Evaluating the Physical Characteristics of Channel Units in an Ozark Stream

Abstract

To evaluate a hierarchical channel-unit-based habitat classification for warmwater streams, we measured the physical characteristics of 11 channel units (CUs) in two different-sized reaches of an Ozark stream. The physical characteristics of CU types differed from one another within and between reaches, although the relative physical characteristics of identical CU types were similar for both reaches. Reach-specific habitat differences were due to local and watershed-level features such as drainage area and channel gradient. Discriminant analysis of physical characteristics indicated that variations in depth and current velocity accounted for more than 81% and 86% of the variance among CUs in headwater and downstream reaches, respectively, and thus that they could be used to differentiate among upper-level CU types (pools and riffles). Additional physical variables (vegetation, woody debris, and substrate composition) were needed to discriminate among secondary-level CUs (types of pools and riffles). A V-fold cross validation classification procedure also indicated that the physical characteristics of CUs were predictable, with an average classification accuracy of 75% and 80% in headwater and downstream reaches, respectively. Our results indicate that the physical characteristics of CUs are distinct and predictable and that they may be useful for defining warmwater stream habitats. However, reach-specific differences suggest that stream biologists should incorporate the effects of local and watershed-level characteristics into study designs.