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Item The role of stream network nutrient uptake kinetics and groundwater exchange in modifying the timing, magnitude, and form of watershed export(Montana State University - Bozeman, College of Agriculture, 2012) Covino, Timothy Patrick; Chairperson, Graduate Committee: Brian L. McGlynn.; Brian L. McGlynn and Rebecca A. McNamara were co-authors of the article, 'Tracer additions for spiraling curve characterization (TASCC): quantifying stream nutrient uptake kinetics from ambient to saturation' in the journal 'Limnology and oceanography: methods' which is contained within this thesis.; Brian McGlynn and Rebecca McNamara were co-authors of the article, 'Land use / land cover and scale influences on in-stream nitrogen uptake kinetics' in the journal 'Journal of geophysical research - biogeosciences' which is contained within this thesis.; Brian McGlynn and John Mallard were co-authors of the article, 'Stream-groundwater exchange and hydrologic turnover at the network scale' in the journal 'Water resources research' which is contained within this thesis.; Brian McGlynn and Michelle Baker were co-authors of the article, 'Separating physical and biological nutrient retention and quantifying uptake kinetics from ambient to saturation in successive mountain stream reaches' in the journal 'Journal of geophysical research - biogeosciences' which is contained within this thesis.In this PhD dissertation research we sought to elucidate stream network biological and physical influences on hydrological and biogeochemical signatures observed along stream networks and at watershed outlets. Our research indicates that stream nutrient uptake and groundwater exchange processes can modify inputs from terrestrial sources and influence the timing and signature of watershed fluxes. We determined that stream nutrient uptake followed Michaelis-Menten kinetics across a broad range of systems and that land use / land cover change can alter stream nutrient uptake magnitudes. Additionally, we found that watershed structure and network geometry exerted strong controls over sourcewater contributions and streamwater compositions along stream networks and at watershed outlets. Combined, this PhD research suggests that uptake kinetics and hydrologic turnover exert strong controls over streamwater composition and sourcewater contributions, and that physical and biological contributions to total nutrient retention and the dynamic and concentration dependent nature of biological uptake combine to control solute and nutrient signatures. We suggest accurate assessment of total retention across stream reaches and stream networks requires quantification of physical retention and the concentration dependent nature of biological uptake, understanding necessary to help mitigate the potentially deleterious influences elevated nutrient export can have on downstream ecosystems.Item Stream-groundwater interactions in a mountain to valley transition : impacts on watershed hydrologic response and stream water chemistry(Montana State University - Bozeman, College of Agriculture, 2005) Covino, Timothy Patrick; Chairperson, Graduate Committee: Brian L. McGlynn.As mountain headwater catchments increase in size to the meso-scale, they incorporate new landscape elements including mountain-valley transition zones. Mountain-valley transition zones form part of the mountain front, influence groundwater (GW)-stream interactions, and impact hydrologic response and stream water composition. Mountain front recharge (MFR) in mountain-valley transition zones and subsequent GW discharge to streams in the valley bottom are important hydrological processes. These GW-stream interactions are dynamic in both space and time, playing a key role in regulating the amount, timing, and chemistry of stream water reaching the valley bottom. I hypothesize that mountain-valley transitions function as hydrologic and biogeochemical buffers via GW recharge and subsequent GW discharge. More specifically, that streams often recharge GW near the mountain front and receive stored GW further downstream. To investigate these processes I applied physical hydrology techniques, and geochemical hydrograph separations in the Humphrey Creek watershed in southwestern Montana. This allowed me to assess the spatial and temporal variability of mountain front GW recharge and GW-stream interactions across a mountain-valley transition. Geochemical signatures were used to partition stream flow into alpine runoff and GW sources. These results indicate that much of the alpine stream water recharged GW at the mountain front and that stored GW of a different chemical composition sustained down-valley stream discharge. Down-valley stream discharge was dominated by GW inputs and responded to GW stage more closely than upstream reaches. A critical GW stage height was necessary for down-valley channel flow, as this was the only major input to channel flow during early and late season base flow. Conversely, GW contributed little to stream flow in the upper reaches of the study area. GW-stream water exchange served as a flow and geochemical buffer, resulting in significant changes in stream chemistry from the alpine, to the MFR zone, to the valley bottom and muting fluctuations in channel flow, both at high and low flow. Implications are that mountain front GW recharge magnitudes can control valley aquifer storage state which combined with alpine runoff magnitude and valley bottom GW discharge controls stream water quantity and geochemical composition downstream.