Carbon dioxide balance of a tropical peat swamp forest in Kalimantan, Indonesia

Abstract

Tropical peatlands, which coexist with swamp forests, have accumulated vast amounts of carbon as soil organic matter. Since the 1970s, however, deforestation and drainage have progressed on an enormous scale. In addition, El Niñ o and Southern Oscillation (ENSO) drought and large-scale fires, which grow larger under the drought condition, are accelerating peatland devastation. That devastation enhances decomposition of soil organic matter and increases the carbon release to the atmosphere as CO 2 . This phenomenon suggests that tropical peatlands have already become a large CO 2 source, but related quantitative information is limited. Therefore, we evaluated the CO 2 balance of a tropical peat swamp forest in Central Kalimantan, Indonesia, using 3 years of CO 2 fluxes measured using the eddy covariance technique from 2002 through 2004. The forest was disturbed by drainage; consequently, groundwater level (GL) was reduced. The net ecosystem CO 2 production (NEP) measurements showed seasonal variation, which was slightly positive or almost zero in the early dry season, and most-negative late in the dry season or early the rainy season. This seasonality is attributable to the seasonal pattern of climate, tree phenology and fires. Slightly positive NEP resulted from smaller ecosystem respiration (RE) and larger gross primary production (GPP) under conditions of high photosynthetic photon flux density (PPFD) and large leaf area index (LAI). The mostnegative NEP resulted from smaller GPP and larger RE. The smaller GPP was related to high vapor pressure deficit (VPD), small LAI and low PPFD because of smoke from fires. The larger RE was related to low GL. Annual NEP values were estimated respectively as À602, À382 and À313 g C m À2 yr À1 for 2002, 2003 and 2004. These negative NEP values show that the tropical peat swamp forest, disturbed by drainage, functioned as a CO 2 source. That source intensity was highest in 2002, an ENSO year, mainly because of low PPFD caused by dense smoke emitted from large fires.

Opportunities for reducing greenhouse gas emissions in tropical peatlands

“…The 2006 IPCC guidelines follow a stock-difference approach for both mineral and organic soils, which is not appropriate for tropical peatlands because it is impossible to estimate carbon stocks in these systems with any reasonable level of certainty. The emissions factors for drained managed forests on organic soils in the guidelines are significantly lower than those reported for forests converted to plantations or agriculture (29)(30)(31). Tropical peats differ from temperate or boreal peats because they are derived from forest vegetation and are very heterogeneous.…”

“…Tropical peats differ from temperate or boreal peats because they are derived from forest vegetation and are very heterogeneous. The soil surface is often very irregular with large hummocks and hollows (29). Tropical peat soils also have logs and undecomposed branches within them.…”

Status of Peatland Degradation and Development in Sumatra and Kalimantan

“…Jauhiainen et al 2005) and disturbed (e.g. Hirano et al 2007;Jauhiainen et al 2008) conditions are needed for estimation of gas emissions with potentially global consequences. However, the results of small-scale studies cannot be reliably propagated to the regional level without large-scale high spatial resolution assessments of the overall status of degradation and development in the peatland areas.…”

Towards sustainable management of Indonesian tropical peatlands

“…Carbon emission results from peat fires and peat oxidation (Hirano et al 2007). Drained peat swamp forests for other peatland uses contribute to peat fires events and increasing peat oxidation that related to increase of CO 2 emission (Hooijer et al 2010), while the increased frequency and duration of flooding will slow down the processes of oxidation and subsidence (Biancalani and Avagyan 2014).…”