Quantifying the global N2O emissions from natural ecosystems using a mechanistically-based biogeochemistry model
Abstract
Nitrous oxide (N2O) has a great influence on atmospheric chemistry and climate. It is not only a major greenhouse gas, but also one of the largest ozone-depleting substances emitted from the biosphere. Process-based biogeochemistry modeling constrained by site-level observations is a feasible approach to quantifying its emissions at large temporal and spatial scales. This study developed a process-based biogeochemistry model of N2O emissions based on an extant biogeochemistry model, the Terrestrial Ecosystem Model (TEM). The model development includes: 1) incorporating the effects of physical conditions on both nitrification and denitrification and 2) implementing principles of the stoichiometry of carbon and nitrogen dynamics in soils. To simulate the global-scale emission, model parameterizations were first conducted using observation data at 11 sites. The model was then used to quantify N2 O emissions at these sites for the period during 1980-2010, driven with data of climate, soils, vegetation, and topography. Finally, the parameterized model simulated global soil N2O emissions for the 20th century. The model sensitivity to parameters and major input data was also conducted. Parameters rpctp, bpctp, Kntf, k and pn2 are influential in model simulations and the variation of rpctp, bpctp (parameters related to precipitation and soil moisture) and Kntf (rate for nitrification) are large. Considering the carbon limitation, a sensitivity analysis suggested that the N2O emissions can change 10-50% depending on sites by varying climate inputs by 20%. Without considering carbon limitation in the model, N2O emissions are increased by 10-30%. These sensitivities vary over season and region. Simulations indicate that there is a slightly decreasing trend form 1900 to 2000 for global N2O emissions. The emissions in 1900 are 1.92 Tg N2O month-1 in summer (July) and 1.46 Tg N2O month-1 in winter (February) , while in 2000 are 1.30 Tg N2O month-1 in summer (July) and 1.07 Tg N2O month-1 in winter (January) respectively. Among all the 11 vegetation types, boreal forests contribute to the most emission because they occupy a large area (45oN north). Considering different latitudes, tropical areas (23.5°N~ 23.5°S) emit more than half of the global emission, because of their warm temperature and moist soils. My future study will improve the representation of microbial dynamics including microbial traits and their effects on N2O emissions in the model. The model will then be used to analyze how global N2O emissions from natural ecosystem soils will change during the 21st century.
Degree
M.S.
Advisors
Zhuang, Purdue University.
Subject Area
Biogeochemistry|Environmental science
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