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

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dc.contributor.advisor Dillaha III, Theo en_US
dc.contributor.advisor Benfield, E. F. en_US
dc.contributor.advisor Valett, H. M. en_US
dc.contributor.advisor Peterson, C. G. en_US
dc.contributor.advisor Webster, J. R. en_US
dc.contributor.author Earl, Stevan Ross en_US
dc.date.accessioned 2011-08-22T19:09:13Z
dc.date.available 2011-08-22T19:09:13Z
dc.date.issued 2004-09-06 en_US
dc.identifier.other etd-10182004-182304 en_US
dc.identifier.uri http://hdl.handle.net/10919/11284
dc.description.abstract This 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.medium ETD en_US
dc.publisher Virginia Tech en_US
dc.relation.haspart etd.pdf en_US
dc.rights The 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.uri http://scholar.lib.vt.edu/theses/available/etd-10182004-182304 en_US
dc.subject stream structure and function en_US
dc.subject nitrogen en_US
dc.subject spiraling en_US
dc.subject stream biogeochemistry en_US
dc.title Nitrogen spiraling in stream ecosystems spanning a gradient of chronic nitrogen loading en_US
dc.type Other - Dissertation en_US
dc.contributor.department Biology en_US
dc.description.degree PHD en_US

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