Geomorphic-Ecological Relationships Highly Variable between Headwater and Network Mountain Streams of Northern Idaho, United States1

Abstract

Abstract:  Headwater streams are critical repositories of biodiversity and are important sources of water, nutrients, and energy to downstream rivers. I investigated relationships between stream geomorphology and habitat, benthic macroinvertebrates, and fish assemblages between headwater and network streams (n = 18) of mountain drainages in northern Idaho, United States. I found that a stream geomorphic condition assessment (rapid geomorphic assessment, RGA) designed to evaluate channel adjustment explained more variation in habitat assessment scores in headwater (R2 = 0.79) than in larger streams (R2 = 0.51). Results from redundancy analysis indicated that geomorphic-biotic relationships were stronger in headwater than in network streams. For aquatic macroinvertebrates, relationships in headwaters were largely related to sediment size and slope. Fish-geomorphic associations in both headwater and network streams were quite variable, although the RGA was correlated with fish diversity in both systems. Large wood was related to macroinvertebrate and fish descriptors in both headwater and network streams, but in distinct ways. This work supports an ecogeomorphic approach to the conservation of headwater streams including the use of tailored stream geomorphic assessment protocols.