OOS 49-7
Prioritizing sites for river restoration based on geomorphic integrity: Do geomorphic indicators predict measures of riparian quality?
Ecological restoration along rivers should be based on knowledge of the dynamic interactions and processes that maintain riparian connectivity, as well as relative costs and benefits of restoring particular sites within the watershed context. We designed a spatial decision support system to prioritize 500-m river segments for preservation, enhancement, and restoration along 365 km of the Walker River (California and Nevada). Over the last century, conversion of riparian landscapes to crops, water demands for agriculture, river channelization, and levee construction have been the primary drivers of habitat alteration in this terminal lake watershed. We used a combination of historic aerial imagery, LiDAR-derived, and field data variables to assess the geomorphic condition of each river segment. We expected these geomorphic indicators to be reflected in measures of biotic integrity such as richness and diversity of vegetation structure, plant communities, and bird populations and historic shifts in riparian vegetation types. To better understand the ecological relevance of geomorphic indicators, we used canonical correlation analysis (CCA) to determine how these indices are related to indicators of riparian biotic quality. CCA allowed us to understand simultaneous interactions between geomorphic and biotic indicators and suggest alternative weightings for these indicators in the decision support system.
Results/Conclusions
A canonical correlation model of multivariate association between two indicator groups of geomorphic integrity (changes in channel width and sinuosity, channel entrenchment, channel adjustment, and wet depressions) and riparian biotic quality (vegetation structural heterogeneity, plant community diversity, proportion of riparian vegetation, post-settlement vegetation transitions, and bird species richness) explained 43.6% of the overall variance. The first canonical dimension explained 29% of variance and represented the relationship between reaches with low entrenchment and more wet depressions (geomorphic indicators) that have a greater proportion of riparian vegetation (biotic indicator). The second canonical dimension explained 14% of variance and reflected that reaches with reduced channel dynamics (sinuosity, channel narrowing) generally have lower bird species richness but more mesic vegetation transitions. Based on these results, the geomorphic indicators most strongly associated with biotic quality are channel entrenchment and channel width change. Channel adjustment was not significantly associated with measures of biotic integrity. Of the biotic indicators, plant community diversity was least related to geomorphic integrity, and historical vegetation transitions showed associations counter to those of other biotic indicators. Efforts to prioritize riparian restoration actions based on spatial data should focus on indicator sets that jointly represent geomorphic and biotic integrity.