The Science of the Total Environment 317 (2003) 73–89 0048-9697/03/$ - see front matter  2003 Elsevier Science B.V. All rights reserved. PII: S0048-9697 Ž 02 . 00615-0 Analyzing trophic transfer of metals in stream food webs using nitrogen isotopes Margaret R. Quinn *, Xiahong Feng , Carol L. Folt , C. Page Chamberlain a, b c Department of Earth Sciences, Dartmouth College, Hanover, NH 03755, USA a Department of Earth Sciences, Dartmouth College, 6105 Fairchild, Hanover, NH 03755, USA b Department of Biological Sciences, Dartmouth College, 6044 Hinman, Hanover, NH 03755, USA c Received 20 March 2002; accepted 7 November 2002 Abstract This study examines detrimental effects of acid mine drainage (AMD) on stream invertebrate communities and tests for a direct relationship between trophic position and accumulation of three metals (Fe, Cu, Zn) by stream invertebrates in situ. On two dates in each of seven stream sites, we measured food chain length, mean trophic level, taxa richness, and trophic position of stream macroinvertebrates comprising the food webs using stable nitrogen isotope ratios. Metals in tissue of representatives of 35 taxa were measured by ICP-OES. Our results are the first direct comparison of uptake of these metals in stream invertebrate taxa according to trophic position as identified by d N. As predicted, metal concentrations were generally greater in water and insects from sites adjacent to mining 15 activity and invertebrate taxa richness was significantly lower. Taxa richness increased with distance away from contaminated headwaters. Despite reductions in diversity at sites nearest AMD, food chain length and mean trophic level did not differ between streams. The relationship between trophic position and metal accumulation differed considerably among metals. Specifically, Fe declined (biodilution) and Zn increased (biomagnification) with trophic level, but trophic position had no effect on Cu levels in these insects. Our results highlight fundamental differences in trophic transfer of specific metals through aquatic food webs and identify ecologically important impacts of AMD on stream invertebrates.  2003 Elsevier Science B.V. All rights reserved. Keywords: Acid mine drainage; Aquatic ecology; Bioaccumulation; Macroinvertebrates; Nitrogen isotopes; Trophic position 1. Introduction Acid mine drainage (AMD) is environmentally damaging. It results in extremely low pH values and high metal concentrations in stream water receiving the drainage (Clements, 1994; Farag et *Corresponding author. P.O. Box 78, East Burke, VT 05832, USA. Tel.: q1-802-626-1516x1466; fax: q1-802-626-3784. E-mail address: margaret.quinn@alum.dartmouth.org (M.R. Quinn). al., 1998; Beltman et al., 1999). Metals such as Fe, Cu, Zn, Cd and Pb are known to be especially high in association with mining activities (Axtm- ann et al., 1997; Pestana et al., 1997). The effects of AMD on the biota may be very pronounced (see Clements et al., 2000; Griffith et al., 2001; Besser et al., 2001). Understanding how AMD affects the structure of the biotic communities can guide policy governing use and remediation after