Dissertation

Modelling the global atmospheric methane uptake by soils in the past, present and future

Murguia-Flores, Fabiola

2019

Overview

Soil bacteria known as methanotrophs are the only biological sink for atmospheric methane (CH4). Soil methanotrophy is controlled by a plethora of factors, including temperature, soil texture, moisture and nitrogen inputs, resulting in spatially and temporally heterogeneous rates of soil methanotrophy across the globe. As a consequence, the exact magnitude of the global soil sink, its temporal and spatial variability and the attribution of the main drivers of change, remain poorly constrained. For this reason, a new model to estimate global atmospheric CH4 uptake by the soil MeMo (Methanotrophy Model) was developed by introducing several advances (i.e the effect of N input via fertilizers) to previous existing models in the light of recent findings. The improved structural and parametrical representation of key drivers of soil methanotrophy in MeMo results in a better fit to observational data in a latitudinal distribution comparison with previous models, representing the first validation of global methanotrophy models. MeMo was then employed to simulate and quantify the uptake of atmospheric CH4 by soils at the global scale through different time periods. The new model runs showed a constant increase in global CH4 uptake since the last glacial maximum to the preindustrial era (from 7 to 17 Tg CH4 y-1), a sharp increase in the last 100 years (from 17-35 Tg CH4 y-1) and likely increase in the future, depending on the scenario (from 23-89 Tg CH4 y-1). The changes were further attributed to fluctuations in atmospheric CH4 concentration during the paleo-record and the last century, however in recent decades temperature and nitrogen inputs started to have a larger influence on regional trends which are likely to be more pronounced in future RCPs.

• Publisher: ProQuest Dissertations & Theses