Exercise 3:\ Figure 7 of Conrad et al. (1999) shows the variation in C-isotopic composition of CO2 as a function of the concentration of methane measured in the soil and aquifers of a site contaminated in the residues of aviation fuels. Explain briefly the aim of these particular\ Tracing biogeochemical processes and fluxes using isotope analysis\ SA 2023\ Lucia Mottet\ measurements made to the environmental study. Also explain briefly why there is a difference in isotopic composition of

CO2

obtained via aerobic degradation and methanogenic degradation of AVGAS (fuel residues as contaminants) and the linear "mixing relationship" noted in Figure 7.\ Fig. 7. Plot of

%CH_(4)

vs the

\\\\delta ^(13)C

values of

CO_(2)

by sample location for all samples containing

CH_(4)

from the study site. The dashed line is a best fit line through the data. Also shown are the approximate fields that would be expected for methanogenic and aerobic degradation of AVGAS, and the trend that would be expected for significant levels of methane oxidation.

Exercise 3: Figure 7 of Conrad et al. (1999) shows the variation in C-isotopic composition of CO2 as a function of the concentration of methane measured in the soil and aquifers of a site contaminated in the residues of aviation fuels. Explain briefly the aim of these particular Tracing biogeochemical processes and fluxes using isotope analysis SA 2023 Lucia Mottet measurements made to the environmental study. Also explain briefly why there is a difference in isotopic composition of CO2 obtained via aerobic degradation and methanogenic degradation of AVGAS (fuel residues as contaminants) and the linear "mixing relationship" noted in Figure 7. Fig. 7. Plot of %CH4 vs the 13C values of CO2 by sample location for all samples containing CH4 from the study site. The dashed line is a best fit line through the data. Also shown are the approximate fields that would be expected for methanogenic and aerobic degradation of AVGAS, and the trend that would be expected for significant levels of methane oxidation