Segura Catalina (Orcid ID: 0000-0002-0924-1172) Noone David (Orcid ID: 0000-0002-8642-7843) Jones Julia Allen (Orcid ID: 0000-0001-9429-8925) Climate, landforms, and geology affect baseflow sources in a mountain catchment Catalina Segura1,*, David Noone2, Dana Warren3,4, Julia Jones5, Johnathan Tenny1, and Lisa Ganio3 1 Forest Engineering, Resources, and Management, Oregon State University, Corvallis, OR, USA 2 College of Earth Ocean & Atmospheric Sciences, Oregon State University 3 Forest Ecosystems and Society, Oregon State University 4 Department of Fisheries and Wildlife, Oregon State University 5 College of Earth, Ocean, and Atmospheric Sciences, Oregon State University *Corresponding author: Catalina Segura (
[email protected]) Key Points: In an average water year isotope patterns of baseflow reflected an elevational- dependent influence of precipitation and seasonal snowpack In a year with low snowpack, baseflow isotope patterns showed greater influence of water stored in colluvial deposits, such as earthflows As snowpacks decline, groundwater stored in colluvial deposits and bedrock will have greater influence on spatial patterns of baseflow This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process which may lead to differences between this version and the Version of Record. Please cite this article as doi: 10.1029/2018WR023551 © 2019 American Geophysical Union. All rights reserved. Abstract Baseflow is essential for stream ecosystems and human water uses, particularly in areas with Mediterranean climates. Yet the factors controlling the temporal and spatial variability of baseflow and its sources are poorly understood. Measurements of oxygen and hydrogen isotopic composition (δ18O and δ2H) were used to evaluate controls on baseflow in the stream network of a 64 km2 catchment in western Oregon.