| Summary: | <p>A method based on a dynamic closed chamber system (DCCS) for measuring
CO<sub>2</sub> effluxes from unsaturated soils and waste-rock piles was developed and tested in
well-constrained unsaturated minicosms (0.58 m dia. x 1.2 m thick), a mesocosm (2.4 m
dia. x 3.2 m thick), and waste-rock piles. The DCCS method was compared and
evaluated against traditional soil respiration measurement methods (e.g., static flux
chamber method, and concentration-gradient calculations). Results of the studies
showed that the DCCS yielded accurate measurements of CO<sub>2</sub> fluxes and that the static
chamber underestimated actual effluxes especially when using long adsorption times (>
24 h). The concentration-gradient method yielded reasonable estimates of CO<sub>2</sub> effluxes
but was time consuming and required the determination of moisture content to calculate
gas diffusion coefficients.</p>
<p>Results of studies carried out on waste-rock piles, showed that the DCCS is a
relatively quick technique (2 to 10 min) that can be used to quantify spatial and temporal
distribution of CO<sub>2</sub> fluxes at the field scale. The DCCS yielded field measurements of
CO<sub>2</sub> fluxes that were reproducible over time at individual chamber locations. The
average CO<sub>2</sub> fluxes obtained over the summer study-period of 2000, for Deilmann north
and Deilmann south waste-rock piles were 181 ± 41 mg CO<sub>2</sub> m<sup>-2</sup> h<sup>-1</sup> (n = 27) and 205 ±
60 mg CO<sub>2</sub> m<sup>-2</sup> h<sup>-1</sup> (n = 48), respectively. A statistical Student's t test yielded no
significant difference between the two sets of data. As a result, the two mean values
were combined to yield an overall mean value of 193 ± 73 mg CO<sub>2</sub> m<sup>-2</sup> h<sup>-1</sup> (n = 68) for
the two waste-rock piles. Most temporal changes were attributed to seasonal variations
in temperature (7.9 to 16.5 °C). The DCCS has the advantage of being able to measure CO<sub>2</sub> fluxes in situ at the same locations using the same chambers without greatly
disturbing the soil. The results of this study will be used in future modeling exercises to
quantify the rates of sulfide oxidation and carbonate buffering reactions in these waste-rock
piles.</p>
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