Effects of Land Use Change From Temperate Grassland to Miscanthus on Aspects of Hydrology and Greenhouse Gas Emissions

Crynodeb

This thesis investigates implications of land conversion from agricultural grassland to the bioenergy crop Miscanthus on soil nitrous oxide (N2O) emissions, soil carbon stocks (SOC), and hydrology. To address concerns of negative impacts on SOC, soils (0-30 cm) were sampled twelve years (T12) after conversion to Mxg and four hybrids. T12 SOC was not different to six year post-planting stocks, but 8 Mg C ha-1 lower than pre-planting. N2O fluxes during conversion are poorly studied therefore commercially available M. x giganteus (Mxg) and a novel hybrid were planted using different tillage methods in a randomised plot trial with an un-cultivated pasture control. Fluxes recorded using static chambers over the first two years revealed no difference between cultivation methods. However, emissions from the Miscanthus plots were 550-819% higher than the control in the first year. Evapotranspiration is important in hydrology. Compared to five years of eddy covariance data from a Mxg plantation the Penman-Monteith model provided the closest estimate of four evapotranspiration formulae tested. New seasonal crop coefficient values are presented: 0.63 (early), 0.85 (main), 1.57 (late), and 1.12 (winter). Canopy precipitation interception (Ci) was estimated as 24% (obtained over nine months using stem-flow, through-flow, and rain gauges). Using the Soil Water Assessment Tool (SWAT) hydrological changes following conversion of 50% and 25% of pasture in west Wales to Mxg or short rotation coppice (SRC) were investigated. Soil water content and streamflow were not significantly changed. Surface runoff was reduced for both crops (by up to 40%). Evapotranspiration was increased with SRC (by up to 5%), and reduced with Mxg (by up to 2%). The need to incorporate conversion related changes in N2O fluxes and SOC into lifecycle analysis assessments is demonstrated. Whilst overall changes to hydrology were minimal, Miscanthus Ci and reductions in surface runoff could benefit flood mitigation schemes.

Dyddiad Dyfarnu	2019
Iaith wreiddiol	Saesneg
Sefydliad Dyfarnu	Prifysgol Aberystwyth
Goruchwyliwr	Iain Donnison (Goruchwylydd), Jon McCalmont (Goruchwylydd), Rebecca Rowe (Goruchwylydd) & Niall McNamara (Goruchwylydd)