<p>Tropical peat swamp forests hold about 15&#8211;19% of the global organic carbon (C) pool of which 77% is found in Southeast Asia. Nonetheless, these ecosystems have been drained, exploited for timber and land for agriculture, leading to frequent fires in the region. Fire alters the physico-chemical characteristics of peat as well as the hydrology, which may convert these ecosystems into a source of C for decades as C emissions to the atmosphere exceeds photosynthesis.</p><p>To understand the long-term impacts of fire on C cycling, we investigated C emissions in intact and degraded PSFs in Brunei Darussalam, which has experienced 7 fires over the last 40 years. We quantified the magnitude and patterns of C loss (CO<sub>2</sub>, CH<sub>4, </sub>and Dissolved Organic carbon) and soil-water quality characteristics along with continuous monitoring of soil temperature and water table level from June 2017 to January 2019. To investigate the age and sources of C contributing to ecosystem respiration (R<sub>eco</sub>) and CH<sub>4</sub>, we used natural tracers such as <sup>14</sup>C.</p><p>We observed a major difference in the physico-chemical parameters, which in turn affected C dynamics, especially CH<sub>4</sub>. In burnt areas (7.8&#177;2.2 mg CH<sub>4 </sub>m<sup>-2</sup> hr<sup>-1</sup>) the CH<sub>4</sub> emission was approximately twice compared to the intact peat swamp forest (4.0&#177;2.0 mg CH<sub>4 </sub>m<sup>-2</sup> hr<sup>-1</sup>) due to prolonged higher water table creating optimum methanogenesis conditions. On the contrary, R<sub>eco</sub> did not show a significant difference between burnt (432&#177;83 mg CO<sub>2 </sub>m<sup>-2</sup> hr<sup>-1</sup>) and intact areas (359&#177;76 mg CO<sub>2 </sub>m<sup>-2</sup> hr<sup>-1</sup>). Further, radiocarbon (<sup>14</sup>C) analysis showed an overall modern signature for both CO<sub>2 </sub>and CH<sub>4</sub> fluxes implying a microbial preference for the more labile C fraction in solution.</p><p>With frequent fires and more flooding in the future, these degraded tropical peat swamp forests areas may remain a hot spot of C emissions as suggested by our findings.</p>
Dissolved organic carbon and physicochemical variables of peat water in tropical peat swamp forests
