Direct and Indirect Effects of Mine Drainage on Bacterial Processes in Mountain Streams
The effects of mine drainage on 2 bacterial processes were examined in Rocky Mountain streams affected by mine drainage. Thymidine incorporation into bacterial DNA was measured as an index of bacterial production, and nitrification was examined because it is sensitive to a variety of stressors. These processes, as well as pH, concentration of dissolved Zn, and deposition rate of metal oxides, all of which are influenced by mine drainage, were measured at 37 sites. The concentrations of inorganic nutrients and dissolved organic carbon (DOC), as well as algal biomass (as chlorophyll a), also were measured at each site. The rate of incorporation of thymidine into DNA was negatively related to deposition of metal oxides and positively related to pH, algal biomass, and concentration of DOC. pH, DOC, and algal biomass together explained 59% of the variation in thymidine incorporation among sites in a multiple regression. Metal oxide deposition probably influenced thymidine incorporation through suppression of algal biomass and through sorption of a fraction of the DOC. The nitrification potential for microbes on gravel substratum removed from streams was estimated as the rate of NO3− production following addition of NH4+. Nitrification was undetectable at pH < 5.3 or Zn > 2 mg/L. Low pH (<6, as a categorical variable), concentration of Zn (which had a negative effect), and algal biomass (which had a positive effect) explained 77% of the variation in nitrification potential. The results suggest that bacterial processes vary in their sensitivity to the stressors from mine drainage, and that they can be disrupted both directly and indirectly. Nitrification was sensitive to direct influences of acid mine drainage, namely acidity and dissolved Zn. Low pH also affected thymidine incorporation. In contrast, acid mine drainage indirectly affected both thymidine incorporation and nitrification potential through its influence on algal biomass, which declined in response to deposition of metal oxides.
D. Niyogi et al., "Direct and Indirect Effects of Mine Drainage on Bacterial Processes in Mountain Streams," Journal of the North American Benthological Society, North American Benthological Society, Jan 2003.
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