Close Window

CD-10 Abstract

Net Ecosystem Exchange of C02 and H20 from Primary Tropical Forest in Central Amazonia

Plínio Barbosa de Camargo — USP - Universidade de Sao Paulo (SA-PI)
Volker W. J. H. Kirchhoff — INPE - Instituto Nacional de Pesquisas Espaciais (SA-PI)
Steven Charles Wofsy — Harvard University (US-PI)


We plan measurements of net ecosystem exchange (NEE) and concentrations of CO2

and H2O using eddy correlation methods for 3-5 years at a primary forest site

110 km south of Santarém (Tapajós National Forest) in central Amazônia, and

measurements of CO2 and other greenhouse gases at a remote coastal site near

Natal. Installation will be in the latter part of 1998 or early 1999, depending on

infrastructure and preparation of equipment.

We will collaborate with Dr. V. Kirchhoff to help install and operate a long-term

coastal site for observations of important trace gases, starting with CO2.

We plan to support the observations of aerosol and other atmospheric components by Dr.

P. Artaxo, however the funding status of this effort is not presently clear.

The objectives of the measurements will be:

1. Define the experimental protocols needed to measure accurately seasonal and annual

net fluxes of CO2, H2O, and energy at a primary forest in the

Tapajós region of Amazônia;

2. Define the net source or sink of CO2 from the undisturbed forest;

3. Determine the variations of net exchange of CO2 seasonally and

inter-annually, and define the response of carbon sequestration in the system to climatic

and other environmental variables;

4. Provide the experimental control for interpretation of the results obtained at a

harvested site (proposed by Goulden, Keller) by recording the CO2 exchange at a

nearby undisturbed site;

5. Provide the flux and gradient measurements for CO2, sensible heat and

momentum needed to define the flux of N2O, CH4, and mineral elements

from sub-canopy concentration changes or from above-canopy gradient measurements of these


6. Determine CO2 boundary layer concentrations at mid-continent and coastal

sites to test models.

Value to LBA

The proposed work focuses on defining the "undisturbed state" of the primary

tropical forest, a requirement "to fill the most critical of gaps and/or to gain the

most leverage on major scientific uncertainties" (NRA-97-MTPE-02). Studies of this

type were specifically requested for LBA: ("Continuous observations of a core set of

measurements (e.g., CO2 fluxes, trace gas fluxes, trace gas concentrations,

micrometeorological conditions, radiation, aerosols) made at the primary field sites over

a period of 3-5 years".


Fluxes of momentum, CO2, H2O, sensible heat, net radiation, and

PAR, atmospheric and soil profiles of temperature, CO2 and H2O, and

wind profiles will be measured continuously using automated instruments on a 65 meter

tower. Fluxes will be measured using eddy correlation, with an infrared gas analyzer

(closed-path) for CO2 and H2O mounted on the tower near the sonic

anemometer. The data will be analyzed to determine net exchange of CO2 and H2O

on hourly, daily, seasonal, and annual time scales. Environmental regulation of variations

in net uptake will be quantitatively elucidated by measuring the response of the system to

climatic variations and by comparison between flux measurements and ecological



The measurements will be made from a 65 m tall, small-cross-section tower of the type

used to support radio antennas (Rohn 45G, Peoria IL), selected to minimize wind distortion

and possible heating artifacts, placing the sensor well above the tallest emergent trees.

The data acquisition system and most instruments and will be housed in a climate

controlled hut 15-30 m west of the tower base, accessible by a dirt road. The CO2-H2O

sensor will be placed close to the sonic anemometer near the top of the tower to keep

tubing short.

The site is in a protected primary forest reserve at km 117 south of Santarem (IBAMA

station S 03o 21.357' W 54o 56.959' in the Floresta Nacional do Tapajos. This site is

extremely flat, an extensive planalto that drops about 30m to the level of the Tapajos

river 10-15 km to the west. Soils are uniform yellow oxisols similar to soils at the site

to be cut, which lies 30 km to the north. The nearest secondary road is 5 km to the east

and the nearest urban area is 100 km to the North (Santarem); otherwise the area is quite


Tower Measurements

Table 1 shows the measurements planned for the site in this and in collaborative

studies. Eddy fluxes of sensible heat, latent heat, CO2, and momentum will

measured at 65 m on the tower. The mixing ratios of CO2 and H2O will

be monitored by sampling 6 to 8 standard liter/min (slpm) from an inlet located directly

behind the vertical axis of the anemometer into a CO2/H2O infrared

gas analyzer (IRGA; Model 6262, LiCor, Lincoln NE). Errors due to separation of the inlet

from the anemometer should be small (1 to 2%, Lee and Black 1994). Wind and temperature

will be measured with a 3-axis sonic anemometer pointed into the dominant wind direction


Table 1. Tapajos Forest Measurements




determined quantity

(data rate)

Sonic Anemometers 65m (3-axis), 6 lvls(2 axis) u,v,w,T Fmom, Fheat (10 Hz, 30-min avg.)
high-speed CO2-H2O

65m CO2 and H2O fluxes

(30-min avg.)
slow CO2-H2O ( IR

8-10 levels CO2, H2O vertical

profiles (2 /hour)
Thermistors, thin-film capacitors 5-6 levels T and R.H. profiles (5,60-min avg.)
Thermistors 2 cm (6 rep), 20cm, 50cm soil temperatures (5,60-min avg.)
Photosynthetically Active Radiation 65,24,2 m (5 min avg.)
Net radiometer 65m radiant heat flux (5,60-min Avg.)

Special note: spares for key equipment

The budget justification includes spare units for key hardware including sonic

anemometers, CO2-H2O IRGA, etc., to be purchased just prior to

deployment to Brazil. It is expected that equipment cannot be imported in passengers'

baggage. Therefore, if a failure occurs, a spare must be present on site, otherwise a

hiatus in the measurements as long as 6-8 weeks might be incurred. Such long data gaps

would clearly impact the goals of this experiment.

Relationship with Other Experiments

The experiment will be closely coordinated with three other LBA projects:

M. Keller: Our flux measurements will help extend the spatial (canopy) and temporal

(years) scales, and provide a quantitative framework, for integrating biogeochemical

measurements to the ecosystem function.

Crill, Silver,and Li and Goulden plan to work at a flux tower on a nearby primary

forest that will be commercially harvested during the observations. Our measurements at an

uncut site nearby will provide the control for this experiment, determining changes in

carbon storage and ecological parameters in the absence of disturbance.

We plan to combine our data with observations of canopy/atmosphere interchange and

energy balance by Fitzjarrald, Moore, to help define the tower footprint and to wring out

systematic errors from the observations.

Collaboration is expected also with Martens (222Rn) and Trumbore and Crill.

(13C/12C) isotopic ratios and turnover rates of soil organic matter

and wood.

Last Updated: May 18, 1998

Close Window