|Shields Jr, Fletcher|
Submitted to: Aquatic Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/24/2007
Publication Date: 7/18/2008
Citation: Shields Jr, F.D., Knight, S.S., Stofleth, J.M. 2008. Stream bed organic carbon and biotic integrity.. Aquatic Conservation. 18:761-779. Interpretive Summary: Stream ecosystems in agricultural watersheds throughout the United States have been degraded by severe erosion, but the links between ecological damage and erosion are often unclear, complicating restoration planning. In order to study one form of erosion-related stream damage, we examined streambed carbon concentrations and fish communities in four streams in northern Mississippi with varying degrees of channel erosion. In general, the lightly degraded streams had higher carbon concentrations and more natural, diverse fish communities, suggesting that rehabilitation of stream ecosystems requires restoring riparian vegetation and in-channel features that retain carbon-rich debris and sediments. These findings are directly useful to workers planning and designing stream channel restoration or management projects.
Technical Abstract: Allochthonous organic matter provides a basis for some stream ecosystems. Channel incision, which is a common result of anthropogenic impacts on watersheds and stream channels, may deplete stream bed C stores due to erosion, less frequent hydrologic exchanges between stream and floodplain, and removal of riparian vegetation and large woody debris. Channel incision may also adversely impact biological integrity through physical habitat degradation. Effects of channel incision on sand-bed stream carbon reservoirs and indicators of biological integrity based on fish collections (IBIs) were examined. Total C concentrations were sampled from the top 10 cm of bed sediments in two severely incised streams and two less degraded reference streams in northern Mississippi. Observed C concentrations ranged from 0.24 + 0.36% for a slightly incised reference site to only 0.01 + 0.02% for a severely incised channel. Carbon concentrations were not significantly correlated with large wood density, perhaps because initial stages of channel incision produced elevated large wood densities. Fish IBI was positively correlated with %C in the bed (r = 0.70, p = 0.003), and IBIs for reference streams were more than 50% greater than those computed for the most severely degraded sites. More testing is needed to determine the efficacy of stream bed C as an indicator, but its importance to warmwater stream ecosystems, and the importance of covarying physical and hydrologic conditions seems evident.