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Peatlands are internationally important ecosystems, and play a vital role in carbon sequestration, water provision and global biodiversity. Fire occurs on peatlands worldwide and includes prescribed burning for purposes including agriculture and wildfire control. Many UK blanket peatlands are subject to prescribed burning to encourage production of the game bird red grouse (Lagopus lagopus scotica), but such burning may not be compatible with environmental outcomes related to carbon, water and biodiversity. Vegetation plays a key role in peatland ecosystem services, so evidence of how fire affects vegetation is needed to inform decisions about the future of prescribed burning. The work in this thesis considers vegetation change in the years following prescribed burning, with a focus on peat-forming Sphagnum mosses. A range of approaches including field monitoring and laboratory experiments were used to investigate the key plant taxa affected, timescales of change, and processes responsible for fire impacts. Important findings include differences in vegetation composition between burned and unburned plots on national and regional scales. Evidence of negative impacts of burning on Sphagnum mosses was found, with lower cover on recently burned plots on a national scale, reduced growth in response to fire-induced changes to peat properties, and increased cell damage after high temperature exposure, although ash addition increased growth. Data from a long-running field experiment revealed that fire impacts on Sphagnum can persist for several decades. Timescales of vegetation change were observed to vary between sites, but in general bare peat and acrocarpous mosses were likely to increase temporarily following burning, and a high abundance of graminoids a few years after fire was followed by dwarf shrub dominance in the longer term. These changes are likely to have consequences for peatland ecosystem services.

This thesis sought to improve understanding of the effects of typical management regimes (conventional pasture and traditional hay meadow under agri-environment schemes) in the British upland grasslands and climate change on soil carbon (C) dynamics. Two upland grassland locations in northern England, UK were investigated. Results showed that the upland grasslands were a net atmospheric C sink (1822 – 2758 g CO2-eq m-2 year-1), with a significant SOC stock (59 – 101 Mg ha-1) which was predominantly (60%) protected in the soil mineral mass. The conventional pasture site receiving inorganic nitrogen (N) addition had a significantly higher SOC stock (101 Mg ha-1) and the greatest ecosystem C uptake (2758 g CO2-eq m-2 year-1) compared to all other sites. Experimental summer climate of late 21st Century (+3°C increase in temperature and -23% decrease in precipitation) resulted in a significant decline in the net ecosystem C sink (-13 to -29%) and plant biomass productivity (-29 to -77%) of the grasslands, regardless of management regimes. Overall, the results indicate that both conventional pasture and hay meadow management regimes maintain C sequestration in the upland grasslands, with the hay meadow management being less efficient. Also, warmer climate and drought by the end of the 21st Century will most likely lead to a significant decline in both C sink and forage production in the upland grasslands regardless of management. Moderate levels of inorganic N fertilizers plus organic manures is recommended to enhance biomass production and C sequestration in the traditional hay meadows. In addition, hay mulching is recommended as a viable management option to mitigate against the potential negative effects of climate change on both biomass productivity and C sequestration. Finally, pilot studies on a greater number of managed grasslands are needed to test the effectiveness of the recommended management changes for providing targeted outcomes.

Soils play a significant role in the movement of Dissolved Organic Carbon (DOC) within a catchment and are a major source of DOC to surface waters. Recent DOC increases in some surface waters in Europe and North America could be indicative of changes in soils leading to greater export of DOC. Organo-mineral soils have the ability to act as both sources and sinks for DOC due to the presence of a large organic layer as well as mineral horizon(s). However, the role of these soils in the movement of DOC within catchments requires further research. This study investigated the factors controlling the sorption and release of DOC in organo-mineral soils. Firstly, the sorptive properties of DOC leached from organic horizons beneath Calluna vulgaris (heather), Molinia caerulea (grass) and Picea sitchensis (forest) were investigated using a batch study and three isotherm models. The forest exhibited greatest adsorption to the mineral soil but released DOC with a high specific ultra-violet absorbance (SUVA). Both the heather and grass showed no net adsorption but released DOC with a lower SUVA. Secondly, the Langmuir isotherm was used to derive sorption parameters for 20 mineral soils collected from 11 UK upland sites. The sorption parameters showed no differences by soil type (gleysol or podzol) or by horizon (A, B, E). The maximum sorption capacity (Qmax) was greater for soils beneath graminoids than for soils beneath forest or shrubs. The amorphous forms of aluminium (Alo) were the most significant predictor of Qmax. However, the occurrence of adsorption was controlled by soil pH; adsorption increased with increasing soil pH. The most significant control on desorption within the soils was Alo. Iron content was not a major contributor to sorption within these soils. Thirdly, a column study was carried out to determine the effect of soil solution retention time on the adsorption of DOC to mineral soil. Sorption equilibrium was reached within 24 hours which would suggest that in soils prone to waterlogging most DOC sorption would occur in 24 hours. Additionally it was observed that there is a fixed sorption equilibrium concentration which differs only by DOC source. The work of this thesis suggests that vegetation cover could be used to manage DOC export in soils. The work here also suggests that the recovery of organo-mineral soils from previous acid deposition is likely to be having the effect of enhancing adsorption in the mineral horizons. However, as mineral horizons recover beyond their optimum pH for adsorption then it is likely that greater release of DOC from the mineral horizons will occur and increases in DOC will be observed in the catchments.