Wyoming-Montana Water Science Center
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The objective of this project is to examine the biogeochemical processes responsible for diel cycling of trace metals using a combination of detailed field studies, laboratory experiments, and theoretical modeling. This research will be used to further the understanding of trace-metal mobility and diel metal cycles.
Research scientists from the USGS, Montana State University, Montana Tech of the University of Montana, University of Wyoming, and Montana Fish, Wildlife and Parks have worked collaboratively for the last several years to improve the understanding of diel metal cycling. Hypothesized causes of these diel metal cycles include streamflow variation, groundwater exchange, temperature- and pH-dependent sorption, precipitation and dissolution of solid phases, redox cycling, and biotic uptake. While recent work has begun to document the extent and magnitude of diel cycling and to measure variables likely related to diel cycling, the relative effect of each of the plausible processes has not been ascertained. Current (2008) research plans are directed at determining the relative importance of these processes and providing guidance on appropriate strategies for sampling streams with diel cycles of metal concentrations.
Six diel data sets were collected in 1990-93 for the Madison and Missouri Rivers in Montana to document diel variation in arsenic concentrations. Eighteen diel data sets were collected during 1995-2002 for 14 sites on 12 streams in Montana and Idaho to demonstrate the widespread occurrence of diel cycling of arsenic, cadmium, nickel, manganese, and zinc in neutral to alkaline streams during low flow. During 2000-03, seven data sets were collected for Prickly Pear Creek to demonstrate the persistence of diel metal cycles throughout the year and during different streamflow conditions. During 2002-03, diel cycling of trace metals and rare earth elements was studied in a stream where pH changed from acidic to neutral over a short distance. During 2003-04, data sets were collected to determine whether mercury concentrations exhibit diel cycles. During 2004-05, field data were collected to determine the relative differences in acute toxicity to aquatic organisms from exposure to constant metal concentrations compared to exposure to varying metal concentrations that follow the diel cycle observed in streams. During 2006, field data were collected from the Rio Tinto and Rio Odiel in southwestern Spain to examine diel cycling of ferrous and ferric iron and how iron photoreduction supplies energy to the microbial population in these rivers. In addition, field study of diel metal cycling in the Animas River and its major tributaries (Mineral and Cement Creeks) in southwestern Colorado was initiated in 2006. During 2007, field data were collected from two streams near the historical Mike Horse mine in the headwaters of the Blackfoot River in western Montana. Data collection during 2008 is planned for mining-affected streams in the headwaters of the Clark Fork in western Montana.
Map showing sites in Montana, Idaho, Colorado and Spain where diel samples sets were collected, 1991-2007 (Click on image for a larger view)