Effects of drain blocking and nitrogen deposition on greenhouse gas emissions from peatlands

Abstract

Peatlands cover between 10 – 15 % of the UK landmass, yet contain 50 % of the UK soil carbon store. This is more than any other ecosystem and makes them the most important carbon store in the UK. Peatlands have been impacted by human activities such as drainage, grazing, burning and atmospheric pollution. Some of these activities are believed to have altered the carbon balance of peatlands, potentially causing them to release the carbon they store, exacerbating global warming. The current state of peatlands in the UK is not fully known and the extent to which carbon exchange is impacted by human impacts is not understood. This study uses field measurements and manipulative experiments to investigate the impact of human activities on carbon exchange. CO2 flux measurements were made at an experimental nitrogen addition field site to investigate the impact of atmospheric pollution. The addition of nitrogen was found to have no significant impact on net ecosystem exchange (NEE), ecosystem respiration (ER), or the vegetation community structure at any concentration of nitrogen deposition. A method was determined for estimating the vegetation biomass and subsequently the LAI and NEE based on a non destructive vegetation survey. Peatland drainage was a widespread management practice across peatlands over the past century, however due to concerns about the practice many drains are currently being blocked. Measurements of water table, CO2 and methane fluxes were made at a drained site before and after it was blocked. The drains were found to have a very limited impact upon water table, only reducing the water table by 6.7 cm within 50 cm of the drain and having no significant effect on gas fluxes. The blocking of drains raised the water table within 50 cm of the grip, however did not have any detectable impact on gas fluxes or vegetation. The carbon balance of a pristine ombrotrophic was measured using continuous measurement methods and modelled fluxes to establish whether it was a sink or source of carbon. The site was found to be a sink of 155.5 g m-2 y-1 for CO2 and source of 4.1 g m-2 y-1 CH4. The site was found to be a sink of 49.3 g m-2 y-1 for carbon once CO2 and CH4 were taken into account.