Regional Estimates of CO2 Fluxes and Stock Losses from Drained Uncultivated Peatlands in West Iceland

Wetlands store substantial portions of terrestrial organic carbon. Their drainage threatens this stock, as it converts these ecosystems from being a carbon sink to being a source, emitting CO2 to the atmosphere. Large areas of wetlands within Iceland have been drained for agricultural purposes. To promote actions to halt or decrease the emission of carbon from drained wetlands and other diffuse land use sources, it is important to provide tools to address this and, eventually, other diffuse land use sources at the local scale. The quantification of each source plays a critical role in motivating and rewarding actions to reduce it. Our objective is to develop such a tool. As an example, we focus on drained uncultivated land on organic soils in the Borgarfjördur region in West Iceland. Our data are based on chamber measurements of CO2 fluxes conducted from 2001 to 2009 associated with on-ground monitoring of PAR, soil, and air temperature. Additionally, for this study, we obtained satellite NDVI data available for the region during the same period. In this study, we developed models to convert chamber flux measurements to annual fluxes of GPP and Reco and calculate NEE. The models were run for three years for the measurement sites and an extended area of comparable land in the region, using 30 by 30 m spatial resolution. The models were evaluated towards independent datasets of chamber measurements in the region, returning R2 values of 0.750 and 0.778 for predicted vs. measured GPP and Reco, respectively. The annual NEE of the measurement sites ranged from 1.67 to 7.87 t C ha− 1, emitted in the form of CO2. The segregation of Reco into its components provided an estimate of carbon loss from accumulated soil organic matter (SOM) at 4.21 t C ha− 1, exceeding the NEE of 3.85 t C ha− 1. Within comparable sites in the region, the annual NEE ranged from − 0.20 t C ha− 1 to 8.25 t C ha− 1. The results show both spatial and interannual variability in fluxes, capturing that variability is beneficial both for policymakers and for improving GHG emission inventories. This study demonstrates how relatively low-cost measurements of CO2 fluxes can be scaled up to regional estimates, capturing spatial and temporal heterogeneity in fluxes and evaluating flows to and from ecosystem carbon stocks.