Assessing geomorphological and ecological responses in restored step-pool systems
Published:May 01, 2009
Anne Chin, Alison H Purcell, Jennifer W.Y Quan, Vincent H Resh, 2009. "Assessing geomorphological and ecological responses in restored step-pool systems", Management and Restoration of Fluvial Systems with Broad Historical Changes and Human Impacts, L. Allan James, Sara L. Rathburn, G. Richard Whittecar
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Although step-pools are increasingly used in stream restoration to stabilize steep channels, few studies have examined artificially manipulated step-pool systems after restoration. Whereas monitoring efforts have emphasized morphological change within restored systems, knowledge of the ecological potential for restoration using step-pool sequences is particularly incomplete. Baxter Creek (El Cerrito, Contra Costa County) and Codornices Creek (Berkeley, Alameda County) in California provide two unique cases of restored step-pool systems with which to assess post-restoration responses. Since restoration was completed in 1996 and 2003, respectively, Baxter Creek and Codornices Creek have achieved geomorphic stability, characterized by maximum flow resistance and minor change in channel cross sections. The integrity of the restored step-pool channels has been maintained through storms that have exceeded the 14–20+ year recurrence interval. Comparison of the types and characteristics of benthic macroinvertebrates in the restored reaches with unrestored sites upstream and downstream, as well as with a reference channel (Wildcat Creek, Contra Costa County), indicates that restoration has effectively created ecological environments consistent with the overall watershed settings within Baxter Creek and Codornices Creek. Biological metrics used to represent ecological conditions indicate that Wildcat Creek, the reference site, had a healthier condition, which was reflected in a higher percentage of sensitive taxa (e.g., Ephemeroptera, Plecoptera, Trichoptera or EPT) and a lower percentage of tolerant taxa (e.g., oligochaetes and midge larvae). No significant differences were found between the restored reaches in Baxter Creek and Codornices Creek, and those upstream and downstream of the restored sites. Comparison of the biological metrics among habitat types (steps, pools, riffles) within each stream and across watersheds indicates a tendency toward higher biological quality (characterized by a higher percentage of sensitive organisms) in steps compared with pools. These findings suggest the ecological potential of stream restoration using step-pools, because step clasts may offer habitats for higher percentages of sensitive and specialized organisms.