

@mastersthesis {6592,
	title = {Temporal and spatial scaling of coupled hydrological and biogeochemical processes in river basins},
	year = {2014},
	note = {3646678},
	school = {University of Illinois at Urbana-Champaign},
	type = {phdPh.{D}.},
	address = {Ann Arbor},
	abstract = {The goal of this dissertation is to understand nutrient delivery processes in river networks, including the processes and factors controlling both the flow generation and nutrient retention mechanisms. An analysis framework that synthesizes the bottom-up and top-down approaches is implemented in this dissertation to explore these questions. In the top-down approach, empirical data from several catchments within the continental United States is analyzed to generate patterns across gradients of scale, climate, and topography to guide the study of the underlying mechanisms as well as to serve as the inspiration to generate hypotheses regarding possible explanations of the empirical observations. In the bottom-up approach, models are developed based on the understanding gained in through the data analysis to test hypotheses and to discover previously hidden relationships and laws which could further facilitate future data collection, data analysis and model development. The dissertation is separated into two parts governing the two major perspectives that underpin nutrient transport and transformation processes in river networks: hydrology and biogeochemistry. Part one focuses on how soil moisture and the dominant hydrological processes change across a climate gradient, the factors governing these spatio-temporal patterns, and in particular, the effects of climate (i.e. aridity, seasonality). Analysis of the flow regime curves reveals the dominant runoff generation processes in catchments across the continental United States and is used in the model development that follows. The study of flow recession curves also reveals insights for the future modeling of the storage-discharge relationship governing subsurface stormflow. These studies demonstrate the overall influence of climate (i.e. seasonality and aridity) on the various hydrologic processes through long-term co-evolution of climate, soils, vegetation and topography. With the understanding gained of the processes related to the movement of water, the carrier and controller of nutrients, the second part of the dissertation looks at the nutrient delivery and uptake processes across the river network: the influence of spatial scale on these processes, and the effects of temporal variability of flow inherited from climate. Empirical relationships between several nutrient uptake metrics and the flow condition and nutrient concentration level are derived from field measurements and are incorporated into a coupled hydrology and biogeochemistry model to simulate the nutrient uptake processes across river networks, from the small headwater streams all the way to big rivers. The effect of hydrologic variability inherited from climate on nutrient uptake is then examined. The studies highlighted the contribution of big rivers downstream to overall nutrient uptake and also have emphasized the important role of flow variability on nutrient retention. The results arising from this dissertation research have helped to significantly improve our understanding of nutrient transport and transformation processes across river networks, which could prove extremely useful to government agencies and community organizations on the effective use of land use management and water quality regulation to alleviate water quality problems in rivers and in receiving waters such as the Gulf of Mexico. On the other hand, this work has demonstrated the feasibility and power of the study framework that combines both the bottom-up and top-down approaches to the study of complex environmental problems, and could be adopted in future studies involving hydrologic and/or biogeochemical processes.},
	keywords = {0368:Physical geography, 0388:Hydrologic sciences, 0425:Biogeochemistry, Biogeochemical processes, Biogeochemistry, Earth sciences, Hydrologic processes, Hydrologic sciences, Nutrient delivery, Physical geography, River basin, Spatial scaling, Temporal scaling},
	url = {http://search.proquest.com/docview/1642727911?accountid=14270},
	author = {Ye, Sheng}
}
