AbstTactWater vapour and CO2 fluxes were measured using the eddy correlation method above and below the overstorey of a 21-m tall aspen stand in the boreal forest of central Saskatchewan as part of the Boreal Ecosystem-Atmosphere Study (BOREAS). Measurements were made at the 39.5-m and 4-m heights using 3-dimensional sonic anemometers (Kaijo-Denki and Solent, respectively) and closed-path gas analysers (LI-COR 6262) with 6-m and 4.7-m long heated sampling tubing, respectively. Continuous measurements were made from early October to mid-November 1993 and from early February to lateSeptember 1994. Soil CO2 flux (respiration) was measured using a LI-COR 6000-09 soil chamber and soil evaporation was measured using lysimetry.The leaf area index of the aspen and hazelnut understorey reached 1.8 and 3.3, respectively. The maximum daily evapotranspiration (£) rate was 5-6 mm d^^ Following leaf-out the hazelnut and soil accounted for 22% of the forest £. The estimated total £ was 403 mm for 1994. About 88% of the precipitation in 1994 was lost as evapotranspiration.During the growing season, the magnitude of half-hourly eddy fluxes of CO2 from the atmosphere into the forest reached 1.2 mg CO2 m'^ s^* (33 |imol C m~^ s"^) during the daytime. Downward eddy fluxes at the 4-m height were observed when the hazelnut was growing rapidly in June and July. Under well-ventilated night-time conditions, the eddy fluxes of CO2 above the aspen and hazelnut, corrected for canopy storage, increased exponentially with soil temperature at the 2-cm depth. Estimates of daytime respiration rates using these relationships agreed well with soil chamber measurements. During the 1994 growing season, the cumulative net ecosystem exchange (N££) was -3.5 t C ha"^ y"^ (a net gain by the system). For 1994, cumulative NEE, ecosystem respiration (K) and gross ecosystem photosynthesis (GEP = R-NEE) were estimated to be -1.3, 8.9 and 10.2 t C ha"^ y~^, respectively. Gross photosynthesis of the hazelnut was 32% of GEP.

Russell, C. A. and Voroney, R. P. 1998. Carbon dioxide efflux from the floor of a boreal aspen forest. I. Relationship to environmental variables and estimates of C respired. Can. J. Soil Sci. 78: 301-310. Soil CO 2 efflux (Soil Fc) in a boreal aspen (Populus tremuloides) forest was related to environmental variables to estimate the mass of carbon (C) annually respired. Measurements of soil Fc were made between April and September with a dynamic closed chamber via an infra-red gas analyzer. Over the course of the study day-time soil Fc ranged from 0.027 to 0.411 mg CO 2 m -2 s -1 . Summertime estimates of soil Fc were higher than expected, and this was attributed to underestimation by static chamber methods. Strong relationships were found between seasonal patterns of (1) soil Fc and soil temperature (Ts) at various depths (R 2 = 0.77 to 0.87, Q 10 = 3.9 to 5.1), (2) soil Fc and humus [CO 2 ] and volumetric moisture (θ v ; R 2 = 0.76 to 0.88) and (3) humus [CO 2 ] and humus Ts and θ v (R 2 = 0.74). On their own, θ v , litter and soil organic matter content explained little (<5%) of the variation in soil Fc. Ts was the single most effective variable used to predict soil Fc.Annual masses of soil Fc C were estimated from the relationship between soil Fc and 0.1 m Ts in 1994. Long-term (49-yr) estimates were generated from monthly mean air temperatures (Ta) using the relationship between Ts (0.10 m) and Ta (2 m) at the site throughout 1994-1995. In both years, Ta explained about 70% of the variability in Ts. Estimates of annual soil Fc C were 905 (1994), 870 (1995) and 809 (long-term) g m -2 . Growing season soil Fc approximated 75% of the annual C mass respired. These annual C fluxes far exceed current estimates for boreal and most temperate forest ecosystems. 1994 soil Fc C also exceeded the site estimate of aboveground net primary productivity (361 g C m -2 yr -1 ). This extreme shortfall, along with the inability of soil organic matter or litter mass to explain soil Fc, suggests that about 60% of annual soil Fc C is attributable to the presence of roots. If soil Fc in vegetated environments is primarily due to the presence of roots then the significance of soil Fc to global C cycling can only be understood with concurrent estimates of net ecosystem C exchange. . Le Fc du sol durant la saison de végétation comptait approximativement pour 75 % de la masse annuelle de C respiré. Ces flux de C excé-daient de beaucoup les valeurs actuellement reconnues pour les écosystèmes boréaux et pour la plupart des écosystèmes forestiers des zones tempérées. En outre, l'efflux de C du sol sous forme de CO 2 en 1994 dépassait les valeurs obtenues à cet emplacement pour la productivité primaire aérienne nette, soit 361 g C m -2 an -1 . Cet écart extrême, ainsi que l'impossibilité d'expliquer les variations de Fc du sol par le contenu en matière organique ou en litière du sol portent à conclure que 60 % des efflux annuels de C sous forme de CO 2 sont imputables à la présence des racines. Si Fc sous couvert végétal est essentiell...

Abstract-Improving energy efficiency of Internet equipment is becoming an increasingly important research topic, motivated by the need to reduce energy costs (and Carbon footprint) for Internet Service Providers, as well as increase power density to achieve more switching capacity per-rack. While recent research has profiled the power consumption of commercial routing equipment, these profiles are coarse-grained (i.e., at the granularity of per line-card or per port), and moreover such platforms are inflexible for experimentation with new energysaving mechanisms. In this paper we therefore consider the NetFPGA platform, which is becoming an increasingly popular routing platform for networking research due to its versatility and low-cost. Using a precise hardware-based traffic generator and high-fidelity energy probe, we conduct several experiments that allow us to decompose the energy consumption of the NetFPGA routing card into fine-grained per-packet and perbyte components with reasonable accuracy. Our quantification of energy consumption on this platform opens the doors for estimating network-wide energy footprints at the granularity of traffic sessions and applications (e.g., due to TCP file transfers), and provides a benchmark against which energy improvements arising from new architectures and protocols can be evaluated.

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