Associating local-scale physical habitat assemblages with reach-scale stream hydrogeomorphological types in mountain headwater catchments

Building an understanding of river ecosystems often involves integrating information from different locations, spatial scales and points in time. Geomorphologists and ecologists have long considered ways to explore river ecosystems at different, hierarchical, spatial scales so that features observed locally can be linked to the character of the larger spatial units within which the features are located. The present research builds on a classification of mountain stream reach types and their associated physical habitat assemblages proposed by Cox et al. for headwater streams across the Republic of Ireland. In this article we augment physical habitat and bed material data collected as part of an integrated investigation of within-catchment variations in water quality, physical habitat and biota in two small, Irish, mountain headwater catchments to explore two main research questions. Do the associations among mountain headwater stream types, physical habitat assemblages and bed material, identified at a national level, persist across short stream reaches within small, Irish, mountain headwater catchments? To what extent do the properties used to assign a stream hydromorphological type to a reach vary spatially along these headwater streams and what are the im-plications of these variations for identifying ‘homogenous’ reaches that can be associated with particular physical habitat assemblages? Our analysis and results from these two small catchments are necessarily exploratory and indicative. Nevertheless, we reveal a number of patterns, associations, and scale-related issues that need to be considered when surveying such streams and which could contribute to a larger, purpose-designed and more comprehensive study.