Stream DOC, nitrate, chloride and SUVA response to land use during winter baseflow conditions in sub-basins of the Willamette River Basin, OR

Graduation date: 2011To better understand the impact of land use on stream nutrient export, a synoptic sampling of 57 sub-basins within the Willamette River basin was conducted during winter baseflow conditions (February 2009). I assessed whether stream dissolved organic carbon (DOC), NO₃⁻ and Cl⁻ and specific ultra-violet absorbance (SUVA) values were correlated with individual watershed land use variables: percent urban, agriculture, and forest. Simple linear regression analysis indicated that stream DOC, NO₃⁻ and Cl⁻ increased significantly with increasing percent agriculture and urban area in sampled watersheds, and decreased significantly with increasing percent forest. Stream order and watershed area were not significantly related to any stream chemistry variables. Simple linear regression analysis indicated that SUVA, a measure of the aromaticity of DOC, decreased significantly with increasing percent urban area in catchments, but was not significantly related to percent agriculture or urban. Ordination of streams on the basis of their chemistry supported simple linear regression analyses, clustering of streams with low SUVA values and higher DOC, NO₃⁻, and Cl concentrations, which were also largely associated with increasing percent urban, and slightly less associated with increasing percent agriculture. Results indicate that stream nutrient concentrations are strongly influenced by associated land use within the watershed. SUVA results suggest a combination of land use and variable hydrologic flowpaths affects the composition of stream DOC under winter baseflow conditions