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dc.contributor.advisorDillaha III, Theoen_US
dc.contributor.advisorBenfield, E. F.en_US
dc.contributor.advisorValett, H. M.en_US
dc.contributor.advisorPeterson, C. G.en_US
dc.contributor.advisorWebster, J. R.en_US
dc.contributor.authorEarl, Stevan Rossen_US
dc.date.accessioned2011-08-22T19:09:13Z
dc.date.available2011-08-22T19:09:13Z
dc.date.issued2004-09-06en_US
dc.identifier.otheretd-10182004-182304en_US
dc.identifier.urihttp://hdl.handle.net/10919/11284
dc.description.abstractThis dissertation is a study of the relationships between nitrogen (N) availability and spiraling (the paired processes of nutrient cycling and advective transport) in stream ecosystems. Anthropogenic activities have greatly increased rates of N loading to aquatic ecosystems. However, streams may be important sites for retention, removal, and transformation of N. In order to identify controls on NO3-N spiraling in anthropogenically impacted streams, I examined relationships among NO3-N spiraling and a suite of chemical, physical, and biological variables in streams spanning a gradient of N concentration. Across all streams, gross primary production (GPP) accounted for most NO3-N demand. Uptake of NO3-N was also related to GPP but was limited by N availability when N concentrations were low. A combination of GPP and NO3-N explained 80% of the variance in uptake. In chapter 3, I conducted a series of short-term nutrient releases in which streamwater NO3-N concentration was incrementally elevated to identify conditions leading to saturation of uptake capacity. Four of six study streams showed signs of N limitation whereas there was no significant change in uptake with increasing NO3-N amendment in two streams, suggesting N saturation. Proximity to saturation was generally correlated to N concentration but was also predicted by the ratio of N:P. My results suggest complex relationships between N spiraling and availability that depend on resident biota and other limiting factors. In chapter 4, I examined nutrient spiraling methodology by comparing differences between ambient and amendment-derived NO3-N spiraling metrics. I quantified spiraling metrics during a short-term NO3-N amendment and under ambient conditions using a stable isotope (15NO3-N) tracer. Uptake lengths measured during amendments were consistently longer than ambient uptake lengths. Amendment-derived NO3-N uptake velocity and uptake were underestimated relative to ambient conditions. Using a technique to estimate ambient uptake length extrapolated from the relationship between uptake length and nutrient amendment concentration for a series of amendments at different concentrations, I found that extrapolated uptake lengths were generally better predictors of ambient uptake lengths than amendment-derived uptake lengths but the technique was less effective in high N streams that showed signs of weak N limitation.en_US
dc.format.mediumETDen_US
dc.publisherVirginia Techen_US
dc.relation.haspartetd.pdfen_US
dc.rightsThe authors of the theses and dissertations are the copyright owners. Virginia Tech's Digital Library and Archives has their permission to store and provide access to these works.en_US
dc.source.urihttp://scholar.lib.vt.edu/theses/available/etd-10182004-182304en_US
dc.subjectstream structure and functionen_US
dc.subjectnitrogenen_US
dc.subjectspiralingen_US
dc.subjectstream biogeochemistryen_US
dc.titleNitrogen spiraling in stream ecosystems spanning a gradient of chronic nitrogen loadingen_US
dc.typeOther - Dissertationen_US
dc.contributor.departmentBiologyen_US
dc.description.degreePHDen_US


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