Redox Processes Controlling Manganese Fate and Transport in a Mountain Stream

Abstract

The biogeochemical processes controlling the speciation and transport of manganese in a Colorado mountain stream were studied using a conservative tracer approach combined with laboratory experiments. The study stream, Lake Fork Creek, receives manganese-rich inflows from a wetland contaminated by acid mine drainage. A conservative tracer experiment was conducted on a 1300-m reach of the stream. Results indicate that manganese was progressively removed from the stream, resulting in a loss of 64 +/- 17 micromol day(-1) m(-1). Laboratory experiments using streamwater, mine effluent, and rocks from the stream showed the importance of surface-catalyzed oxidation and photoreduction on the speciation of manganese. The field and modeling results indicate that light generally promotes oxidation and removal of manganese from the stream, presumably through a photosynthetically enhanced oxidation process. Differences in Mn speciation within the stream suggest that reductive processes affect Mn speciation within the water column. These results identify the rapid oxidation and precipitation of MnOx as a dominant process within this freshwater stream.

Spatial and temporal variability of widespread dark production and decay of hydrogen peroxide in freshwater

“…catalase and superoxide dismutase) that break down ROS in the environment (Cooper and Zepp 1990;Cooper et al 1994). While we cannot rule out reactions with inorganic particulates larger than 0.22 lm as a loss mechanism, these reactions are probably too slow to account for the rapid decay rates we observed in these systems (Kwan and Voelker 2002;Petigara et al 2002;Scott et al 2002).…”

Development of a Manganese Speciation Method for Atmospheric Aerosols in Biologically and Environmentally Relevant Fluids

“…In the presence of dissolved organic matter, the reductive dissolution of manganese oxides can be significant in a matter of hours. Upon illumination, significant dissolution of manganese oxides occur within minutes (Scott et al 2002). Oxidation of Mn(II) compounds have also been observed in the presence of humic substances upon illumination, in a time-scale of one hour.…”

“…However, in most environmental and biological fluids, the rapid oxidation of Mn(0) and the instability of Mn(VI) and Mn(VII) in dilute solutions results in most manganese to be in the forms of Mn(II), Mn(III), and Mn(IV), with inter-conversion between the forms possible. For example, both photo-oxidation and photoreduction of manganese species have been observed in seawater (Nico et al 2002;Sunda and Huntsman 1994) while catalytic reactions have been shown to oxidize manganese on the surface in streams (Scott et al 2002). In the presence of dissolved organic matter, the reductive dissolution of manganese oxides can be significant in a matter of hours.…”

Effects of Manganese Mining on Water Quality in the Caucasus Mountains, Republic of Georgia

“…Mn speciation is governed by pH and redox conditions, with Mn 2? dominating at lower pH and redox potential, and an increasing proportion of colloidal Mn oxy-hydroxides above pH 5.5 (Scott et al 2002). Dissolved concentrations undergo diel variations in streams (Brick and Moore 1996;Filipek et al 1987).…”

“…Toxic metals and nutrients can co-precipitate with or sorb to Mn oxides (MnOx) on the streambed. Surface catalyzed oxidation and photoreduction can be important processes with regard to fate and transport, particularly in mountain streams (Scott et al 2002). Light promotes oxidation, precipitation of MnOx, and removal from streams through photosynthetically enhanced oxidation processes (Scott et al 2002).…”