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Riddle, C. 2006. Towards standards for measuring greenhouse gas fluxes from agricultural fields using instrumented towers. Can. J. Soil Sci. Can. J. Soil Sci. 86: 373-400. This is a discussion of the available technology for measuring turbulent fluxes using instrumented towers. This review focuses on the flux measurements of carbon dioxide (CO 2 ), methane (CH 4 ) and nitrous oxide (N 2 O) for agricultural systems and the development of standards and protocols for measuring them. Agroecosystems present unique challenges because they undergo large leaf area index (LAI) and canopy architecture changes in a relatively short period of time (i.e., months) coupled with the fact that many of the greenhouse gas sources are diffuse. This review examines all aspects of the theory and application of the micrometeorological techniques, with focus on the flux gradient, eddy accumulation and eddy covariance techniques. Instrument placement, sensor response and noise characteristics are also explored. Innovative applications of micrometeorological methods are discussed for closed-and open-path trace gas sensors and commonly used meteorological instrumentation. The use of fastresponse single-pass optical tunable diode laser (i.e., CH 4 , N 2 O) and infrared gas analyzers (i.e., CO 2 , H 2 O) is described. Consideration is also taken of the trace gas sensors' flow system design, mixing ratio measurement, and data acquisition and reduction requirements for micrometeorological flux measurement. Procedures are outlined for the meteorological instrumentation necessary for eddy covariance-based energy budget measurement including ultrasonic anemometry. Les écosystèmes agricoles présentent des contraintes spécifiques du fait que l'indice foliaire et l'architecture du couvert végétal subissent d'importants changements durant la saison de croissance (quelques mois) et que la plupart des sources de gaz à effet de serre sont diffuses. Les auteurs examinent les principes et les applications de la micrométéorologie sous toutes leurs facettes, en insistant sur les techniques des gradients de flux, d'accumulation des tourbillons et la covariance des fluctuations. Ils abordent aussi l'installation des instruments, la sensibilité des capteurs et les caractéristiques du bruit de fond. Les auteurs présentent des applications novatrices de la micrométéorologie pour les capteurs de gaz à l'état de traces à parcours ouvert et fermé ainsi que des instruments employés couramment en météorologie. Ils décrivent l'utilisation de diode laser accordable à parcours optique unique et à réponse rapide (pour le CH 4 et le N 2 O) et d'analyseurs de gaz à infrarouge (pour le CO 2 et H 2 O). Enfin, ils tiennent compte de la conception du système captant les gaz à l'état de traces, des mesures du rapport de mélange ainsi que de l'acquisition des données et de leur réduction afin de mesurer les flux micrométéorologiques. Suit la description des méthodes servant aux instruments nécessaire à la mesure du bilan énergétique par la covariance des fluctuations, tels que...

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In order to manage increased enrolment in a third-year course in microclimatology, group work was introduced with seminar presentations and term papers. A peer-and self-assessment strategy was developed that provided individual group members the opportunity to appraise their own and partners' performance. The course instructor worked with an adviser from the university's educational development unit throughout the term to develop and critique the technique for this class. The techniques used, collaboration with the educational development unit, and student responses are described and explored within the context of an action-based research project. Students indicated that the group work was a valuable and enjoyable learning experience which helped them to develop skills in independent research, collaboration and communication. The 'zero-sum' assessment technique used in the course did help the instructor make a more accurate assessment of student performance in groups. Most students appreciated the use of self and peer assessment and believed it was used appropriately. The primary recommendation is to make the process as inclusive and participatory as possible. It is concluded that a 'zero-sum' approach to self and peer assessment of group work is effective, and that a collaborative approach to educational development can be a positive experience that ultimately benefits students. KEYWORDSPeer and self assessment, group work

Accounting for temporal changes in carbon dioxide (CO 2 ) emissions from freshwaters remains a challenge for global and regional carbon budgets. Here, we synthesize 171 site-months of eddy covariance flux measurements of CO 2 from 13 lakes and reservoirs in the Northern Hemisphere (NH) and quantify the magnitude and dynamics at multiple temporal scales. We found pronounced diel and sub-monthly oscillatory variations in CO 2 flux at all sites. Diel variation converted sites to daily net sinks of CO 2 in only 11% of site-months. Upscaled annual emissions had an average of 25% (range 3-58%) interannual variation. Given temporal variation remains under-represented in inventories of CO 2 emissions from lakes and reservoirs, revisions in CO 2 flux are needed using a better representation of sub-daily to interannual variability. Constraining short-and long-term variability is necessary to improve detection of temporal changes of CO 2 fluxes in response to natural and anthropogenic drivers.