Investigations into the causes of diel cycling of heavy metals in streamsEPA Grant Number: R829400E01
Title: Investigations into the causes of diel cycling of heavy metals in streams
Investigators: Gammons, Christopher H. , Hobbs, David , Moore, Johnnie , Nimick, David
Institution: Montana Tech of the University of Montana , United States Geological Survey [USGS]
EPA Project Officer: Hunt, Sherri
Project Period: October 1, 2001 through September 30, 2003 (Extended to September 22, 2004)
Project Amount: $140,000
RFA: EPSCoR (Experimental Program to Stimulate Competitive Research) (2000) RFA Text | Recipients Lists
Research Category: EPSCoR (The Experimental Program to Stimulate Competitive Research)
Recent field research has shown that many metals ? including zinc, cadmium, manganese, and arsenic ? show large and reproducible diel (24 hour) fluctuations in dissolved concentration in streams draining abandoned mine lands in Montana. The objective of this project is to examine the chemical processes responsible for these day-night cycles.
Although previous workers have documented diel fluctuations in dissolved arsenic in mining-contaminated streams, fluctuations in heavy metals have not been observed until very recently. A number of possible mechanisms may control these cycles, including: pH- or temperature-dependent adsorption onto Fe or Mn oxides; pH- or light-dependent uptake of metals by benthic biofilms; changes in flux of hyporheic water across the stream/groundwater interface; precipitation or dissolution of secondary minerals; photo-chemical reactions. One of the objectives of this study is to rule out certain of these mechanisms, while at the same time determining which process exerts the dominant influence.
A combination of field studies, laboratory experiments, statistical analysis, and theoretical modeling are being used. Field studies employ 24-hour automatic samplers and continuous data recorders to track diel changes in temperature, pH, metal concentration, and other parameters. Mesocosm experiments attempt to re-create the stream environment under laboratory conditions where environmental parameters can be more precisely controlled. Statistical analysis will employ multi-variable linear regression and factor analysis to see which environmental parameters exert a greater control on metal fluctuations. Geochemical modeling will be used to simulate mineral dissolution/precipitation or adsorption/desorption reactions.
The results of this study will provide a scientific framework that will allow scientists, engineers, and regulatory agencies (such as EPA) to better evaluate the phenomenon of diel metal cycling in fluvial systems. Conclusions will be drawn as to what types of water bodies are most likely to display large diel variations in trace metal content, and why these variations occur. This information can then be used to refine existing protocols for monitoring the quality of water in mining-impacted watersheds.