Seven streams, one of them permanent, were studied in western Oregon, USA. The research was designed to assess the value of summer-dry headwaters for conservation oriented landscape management. Streams were categorized primarily according to exposure (forest versus meadow sites) and secondarily according to flow duration (ephemeral = short-flow versus temporary = long-flow sites). Ephemeral streams have discontinuous flow and last less than three months annually. Temporary streams have continuous flow for more than five months each season. Ephemeral forest streams were highly efficient at filtering road-generated sediment. Uptake lengths for suspended sediment were short (36 m-105 m) at moderately elevated input concentrations. As a result of the filtration mechanism, filtration efficiency is expected to increase as annual flow duration decreases. Injection experiments yielded nitrate uptake rates of almost 1% per m of temporary stream channel. Exchange with subsurface flow was the most important route for nitrate removal from the water column. Biological uptake was insignificant in a light-limited forest stream, whereas a considerable amount of nitrate was retained by the biota a nutrient-limited meadow channel. At least 207 insect species were collected from the summer-dry streams. Species richness recorded from temporary forest streams exceeded that in an adjacent permanent headwater and there was high overlap between the fauna of the permanent and the temporary streams. Species richness in ephemeral channels was only 1/4 to 1/3 of that in long-flow forest streams. Multivariate analysis of community structure revealed flow duration and microhabitat pattern (riffle-pool) as the most important environmental factors determining faunal composition in temporary forest streams. Summer drought conditions at the sample sites also were important. By providing habitat and contributing to water quality in permanent downstream reaches, summer-dry streams have the potential to serve multiple purposes in conservation management. Their value from a conservation perspective is unexpectedly high. Landscape management therefore should be directed toward the preservation and protection of ephemeral and temporary streams. / Graduation date: 1993

In spite of decades of related research, stream channel initiation is still not well understood. Current theories of channel initiation are grounded in research conducted by Montgomery and Dietrich, largely in the transport limited, temperate, humid climate of the Pacific Northwest, USA. This field data driven work concluded that the drainage area required for channel initiation is directly correlated to the slope of the contributing area. However, there are a host of related variables that have yet to be examined in the field. This study revisits the slope-area relationship focusing on ephemeral overland flow in headwaters of both the Pacific Northwest and an environmentally contrasting island in Greece. By seeking greater understanding of the variables, such as soil properties, vegetation type, and lithology that may influence channel initiation, the study sought to find an equation for remote determination of where ephemeral flow concentrates. However, results indicated that a universal equation does not exist. Rather, the location of ephemeral flow concentration is linked to landscape type, transport versus weathering limited slopes, and corresponding overland flow type. As a result, there is potential for regional models to be developed. Two such models were found as part of this study. One indicates that in a weathering limited environment, Hortonian overland flow is the dominant ephemeral flow type and the driving force behind where it concentrates on the landscape. The other demonstrates that in a transport limited environment, ephemeral flow concentration is due saturated overland flow, with the key to location of concentration being the point of return flow.