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
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
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
|65m (3-axis), 6 lvls(2 axis)|
|u,v,w,T Fmom, Fheat (10 Hz, 30-min avg.)|
|CO2 and H2O fluxes|
|slow CO2-H2O ( IR|
|CO2, H2O vertical|
profiles (2 /hour)
|Thermistors, thin-film capacitors|
|T and R.H. profiles (5,60-min avg.)|
|2 cm (6 rep), 20cm, 50cm|
|soil temperatures (5,60-min avg.)|
|Photosynthetically Active Radiation|
|(5 min avg.)|
|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
Last Updated: May 18, 1998