Regional carbon fluxes in heterogenous landscapes: Challenges and opportunities

Over the past decade, a plethora of techniques for quantifying surface-atmosphere exchange of greenhouse gases have been applied to regional carbon cycle questions. Regional fluxes are fundamentally difficult to estimate as it goes beyond the plot and stand scale of ecological and micrometeorological techniques, but falls below detection thresholds for many atmospheric inverse methods. Yet, it is precisely this scale where the impacts of climate change are more directly felt. Consequently, there are fundamental gains that could be made by basic research on the response of landscape and watershed scales surface fluxes to climate variability and ecological trends. As a co-benefit, this research also reduces the current large uncertainty of land use and water cycle policy decisions on ecosystem biogeochemistry, since policies typically apply at this scale.

I will present recent results from two projects that have attempted to compare state-of-the-art techniques for quantifying carbon dioxide exchange between regional landscapes and the atmosphere from both bottom-up scaling techniques and top-down atmospheric budgets. The first focuses on the complex heterogenous landscape of the upper Midwest USA, where significant sub-grid variation in wetlands, lakes, and forests complicates upscaling approaches and leads to a difference in estimates of the sensitivity of regional and local carbon cycles to climate variability. The second highlights activities undertaken during the Carbon in the Mountains Experiment in the central Rocky Mountains USA. The lack of detailed spatial sampling in this region necessitates development of novel airborne budget and inverse techniques. Lessons learned from these two field campaigns will be presented and suggestions for directions forward in this field will be suggested.