Soil disturbance in wetlands by feral pigs increases greenhouse gas emissions

Abstract. Multiple approaches are needed to decrease greenhouse gas emissions and reduce the pace of climate change. Wetlands are among the most carbon-rich ecosystems on the planet, and when disturbed, they can generate disproportionately high emissions. Invasive hoofed mammals, such as feral pigs (Sus scrofa), cause significant soil disturbances by trampling, grubbing, and digging in wetlands. We tested whether soil disturbances by feral pigs would increase greenhouse gas emissions (carbon dioxide, CO₂, methane, CH₄, and nitrous oxide, N₂O) as a result of reduced soil oxygen and plant cover, and increased nitrogen. Six paired sites were sampled in Kakadu National Park, northern Australia, a site of immense cultural and natural significance. Fluxes of CH₄ were significantly different among treatments, with emissions being higher at disturbed plots (663 ± 740, 54 to 4,820 µg m⁻² hr⁻¹) compared to reference plots (375 ± 292, −8.6 to 1,785 µg m⁻² hr⁻¹). The most notable differences were observed for N2O, with significantly higher emissions at disturbed plots (81 ± 88.7, 26.6 to 548 µg m⁻² hr⁻¹), which were up to an order of magnitude higher than those for the reference plots (11.9 ± 3.0, 2.7 to 20.4 µg m⁻² hr⁻¹). Soil redox values were correlated with emissions in plots disturbed by pigs, with negative values associated with high CH₄ emissions. The highest emissions were found in recently disturbed sites. This study provides another compelling example of how animal populations can significantly impact the carbon cycle at the landscape scale. It also provides evidence for the viability of a carbon methodology to reduce greenhouse gas emissions through feral pig management, which will support both culture and nature.