Saltwater intrusion may aggravate carbon loss from tropical peatlands

Tropical peatlands, covering approximately 23 million hectares, constitute 6% of the global peatlands, predominantly situated in low-lying coastal regions of Indonesia, Malaysia, Borneo, and Papua. Unfortunately, due to land-use change and accompanying subsidence, these low-lying coastal peatlands may be inundated with seawater due to sea level rise in response to climate warming in the coming decades. This would not only result in carbon losses in fluvial form but may also alter the biogeochemistry of peat, thereby affecting the peat decomposition process. Therefore, in this peat incubation study, we attempted to simulate the effect of saltwater intrusion on CO₂ emissions under a factorial setup of two salinity levels (15 ppt, 30 ppt), tidal cycle (high tide as flooded peat vs low tide as mesic peat), and labile carbon mimicking plant root exudates (in the form of glucose addition @ 0.1 mgC/g of peat/day) with peat incubated at 28 °C (the long-term average temperature at site).

            We found that salinity and carbon addition significantly (p < 0.01) affected the rate of CO₂ emissions with the highest mean values for treatment with 30 ppt salinity (251.7 ± 61.3 mgCO₂/g of peat/hr), which was approximately three times higher than the control (72.3 ± 9.3 mgCO₂/g of peat/hr). Similarly, we found that the mesic peat (reflecting low tide) showed almost twice the mean CO₂ values (150 ± 36 mgCO₂/g of peat/hr) compared to flooded peat (79.9 ± 15.1 mgCO₂/g of peat/hr). These results underscore the vulnerability of these ecosystems to future sea level rise, potentially transforming them into a significant carbon source. The urgency to conserve these vital terrestrial carbon reserves is further emphasized by the implications of our study, emphasizing the need for proactive measures to mitigate the impact of land use and climate change on tropical peatlands.