Geography and Geographic Information Science

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Sheng Ye - Effect of Seasonality on Dissolved Nutrient Transformation and Transport over Hillslope to River Basin Scales

Event Type
Geography and Geographic Information Science
219 Davenport Hall
Feb 15, 2013   3:00 - 4:00 pm  
Matt Cohn

Nutrient transformation, retention, and transport from hillslopes to the river network are moderated by climatic, topographic, hydrological and biogeochemical processes. Modeling of the attenuation and aggregation of nutrient loads requires dynamic coupling of hydrology and biogeochemistry in the soil at local scale and then its propagation and reach-scale attenuation along the rivet network. Previous work has emphasized the significant influence of climate seasonality on flow generation mechanisms, which interacts closely with nutrient cycle processes in the soil and in the channel. The focus of this proposal is to understand the nutrient cycling from point, to hillslope and then to catchment scale, including what role hydrological seasonality, inherited from climate, plays in the nutrient cycling. Both empirical data analysis and physical-based model simulations would be used for both flow and dissolved nutrient (i.e. nitrogen) transport in soil and in the river network. Daily flow data along with soil properties and other landscape characteristics will be examined in 428 MOPEX catchments across the continental United States to derive empirical regressions between catchment characteristics and storage-discharge relationships. A comparative modeling approach is then adopted to evaluate the dominant flow generation processes that can help interpret the flow regimes in these catchments that have resulted from their co-evolution in response to climate. The modeling approach starts with a simple two-stage bucket model, which is systematically enhanced through addition of new processes on the basis of model performance assessment in relation to observations. Empirical data analysis of the dissolved nutrient load in several LTER sites across the country along a gradient of climates will be conducted to generate insightful patterns of the effects of seasonality on nutrient cycle at the hillslope scale. These patterns will then be interpreted through the use of a coupled hillslope hydrological (adapted from the previous hydrology model) and biogeochemical model. This coupled model will be used to describe the dissolved nutrient cycling in soil and to estimate their loading to streams, which will then be used as input to the dynamic hydrologic network model, which is coupled a transient storage zone solute transport model, to simulate nutrient retention processes during transient flow events at the river basin scale. Together, these coupled hydrologic and biogeochemical models will be able to give a broad perspective of dissolved nutrient transformation and transport processes from terrestrial landscapes to river outlet, across a range of scales. Empirical patterns learned from the differences among a range of catchments, and across  a range of spatial scales, will shed light on what kind of model is best for such applications, which processes could be neglected, and which dominant processes must be explicitly resolved in the simulations.

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