Drivers of peatland CO₂ balance: a fusion of UAV remote sensing and micrometeorology

Abstract

Northern peatlands are carbon stores of global significance, having accumulated around one third of global soil carbon in the form of peat since the Holocene. Carbon storage in these ecosystems is regulated by their cool, wet climatic conditions and key vegetation species (e.g. Sphagnum mosses) which inhibit the decomposition of organic matter.

As such, peatland ecosystems are vulnerable to climate change. Studies conducting flux measurements at the ecosystem- (100-106 m²) and microsite-scales (0.1-1 m²) report a large inter-annual variability in the Net Ecosystem Exchange (NEE) of CO2, and find that some peatlands can shift from functioning as a net sink of CO2 to a net source between years. This temporal variability has been linked to the impact of weather events (e.g. drought, heatwaves), although studies also highlight the important role of vegetation phenology (i.e. the seasonal lifecycle of plants). Disentangling the drivers of inter-annual variability in CO2 exchange is challenging; hampered by both a lack of long-term monitoring data and the strong spatial heterogeneity characterising peatland environments at scales of < 1 m. To date, monitoring of peatland vegetation has been particularly limited, with studies often employing datasets of coarse spatial and temporal resolution (e.g. aerial and satellite imagery) to examine broad changes in vegetation type. Recent advances in the development of Uncrewed Aerial Vehicle (UAV) platforms however make it possible to collect data at ultra-high spatial resolution, and show much potential for improving current understanding of peatland carbon dynamics and predictions of future change. This thesis examines centimetre-resolution multispectral UAV data and CO2 flux data collected over four years at a Scottish temperate peatland. These data are used to explore: (i) the suitability of ultra-high resolution UAV data for mapping peatland vegetation; (ii) temporal and spatial variability in CO2 fluxes; and (iii) the role of phenology and weather in modulating peatland carbon dynamics.