D. Debeer et al., A FAST-RESPONDING CO2 MICROELECTRODE FOR PROFILING SEDIMENTS, MICROBIAL MATS, AND BIOFILMS, Limnology and oceanography, 42(7), 1997, pp. 1590-1600
A new CO2 microelectrode with a tip diameter of 10 mu m and a response
time (t(90)) of similar to 10 s is presented. The sensor allows CO2 m
easurements with a detection limit of <3 mu M. The microsensor was tes
ted in experimental systems of increasing complexity. A diffusion-reac
tion simulation model was used to calculate CO2 profiles in order to c
heck the reliability of the measured profiles. Measured CO2 and O-2 pr
ofiles showed that, in highly active layers with photosynthetic and re
spiratory organisms, local equilibrium of the carbonate system cannot
be assumed. In such highly active systems, the CO2 profiles were deter
mined by the slow CO2 hydration rate, the biological conversion rates,
and the diffusion of all species of the carbonate system. We conclude
d that measured CO2 profiles cannot easily be extrapolated to describe
the total carbonate concentration profile, because CO2 may not be in
equilibrium with the rest of the carbonate system, and because a very
accurate alignment of pH and CO2 profiles is needed to calculate C-T.
However, the new CO2 microelectrode is useful in research involving bi
ological processes directly producing or consuming CO2 such as photosy
nthesis or respiration.