TG-04  Abstract

Radon-222 and Stable Carbon Isotope Tracing of Carbon Exchange and Trace Gas Fluxes in Old Growth and Selectively Logged Amazonian Forests

Christopher S. Martens, University of North Carolina (US-PI)
Osvaldo Luiz Leal de Moraes, Universidade Federal de Santa Maria (UFSM) (SA-PI)
Marcelo Zacharias Moreira, CENA/USP (SA-PI)

We propose to continue studies of the rates and mechanisms of processes controlling carbon dioxide and trace gas fluxes at old growth forest and selectively-logged forest sites in the Tapajos National Forest and at pasture sites south of Santarém, Pará, Brazil using a unique suite of state-of-the-art radon and stable isotope measurements. The continuing work is fully integrated with LBA-ECO tower eddy covariance flux, forest canopy gas inventory and soil gas flux studies led by Keller et al. (TG-07), Goulden and Rocha (CD-04), and Wofsy et al. (CD-10). In addition, we propose to make tower and portable field radon measurements that will contribute to larger scale studies of gas transport processes associated with the development of nocturnal and convective boundary layers led by Fitzjarrald and Moraes (CD-03) and other LBA-ECO Science Team members. Brazilian collaborators and students lead or are involved in many aspects of the proposed project. All of the proposed radon-222 and stable isotope measurements will be made in Brazil except for limited laboratory intercalibration studies that are essential for achieving maximum analytical accuracy. The proposed research will quantitatively address two theme areas in LBA-ECO: Carbon Dynamics and Trace Gas and Aerosol Fluxes. The proposed work is focused on four primary objectives:

  1. Quantification of net CO2 and trace gas exchange rates between the atmosphere and old growth and selectively logged forests and pastures utilizing tower and soil flux radon-222 measurements. Direct comparison of exchange rates from radon versus eddy covariance rates using the same canopy gas inventory measurements.

  2. Radon tracing of periodic and spatially inhomogeneous vertical and horizontal gas transport on a regional scale up to the top of the convective boundary layer (CBL) including quantification of nocturnal and CBL vertical scales and inhomogeneity and initial investigations of horizontal air drainage from the FLONA Tapajos.    

  3. Quantification of CO2 and trace gas soil fluxes and production/consumption rates versus height within the forest canopy using measured radon-222 flux divergence. Direct comparison of these rates with results from auto-chamber soil flux and canopy respiration rate measurements.

  4. Utilization of methane canopy inventory, soil flux and d13C-CH4 measurements to distinguish the sources, canopy height source distribution, and net flux of methane from soils and dispersed forest sources to the atmosphere.

All of the proposed research is relevant to the broad LBA-ECO science question: How do tropical forest conversion, re-growth, and selective logging, influence carbon storage, nutrient dynamics, trace gas fluxes, and the prospect for sustainable land use in Amazônia. Completion of the objectives should help to answer Questions CD-Q1 and CD-Q3b under the Carbon Dynamics theme and Questions TG-Q1 and TG-Q3 under the Trace Gas and Aerosol Flux theme.