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This study reports on the radiation and energy balance of three sites (rural, suburban, and urban) located along an urbanization gradient in the Montreal, QC, region for two winters (December-March) with contrasting snow regimes. The urban and suburban sites had similar albedo which was about half that at the rural site during the snow-cover period. Temporal variability in albedo was attributable to the presence of snow on rooftops at the urban site and to a site-specific response to cloudiness at the suburban site. As compared to the suburban site, the urban site showed higher albedo inducing lower net radiation ( Q*) which was compensated for by greater anthropogenic heat flux ( QF), so that the urban site had highest total available energy ( Q* + QF). Hourly QF estimates were a significant term in the winter energy budget analysis. QF was dominated by building heating at both urbanized sites, while vehicular traffic contributed to rush hour peaks. Daytime total available energy was mostly dissipated as sensible heat flux ( QH) at the beginning of the winter season and mostly stored (Δ QS) towards the end of the winter at both urbanized sites. Daytime energy partitioning into QH and Δ QS was correlated with air temperature with no significant differences between urbanized sites. On a daily time scale, available energy was mostly stored before noon and dissipated as QH in the afternoon at both urbanized sites. Urbanized sites showed differences in diurnal variability of QH and Δ QS occurring in the afternoon and evening. Latent heat flux ( QE) was low throughout winter and accounted for 10% of the total available energy during daytime at the urbanized sites. Water vapour emissions showed intra-urban differences in their response to wintertime climatic conditions. Copyright © 2010 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

Abstract: Urban environments can modify the local climate and are net CO2 emitters, both of which can affect the life of an increasing proportion of the world’s population that lives in and around cities. Observational information on the seasonal and diurnal variations of CO2 fluxes as well as on the contribution from the different CO2 sources and sinks is needed at fine spatial resolution to help develop and validate weather prediction and atmospheric dispersion models. This study reports on measured using the eddy covariance technique for a two-year period over a suburban and an urban residential area as well as a reference agricultural site located in the Montreal region, which experiences cold winters and warm summers. The seasonal and diurnal variability of and its response to incoming light and to air temperature was analysed. Typical weekday and weekend vehicular traffic CO2 emissions (EVT) were estimated from inventory data for both residential sites. The urban site was a net source of CO2 throughout the entire measurement period on the order of 200 t CO2 ha−1 year−1. The suburban site was a winter source and a summer daytime sink of CO2 resulting in a net source of 50 t CO2 ha−1 y−1. Lower emissions at the suburban site are attributed to the large biological uptake in summer and to its low anthropogenic emissions. Higher emissions at the urban site are partly associated with its greater population and building density, promoting higher emissions from vehicular traffic and heating fuel combustion. The cold climate induced increased heating fuel combustion as compared to cities under a warmer climate. [Copyright &y& Elsevier]

Although mature black spruce forests are a dominant cover type in the boreal forest of North America, it is not clear how their carbon (C) budgets vary across the continent. The installation of an eddy covariance flux tower on an Old Black Spruce (OBS) site in eastern Canada (EOBS, Québec) provided a first opportunity to compare and contrast its annual (2004) and seasonal C exchange with two other pre-existing OBS flux sites from different climatic regions located in Saskatchewan [Southern OBS (SOBS)] and Manitoba [Northern OBS (NOBS)]. Although there was a relatively uniform seasonal pattern of net ecosystem productivity (NEP) among sites, EOBS had a lower total annual NEP than the other two sites. This was primarily because warmer soil under a thicker snowpack at EOBS appeared to increase winter C losses and low light suppressed both NEP and gross ecosystem productivity (GEP) in June. Across sites, greater total annual GEP and ecosystem respiration ( R) were associated with greater mean annual air temperatures and an earlier beginning of the growing season. Also, GEP at all three sites showed a stronger relationship with air temperature in spring and early summer compared with later in the growing season, highlighting the importance of springtime conditions to the C budget of these boreal ecosystems. The three sites had different parameter estimates describing the responses of R and GEP at the half hour time scale to near surface temperature and light, respectively. On the other hand, the responses of both R and GEP to temperature at the monthly scale did not differ among sites. These results suggest that a general parameterization could be sufficient at coarse time resolutions to model the response of C exchange to environmental factors of mature black spruce forests from different climatic regions. [ABSTRACT FROM AUTHOR]

Air-slit containerized (IPL 25-350A) black spruce [Picea mariana (Mill) BSP; 1+0] seedlings, were subjected to four irrigation regimes (IR-15%, IR-30%, IR-45%, and IR-60%, by volume, cm³ water/cm³ substrate) under tunnel conditions in a forest nursery. Irrigation regimes were controlled by time-domain reflectometry during the first growing season. With exception of midday water potential, water relation and gas exchange variables were unaffected by substrate water content. There were no significant differences in height, diameter or number of needle primordia of the seedlings grown under IR-15%, IR-30%, and IR-45%. Seedlings grown in a substrate with a high water content (IR-60%) had lower oven-dry biomass and higher cuticular transpiration rates than seedlings grown under the three other irrigation regimes. Root hydraulic conductivity was not affected by irrigation regime, but showed a general decrease towards the end of the growing season. Variation in root hydraulic conductivity was most likely related to root growth and degree of lignification. Seedlings that had been exposed to IR-60% during the first growing season remained smaller than the other seedlings throughout the second growing season. Results of this study indicate that nursery managers can reduce the quantity of irrigation water used without significantly affecting the growth or physiology of air-slit containerized black spruce seedlings (1+0) grown under tunnel conditions. [ABSTRACT FROM AUTHOR]