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Please use this identifier to cite or link to this item: http://hdl.handle.net/1807/11285

Title: Spatially Explicit Modeling of Hydrologically Controlled Carbon Cycles in a Boreal Ecosystem
Authors: Govind, Ajit
Advisor: Chen, Jing Ming
Department: Geography
Keywords: hydrology
soil science
carbon cycle
Issue Date: 5-Aug-2008
Abstract: Current estimates of terrestrial carbon (C) fluxes overlook explicit hydrological controls. In this research project, a spatially explicit hydro-ecological model, BEPS-TerrainLab V2.0 was further developed to improve our understanding of the non-linearities associated with various hydro-ecological processes. A modeling study was conducted in a humid boreal ecosystem in north central Quebec, Canada. The sizes and nature of various ecosystem-C-pools were comprehensively reconstructed under a climate change and disturbance scenario prior to simulation in order to ensure realistic biogeochemical modeling. Further, several ecosystem processes were simulated and validated using field measurements for two years. A sensitivity analysis was also performed. After gaining confidence in the model’s ability to simulate various hydrologically controlled ecophysiological and biogeochemical processes and having understood that topographically driven sub-surface baseflow is the main process determining the soil moisture regime in humid boreal ecosystem, its influence on ecophysiological and biogeochemical processes were investigated. Three modeling scenarios were designed that represent strategies that are currently used in ecological models to represent hydrological controls. These scenarios were: 1) Explicit, where realistic lateral water routing was considered 2) Implicit, where calculations were based on a bucket-modeling approach 3) NoFlow, where the lateral sub-surface flow was turned off in the model. In general, the Implicit scenario overestimated GPP, ET and NEP, as opposed to the Explicit scenario. The NoFlow scenario underestimated GPP and ET but overestimated NEP. The key processes controlling the differences were due to the combined effects of variations in plant physiology, photosynthesis, heterotrophic respiration, autotrophic respiration and nitrogen mineralization; all of which occurred simultaneously in different directions, at different rates, affecting the spatio-temporal distribution of terrestrial C-sources or sinks (NEP). From these results it was clear that lateral water flow does play a significant role in the net terrestrial C distribution and it was discovered that non-explicit forms of hydrological representations underestimate the sizes of terrestrial C-sources rather than C-sinks. The scientific implication of this work demonstrates that regional or global scale terrestrial C estimates could have significant errors if proper hydrological constraints are not considered for modeling ecological processes due to large topographic variations of the Earth’s surface.
URI: http://hdl.handle.net/1807/11285
Appears in Collections:Doctoral
Department of Geography - Doctoral theses

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