Fluxes of greenhouse gases in an anthropogenic peatland of Chiloé island under different types of use

Abstract

Peatlands are wetlands of global importance because they are large reservoirs of carbon (C) and water. Permanently waterlogged soils in peatlands generate an anoxic environment, which decreases the rate of decomposition and favors accumulation of organic matter. However, changes in environmental factors can alter the decomposition process and the magnitude of fluxes of the greenhouse gases (GHG) carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O). In Chile, peatlands are distributed from 39° to 55° S latitude, including postglacial and comparative young anthropogenic peatlands dominated by Sphagnum magellanicum moss. Within this range of distribution, peatlands in Chiloé Island are expected to suffer the greatest changes in temperature and precipitation due to the ongoing climate change. The previous studies on the field are concentrated on Northern Hemisphere thus there are uncertainties about ecohydrological response of southern peatlands to the climate change and their role in the GHG balance. In addition, some anthropogenic peatlands in this area are under agricultural use, being exposed to activities such Sphagnum moss harvesting and cattle grazing. These activities alter vegetation cover and soil compaction, but it is unknown what will be the effect of this process on GHG emissions. The aim of this study was to estimate GHG fluxes in an anthropogenic peatland in Chiloé Island, evaluate what is their relation with environmental factors and compare GHG balance between agricultural land use, including moss harvesting and cattle grazing, and conservation land use, where only tourisms and scientific activities are practiced. We selected an anthropogenic peatland located in the north of Chiloé Island. This peatland is physically divided in two sections, one section is under strict conservation use and the other is under agricultural use. Fluxes of CO2, gross primary productivity (GPP) and ecosystem respiration (Reco), and net ecosystem exchange of CO2 (NEE) were estimated using the Eddy covariance technique. Fluxes of CH4 and N2O were estimated using a closed chamber system and a spectroscopic gas analyzer. Simultaneously, environmental factors were sampled. Correlation analysis and different models were constructed to evaluate the relation of GHG fluxes with environmental factors. GHG balance was estimated as the summation of GHG annual fluxes in CO2 equivalent For the study period, the peatland section under conservation use acted as a larger sink of CO2 than the agricultural managed area. The peatland under conservation use showed higher values of GPP, and the grazed and harvested area showed higher values of Reco. The main environmental drivers of GPP were temperature and photosynthetically active radiation, and the main drivers for Reco were water table depth and soil water content. Both land use sections of the anthropogenic peatland acted as a source of CH4, however, agricultural area was three times greater source than the conservation area. Fluxes of CH4 have a positive relation with total nitrogen in soil and the coverage of Juncus procerus, plant species that have aerenchymous tissue. The results of this study suggest that conservation section of the peatland acted as a sink of N2O in contrast to the agricultural use area which acted as a source of N2O. Nevertheless, this difference was not statistically significant. In addition, no significant relation was found between N2O fluxes and the environmental variables measured in this study. After de GHG balance estimation, we determined that conservation land use section of the peatland acted as a sink of GHG and the agricultural managed section acted as a source of GHG. Land uses on anthropogenic peatland generated significant differences on their GHG fluxes and balance. Agricultural land use reduce the C sink capacity. Type of land use also generate differences on CH4 and N2O fluxes. Changes on vegetation and soil conditions due to the agricultural land use could modify the GHG balance and transform the anthropogenic peatland from a sink to a source of GHG.