Nitrogen spiraling in stream ecosystems spanning a gradient of chronic nitrogen loading

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dc.contributor.authorEarl, Stevan Rossen
dc.contributor.committeechairValett, H. Mauriceen
dc.contributor.committeememberDillaha, Theo A. IIIen
dc.contributor.committeememberBenfield, Ernest F.en
dc.contributor.committeememberPeterson, C. G.en
dc.contributor.committeememberWebster, Jackson R.en
dc.contributor.departmentBiologyen
dc.date.accessioned2011-08-22T19:09:13Zen
dc.date.adate2004-10-26en
dc.date.available2011-08-22T19:09:13Zen
dc.date.issued2004-09-06en
dc.date.rdate2006-10-26en
dc.date.sdate2004-10-18en
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
dc.description.degreePh. D.en
dc.format.mediumETDen
dc.identifier.otheretd-10182004-182304en
dc.identifier.sourceurlhttp://scholar.lib.vt.edu/theses/available/etd-10182004-182304en
dc.identifier.urihttp://hdl.handle.net/10919/11284en
dc.publisherVirginia Techen
dc.relation.haspartetd.pdfen
dc.rightsIn Copyrighten
dc.rights.urihttp://rightsstatements.org/vocab/InC/1.0/en
dc.subjectstream structure and functionen
dc.subjectNitrogenen
dc.subjectspiralingen
dc.subjectstream biogeochemistryen
dc.titleNitrogen spiraling in stream ecosystems spanning a gradient of chronic nitrogen loadingen
dc.typeDissertationen
thesis.degree.disciplineBiologyen
thesis.degree.grantorVirginia Polytechnic Institute and State Universityen
thesis.degree.leveldoctoralen
thesis.degree.namePh. D.en

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