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LANDSCAPE CHARACTERISTICS AND HIGH STREAM NITROGEN IN THE OREGON COAST RANGE: RED ALDER COMPLICATES USE OF NUTRIENT CRITERIA
Greathouse, E. AND J. Van Sickle. LANDSCAPE CHARACTERISTICS AND HIGH STREAM NITROGEN IN THE OREGON COAST RANGE: RED ALDER COMPLICATES USE OF NUTRIENT CRITERIA. Presented at Joint Aquatic Sciences Meeting, Portland, OR, May 18 - 23, 2014.
Stream nitrogen concentrations are variable and often high in the Oregon Coast Range, uncharacteristic for a predominantly forested region. We compiled stream nitrogen data and GIS-derived landscape characteristics in order to examine variation in nitrogen across the region. In simple linear regressions, basal area of N-fixing alder trees, expressed as a percent of watershed area, accounted for 37% and 38% of the variation in summer nitrate and total nitrogen concentrations, respectively. Relationships between alder and nitrate were strongest in winter when streamflow and landscape connectivity are highest. In multiple linear regressions, nitrate concentrations were positively related to distance to the coast and latitude (potential surrogates for sea salt inputs), and to watershed area. The model with the lowest AIC did not include developed or agricultural land cover, since few watersheds in our database had substantial levels of these land cover classes. Our results provide evidence that background sources and processes cause many Coast Range streams to exceed proposed nutrient criteria, and that the prevalence of a single N-fixing species exerts a dominant control over stream N concentrations across this region.
This abstract is for a talk to be given at the Joint Aquatic Sciences Meeting in Portland, Oregon, May 2014. This work was part of the EPA research program in freshwater habitat, and examines the controls on nitrogen concentrations in the Oregon Coast Range. The researchers used a novel statistical and data mining approach to examine the relationship between natural background sources of nitrogen, such as N-fixing red alder using data collected by a variety of agencies and researchers. They found that this one plant species is the dominant driver of nitrogen concentrations in the region, and that understanding this effect will be instrumental to the development of nutrient criteria in the region. In addition, the researchers found that the drivers were similar in summer and winter but that winter concentrations were greater than summer concentrations, and thus these trends should be considered when examining summer only data, for example the National Aquatic Survey data.
Record Details:Record Type: DOCUMENT (PRESENTATION/ABSTRACT)
Organization:U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RESEARCH AND DEVELOPMENT
NATIONAL HEALTH AND ENVIRONMENTAL EFFECTS RESEARCH LAB
WESTERN ECOLOGY DIVISION
FRESHWATER ECOLOGY BRANCH