The Earth is being influenced by environmental changes such as elevated atmospheric trace gas concentrations and associated shifts in climate. There is much uncertainty about the consequences of these changes for ecosystem function and for potential feedbacks to the climate system. Terrestrial ecosystems, in particular, present a significant problem for analyzing global change because of the great diversity among ecosystems in species composition, physiological properties, physical structure and environmental conditions. A major objective of my research program is to further understand the fundamental processes that occur during terrestrial ecosystem-atmosphere interactions. In my research I make use of tools and technologies from a range of disciplines (plant physiology, ecology, geochemistry and meteorology).
I am currently studying ecosystem CO2, water vapor and energy exchange using the eddy covariance technique in grassland and peatland ecosystems in Alberta as part of the Fluxnet-Canada and Ameriflux research networks. These long-term measurement programs contribute in a number of ways to better understand ecosystem response to global environmental change. In collaboration with Canadian colleagues, measurements of ecosystem-level CO2, water and energy exchange at my research sites have been used to test and evaluate the ecosys and CLASS models. Both the ecosys and CLASS models are being used to support studies of carbon accounting and management. In addition, the CLASS model is used as a component in the Canadian Regional and Global Climate models.
Interaction and feedback between vegetation and the atmosphere occurs via exchanges of CO2 and H2O gases during photosynthesis, evapo-transpiration, and respiration. On seasonal and annual time scales, changes in the stable isotope ratio of atmospheric CO2 result from isotope effects that occur during these ecosystem-atmosphere gas exchange processes. Monitoring shifts in the stable isotope ratio of atmospheric CO2 can potentially be used as a tool to study large-scale ecosystem-atmosphere interactions. Such an application requires, however, a detailed understanding of the mechanisms causing the isotope effects. A long-term objective of my research program is to determine the physiological mechanisms causing stable isotope fractionation during photosynthesis, transpiration, and respiration at both the leaf and ecosystem levels. We have recently developed a mechanistic, ecosystem-scale model of stable carbon isotope effects that occur during photosynthesis and respiration. This model is currently being applied and tested with empirical measurements made during the Fluxnet-Canada program at several research sites across the country. We have also recently completed a synthesis study involving our stable isotope measurements in Canada in comparison with similar measurements made at Ameriflux sites in the USA.
Remote sensing of biophysical properties of the land surface combined with climate data potentially allows calculation and extrapolation of ecological and physiological characteristics of ecosystems to larger spatial scales. The MODIS sensor on the Aqua and Terra satellites launched by NASA collects surface reflectance data and uses this data in conjunction with ecosystem models to calculate a variety of physiological and ecological attributes of ecosystems on a global basis. Testing of the relationships between the reflectance characteristics of vegetation and associated physiological changes is an important aspect of current research being conducted to evaluate the performance and quality of information provided by the MODIS sensor. My grassland research site is one of a select number of research sites chosen for testing and evaluating the MODIS calculations used to convert reflectance measurements into ecosystem physiological and ecological information.
Peatland ecosystems are very tightly coupled to climate and the hydrological cycle, and are very susceptible to the effects of climate change. Relatively small changes in soil moisture and temperature can dramatically alter carbon cycling in peatlands. For example, warmer temperatures and a lowering of the water table may increase the release of CO2 and convert these ecosystems from a net sink to a net source of carbon dioxide to the atmosphere. Shifts in the water table may also influence the production and release of methane to the atmosphere. I have initiated studies of the controls on methane exchange to complement my on-going studies of CO2 and water vapor exchange in peatlands in northern Alberta.