Identifying the role of environmental drivers in organic carbon export from a forested peat catchment

Abstract

Carbon export in streams draining peat catchments represents a potential loss of carbon from long-term stores to downstream aquatic systems and ultimately, through mineralisation, to the atmosphere. There is now a large body of evidence that dissolved organic carbon (DOC) export has increased significantly in recent decades at many sites, although there is still debate about the drivers of this increase. In this study, DOC export and particulate organic carbon (POC) export were quantified from a forested peatland catchment in the west of Ireland over two years at a fine temporal resolution. The principle drivers of change in stream DOC and POC concentrations were investigated using a general additive modelling (GAM) approach. The study period included drought conditions in the early summer of 2010 and clearfelling of some commercial forestry in early 2011. The results indicated that annual loads of 9.5 t DOC km2 year− 1 and 6.2 t POC km2 year− 1 were exported from the catchment in 2010. This combined annual load of 15.7 t C km2 year− 1 would represent between 0.01% and 0.02% of typical estimates for peat soil carbon storage in the region. Soil temperature, river discharge and drought explained 59.7% the deviance in DOC concentrations, while soil temperature, river discharge, and rainfall were the significant drivers of variation in POC concentrations, explaining 58.3% of deviance. Although clearfelling was not a significant factor in either model, large spikes in POC export occurred in 2011 after the first forestry clearance. The results illustrate the complexity of the interactions between climate and land management in driving stream water carbon export. They also highlight the sensitivity of peatland carbon stores to changes in temperature and precipitation, which are projected to be more extreme and variable under future climate scenarios.