Linking Landscape Characteristics and High Stream Nitrogen in the Oregon Coast Range: Red Alder Complicates Use of Nutrient Criteria

Red alder (Alnus rubra), a nitrogen(N)-fixing deciduous broadleaf tree, can strongly influence N concentrations in western Oregon and Washington. We compiled a database of stream N and GIS-derived landscape characteristics in order to examine geographic variation in N across the Oregon Coast Range. Basal area of alder, expressed as a percent of watershed area, accounted for 37% and 38% of the variation in summer nitrate and total N (TN) concentrations, respectively. Relationships between alder and nitrate were strongest in winter when streamflow and landscape connections are highest. Distance to the coast and latitude, potential surrogates for sea salt inputs, and watershed area were also related to nitrate concentrations in an all-subsets regression analysis, which accounted for 46% of the variation in summer nitrate concentrations. The model with the lowest Akaike’s Information Criterion did not include developed or agricultural land cover, probably because few watersheds in our database had substantial levels of these land cover classes. Our results provide evidence, at a regional scale, that background sources and processes cause many Coast Range streams to exceed proposed nutrient criteria, and that the prevalence of a single tree species (N-fixing red alder) exerts a dominant control over stream N concentrations across this region.Keywords: Forests, Rivers/streams, Environmental regulations, Biogeochemistry, Pacific Northwest, Nutrient

GreathouseEffieForestryLinkingLandscapeCharacteristics_AppendixS1.pdf

Red alder (Alnus rubra), a nitrogen(N)-fixing deciduous broadleaf tree, can strongly influence N concentrations in western Oregon and Washington. We compiled a database of stream N and GIS-derived landscape characteristics in order to examine geographic variation in N across the Oregon Coast Range. Basal area of alder, expressed as a percent of watershed area, accounted for 37% and 38% of the variation in summer nitrate and total N (TN) concentrations, respectively. Relationships between alder and nitrate were strongest in winter when streamflow and landscape connections are highest. Distance to the coast and latitude, potential surrogates for sea salt inputs, and watershed area were also related to nitrate concentrations in an all-subsets regression analysis, which accounted for 46% of the variation in summer nitrate concentrations. The model with the lowest Akaike’s Information Criterion did not include developed or agricultural land cover, probably because few watersheds in our database had substantial levels of these land cover classes. Our results provide evidence, at a regional scale, that background sources and processes cause many Coast Range streams to exceed proposed nutrient criteria, and that the prevalence of a single tree species (N-fixing red alder) exerts a dominant control over stream N concentrations across this region.Keywords: Nutrients, Biogeochemistry, Forests, Environmental regulations, Pacific Northwest, Rivers/streamsKeywords: Nutrients, Biogeochemistry, Forests, Environmental regulations, Pacific Northwest, Rivers/streamsKeywords: Nutrients, Biogeochemistry, Forests, Environmental regulations, Pacific Northwest, Rivers/streamsKeywords: Nutrients, Biogeochemistry, Forests, Environmental regulations, Pacific Northwest, Rivers/stream

Appendix A. A description of methods used to determine physical and chemical parameters at high- and low-gradient survey sites and a table showing additional physical parameters at high-gradient sites.

A description of methods used to determine physical and chemical parameters at high- and low-gradient survey sites and a table showing additional physical parameters at high-gradient sites

Geographic and ecological setting of the Luquillo Mountains

This chapter describes the geologic, geographic, and ecological context of the location of Luquillo Mountains, particularly the factors affecting the response mechanisms of terrestrial and aquatic ecosystems to disturbance. It describes the existing conditions of the physical environment, chemical environment, and the biota of the Luquillo Mountains as they respond to disturbances. It then merges the decade-long research about the Mountains with the other tropical ecosystems around the globe