COS 17-5 - CANCELLED - Stream sensitivity and riparian ecosystem resilience: New concepts and tools for prioritizing management

Background/Question/Methods

Water is a critical resource in dryland regions of the western United States. Determining appropriate management strategies for stream and riparian ecosystems is challenging because watersheds, stream systems, and their associated riparian ecosystems have varying geomorphic, hydrologic, and vegetation conditions and respond differently to natural and anthropogenic disturbances. Understanding the factors that control watershed response to disturbances is key to effective management. We developed a conceptual framework and assessment protocol for evaluating the geomorphic sensitivity of streams and ecological resilience of riparian ecosystems in the Great Basin. We asked: (1) What are the watershed, stream, and riparian ecosystem characteristics that determine sensitivity and resilience? (2) How do sensitivity and resilience differ among watersheds? We used aerial photographs to evaluate watershed area, runoff regimes, basin types and characteristics, dominant riparian vegetation, and evidence of past disturbance. We used extensive field surveys to examine watershed segment and stream reach geomorphic characteristics, including channel character and form, sediment availability, size, and mobility, and evidence of incision or avulsion; and riparian vegetation characteristics, including indicator species and aerial cover, vigor and mortality, and successional status. We developed a categorization of watershed sensitivity and resilience for assessing response to disturbance and prioritizing management actions.

Results/Conclusions

We identified five watershed types with different geomorphic sensitivity and ecological resilience, including flood dominated, armored, fan dominated, deeply incised, and pseudostable. For example, fan dominated watersheds are characterized by low to moderate sensitivity because of large side valley fans that act as base level controls. Upstream of fans, stream channels have low gradients and may experience slow but continuous incision. Meadow complexes often occur upstream of the fans and low rates of incision result in moderate to high resilience. In contrast, deeply incised watersheds are characterized by fine-grained, mobile sediment that can be eroded by surface or groundwater. Potential for extensive incision during large runoff events results in moderate to high sensitivity. Riparian resilience is low to moderate because incision results in lowered water tables and significant changes in riparian extent and composition. In fan dominated watersheds restoration potential is high as stream and meadow ecosystems can be maintained by stabilizing the fans. In deeply incised systems management strategies are recognizing the potential for incision, preventing large-scale disturbance, and keeping roads out of valley bottoms. A protocol has been developed for assessing sensitivity and resilience that provides the ability to prioritize areas for management and determine appropriate management strategies.