Streams affected by acid mine drainage (AMD) are highly stressed ecosystems and occur worldwide. These streams typically have low pH, high concentrations of dissolved metals, and substrata coated with metal hydroxide precipitates. This combination of chemical and physical stressors creates a challenging environment for aquatic biota. We provide a synthesis of the effects of AMD on stream food webs to provide a holistic perspective of these highly stressed ecosystems. First, we reviewed the effects of AMD on the structure and function of algal, microbial, invertebrate, and fish communities. Then, we used this published information to propose generalized food webs and identify areas for future research. In general, AMD-affected streams have depauperate communities that are dominated by a few tolerant species, and ecosystem processes (e.g., decomposition) are often impaired. Biota respond differently to the individual stressors (e.g., pH compared to precipitates), which may complicate remediation efforts that focus primarily on neutralizing acidity and removing metals from mine discharges. Food webs in these streams are substantially altered because basal resources are less productive or inaccessible, microbial processing of organic matter is slow, many grazers and shredders are absent, and fish are replaced by invertebrates as top predators. Structurally, declines in species diversity and the loss of fish shorten and simplify food webs by decreasing the number of interactions among species. Functionally, most energy pathways are weakened by disrupted trophic links, and this problem should to be a key target of restoration efforts. We think research that focuses on species interactions in a foodweb context is needed to provide a better understanding of community organization and functioning in these highly stressed ecosystems.
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Vol. 31 • No. 1