| 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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