A Pilot Study for Assessing the Carbon and Energy Balance of a Transitional Tropical Forest in Southwest Amazonia
Nicolau Priante Filho UFMT - Universidade Federal do Mato Grosso (SA-PI)
The objective of this pilot study is to quantify the mass (CO2 and H2O vapor) and energy exchange of a mature transitional tropical forest stand over portions of the wet and dry season and to determine the meteorological and seasonal controls on these mass and energy fluxes. As a pilot study, our goal is to collect preliminary field data over a 6-month period that extends over portions of the wet and dry seasons. Measurements were initiated on 17 August, 1999 and will be continued (at a minimum) until 2 February, 2000.
Location and Description of the Study Site
The study area is located near the city of Sinop in NW Mato Grosso, Brazil (11°24.75'S: 55°19.50'W). This region is located near the ecotone of two major ecosystem types of South America (wet evergreen rainforest and
Eddy Covariance Measurements of Net CO2 Exchange
Net CO2 exchange, evapotranspiration (ET), and convective (sensible) heat flux (H) of the mature cerradćo stand are currently measured using tower-based eddy covariance. The
The relatively low mean wind speed of the Sinop area (1961-1994 average = 1.5 m/s) is likely to result in low turbulent transport and high atmospheric stability, which in turn, can cause CO2 to be stored in the canopy. Because canopy CO2 storage can lead to errors in the measurement of surface-atmosphere CO2 exchange, canopy CO2 storage (ĘS) is quantified by determining the rate of change of CO2 in the air column between the ground surface and the eddy covariance sensors. The vertical CO2 concentration profile is measured every 30 seconds at 1, 4, 12, 20, and 28 m above ground level using a closed-path CO2 analyzer (LI-6251). Samples are drawn from each height using a diaphragm pump and plastic (3-5 mm diameter) tubing, and air samples are switched using a solenoid switching manifold system controlled by a datalogger (Campbell Scientific Inc., Model CR-10X).
Net ecosystem CO2 flux (Fc) is calculated as Fc = Fm + ĘS, where Fm is the net CO2 flux measured at the top of the tower and
The measurement system is powered using 12 V batteries charged by solar panels, with occasional use of a gasoline-powered generator to rapidly re-charge the battery bank.
Measurements of net radiation are made above the canopy using a ventilated net radiometer
Although data reduction and analysis are ongoing, modeling and other statistical analyses will be conducted after completion of the field study (February-May 2000). Regression-based, non-linear physiological models will be used to assess the effects of seasonality (rainfall) and meteorology (radiation, humidity, and temperature) on stand-scale physiology.
Last Updated: August 26, 1999