Impact of the electron donor on in situ microbial nitrate reduction in Opalinus Clay: results from the Mont Terri rock laboratory (Switzerland)

Swiss Journal of Geosciences

Table 1 Chemical composition (concentrations in mM) of the artificial pore-water (APW) used to saturate the intervals [target composition derived from Pearson (1999) and Pearson et al. (2003)] and of the interval solutions after saturation of the borehole and equilibration of the surrounding clay for ~8 months

Component	APW	Interval 1	Interval 2	Interval 3
Na⁺	162	174.0	174.0	174.0
K⁺	1.05	1.2	1.2	1.2
Ca²⁺	12.6	11.7	11.0	10.7
Mg²⁺	8.6	9.7	9.5	9.1
Sr²⁺	0.4	0.4	0.4	0.4
Total dissolved Fe	–	n.a.	n.a.	<0.0004
Cl⁻	181	203.1	205.9	203.1
\({\text{SO}}_{4}^{2 - }\)	12.28	11.03	11.66	11.66
\({\text{NO}}_{3}^{ - }\)	–	<0.01	<0.01	<0.01
\({\text{NO}}_{2}^{ - }\)	–	<0.1	<0.1	<0.1
\({\text{NH}}_{4}^{ + }\)	–	n.a.	n.a.	0.083
CHOO⁻	–	<0.0056	<0.0056	<0.0056
CH₃COO⁻	–	<0.009	<0.009	<0.009
\({\text{C}}_{2} {\text{O}}_{4}^{2 - }\)	–	<0.006	<0.006	<0.006
TIC	2.8	5.2	2.8	2.8
TOC	–	0.7	0.92	0.8
pH (−)	7.8	7.1	7.2	7.4

The errors on the concentrations are 4% ([\({\text{SO}}_{4}^{2 - }\)]), 5.5% ([\({\text{NO}}_{3}^{ - }\)]), 6% ([Cl⁻]), 10% ([Na⁺], [K⁺], [Ca²⁺], [Mg²⁺], [Sr²⁺], [\({\text{NH}}_{4}^{ + }\)], [CHOO⁻], [CH₃COO^-], [\({\text{C}}_{2} {\text{O}}_{4}^{2 - }\)] and TIC), 15% ([\({\text{NO}}_{2}^{ - }\)], [total dissolved Fe]) and 30% (TOC) (95% confidence), while the uncertainty on the pH is estimated to be 0.1 pH unit (95% confidence)
n.a. not analyzed