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Quantifying Biologically Mediated Fluxes of Stream Metals to Riparian Food Webs: Johanna Kraus

Project Title: Quantifying Biologically Mediated Fluxes of Stream Metals to Riparian Food Webs
Mendenhall Fellow: Johanna Kraus, (970) 226-9436,
Duty Station: Fort Collins, CO
Start Date: February 2, 2011
Education: Ph.D. (Biology), University of Virginia, 2006
Research Advisors: Rich Wanty, (303) 236-1819,; Travis Schmidt (970) 226-9470,; David Walters, (970) 226-9484,
      Johanna Kraus

  Project Description: Trace-metal contamination of aquatic ecosystems is a major health and environmental concern globally, leading to alterations of aquatic communities, decreased fisheries and bioaccumulation in higher trophic levels. In the Rocky Mountains, metals mobilized from the mineralized bedrock underlying watersheds are one of the major factors shaping aquatic communities in perennial streams. The geologic processes that affect distribution of metals within central Colorado streams such as mining and mineralization are well characterized, but little is known about the repercussions of these effects for neighboring terrestrial ecosystems. Aquatic insects, which comprise a large component of stream food webs as larvae, emerge from streams as adults where they are consumed by terrestrial predators such as spiders. Thus, insects can transport metals from aquatic to terrestrial food webs by carrying them within their adult bodies. The primary objectives of this research are to (1) establish the relationship between metal accumulation in riparian predators (that is, spiders), stream trace-metal concentrations and underlying rock type, (2) measure insect emergence, production and metal flux during the growing season, and (3) test how fish, an important top predator, alter metal flux to riparian food webs in contaminated streams. We hypothesize that the relationship between stream metal bioavailability and flux to terrestrial food webs may not be straightforward. Since trace metals directly reduce the abundance of aquatic insects in streams, aquatic insect mediated metal flux to terrestrial ecosystems may be greatly reduced in areas of highest contamination.  Also, fish are known to have top-down effects on number of insects emerging from streams; thus in areas where fish are present, metal flux in emerging aquatic insects could also be reduced. Data from this multidisciplinary study will be used to construct a predictive framework based on geology, toxicology, and ecology for understanding when and where fluxes of aquatically derived metals to terrestrial food webs are important. The outcomes of this research will have large implications for stream restoration and management in the National Forests and Parks where this study takes place, since decisions about aquatic ecosystems could have large implications for metal transfer to riparian food webs.


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