Measurements of soil and canopy exchange rates in the Amazon rain forest using sup 222 Rn

Journal Article · Thu Sep 20 00:00:00 EDT 1990 · Journal of Geophysical Research; (USA)

OSTI ID:6104381

Trumbore, S E ^[1]; Keller, M ^[2]; Wofsy, S C ^[3]; Da Costa, J M ^[4]

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1. Columbia Univ., Palisades, NY (USA) Lamont-Doherty Geological Observatory, Palisades, NY (USA)
2. Princeton Univ., NJ (USA)
3. Harvard Univ., Cambridge, MA (USA)
4. Universidad Federal de Vicosa, Minas Gerais (Brazil)

Measurements of the emission of {sup 222}Rn from Amazon forest soils, and profiles of {sup 222}Rn in air were used to study the ventilation of the soil atmosphere and the nocturnal forest canopy. The emission of {sup 222}Rn from the yellow clay soils dominant in the study area averaged 0.38 {plus minus} 0.07 atom cm{sup {minus}2} s{sup {minus}1}. Nearby sand soils had similar fluxes, averaging 0.30 {plus minus} 0.07 atom cm{sup {minus}2} s{sup {minus}1}. The effective diffusivity in the clay soil (0.008 {plus minus} 0.004 cm{sup 2} s{sup {minus}1}), was lower than that for the sand soil (0.033 {plus minus} 0.030 cm{sup 2} s{sup {minus}1}). Profiles of {sup 222}Rn and CO{sub 2} in air showed steepest concentration gradients in the layer between 0 and 3 m above the soil surface. Aerodynamic resistances calculated for this layer from {sup 222}Rn and CO{sub 2} varied from 1.6 to 18 s cm{sup {minus}1}, with greater resistance during the afternoon than at night. Time averaged profiles of {sup 222}Rn in the forest canopy measured during the evening and night were combined with the soil flux measurements to compute the resistance of the subcanopy to exchange with overlying air. The integrated nocturnal rate of gas exchange between the canopy layer (0 to 41 m) and overlying atmosphere based on {sup 222}Rn averaged 0.33 {plus minus} 0.15 cm s{sup {minus}1}. An independent estimate of gas exchange, based on 13 nights of CO{sub 2} profiles, averaged 0.21 {plus minus} 0.40 cm s{sup {minus}1}. These exchange rates correspond to flushing times for the 41 m canopy layer of 3.4 and 5.5 hours, respectively. Comparison of {sup 222}Rn and CO{sub 2} profiles show that the nocturnal production of CO{sub 2} by above-ground vegetation was about 20% of the soil emission source, consistent with data from eddy-correlation experiments.

• OSTI ID: 6104381
• Journal Information: Journal of Geophysical Research; (USA), Vol. 95:D10; ISSN 0148-0227
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
BRAZIL
AIR POLLUTION
RADON 222
ENVIRONMENTAL TRANSPORT
SOILS
DEGASSING
AIR-BIOSPHERE INTERACTIONS
AMAZON RIVER
CANOPIES
CARBON DIOXIDE
CLAYS
DAILY VARIATIONS
DIFFUSION
ECOLOGICAL CONCENTRATION
EMISSION
FORESTS
POLLUTION SOURCES
SAND
VENTILATION
ALPHA DECAY RADIOISOTOPES
CARBON COMPOUNDS
CARBON OXIDES
CHALCOGENIDES
DAYS LIVING RADIOISOTOPES
DEVELOPING COUNTRIES
EVEN-EVEN NUCLEI
HEAVY NUCLEI
ISOTOPES
LATIN AMERICA
MASS TRANSFER
NUCLEI
OXIDES
OXYGEN COMPOUNDS
POLLUTION
RADIOISOTOPES
RADON ISOTOPES
RIVERS
SOUTH AMERICA
STREAMS
SURFACE WATERS
VARIATIONS
540110*
540210 - Environment
Terrestrial- Basic Studies- (1990-)