Evaluating the Status and Trends of Physical Stream Habitat in Headwater Streams within the Interior Columbia River and Upper Missouri River Basins Using an Index Approach

Abstract

Identifying the overall status of freshwater streams is an important step in evaluating effects of land management and prioritizing restoration activities. To address these needs, we developed an index of physical habitat condition for headwater streams based on physical stream habitat data (2003–2007) and evaluated the condition status of 217 reference streams and 934 managed streams in the interior Columbia River and upper Missouri River basins. We used data collected from reference reaches to generate this index, which consisted of eight commonly collected metrics used in stream habitat monitoring. We incorporated landscape and climatic covariates into multiple linear regression analyses to control for inherent differences in physical habitat attributes among reaches, and we scored the overall condition of reaches with index values ranging from 0 to 100. Our results indicated that the condition index score of physical habitat was significantly higher in reference reaches (mean ± SE = 47.1 ± 1.4) than in managed reaches (30.4 ± 0.7); relative to reference reaches, a greater frequency of managed reaches had low habitat condition and a lower frequency of managed reaches had high habitat condition. Analyses evaluating the relationship between management activities and the condition of physical habitat in streams indicated a significant negative relationship with lower index scores in stream reaches within catchments containing higher densities of roads. When roads and livestock grazing occurred within catchments, we found the presence of grazing had an additional, significant negative effect on the relationship between road density and the condition of physical habitat of streams. Our results suggested that once natural variability and geoclimatic differences among reaches are accounted for, a multimetric index approach can provide managers with an easily interpretable tool to monitor the status of the overall condition of physical habitat.