Eddy covariance flux measurements of net ecosystem carbon dioxide exchange from a lowland peatland flux tower network in England and Wales

摘要

Peatlands store disproportionately large amounts of soil carbon relative to other terrestrial ecosystems. Over recentuddecades, the large amount of carbon stored as peat has proved vulnerable to a range of land use pressures as welludas the increasing impacts of climate change. In temperate Europe and elsewhere, large tracts of lowland peatlandudhave been drained and converted to agricultural land use. Such changes have resulted in widespread losses ofudlowland peatland habitat, land subsidence across extensive areas and the transfer of historically accumulated soiludcarbon to the atmosphere as carbon dioxide (CO2). More recently, there has been growth in activities aimingudto reduce these impacts through improved land management and peatland restoration. Despite a long history ofudproductive land use and management, the magnitude and controls on greenhouse gas emissions from lowlandudpeatland environments remain poorly quantified.udHere, results of surface-atmosphere measurements of net ecosystem CO2 exchange (NEE) from a networkudof seven eddy covariance (EC) flux towers located at a range of lowland peatland ecosystems across the UnitedudKingdom (UK) are presented. This spatially-dense peatland flux tower network forms part of a wider observationudprogramme aiming to quantify carbon, water and greenhouse gas balances for lowland peatlands across theudUK. EC measurements totalling over seventeen site years were obtained at sites exhibiting large differences inudvegetation cover, hydrological functioning and land management.ududThe sites in the network show remarkable spatial and temporal variability in NEE. Across sites, annualudNEE ranged from a net sink of -194 ±38 g CO 2-C m-2 yr-1 to a net source of 784 ±70 g CO2-C m-2 yr-1. Theudresults suggest that semi-natural sites remain net sinks for atmospheric CO2. Sites that are drained for intensiveudagricultural production range from a small net sink to the largest observed source for atmospheric CO2 within theudflux tower network. Extensively managed grassland and a site that was restored from intensive arable land useudrepresent modest CO2 sources. Temporal variations in CO2 fluxes at sites with permanent vegetation cover areudcoupled to seasonal and interannual variations in weather conditions and phenology. The type of crop producedudand agricultural management drive large temporal differences in the CO2 fluxes of croplands on drained lowland peat soils. The main environmental controls on the spatial and temporal variations in CO2 exchange processes will be discussed.