Grantee Research Project Results

1998 Progress Report: Photochemical Processes Controlling Manganese Chemistry in Pristine and Contaminated Mountain Streams

EPA Grant Number: R826649
Title: Photochemical Processes Controlling Manganese Chemistry in Pristine and Contaminated Mountain Streams
Investigators: McKnight, Diane M. , Hrncir, Duane
Institution: University of Colorado at Boulder , The University of Texas at Dallas
EPA Project Officer: Aja, Hayley
Project Period: October 1, 1998 through September 30, 2001
Project Period Covered by this Report: October 1, 1998 through September 30, 1999
Project Amount: $351,175
RFA: Exploratory Research - Environmental Chemistry (1998) RFA Text | Recipients Lists
Research Category: Air , Safer Chemicals , Land and Waste Management , Sustainable and Healthy Communities

Objective:

Mountain streams receiving acid mine drainage are typically enriched in Al, Fe, and Mn. For Fe, photochemical reactions control critical chemical speciation and transport. We hypothesize that Mn photochemistry is also important in controlling Mn speciation and transport. We will characterize diel variations in Mn speciation and quantify rates of photochemical reactions at the stream scale, and evaluate how the relative concentrations of iron and manganese, pH and DOC control the rates of reactions.

Progress Summary:

Our main activity has been further assessment of field sites in preparation for the field experiments to be conducted during the summer, and conducting laboratory experiments. In October 1998, we studied a neutral pH stream receiving mine drainage in the headwaters of the West Fork of Clear Creek. Near the outflow, the acid mine drainage has high Mn concentrations and Mn oxides are abundant on the rocks. The mine drainage then flows through a wetland area before entering the stream. We collected water samples at 3 sites in the stream over a 24 hour period, with the goal of quantifying a diel variations in Mn and Fe associated with photoreduction. During mid and late morning we observed a modest rise in both dissolved Fe and Mn, with dissolved Mn reaching 0.05 mg/L, which could be evidence for Mn photoreduction. In the early afternoon, however, a large and abrupt increase in Mn, Fe and Al occurred which lasted for only one hour. Dissolved Mn increased to 0.15 mg/L, dissolved Fe increased from 0.3 to 1.0 mg/l, and dissolved Al increased from being undetectable (less than 0.005 mg/L) to 0.4 mg/L. This pulse of dissolved metals into the stream was associated with the early afternoon thawing out of the wetland, releasing metal-enriched water from the wetland into the stream, rather than any in-stream chemical processes. On a daily flux basis, this pulse of released metals was significant, especially for dissolved aluminum. As part of this reconnaissance, students in a graduate level stream ecology class determined the metal concentrations in the wetland plants and in benthic invertebrates in the stream. We conclude that in mid-summer this field site will be suitable for studying Mn photochemistry. We intend to further study the pulsed hydrologic transport of metals to the stream associated with daily thawing of wetlands, as this phenomenon could influence the effectiveness of natural and constructed wetlands in remediating acid mine drainage in mountainous regions, where it is a common problem.

Future Activities:

This spring we will continue with laboratory experiments to quantify rates of Mn oxide photoreduction. During the summer, we will conduct field experiments at the Snake River, Deer Creek, and North Fork Clear Creek field sites to quantify the in-stream rates of Mn and Fe photochemical reactions.

Journal Articles:

No journal articles submitted with this report: View all 13 publications for this project

Supplemental Keywords:

chemical transport, manganese, iron, photochemistry, diel, acid mine drainage, Air, Scientific Discipline, Geographic Area, EPA Region, State, Chemistry, Environmental Chemistry, Engineering, Chemistry, & Physics, Hydrology, heavy metals, stream ecosystems, chemical transport modeling, acid mine drainage, Region 8, fate and transport, manganese speciation, chemical kinetics, photochemical processes, Colorado (CO)

Relevant Websites:

http://huey.colorado.edu/~mcknight/fall98_reports/ Exit EPA icon (under W. Clear Creek and Jones Pass)

Progress and Final Reports:

Original Abstract

The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.