A field-based method for simultaneous measurements of the δ<sup>18</sup>O and δ<sup>13</sup>C of soil CO<sub>2</sub> efflux
Three approaches for determining the stable isotopic composition (δ<sup>13</sup>C and δ<sup>18</sup>O) of soil CO efflux were compared. A new technique employed mini-towers, constructed of open-topped piping, that were placed on the soil surface to collect...
| Main Authors: | , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2004-01-01
|
| Series: | Biogeosciences |
| Online Access: | http://www.biogeosciences.net/1/1/2004/bg-1-1-2004.pdf |
| Summary: | Three approaches for determining the stable isotopic composition (δ<sup>13</sup>C and δ<sup>18</sup>O) of soil CO efflux were compared. A new technique employed mini-towers, constructed of open-topped piping, that were placed on the soil surface to collect soil-emitted CO<sub>2</sub>. Samples were collected along a vertical gradient and analyzed for CO<sub>2</sub> concentration and isotopic composition. These data were then used to produce Keeling plots to determine the δ<sup>18</sup>O and δ<sup>13</sup>C of CO<sub>2</sub> emitted from the soil. These results were then compared to the δ<sup>18</sup>O and δ<sup>13</sup>C of soil-respired CO<sub>2</sub> measured with two other techniques: (1) flux chambers and (2) estimation from the application of the diffusional fractionation factor to measured values of below ground soil CO<sub>2</sub> and to CO<sub>2</sub> in equilibrium with soil water δ<sup>18</sup>O. Mini-tower δ<sup>18</sup>O Keeling plots were linear and highly significant (0.81< r <sup>2</sup> > 0.96), in contrast to chamber δ<sup>18</sup>O Keeling plots, which showed significant curvature, necessitating the use of a mass balance to calculate the δ<sup>18</sup>O of respired CO<sub>2</sub>. In the chambers, the values determined for the δ<sup>18</sup>O of soil respired CO<sub>2</sub> approached the value of CO<sub>2</sub> in equilibrium with surficial soil water, and the results were significantly δ<sup>18</sup>O enriched relative to the mini-tower results and the δ<sup>18</sup>O of soil CO<sub>2</sub> efflux determined from soil CO<sub>2</sub>. There were close agreements between the three methods for the determination of the δ<sup>13</sup>C of soil efflux CO<sub>2</sub>. Results suggest that the mini-towers can be effectively used in the field for determining the δ<sup>18</sup>O and the δ<sup>13</sup>C of soil-respired CO<sub>2</sub>. |
|---|---|
| ISSN: | 1726-4170 1726-4189 |