[en] The systematic decline in delta sub(a) ¹⁵N (per mill ¹⁵N excess) of plant material with application of fertilizer under field conditions was verified in a growth chamber experiment with soil columns. The delta sub(a) ¹⁵N of NO₃ -N in the zones of the high NO₃ -N accululation was lower than that of the soil-derived NO₃ -N but not necessarily lower than the delta sub(a) ¹⁵N of the fertilizer material as was the case in previously reported field experiments. Calculation of the fate of the fertilizer N based on the principle of isotopic dilution provided semi-quantitative estimates of the added N found in the plant, the soil, and the leachate

[en] Volumetric water content was measured by time domain reflectometry (TDR) and by a single-beam γ-ray attenuation at eight positions on each of three soil columns. Both methods measured equally well at single locations and both showed some position dependence, which was greater for γ-ray attenuation than for TDR. An error analysis showed the major contributor to variance in the γ-ray measurement was the unknown variability of bulk density which gave rise to uncertainty of +-0.05 cmsup(3.)cmsup(-3) for three soils. For the TDR technique all sources of variance resulted in a total uncertainty of +-0.02 cmsup(3.)cmsup(+3). The greater sampling volume of the TDR as used in this experiment was advantageous with the naturally structured heterogeneous soils

[en] Mineral composition of the parent material is a major factor controlling natural radioactivity of soils. The objective of this study was to investigate the relationship between the natural radioactivity of 18 till and six lacustrine parent materials and their properties measured during soil surveys. Gamma spectroscopy was used to estimate ⁴⁰K and daughters of ²³⁸U and ²³²Th; neutron activation analysis was used to determine total U; and alpha counting was used to measure ²²²Rn release from the soil. The amounts of the various radioisotopes were positively correlated with each other and with clay content; the correlation with sand content was negative; and the correlations with silt and inorganic C content were generally not significant. Adding the fine/total clay ratio as a further independent variable considerably improved the correlation between ⁴⁰K and clay content. The data suggested considerable disequilibrium in the ²³⁸U decay chain, which appeared to be in part related to the mode of deposition of the parent materials. Soil survey information — in particular, texture — thus appears a readily available tool for preliminary screening of terrestrial radiation in Saskatchewan. (author)

[en] The accumulation of four naturally occurring radionuclides of the sup(238)U series, uranium, sup(226)Ra, sup(210)Pb and sup(210)Po, in 15 species of native plants was investigated. Of the plants sampled some accumulated, but none concentrated uranium or sup(226)Ra. Grouseberry (Vaccinium scoparium Leiberg) appeared to concentrate sup(210)Pb and sup(210)Po. There were marked seasonal variations in the accumulation of uranium by grass (Calamagrostis rubescens Buckl.), and of sup(210)Pb and sup(210)Po by grass and fireweed (Epilobium angustifolium L.). High positive correlations between soil and vegetation radionuclide content were found for uranium in fireweed and grouseberry in spring, sup(226)Ra in willow (Salix scouleriana L.) in spring, and uranium in fireweed in summer

[en] Records of radioactive fallout on the Canadian Prairies indicate that ¹³⁷Cs should be present in soils at levels that can be counted relatively accurately. Less than 7% of total ¹³⁷CS appears to have fallen during the winter months, so that redistribution of ¹³⁷Cs with blowing snow should not seriously impair the possibility of using ¹³⁷Cs as a tracer for soil erosion. Methodology for measuring ¹³⁷Cs in soil samples is described, as is a semi-empirical method for correcting for the effect of bulk density of the sample on counting efficiency. Preliminary data indicate that noneroded soils in the Saskatoon area contain about 6.4 pC ¹³⁷Cs/cm². There was little variation in ¹³⁷Cs with slope position on gently rolling sites under native vegetation, whereas there was considerable redistribution in cultivated fields. It was estimated that a knoll in one cultivated field had lost about 10% of its topsoil since the early 1960s when most ¹³⁷Cs was deposited

[en] The nuclear industry uses computer models to calculate and assess the impact of its present and future releases to the environment, both from operating reactors and from existing licensed and planned waste management facilities. We review four soil models varying in complexity that could be useful for environmental impact assessment. The goal of this comparison is to direct the combined use of these models in order to preserve simplicity, yet increase the rigor of Canadian environmental assessment calculations involving soil transport pathways. The four models chosen are: the Soil Chemical Exchange and Migration of Radionuclides (SCEMR1) model; the Baes and Sharp/Preclosure PREAC soil model; both used in Canada's nuclear fuel waste management program; the Convection-Dispersion Equation (CDE) model, commonly used in contaminant transport applications; and the Canadian Standards Association (CSA) derived release limit model used for normal operations at nuclear facilities. We discuss how each model operates, its timestop and depth increment options and the limitations of each of the models. Major model assumptions are discusses and the performance of these models is compared quantitatively for a scenario involving surface deposition or irrigation. A sensitivity analysis of the CDE model illustrates the influence of the important model parameters: amount of infiltrating water, V; the hydrodynamic dispersion coefficient, D; and the soil retention or partition coefficient, Kd. The important parameters in the other models are also identified. This work shows we need tested, robust, mechanistic unsaturated soil models with easily understood and measurable inputs, including data for the sensitive or important model parameters for Canada's priority contaminants. Soil scientists need to assist industry and its regulators by recommending a selection of models and supporting them with the provision of validation data to ensure high-quality environmental risk assessments are carried out in Canada. (author)

[en] Stable isotope probing of phospholipid fatty acids (PLFA-SIP) is useful when studying bacterial contributions to soil processes, and it is an effective way to separate fungal and bacterial activity by linking ¹³C enrichment to specific PLFAs. Distinguishing bacterial contributions to soil processes often employs selective inhibitors; however, studies demonstrating their efficacy when using PLFA-SIP are less common. Here, we determined the effect of the fungal inhibitor cycloheximide (4.8 mg g ⁻¹ dry soil) and the bacterial inhibitor bronopol (0.48 mg g ⁻¹ dry soil) on microbial communities white spruce [ Picea glauca (Moench) Voss] forest floor by measuring the uptake of ¹³C-enriched glucose (2 mg g⁻¹ dry soil) in microbial PLFAs. We targeted [¹³C] glucose uptake by the bacterial community conditioned to a stable soil environment of 23 ° C for over 2 wk rather than new bacteria generated from active colony growth caused by glucose addition. Nearly all bacterial PLFAs exhibited pronounced inhibition of ¹³C enrichment in the presence of bronopol. Limited inhibition of ¹³C enrichment in the presence of cycloheximide was observed as bacterial PLFA affected by cycloheximide had roughly one third less ¹³C enrichment than samples emended with [¹³C] glucose alone. Inhibitory effects only reduced ¹³C enrichment and did not affect total PLFA concentrations, implying that the inhibitors in the concentrations applied were impeding bacterial activity without causing cell death. Based on this work, we conclude that bronopol is an effective inhibitor for bacteria. Additionally, non-targeted effects of cycloheximide on soil bacteria must be accounted for when it is used in soil incubations. (author)

[en] Crop water demand in the Okanagan Basin was determined for 1961 to 1990, 2010 to 2039, 2040 to 2069, and 2070 to 2099. Daily station temperature data were spatially interpolated to a 1 x 1 km grid and adjusted for elevation. Daily precipitation data were estimated across four climatic regions. Output from three global climate models (GCM), CGCM2, CSIROMk2 and HadCM3 was used to create future daily climate. Daily potential evapo-transpiration (grass reference) was estimated from an empirical relationship between Bellani-plate atmometer readings, temperature and extra-terrestrial solar radiation, and then modified by crop coefficients for all crops except pasture. Depending on GCM, projected water demand increased by 12-20% (2010 to 2039), 24-38% (2040 to 2069) and 40-61% (2070 to 2099). Possible elevated CO₂ effects on stomatal conductance which may reduce water demand were not accounted for. Comparisons with modeled Okanagan Lake inflows indicated that, on average, high water demand and low supply scenarios coincided. In one sub-basin, supply and demand thresholds were exceeded 1 yr in 6 (HadCM3) in the 2050s and at least 1 yr in 4 for all GCMs by the 2080s, and existing water supply infrastructure may be inadequate. Crop growing seasons were defined empirically from growing degree days or threshold temperatures. The growing season lengthened up to 30-35% leading to higher demand in fall and shortages due to low stream flows. (author)

[en] Evaporation ponds used for agricultural subsurface drainage water disposal in the Tulare Lake Bed (TLB) of the San Joaquin Valley, California, USA have elevated levels of U. Waterfowl which inhabit and forage the ponds and surrounding areas are threatened by exposure to U. The ponds, which receive irrigation drainage waters and seasonal rain, are subject to wetting and drying periods. The periods result in the accumulation of decaying algae and other organic material in surface sediments. Sediment and waters in the ponds were sampled to determine what factors control U solubility and sediment U concentrations. Data from a 1990 study conducted by Chilcott et al. in 1989 on the TLB ponds were used to help identify what factors may control U solubility. Pond sediment U concentrations decreased abruptly with depth and surface sediment U concentrations were related to dissolved Ca:HCO₃ ratios. Pond algal U bioaccumulation was favored in waters with high Ca:HCO₃ ratios, which had lower pH values and carbonate alkalinities than waters with low CA:HCO₃ ratios. Ponds with high salinities and high carbonate alkalinities contained the highest aqueous U concentrations relative to other TLB ponds. Sediment total organic carbon (TOC) was correlated with sediment U concentrations, suggesting that U is bound to organic matter. The source of TOC is most likely from algae deposition. (author)

[en] Few nmr studies with whole soil have been successfully attempted. Solid-state sup(13)C nmr spectra were obtained for Bainsville clay loam, an orthic humic gleysol with 3 percent carbon, using the CPMAS technique (cross-polarization magic-angle spinning). Results for the whole soil were limited by poor signal/noise and lack of resolution, possibly due to line-broadening by iron. Better results were obtained by employing a < 50 μm fine-size fraction, and difference spectra techniques, allowing observation of added sup(13)C-labelled acetate, and its transformation during incubation