Model with Measured Values for Dissolved Iron

5 Validation of the Model with Measured Values for Dissolved Iron 

Reaction kinetics between DOC and iron(hydr)oxides are certainly governed by the specific situation of the aquifer. Thus, neither the reaction rates nor their constancy for the entire aquifer may be transferred to other systems. 

If we assume that the reaction mentioned in Section 10.3.2 is a fundamental description of the processes controlling the concentration of DOC in groundwater, then this reaction would also control the concentration of iron in groundwater at the same time. An easy way to check this was to run two model calculations, both with identical model parameters. However, one of these calculations was run without considering the reduction of DOC. In this case the distribution of DOC is only controlled by the input from the river Oder and the physical transport with advection and dispersion along the flow through the aquifer. The difference between calculated distribution of concentration with reaction and distribution calculated at same conditions but without reduction of DOC will show the reduced quantity of DOC for each point of the flow field. Now this quantity can be converted stoichiometricly into the equivalent quantity of dissolved iron. Thus one mol of CO2 from oxidised DOC corresponds with four times the amount of used iron(III)oxide and the resulting Fe + in solution. 

The model introduced within this paper can be seen as one attempt towards developing a virtual aquifer out of only a scarce data-set that resembles natural geological patterns as well as towards increasing the dimensionality of coupled transport and reaction models. This could only be done on behalf of the systems complexity. It is essential to fully imderstand a system in order to reduce it to the major governing 

Firstly only one redox process, the one we thought to be the dominant one consuming the available DOC, has been considered. Other redox processes observed at the field site Bahnbriicke are discussed in Chapter 11. We calibrated the DOC oxidation reaction with measured DOC concentrations in the flow field and calculated the iron content of the water with the DOC concentrations. The fact that the calculated iron concentrations strongly resembled the observed iron concentrations in the field supports the presumption, that iron(hydr)oxide reduction really is the dominant DOC consuming process. If another redox process would be of importance, the calculated iron concentrations would have been higher than the observed ones which was not the case. Our presumption is therefore reasonable. 

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