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TRAJECTORY OF ECOSYSTEM RECOVERY IN RESTORED RIPARIAN ZONES IN URBAN SETTINGS
Impact/Purpose:
Intact riparian zones remove nutrients, particularly nitrogen and phosphorus, from groundwater and surface runoff, thus improving water quality. Because streams and riparian zones in many urban areas are degraded and have diminished ecological functions, stream and floodplain restoration is becoming important to water quality management strategies. Understanding how riparian zones regain ecological functions following restoration is key to setting realistic performance criteria. This project will examine stream restoration sites along an age gradient study ecosystem development following disturbance and the role of restored riparian zones in processing nutrients.
This project will examine stream restoration sites along an age gradient, as a proxy for a long-term study, to address basic questions about ecosystem development following disturbance, as well as practical considerations for understanding the role of restored riparian zones in processing nutrients. By examining stream and floodplain restoration sites completed between 1989 and 2005, and comparing them to unrestored sites in non-urban areas and urban, degraded areas, I will test these general hypotheses: 1. Hydraulic connectivity is key to the recovery of ecosystem processes in restored riparian zones: successful restoration will lead to more variable water table depths and less incised channels; 2. Time since restoration will explain differences in ecosystem functions in restored riparian zones, as vegetation and soil processes begin to approach those of natural riparian zones; 3. Abiotic mechanisms of nutrient retention (e.g., P sorption) will be more important in younger restored sites, while biotic processes (e.g., microbial assimilation, denitrification, plant uptake) will be increasingly important controls on nutrient biogeochemistry in older restored sites.
Description:
Phase I: These results will enable an evaluation of channel incision following restoration. I expect to find that sites restored longer ago will have more stable, less incised channels than more recently restored sites, as the older sites will have had more time to establish a new equilibrium. Publication of these results will be relevant to watershed planners and engineers who design stream restoration projects.
Phase II: I anticipate that ecological functions in restored riparian zones will begin to approach patterns in non-urban reference sites with increasing age. I expect that the five ecological functions will follow different trajectories, with hydrology and decomposition recovering earlier than the plant community and biogeochemical characteristics. Productivity in a restored site would likely approach reference conditions more slowly than other parameters. These results may validate the use of ecosystem surface response models as tools for assessing the success of ecological restoration.
Phase III: I anticipate that abiotic processes (e.g., phosphorus sorption) will be more important in the younger restored site, while biotic processes (e.g., microbial assimilation, denitrification, plant uptake) will be increasingly important controls on nutrient biogeochemistry in the older restored site and the reference site.