State Water Resources Research Institute Program

Project ID: 2007MT145B
Title: Temporal and spatial changes in the concentration and isotopic composition of nutrients in the upper Silver Bow Creek drainage, Montana: Year 2
Project Type: Research
Start Date: 3/01/2007
End Date: 12/31/2008
Congressional District: at large
Focus Categories: Nitrate Contamination, Hydrogeochemistry, Surface Water
Keywords: nutrients; isotopic concentration; Silver Bow Creek; Montana; water chemistry
Principal Investigator: Gammons, Chris
Federal Funds: $ 6,800
Non-Federal Matching Funds: $ 13,761
Abstract: This proposal seeks a second year of 104b funding (at a reduced level) for our ongoing investigation of nutrient loading and bio-geochemical nitrogen cycling in upper Silver Bow Creek, Butte, Montana. After many years of extensive and expensive reclamation work focusing on removal of toxic mine wastes from the floodplain, Silver Bow Creek remains a stream essentially devoid of any viable fishery. One of the main goals of our project is to find out why. In the summer of 2006, our research team documented the existence of a 4 mile long "dead zone" in upper Silver Bow Creek below the Butte waste-water treatment plant (WWTP) where dissolved oxygen (DO) levels dropped well below the lethal threshold for trout at night. In the center of the dead zone, DO concentrations dropped below 1 mg/L for a 12 hour period. In the colder seasons, DO consumption does not appear to be a critical problem. However, synoptic sampling in October 2006 showed highly elevated concentrations of ammonium ion (NH4+) and nitrite (NO2-) - both toxic to salmonid fish - traceable over 30 km all the way downstream to the mouth of Silver Bow Creek at the inlet to Warm Springs lime treatment ponds. The major source of this contamination is the Butte WWTP, although our work also shows additional loading of nitrate (NO3-) and phosphate from other point sources (mainly as discharge from two groundwater treatment facilities) as well as non-point sources (fertilizer, animal waste, septics).

An important objective of Year 2 of this study will be to continue our nutrient monitoring through a second water year. As well, using what we have learned from Year 1, we intend to examine in greater detail the evolution of the oxygen "dead zone", and to document the biogeochemical processes responsible for this phenomenon. In particular, we are interested in microbial transformations of nitrogen between the ammonia, nitrate, and nitrite pools, and how the rates of these transformations differ with the time of day (diurnal sampling) and the time of year (seasonal sampling). One of our hypotheses is that oxidation of ammonia to nitrite and/or nitrate is a major source of chemical oxygen demand during the summer months, and this will be tested with bench-scale experiments. Finally, we will continue to explore the use of stable isotopes of nitrate, ammonia, and dissolved N2 gas in Silver Bow Creek and its tributary waters. We postulate that stable isotopes may be used to fingerprint different sources of nutrient contamination, and furthermore anticipate that diurnal changes in 15N of different dissolved nitrogenous species can be used to shed insight into the mechanisms of redox transformation and biological cycling of nitrogen in this highly publicized and (still) heavily polluted watershed.

Progress/Completion Report, PDF

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