The impact of Indonesian peatland degradation on downstream marine ecosystems and the global carbon cycle.

Tropical peatlands are among the most space-efficient stores of carbon on Earth containing approximately 89 Gt C. Of this, 57 Gt (65%) are stored in Indonesian peatlands. Large-scale exploitation of land, including deforestation and drainage for the establishment of oil palm plantations, is changing the carbon balance of Indonesian peatlands, turning them from a natural sink to a source via outgassing of CO2 to the atmosphere and leakage of dissolved organic carbon (DOC) into the coastal ocean. The impacts of this perturbation to the coastal environment and at the global scale are largely unknown. Here, we evaluate the downstream effects of released Indonesian peat carbon on coastal ecosystems and on the global carbon cycle. We use a biogeochemical box model in combination with novel and literature observations to investigate the impact of different carbon emission scenarios on the combined ocean-atmosphere system. The release of all carbon stored in the Indonesian peat pool, considered as a worst-case scenario, will increase atmospheric pCO2 by 8 ppm to 15 ppm within the next 200 years. The expected impact on the Java Sea ecosystems is most significant on the short term (over a few hundred years) and is characterized by an increase of 3.3% in phytoplankton, 32% in seagrass biomass, and 5% decrease in coral biomass. On the long term, however, the coastal ecosystems will recover to reach near pre-excursion conditions. Our results suggest that the ultimate fate of the peat carbon is in the deep ocean with 69% of it landing in the deep DIC pool after 1000 years, but the effects on the global ocean carbonate chemistry will be marginal.