Automated measurements of soil-atmosphere methane, carbon dioxide, and nitrous oxide fluxes in an undisturbed forest in the Brazilian Amazon
Abstract
The soil-atmosphere fluxes of methane (CH4), carbon dioxide (CO2), and nitrous oxide (N2O) depend upon the interactions of biological processes of production and consumption and the physical transport of these gases. Soil temperature and moisture exert strong controls on the soil-atmosphere exchange of all three trace gas fluxes. We measured the soil-atmosphere flux of CH4, CO2, and N2O with an automated chamber system that was installed in April 2001 in the Tapajos National Forest, Para, Brazil. This is a mature forest on a clay Oxisol. The mean annual temperature is 25C with the diurnal range often exceeding the variability in the annual daily means. The mean annual precipitation is about 2000 mm per year with a distinct dry season from July to December. Eighteen aluminum chambers were installed in a 0.5 ha area close to the flux tower at the km 67 LBA site. Eight of these chambers were sampled about 5 times per day (closed 7% daily) and the other 10 chambers were sampled individually approximately once per day (closed 1.5% daily). As expected, the drained upland soils were most often a weak CH4 sink. Methane fluxes averaged -0.31 +/- 0.6 mg CH4 m-2 d-1 during the dry season and -0.08 +/- 0.26 mg CH4 m-2 d-1 during the wet season. Episodic positive fluxes of up to 18 mg CH4 m-2 d-1 were observed in the wet season following sustained rainfall events. For the 8 frequently sampled chambers, annual mean flux ranged between from 2.6 to 3.0 µmol CO2 m-2 s-1 over the 4-year period. Dry season fluxes averaged 2.3 to 2.7 micromol CO2 m-2 s-1 and the wet season averages ranged between 2.8 to 3.3 micromol CO2 m-2 s-1. Nitrous oxide fluxes ranged between 0.8 and 2.8 ng N-N2O cm-2 h-1 during the dry season and 0.02 to 0.7 ng N-N2O cm-2 h-1 during the dry season. Fluxes of CH4 showed no correlation with soil temperature or moisture on the diel scale. On the diel scale, soil CO2 flux was positively correlated with soil temperature and negatively correlated with soil moisture content during the dry season. Wet season fluxes of CO2 were also positively correlated with 5 cm soil temperature. Nitrous oxide fluxes correlated with 5 cm soil temperature over the diel cycle only during the wet season.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2007
- Bibcode:
- 2007AGUFM.B53A0932V
- Keywords:
-
- 0426 Biosphere/atmosphere interactions (0315);
- 0428 Carbon cycling (4806);
- 0490 Trace gases;
- 1615 Biogeochemical cycles;
- processes;
- and modeling (0412;
- 0414;
- 0793;
- 4805;
- 4912);
- 1631 Land/atmosphere interactions (1218;
- 1843;
- 3322)