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Pow, Patrick Ka Chun

University of British Columbia

Agricultural croplands can be significant sources of greenhouse gases (GHGs), including carbon dioxide (CO₂), nitrous oxide (N₂O), and methane (CH₄) and are estimated to contribute substantially to global GHG emissions, which has implications for future climate change. In Canada, there has been some evidence that suggests agricultural lands are sequestering carbon (C), which may offset the emission of non-CO₂ agricultural GHGs. This thesis quantifies the net ecosystem carbon balance (NECB), the water balance, and the net GHG balance (NGB) using eddy-covariance (EC) measurements for an intensively managed grassland in Agassiz, British Columbia, Canada. While EC was the primary method used to determine annual mass exchange, the flux-gradient (FG) method was implemented concurrently to assess the viability of flux-profile relationships for determining the fluxes of CO₂, N₂O, and water vapour. In Chapter 2, the NECB of the intensively managed grassland was determined and it was found that C was lost from the field annually, which has implications for GHG mitigation. In Chapter 3, water vapour flux was revisited to calculate the water balance of the field and to quantify the degree to which the field exerted physiological control over evapotranspiration (ET). Surface conductance (gs) was modeled using the Jarvis-Stewart (JS) style mixed multiplicative (MM) and Ball-Woodrow-Berry (BWB) models, and in addition to using gs, ET was also modeled using a modified Priestley-Taylor α approach. In Chapter 4, the NECB was combined with measurements of N₂O and CH4 to determine the NGB which showed that harvesting, slurry manure application, and climate had strong influences on net GHG emissions. In Chapter 5, simultaneous measurements of vertical mixing-ratio gradients and fluxes of CO₂, N₂O, and water vapour above the forage field showed good correspondence between FG- and EC-measured fluxes. Chapter 5 also indicated that FG-measured fluxes measured with the assumption of trace-gas similarity was less variable on a half-hourly basis compared to using the widely accepted sensible heat similarity function with its empirical stability correction when both methods were compared to EC-measured fluxes.

Text

2024-08-29

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/89081

Soil Science

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/