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| Saleska Research
I. Current Projects
A. New technologies to measure whole-ecosystem isotopic exchange and partition carbon fluxes Recently developed quantum cascade laser (QCL)-based absorption spectrometers measure atmospheric trace gases to extremely high precision without the need for liquid-nitrogen cooling (needed in lead-salt laser technologies). This opens the way for making in situ measurements of a quality previously unobtainable at most remote field sites. We are collaborating with Aerodyne Research, Inc (a small business specializing in the development of high-precision optical instrumentation) to deploy a new QCL spectrometer to measure isotopic composition (13C/12C and 18O/16O) of ecosystem fluxes of CO2, with a goal of widening our window into physiological and ecological mechanisms controlling whole-ecosystem carbon exchange. Our DOE-NICCR project (Isotope ratio partitioning of ecosystem CO2 fluxes to understand forest response to climate change: long-term measurements with novel instrumentation) (contact me if you would like a copy of the proposal) supports deployment of a new QCL Isotope Ratio Spectrometer (Nelson et al., in press) at Harvard Forest (near Petersham, MA). Our simulations based on eddy flux measurements of net CO2 exchange and flask isotope data (pdf: Saleska et al., 2006 ) suggest that instrument characteristics are more than adequate to achieve science goals. B. Understanding Amazon forest carbon dynamics 
(right: Long-term eddy flux tower for measuring net ecosystem exchange of CO2 in central eastern Amazon forest of Brazil) Our current Amazon work -- supported by NASA (proposal) and by NSF Partnerships for International Research and Education (Amazon-PIRE) -- focuses on integrating remote sensing techniques and ground based measurements to extrapolate our understanding of local controls on carbon cycling in old-growth Amazon forest to derive landscape and regional scale carbon balance. The goal of this work is to build upon our ongoing investigations of how forest demography and disturbance dynamics control carbon cycling in old-growth Amazon forest, which uses long-term eddy covariance observations of net ecosystem exchange of CO2, integrated with classical methods of forest ecology. Our ground-based site is the Tapajós National Forest near Santarém (see figure, above right, of long-term eddy flux tower for measuring net ecosystem exchange of CO2 in this central eastern Amazon forest of Brazil). The net CO2 flux from this tower shows the forest losing carbon, an observation not previously seen in the Amazon that will help reconcile an Amazon carbon-budget problem (See Saleska et al., 2003 view pdf for details). The carbon budget problem arose from previous studies showing carbon uptake of 1-3 Pg C yr-1 in Amazônia alone, comparable to the whole global terrestrial carbon sink. Because this problem made eddy flux measurements of CO2 in the tropics somewhat controversial, we collaborated with Chris Martens at UNC to test of the accuracy of our eddy flux measurements using radon gas as a transport tracer (see Martens et al., 2004; view pdf). This work independently confirms our approach to estimating carbon balance using eddy flux measurements. Forest biometric observations allow us to attribute observed carbon loss to ecological mechanism: disturbance-recovery dynamics thought characteristic of old-growth forest but not yet observed in tropical carbon balance studies. For a good paper on what we are learning from the vegetation dynamics, see Rice et al., 2004 (view pdf), first-authored by an undergraduate who worked with me in Brazil. This work is part of the Large-Scale Biosphere-Atmosphere Experiment in Amazonia (LBA). Project data available via ftp For more details on the Tapajós project (begun when I was a post-doc with Steve Wofsy at Harvard University). Data from the project is available. Click on thumbnails for larger versions of photos (60-70kb)
Previous Projects My Ph.D. dissertation at the Rocky Mountain Biological Laboratory in Colorado investigated ecological feedbacks to climate by examining how an ecosystem warming manipulation affected the carbon-cycle of a Rocky Mountain meadow. For this I used a simple model to integrate data acquired at very different scales: (1) experimental manipulation at the plot scale to investigate short-term warming effects, and (2) a climate-gradient analysis at the landscape-scale to investigate long-term effects of climatic differences. This analysis (Saleska et al 2002, view pdf) shows that shifts in plant community composition, brought about by heat-induced drought stress, can be more important to carbon balance than decomposition rates of soil organic carbon (assumed key in most global models). This work (with John Harte at U.C. Berkeley) implies that future atmospheric CO2 (and hence, future climate change) may depend on how species interactions structure ecosystem biogeochemistry.
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