Catchment controls on mire properties in the post-glacial landscape

Abstract: Mires are key ecosystems in the boreal biome which provide services related to carbon uptake, biodiversity, and regulation of hydrological and biogeochemical cycles. Minerogenic mires are supported by their upslope catchment area and underlying mineral soil, but a more detailed understanding and quantification of landscape drivers behind mire properties is needed. My thesis is focused on catchment controls on mire vegetation, and peat accumulation and expansion rates. The study was conducted in the Sävar Rising Coastline Mire Chronosequence in northern Sweden, where strong isostatic rebound has formed a natural age gradient that can be used for landscape level studies covering the Holocene. Given the similar climate, bedrock, and mineral soil properties across the area, the role of catchment eco-hydrological settings can be distinguished from that of mire ageing. Our results show that mire vegetation and recent nitrogen accumulation rates responded to catchment nutrient support, but older mires with deeper peat were also associated with lower plant productivity. In contrast, recent peat and carbon accumulation rates increased with mire age and a lower catchment supply of nutrients. The increase in peat and carbon accumulation rates with mire age was faster in hummocks than lawns, and after four thousand years hummock accumulation rates exceeded those in lawns. Mires in the area expanded non-linearly across the landscape depending on the availability of suitably wet areas. Mires occupied the wettest locations within one to two thousand years after land exposure and the slightly drier areas within three to four thousand years. Except for mires younger than a thousand years old, mire abundance was controlled by topography, while total mire area increase was a function of time and the formation of larger mire complexes. The results of this thesis contribute to the understanding of mire development at high latitudes and to scaling up our understanding of mire properties to the wider landscape level.