Impacts of warming, drought and sea level rise on ombrotrophic peatlands

Kay, Martin (2019) Impacts of warming, drought and sea level rise on ombrotrophic peatlands. Doctoral thesis (PhD), Manchester Metropolitan University.

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Abstract

Northern ombrotrophic peatlands have sequestered and stored carbon in their soils over millennia, during a period of relatively stable, long term climatic conditions. Global climate change, including increasing mean annual temperatures, increased frequency of summer droughts and increased likelihood of seawater flooding poses threats to the balance of conditions that peatlands require to continue performing these ecosystem services. This research was based at Cors Fochno lowland raised bog in Ceredigion, West Wales, UK. As a temperate maritime peatland on the edge of the ecosystem’s bioclimatic envelope and lying within one km of the coastline of the Irish Sea, it offers an ideal opportunity to investigate peatland responses to the impacts of climate change; in particular responses to seawater flooding, increased mean annual temperatures and drought events. In laboratory conditions, two Sphagnum moss species (Sphagnum pulchrum and Sphagnum cuspidatum) were immersed in seawater for 72 hours, in otherwise optimised growth conditions, in order to identify photosynthetic responses to inundation. Measurements following removal of the seawater showed both species’ photosynthetic rates declined sharply following treatment, with no signs of recovery. When in-situ peat monoliths with intact vegetation were flooded with seawater, the rate of net ecosystem CO2 exchange was reduced, and methane emissions to the atmosphere were also inhibited. Damage to vegetation was evident, resulting in an overall reduction of both CO2 and CH4 exchange from the peatland to the atmosphere. In another long-term field experiment manipulating peatland plots with passive warming and summer droughts, short-term carbon dioxide gas flux responses were measured during an enforced drought. Net ecosystem exchange flux rates were significantly lower in combined warm and drought treatments than controls, indicating that the longer-term effects of the treatment may lead to a shift from a CO2 sink to a CO2 source. This body of work provides new data for a baseline of peatland and Sphagnum responses to seawater inundation, adding to the developing body of evidence on combined temperature and hydrology impacts on carbon gas fluxes, which can aid in the development of management policies to mitigate the negative impacts of climate change.