『Abstract
The biogeochemical cycling of Fe in acid rock drainage (ARD)
streams has presented ongoing challenges to reactive solute transport
modeling. Previous studies have relied on the pH-dependent solubility
of Fe oxides as the main control of the mid-day Fe(II) maxima
concentration in ARD streams. In this study, the authors assess
the potential for Fe(II)-oxidizing reactions, including the Fenton
and microbial oxidation reactions, to constrain the mid-day Fe(II)
maxima concentration. At mid-day, pseudo-equilibrium between Fe(II)
oxidizing reactions and photoreduction was assumed in order to
evaluate the observed Fe(II) maxima and develop an equation to
represent this steady state scenario. This steady state condition
is assumed only while light intensity, reactivity of oxides and
dissolved organic matter (DOM), and microbial populations remain
approximately constant. Three Rocky Mountain ARD streams with
known values for Fe(II) were evaluated and average photoreduction
rates ranging from 5.56×10-4 to 1.39×10-3μM/s
were found during mid-day steady state Fe(II) maxima. Application
of Fe redox biogeochemistry to reactive solute transport modeling
may improve predictive capabilities of various trace metal and
solute interactions incorporated with the cycling of Fe within
ARD streams. Further, model improvement of Fe cycling may enable
more accurate remediation predictions for ARD streams.』
1. Introduction
1.1. Site description
1.2. Biogeochemical processes influencing Fe and DOM in ARD streams
2. Results and discussion
2.1. Rate processes determining midday “pseudo-equilibrium”
Fe(II) concentrations in acidic, metal-enriched streams
2.2. Stream-scale estimates of Fe(II) oxidation rates
2.3. Evaluation of mid-day photoreduction rates
3. Summary
Acknowledgements
References