Reply [to “Comment on ‘Modeling of Multicomponent Transport With Microbial Transformation in Groundwater: The Fuhrberg Case’ by E. O. Frind et al.”]

Kinetics of N<sub>2</sub>O production and reduction in a nitrate-contaminated aquifer inferred from laboratory incubation experiments

“…They found an ongoing sulfate formation during a 284-days-period and calculated the potential of autotrophic denitrification on the basis of pyrite oxidation. In the case of the near-surface groundwater, von der confirmed former assumptions that heterotrophic denitrification with organic carbon as an electron donor replaced autotrophic denitrification due to an exhaustion of pyrite (Kölle et al, 1983;Böttcher et al, 1991):…”

“…Korom (1991) showed thermodynamically, that organic carbon used as an electron donor in the sulfatereducing zone of the FFA would preferentially be used by bacteria for heterotrophic denitrification. On the other hand, Böttcher et al (1991) stated that as long as pyrite is available in the FFA, simultaneous heterotrophic denitrification is unlikely for several reasons. For example, the authors emphasized that the microbial availability of the organic lignitic pebbles is probably poor and might superimpose the thermodynamic "advantage" of heterotrophic denitrification.…”

“…The FFA has been a subject of extensive research activities since the 1980s (reviewed in Korom, 1992), since the catchment is in an area of conflict between drinking water supply on the one hand and agricultural activities causing considerable inputs of pollutants via seepage, especially of nitrate, on the other hand (Kölle et al, 1985;Frind et al, 1990). In the FFA, substantial microbially mediated processes and reactions like denitrification and desulfurication (heterotrophic reduction of sulfate, Korom, 1991Korom, , 1992Böttcher et al, 1991) occur, strongly influencing groundwater geochemistry. Autotrophic denitrification with pyrite as an electron donor was identified as the dominant microbial reaction for NO − 3 elimination (Kölle et al, 1985) in depths beyond 2-3 m below the groundwater table (Böttcher et al, 1992).…”

Denitrification coupled to pyrite oxidation and changes in groundwater quality in a shallow sandy aquifer

“…In a sandy aquifer in Denmark, the dominance of pyrite oxidation was attributed to the low in situ reactivity of the organic matter (Postma et al, 1991). Several modeling studies focusing on denitrification in groundwater also include pyrite oxidation (Frind et al, 1990;Boettcher et al, 1991;Wriedt and Rode, 2006;Spiteri et al, 2008). They further illustrate the potential role of kinetic factors related to the reactivities of pyrite and organic matter in determining which denitrification process is most important in a given aquifer.…”

Redox: fundamentals, processes, and applications

“…Yet, denitrification by organic matter is thermodynamically favourable (KOROM, 1991) and the excess of organic matter over pyrite, nitrate nevertheless is reduced by pyrite. This means that the reactivity of organic matter in denitrification is much lower than the reactivity of pyrite (BÖTTCHER al., 1991). The continuous and depth-dependant decrease in the concentration of nitrate in the presence of pyrite is very conspicuous.…”