPGe detector, utilising point sources at different depths, are presented. It was found that the method can be useful for mobile measurements with a measuring time of 5-10 min for activity concentrations of about 100 kBq.m(-2) or higher, resulting in an uncertainty in the estimate of the true activity of about 50%.     

Attenuation effects on the kerma rates in air after cesium depositions on grasslands

Since the reactor accident of Chernobyl, cesium depth profiles and nuclide-specific kerma rates in air have been determined for various grassland sites in south Bavaria and in Ukraine. The sites are described by soil characteristics, annual precipitation, distance from release point, mode of deposition, and activity per unit area. The effects of surface roughness and migration of cesium into the soil on the kerma rate in air over grasslands was determined by two methods. The kerma rates in air obtained by the evaluations of in situ gamma-ray spectrometry results and of measured activity distributions in the soil showed only negligible differences for the observation period of 6 years after deposition. For the sites in Ukraine the kerma rate in air per activity per unit area was found to be systematically 40% higher than in Bavaria. The results from Bavaria on the attenuation of the kerma rate and a data set, including experiences from the weapons test fallout, are analytically approximated as a function of time up to 25 years after deposition.     

Effectiveness of soil N availability indices in predicting site productivity in the oil sands region of Alberta

Background and aims

Quantitative relationships between soil N availability indices and tree growth are lacking in the oil sands region of Alberta and this can hinder the development of guidelines for the reclamation of the disturbed landscape after oil sands extraction. The aim of this paper was to establish quantitative relationships between soil N availability indices and tree growth in the oil sands region of Alberta.

Methods

In situ N mineralization rates, in situ N availability measured in the field using Plant Root Simulators (PRS? probes), laboratory aerobic and anaerobic soil N mineralization rates, and soil C/N and N content were determined for both the forest floor and the 0–20?cm mineral soil in eight jack pine (Pinus banksiana Lamb.) stands in the oil sands region in northern Alberta. Tree growth rates were determined based on changes in tree ring width in the last 6?years and as mean annual aboveground biomass increment.

Results

Soil N availability indices across those forest stands varied and for each stand it was several times higher in the forest floor than in the mineral soil. The in situ and laboratory aerobic and anaerobic soil N mineralization rates, soil mineralized N, in situ N availability measured using PRS probes, soil C/N ratio and N content in both the forest floor and mineral soil, as well as stand age were linearly correlated with tree ring width of jack pine trees across the selected forest stands, consistent with patterns seen in other published studies and suggesting that N availability could be a limiting factor in the range of jack pine stands studied.

Conclusions

In situ and laboratory aerobic and anaerobic N mineralization rates and soil C/N ratio and N content can be used for predicting tree growth in jack pine forests in the oil sand region. Laboratory based measurements such as aerobic and anaerobic N mineralization rates and soil C/N ratio and N content would be preferable as they are more cost effective and equally effective for predicting jack pine growth.     

Radon and thoron exposures for cave residents in Shanxi and Shaanxi provinces

Measurements of natural radiation were carried out in cave dwellings distributed in the Chinese loess plateau. Those dwellings are located in Shanxi and Shaanxi provinces. Radon and thoron gas concentrations were measured using a passive integrating radon-thoron discriminative detector. Concentrations of thoron decay products were estimated from measurements of their deposition rates. A detector was placed at the center of each dwelling for 6 months and replaced with a fresh one for another 6 months. Measurements were conducted in 202 dwellings from August 2001 through August 2002. A short-term measurement was conducted during the observation period. In addition, gamma-ray dose rates were measured both indoors and outdoors with an electronic pocket dosimeter. Radioactivities in soil were determined by gamma-ray spectrometry with a pure germanium detector. Among 193 dwellings, indoor radon concentrations ranged from 19 to 195 Bq m(-3) with a geometric mean (GM) of 57 Bq m(-3), indoor thoron concentrations ranged from 10 to 865 Bq m(-3) with a GM of 153 Bq m(-3), and indoor equilibrium equivalent thoron concentrations ranged from 0.3 to 4.9 Bq m(-3) with a GM of 1.6 Bq m(-3). Arithmetic means of the gamma-ray dose rates were estimated to be 140 nGy h(-1) indoors and 110 nGy h(-1) outdoors. The present study revealed that the presence of thoron is not negligible for accurate radon measurements and thus that special attention should be paid to thoron and its decay products for dose assessment in such an environment. More systematic studies are necessary for a better understanding of thoron and its decay products.     

Two independent estimations of stand-level root respiration on clonal Eucalyptus stands in Congo: up scaling of direct measurements on roots versus the trenched-plot technique

Root respiration at the level of a forest stand, an important component of ecosystem carbon balance, has been estimated in the past using various methods, most of them being indirect and relying on soil respiration measurements. On a 3-yr-old Eucalyptus stand in Congo-Brazzaville, a method involving the upscaling of direct measurements made on roots in situ, was compared with an independent approach using soil respiration measurements conducted on control and trenched plots (i.e. without living roots). The first estimation was based on the knowledge of root-diameter distribution and on a relationship between root diameter and specific respiration rates. The direct technique involving the upscaling of direct measurements on roots resulted in an estimation of 1.53 micromol m(-2) s(-1), c. 50% higher than the mean estimation obtained with the indirect technique (1.05 micromol m(-2) s(-1)). Monte-Carlo simulations showed that the results carried high uncertainty, but this uncertainty was no higher for the direct method than for the trenched-plot method. The reduction of the uncertainties on upscaled results requires more extensive knowledge of temperature sensitivity and more confidence and precision on the respiration rates and biomasses of fine roots.     

Measuring tree root respiration using (13)C natural abundance: rooting medium matters

Tree root respiration utilizes a major portion of the primary production in forests and is an important process in the global carbon cycle. Because of the lack of ecologically relevant methods, tree root respiration in situ is much less studied compared with above-ground processes such as photosynthesis and leaf respiration. This study introduces a new (13)C natural tracer method for measuring tree root respiration in situ. The method partitions tree root respiration from soil respiration in buried root chambers. Rooting media substantially influenced root respiration rates. Measured in three media, the fine root respiration rates of longleaf pine were 0.78, 0.27 and 0.18 mg CO(2) carbon mg(-1) root nitrogen d(-1) at 25 degrees C in the native soil, tallgrass prairie soil, and sand-vermiculite mixture, respectively. Compared with the root excision method, the root respiration rate of longleaf pine measured by the field chamber method was 18% higher when using the native soil as rooting medium, was similar in the prairie soil, but was 42% lower if in the sand-vermiculite medium. This natural tracer method allows the use of an appropriate rooting medium and is capable of measuring root respiration nondestructively in natural forest conditions.     

Estimation of field soil nitrogen mineralization and nitrification rates using soil N transformation parameters obtained through laboratory incubation

We tested the potential of estimating in-field (in situ) nitrogen (N) transformation rates based on soil temperature data and N transformation parameters (Q₁₀ and N transformation rates at standard temperature) obtained through laboratory incubations at three constant temperatures for 4 weeks. This test was conducted based on a comparison between in situ measurements and estimates using soils from 16 sites across 9 regions within the Japanese archipelago. The actual in situ N mineralization and nitrification rates measured using the buried-bag method at 0–50-cm-soil depth were 111 ± 34 and 106 ± 45 kg N ha^?1 year^?1, respectively, and estimates of both the rate and the amount were largely accurate. For rate alone, estimates were accurate in the 0–10-cm soil layer for annual and seasonal averages (except for spring–summer) whereas for amount alone, estimates were accurate to depths of 50 and 30 cm for N mineralization and nitrification, respectively. Thus, estimates of the rates and amounts were approximately equal to the actual in situ rate/amount, given the wide range of prediction intervals of the field measurement data. The differences between the estimates of N transformation rates derived from hourly measured and monthly average soil temperatures were negligible. Therefore, in situ soil N transformations, which are laborious to measure in the field, have the potential to be estimated from a combination of monthly average soil temperatures and N transformation parameters, which are relatively straightforward to obtain through laboratory incubation.     

三江平原典型小叶章湿地土壤氮素净矿化与硝化作用

2004年6月—2005年7月,利用PVC顶盖原位培育法研究了三江平原典型草甸小叶章湿地和沼泽化草甸小叶章湿地土壤(0~15cm)无机氮库、净矿化/硝化速率动态、影响因素及年净矿化/硝化量.结果表明:两种湿地土壤的无机氮均呈明显的动态变化特征,其NH4 -N、NO3-N含量均表现为典型草甸小叶章湿地>沼泽化草甸小叶章湿地.两种湿地土壤的净矿化/硝化速率均呈明显的波动变化,生物固持作用、反硝化作用以及雨季较多降水是导致净矿化/硝化速率出现负值的主要原因.温度、降水、土壤有机质含量、C/N和pH是引起二者土壤无机氮库、净矿化/硝化速率存在明显差异的重要原因.典型草甸小叶章湿地的年净矿化量(19.41kg·hm-2)、年净硝化量(4.27kg·hm-2)以及净硝化量占净矿化量的百分比(22.00%)明显高于沼泽化草甸小叶章湿地(5.51kg·hm-2、0.28kg·hm-2和5.08%),说明前者的氮有效性以及维持可利用氮的能力明显高于后者.     

Direct flux and 15N tracer methods for measuring denitrification in forest soils

Estimates of denitrification are one of the key uncertainties in the terrestrial nitrogen (N) cycle, primarily because reliable measurements of this highly variable process—especially the production of its terminal product (N₂)—are difficult to obtain. We evaluated the ability of gas-flow soil core and ¹⁵N tracer methods to provide reliable estimates of denitrification in forest soils. Our objectives were to: (1) describe and present typical results from new gas-flow soil core and in situ ¹⁵N tracer methods for measuring denitrification, (2) discuss factors that affect the relevance of these methods to actual in situ denitrification, and (3) compare denitrification estimates produced by the two methods for a series of sites in a northern hardwood forest ecosystem. Both methods were able to measure accumulations of N₂ over relatively short (2–5 h) incubations of either unamended or tracer-amended intact soils. Denitrification rates measured by the direct flux soil core method were very sensitive to incubation oxygen (O₂) concentration and decreased with increased O₂ levels. Denitrification rates measured by the in situ ¹⁵N tracer method were very sensitive to the ¹⁵N content of the nitrate (NO₃ ^?) pool undergoing denitrification, which limits the applicability of this method for quantifying denitrification in N-poor ecosystems. While its ability to provide accurate estimates of denitrification was limited, the ¹⁵N tracer method provided estimates of the short-term abiotic and biotic transformations of atmospheric N deposition to gas. Furthermore, results suggest that denitrification is higher and that N₂O:N₂ ratios are lower (<0.02) than previously thought in the northern hardwood forest and that short-term abiotic and biotic transformations of atmospheric N deposition to gas are significant in this ecosystem.     

Measurement of soil respiration using closed chamber method: An IRGA technique

A closed chamber method (CC-method) using an infra-red gas analyzer (IRGA) for measuring soil respiration was examined. Two major factors which potentially cause errors: (i) volume of air sampled from the chamber; and (ii) measuring period of time, were examined in laboratory experiments. Field measurements were also conducted with both the CC-method and the open-flow IRGA method (OF-method) throughout a year. The results of laboratory experiments showed that (i) sampling volume of air should be less than 0.2% of the volume of the chamber; and (ii) the air within the chamber should be sampled several times within 20 min. Field measurements showed that soil respiration rates measured by the CC-method were not significantly different from those by the OF-method. The results of this study indicate that the CC-method is as effective for the measurement of the soil respiration rates as the OF-method.     

Light conditions affect the measurement of oceanic bacterial production via leucine uptake

The effect of irradiance in the range of 400 to 700 nm or photosynthetically active radiation (PAR) on bacterial heterotrophic production estimated by the incorporation of 3H-leucine (referred to herein as Leu) was investigated in the northwestern Mediterranean Sea and in a coastal North Atlantic site, with Leu uptake rates ranging over 3 orders of magnitude. We performed in situ incubations under natural irradiance levels of Mediterranean samples taken from five depths around solar noon and compared them to incubations in the dark. In two of the three stations large differences were found between light and dark uptake rates for the surface most samples, with dark values being on average 133 and 109% higher than in situ ones. Data obtained in coastal North Atlantic waters confirmed that dark enclosure may increase Leu uptake rates more than threefold. To explain these differences, on-board experiments of Leu uptake versus irradiance were performed with Mediterranean samples from depths of 5 and 40 m. Incubations under a gradient of 12 to 1,731 micromol of photons m(-2) x s(-1) evidenced a significant increase in incorporation rates with increasing PAR in most of the experiments, with dark-incubated samples departing from this pattern. These results were not attributed to inhibition of Leu uptake in the light but to enhanced bacterial response when transferred to dark conditions. The ratio of dark to light uptake rates increased as dissolved inorganic nitrogen concentrations decreased, suggesting that bacterial nutrient deficiency was overcome by some process occurring only in the dark bottles.     

A simple technique for measuring buoyant weight increment of entire, transplanted coral colonies in the field

Estimating the impacts of global and local threats on coral reefs requires monitoring reef health and measuring coral growth and calcification rates at different time scales. This has traditionally been mostly performed in short-term experimental studies in which coral fragments were grown in the laboratory or in the field but measured ex situ. Practical techniques in which growth and measurements are performed over the long term in situ are rare. Apart from photographic approaches, weight increment measurements have also been applied. Past buoyant weight measurements under water involved a complicated and little-used apparatus. We introduce a new method that combines previous field and laboratory techniques to measure the buoyant weight of entire, transplanted corals under water. This method uses an electronic balance fitted into an acrylic glass underwater housing and placed atop of an acrylic glass cube. Within this cube, corals transplanted onto artificial bases can be attached to the balance and weighed at predetermined intervals while they continue growth in the field. We also provide a set of simple equations for the volume and weight determinations required to calculate net growth rates. The new technique is highly accurate: low error of weight determinations due to variation of coral density (< 0.08%) and low standard error (< 0.01%) for repeated measurements of the same corals. We outline a transplantation technique for properly preparing corals for such long-term in situ experiments and measurements.     

A new net mineralizable nitrogen assay improves predictions of floristic composition

Question: Can a simple measurement of nitrogen (N) availability be related to an ecologically relevant response, i.e. mean Ellenberg N indicator value (E_N)? Location: UK (England, Wales and Scotland). Methods: Soil cores from a stratified sample of UK habitats were analysed for mineralizable N with a conventional incubation and a new flushing method, which uses a single mineral N extraction. Predictions of mean E_N using mineralizable N and other soil measurements were assessed by fitting linear mixed‐effect models, using the Akaike information criterion (AIC) as a measure of model parsimony. Results: Mineralizable N measurements using the flushing method described a component of the variation in mean E_N that was more orthogonal to bulk soil properties such as moisture content, total N/C ratio and pH than that described by conventionally measured mineralizable N. Mineralizable N as measured using the flushing method improved the accuracy of predictions obtained using only bulk soil measurements, and appeared in the best two‐term and three‐term models. Conclusions: Much of the variation in mean E_N can be related to soil N/C ratio, pH or moisture content, but mineralizable N distinguishes variation in mean E_N that is independent of these bulk soil properties. The new measure will be useful for studies of the exposure of plants to N, in particular when assessing N pollution effects on plant species composition.     

Changes in wheat germination following gamma-ray irradiation: an in vivo electronic paramagnetic resonance spin-probe study

Embryos excised from wheat (Triticum aestivum) grains following gamma-ray irradiation at different doses were analyzed on membrane permeability by electron paramagnetic resonance (EPR) technique with 4-oxo-2, 2, 6, 6-tetramethyl-1-piperidinyloxy (TEMPONE) as spin probe to acquire an EPR spectrum. The broadening agent ferricyanide added leads to changes in the high-field region of the EPR spectrum, which reflects differences in membrane permeability. R-value, defined as the ratio of water (W) to lipid (L) component in height in the high-field region of the EPR spectrum, symbolizes membrane permeability for a given sample. The R-values corresponding to a certain dose treatment of grains displayed a definitive distribution pattern. A unit row vector with 20 components was used to describe the R-value distribution pattern for a given treatment. The transaction angle between vectors corresponding to grains irradiated and unirradiated, θ, was used as quantitative index for membrane permeability changes following gamma-ray irradiation. gamma-Ray irradiated grains germinated at low rates, and the regression equation of germination rate as a function of the irradiation dose is: Germination Rate (%)=94.8 exp[-0.264xIrradiation Dose (kGy)] (r(2)=0.991, P<0.001). Embryos excised from grains following gamma-ray irradiation show increases in θ values with irradiation dose. The θ value is negatively linearly correlated with the germination rate. It suggests that gamma-ray irradiation leading to increases in membrane permeability is consistent with that leading to low germination rate of grains. The introduction to vector analysis method on membrane permeability changes in this study is very practical.     

Can chlorophyll fluorescence be used to estimate photosynthetic production in the seagrass Zostera noltii?

Seagrass photosynthesis is usually measured in laboratory experiments, following oxygen evolution in closed chambers. Pulse amplitude modulated (PAM) fluorometry constitutes an alternative and non-intrusive method of measuring photosynthesis in the field. Validation of electron transport rate (ETR) measurements as reliable estimators of actual photosynthetic production requires that a significant linear relationship between oxygen production and ETR is demonstrated, and also that a 0.25 molar ratio between these two measures is verified. In this work, both parameters were measured simultaneously in laboratory experiments, over a range of light intensities, under well-defined and controlled conditions. A linear relationship was observed between the average rates of oxygen production and the electron transport rates for Zostera noltii (Hornemann) obtained at several irradiances. The molar ratio found between oxygen production and ETR was 0.15±0.02, lower than the theoretically expected value of 0.25. The use of PAM fluorescence as a valid proxy for photosynthetic production was validated for the range of 35-490 μmol photons m⁻² s⁻¹ (PAR), under the assumption that the electron sinks responsible for the molar ratio deviation remain constant in similar experimental conditions.     

Light Conditions Affect the Measurement of Oceanic Bacterial Production via Leucine Uptake

The effect of irradiance in the range of 400 to 700 nm or photosynthetically active radiation (PAR) on bacterial heterotrophic production estimated by the incorporation of ³H-leucine (referred to herein as Leu) was investigated in the northwestern Mediterranean Sea and in a coastal North Atlantic site, with Leu uptake rates ranging over 3 orders of magnitude. We performed in situ incubations under natural irradiance levels of Mediterranean samples taken from five depths around solar noon and compared them to incubations in the dark. In two of the three stations large differences were found between light and dark uptake rates for the surfacemost samples, with dark values being on average 133 and 109% higher than in situ ones. Data obtained in coastal North Atlantic waters confirmed that dark enclosure may increase Leu uptake rates more than threefold. To explain these differences, on-board experiments of Leu uptake versus irradiance were performed with Mediterranean samples from depths of 5 and 40 m. Incubations under a gradient of 12 to 1,731 μmol of photons m⁻² s⁻¹ evidenced a significant increase in incorporation rates with increasing PAR in most of the experiments, with dark-incubated samples departing from this pattern. These results were not attributed to inhibition of Leu uptake in the light but to enhanced bacterial response when transferred to dark conditions. The ratio of dark to light uptake rates increased as dissolved inorganic nitrogen concentrations decreased, suggesting that bacterial nutrient deficiency was overcome by some process occurring only in the dark bottles.     

Radiation quality and rat motor performance

The effects of bremsstrahlung, electron, gamma, and neutron radiations were investigated on the motor performance of male Sprague-Dawley rats. Rats were irradiated at a midline tissue dose rate of 20 Gy/min +/- 1 with one of the following: 18.6-MeV electrons (N = 40) or 18.1-MVp bremsstrahlung (N = 57) from a linear accelerator, 60Co 1.25-MeV gamma-ray photons (N = 48), or reactor neutrons at 1.67 MeV tissue-kerma weighted-mean energy (N = 43). Radiation effects were determined by establishing median effective doses (ED50) for rats trained on an accelerod, a shock-avoidance motor performance test. ED50's were based on 10-min postexposure performance. The ED50's were 61 Gy for electrons, 81 Gy for bremsstrahlung, 89 Gy for gamma-ray photons, and 98 Gy for neutrons. In terms of relative biological effectiveness to produce early performance decrement (10 min from the start of irradiation), significant differences existed between the electrons and the other three fields and between the bremsstrahlung and neutron fields. These differences could not be explained by macroscopic dose distribution patterns in the irradiated animals. The data imply that different radiation qualities are not equally effective at disrupting performance, with high-energy electrons being the most effective and neutrons the least.     

农牧交错区不同植物群落土壤呼吸的日动态观测与测定方法比较

 采用动态密闭气室法（IRGA）对农牧交错区10种植物群落最大生物量时期的土壤呼吸日动态进行了测定,并将该方法得到的土壤日呼吸速率与碱液吸收法（AA）进行了比较。结果表明：1）10个群落土壤呼吸的昼夜变化比较明显,均为单峰型曲线,主要受土壤温度的驱动,但同时也受到当日降水情况和云量、风速等气象因子的较大影响。因此,这些群落土壤呼吸日动态的一致性较差,规律性并不明显。2）用碱液吸收法和动态密闭气室法测定的10个群落的土壤呼吸速率变化范围分别为394～894 mg C·m-2·d-1和313～2043 mg C·m-2·d-1,其中碱液吸收法测定结果平均为动态气室法的67.5%,明显低于动态密闭气室法。3）两种测定方法具有很好的相关性,R2为0.873 9。本研究中发现,在土壤呼吸速率低的情况下,两种方法的测定结果十分接近甚至碱液吸收法测定结果稍大于动态密闭气室法,而在土壤呼吸速率较高的情况下,动态密闭气室法测定结果则显著高于碱液吸收法。上述结果与国内外同类研究的结果高度一致,从而为校正以往采用碱液吸收法在该区域的测定结果提供了可靠依据。     

原位酶谱技术在土壤酶活性研究中的应用进展

原位酶谱可方便、直观地展示土壤中酶活性的二维空间变异,近些年来通过与其他成像技术和分析方法相结合,土壤原位酶谱已发展成为分析土壤微观生态过程及土壤-根系-土壤动物相互作用界面过程的有效方法。然而,土壤原位酶谱技术尚未成熟,亟待深入分析其技术不足、完善技术方法,梳理其在不同领域中的应用现状,拓展并深化其在更多领域研究中的应用前景。基于此,综述并分析了该技术在土壤酶相关研究领域的应用现状,结合原位酶谱技术在底物载体选择与酶活定量方法的优化历程,分析了其存在的问题,发现：(1)可供研究的酶种类较少;(2)结果准确性仍有质疑;(3)在除根际研究外其他领域的研究较少、缺乏系统性,难以直接借鉴。这三者仍是阻碍原位酶谱技术在多领域中推广的最大障碍。综上所述,土壤原位酶谱技术虽仍存在缺陷,但其具有操作简便、测量结果的时空分辨率高等优势,在未来土壤酶学领域研究中仍潜力巨大,研究旨在为推进原位酶谱技术在土壤学和生态学等学科研究中的应用和发展提供理论指导。     

The earthworm gut: an ideal habitat for ingested N2O-producing microorganisms

The in vivo production of nitrous oxide (N(2)O) by earthworms is due to their gut microbiota, and it is hypothesized that the microenvironment of the gut activates ingested N(2)O-producing soil bacteria. In situ measurement of N(2)O and O(2) with microsensors demonstrated that the earthworm gut is anoxic and the site of N(2)O production. The gut had a pH of 6.9 and an average water content of approximately 50%. The water content within the gut decreased from the anterior end to the posterior end. In contrast, the concentration of N(2)O increased from the anterior end to the mid-gut region and then decreased along the posterior part of the gut. Compared to the soil in which worms lived and fed, the gut of the earthworm was highly enriched in total carbon, organic carbon, and total nitrogen and had a C/N ratio of 7 (compared to a C/N ratio of 12 in soil). The aqueous phase of gut contents contained up to 80 mM glucose and numerous compounds that were indicative of anaerobic metabolism, including up to 9 mM formate, 8 mM acetate, 3 mM lactate, and 2 mM succinate. Compared to the soil contents, nitrite and ammonium were enriched in the gut up to 10- and 100-fold, respectively. The production of N(2)O by soil was induced when the gut environment was simulated in anoxic microcosms for 24 h (the approximate time for passage of soil through the earthworm). Anoxia, high osmolarity, nitrite, and nitrate were the dominant factors that stimulated the production of N(2)O. Supplemental organic carbon had a very minimal stimulatory effect on the production of N(2)O, and addition of buffer or ammonium had essentially no effect on the initial N(2)O production rates. However, a combination of supplements yielded rates greater than that obtained mathematically for single supplements, suggesting that the maximum rates observed were due to synergistic effects of supplements. Collectively, these results indicate that the special microenvironment of the earthworm gut is ideally suited for N(2)O-producing bacteria and support the hypothesis that the in situ conditions of the earthworm gut activate ingested N(2)O-producing soil bacteria during gut passage.