A model for total phosphorus concentrations during both the trophic upsurge and depression phases in new reservoirs has been developed by a convolution of the rate of phosphorus leaching from flooded lands and the rate of reservoir filling. Model parameters for phosphorus sedimentation and leaching coefficients were estimated from data available on the Smallwood Reservoir (impoundment 1971) in Labrador. The model was subsequently applied to predict phosphorus concentrations during the trophic upsurge phase in the La Grande-2 (LG2) Reservoir (impoundment 1978) in the James Bay region of Quebec. Because the sparse data available on other new or old reservoirs during the trophic upsurge phase does not permit an analysis of the confidence limits in model output, we include discussion of the calculated values of model parameters and their relationship to the real phenomena. An evaluation of the rates of phosphorus leaching from flooded soils and vegetation and the specific leaching coefficient of phosphorus from various lands has shown indirectly that the proposed model approximates the dynamics of new reservoir phosphorus concentrations. We conclude that the model has a good potential as an empirical predictive tool in the management of large new reservoirs on the Canadian Shield.Key words: reservoir, phosphorus, model, trophic state

Abstract. Despite the length of winter in cold temperate climates, few studies refer to greenhouse gas emissions from soils during the nongrowing season. In this study, N20 and CO2 fluxes from agricultural and forest soils in southeastern Quebec (Canada) were measured during winter and spring from 1994 to 1997, and the influences of climate, soil, and snow properties on the gaseous emissions were examined. N20 fluxes were far greater from the agricultural soil (2-187 ng N20 m -2 s 'l) than from the forest soil (< 3 ng N20 m -2 s-I), but CO2 fluxes were equivalent for both soil systems (2-102 gg CO2 m -2 s-i). The higher N20 concentrations in the lower soil horizons could be explained by positive temperature gradients with depth and concomitant negative gas solubility gradients. However, the higher N20 concentrations could also be explained by variations in the expression of N20 reductase with depth, which can modify the N2/N20 ratios in relation to the availability of 02. Calculated N20-N fluxes showed that N losses by gaseous emissions from soils during winter and spring were comparable to, or exceeded, similar reported N losses during the growing season. The highest winter fluxes observed in 1997 were interpreted to be due to favorable meteorological conditions that prevailed for denitrification through high soil water content in summer and fall of 1996. Although interannual and interseasonal variations of fluxes are important, this study shows that wintertime losses of N20 from agricultural soil can be up to 2 to 4 times greater than emissions measured during the growing season in similar agroecosystems.

Abstract. We investigated soil and snow cover gas concentrations at two agricultural sites (St-Lambert; Chapais) in Quebec, Canada, during winter 1998-1999. Both sites showed frozen and unfrozen soils and complex snow cover structure. At St-Lambert we measured

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In a subalpine balsam fir forest in Quebec, Canada, mass losses, respiration rates, and nitrogen and sulphur dynamics were measured on fir needles, birch leaves, lichens (mixed species), and small twigs decomposing under deep (> 1.5 m) winter snow for 6 months. Mass losses ranged from <6% (twigs) to 70% (lichens) and relative decomposition rates of needles and leaves were reversed from those expected at higher temperatures. Isolation of fir needles from direct contact with the snow did not affect decay rate, nor was decay accelerated by spring snowmelt. In situ respiration rates increased from about 1 mg CO2/(g∙day)) in February to 3–5 mg CO2/(g∙day)) in May, mostly because of rising temperatures. Summer respiration rates were much higher (> 6 mg CO2/(g∙day)). Nitrogen and suphur concentrations increased in all nonwoody litter over winter, but only birch leaves and some fir needles appeared to assimilate nutrients from the environment. Melting snow could easily have provided all of the nitrogen and sulphur taken up by decomposing litter. Decomposing lichens released 40 and 60%, respectively, of their initial nitrogen and sulphur contents. A literature review indicates mass losses from leaf litter decomposing under deep snow vary according to the proportion of labile material in the litter and usually constitute 40–60% of total first-year mass losses. Key words: decomposition, winter, balsam fir, snow.

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Under controlled laboratory conditions, artificial rain leaches solute from snow columns, and gives rise to leachate with a composition similar to snowmelt, in addition to the solute initially present in the artificial rain. The initial concentration of ions in the leachate, normalized to the concentration of ions found in the original snow and corrected for the solute present in the artificial rain, is similar to those reported in other laboratory and field studies of snowmelt composition, but there is some evidence that the concentration of leached ions declines more rapidly than during snowmelt. Similarly, as in snowmelt studies, not all ions are leached with the same efficiency. Bearing in mind the confounding influences of snow crystal morphology and snow column hydrology, it seems likely that rain will leach solute from snowpack during rain-on-snow events, in a manner similar to leaching by snowmelt, and that the precise composition of the leachate will depend on the hydrological routing of rain-meltwater mixtures through the snowpack.

Abstract:The physical characteristics and CO 2 concentrations of snow cover in the western Canadian arctic were examined at sites with dierent landscape forms (valley¯oor, hillslope, plateau). The greater exposure of plateau snow cover to blowing snow results in dierences in the structure of the snow cover and dierent snow strata compared with snow covers on the other landscape forms. Both higher in-pack concentrations of CO 2 and the largest vertical CO 2 concentration gradients were found in plateau snow cover, the smallest in the deeper hillslope and valley snows. CO 2 gradients in all landscape snow covers followed two patterns, i.e. where concentrations at the soil±snow interface are higher than those just below (5 cm) and the snow±atmosphere interface and vice versa. The latter pattern is due to the transport of the gas from the lower levels to the upper levels of the snowpack by wind-induced advection (windpumping) and is indicative of non steady-state, nondiusive processes. These latter processes should thus be considered in any studies on CO 2¯u xes from Arctic soil where snow cover topography and winds are conducive to windpumping and where concentration gradients resulting from diusive processes have not been clearly identi®ed.