PARENT SESSION
Oral Session 12: Restoration Ecology I: Streams and Wetlands.
Presiding: M Wu
Monday, August 2, 8:00 AM to 11:30 AM, Meeting Room D 133.
Ecological impacts of dams: Size-related effects and implications for dam removal.
Brown, Rebecca*,1, Hart, David1, Velinsky, David1, Pizzuto, James2, Charles, Don1, Horwitz, Richard1, Kreeger, Danielle1, Johnson, Thomas1, Skalak, Katherine2, Winter, Diane1, Nightengale, Timothy1, Carr, Jamie1, McNair, James1, 1 Patrick Center for Environmental Research, Philadelphia, PA2 University of Delaware, Newark, DE
ABSTRACT- Understanding the relationship between a dam's size and its ecological impact is important for prioritization of river restoration efforts based on dam removal. Although much is known about the effects of large storage dams, this information may not be applicable to small run-of-river dams, which represent the vast majority of dams being considered for removal. To better understand how dam impacts vary with size, we conducted an integrative study of the downstream effect of dams on a range of ecological characteristics (e.g., geomorphology, water chemistry, algae, macroinvertebrates, fish, and riparian vegetation). We measured various ecological characteristics downstream of dams and in upstream reference sites for 15 dams in the mid-Atlantic region ranging from 0.9 to 57 m high, with hydraulic residence times (HRT) ranging from 30 minutes to 1.5 years. We used linear regression to examine how dam impacts (expressed as the difference in ecological conditions between downstream and upstream sites) varied with dam characteristics (volume, height, and HRT). For most ecological attributes, larger dams had substantially larger impacts. For example, the decrease in dissolved oxygen and increase in temperature below dams became more pronounced with increasing HRT. Macroinvertebrate assemblages likewise showed increasing differences in pollution tolerance with increasing dam size (with greater pollution tolerance below dams). One exception to this pattern was sediment grain size: fine sediment was significantly less abundant in downstream reaches, but this effect was unrelated to dam size. We show how these results can be used in predicting ecological responses to dam removal.
Key words: river restoration, riparian ecology, dams, aquatic ecology