Fluvial organic carbon fluxes from oil palm plantations on tropical peatland

Abstract

Intact tropical peatlands are dense long-term stores of carbon. However, the future security of these ecosystems is at risk from land conversion and extensive peatland drainage. This can enhance peat oxidation and convert long-term carbon sinks into significant carbon sources. In Southeast Asia, the largest land use on peatland is for oil palm plantation agriculture. Here, we present the first annual estimate of exported fluvial organic carbon in the drainage waters of four peatland oil palm plantation areas in Sarawak, Malaysia. Total organic carbon (TOC) fluxes from the plantation second-and third-order drains were dominated (91 %) by dissolved organic carbon (DOC) and ranged from 34.4 ± 9.7 C m −2 yr −1 to 57.7 %, 16.3 g C m −2 yr −1 (± 95 % confidence interval). These fluxes represent a single-year survey which was strongly influenced by an El Ninõ event and therefore lower discharge than usual was observed. The magnitude of the flux was found to be influenced by water table depth, with higher TOC fluxes observed from more deeply drained sites. Radiocarbon dating on the DOC component indicated the presence of old (pre-1950s) carbon in all samples collected, with DOC at the most deeply drained site having a mean age of 735 years. Overall, our estimates suggest fluvial TOC contributes ∼ 5 % of total carbon losses from oil palm plantations on peat. Maintenance of high and stable water tables in oil palm plantations appears to be key to minimising TOC losses. This reinforces the importance of considering all carbon loss pathways, rather than just CO 2 emissions from the peat surface, in studies of tropical peatland land conversion.

Peatland Contribution to Stream Organic Carbon Exports From a Montane Watershed

“…Quantified over the 3‐year period, POC exports account for 17% ± 2% of the TOC exports at the outlet of the Bernadouze peatland. This is a relatively high ratio since typical values range from 0.6% ((Laudon et al, ) in boreal peatlands, to 5% (Dinsmore et al, ) in a northern temperate peatland and from 2% to 8% (Cook et al, ; Moore et al, ) in tropical peatlands. Higher POC export ratios from peatland have already been reported in the literature by Pawson et al () who found a 40% ratio from an eroded blanket peatland in the UK and by Ryder et al () who reported a similar ratio in a forested peatland using high‐frequency monitoring.…”

From canals to the coast: dissolved organic matter and trace metal composition in rivers draining degraded tropical peatlands in Indonesia

“…The fluorescence index was calculated as defined by McKnight et al (2001) and adapted by Jaffé et al (2008): by the ratio of the fluorescence intensity at 470 nm to the fluorescence intensity at 520 nm for a 370 nm excitation. The shape of the excitation spectra was checked following the recommendation of Cory et al (2010). The PARAFAC analysis (parallel factor analysis; Bro, 1997) was performed on all samples using the PROGMEEF program in MATLAB (Luciani et al, 2008).…”

An assessment of oil palm plantation aboveground biomass stocks on tropical peat using destructive and non-destructive methods

“…Prior to conversion the site was covered in logged mixed peat swamp forest (PSF). Land preparation included the removal of remaining large trees and vegetation, the establishment of a drainage system and peat compaction using heavy machinery 31 . OPs are planted at a density of 160 palms per hectare and at the time of measurement ranged from 3 to 12 years after planting (YAP).…”

“…OP plantations on peat are markedly different to those on mineral soils with potential impacts on AGB stock estimations. Following the clearance of forest biomass, peatlands are drained to an optimum water table depth 0.4-0.6 m from the peat surface to allow cultivation [31][32][33] . Peat bulk density is increased to ~0.20 g cm −1 by mechanical compaction using heavy machinery, often including the compaction of residual forest material into the peat 31,34,35 .…”

“…Following the clearance of forest biomass, peatlands are drained to an optimum water table depth 0.4-0.6 m from the peat surface to allow cultivation [31][32][33] . Peat bulk density is increased to ~0.20 g cm −1 by mechanical compaction using heavy machinery, often including the compaction of residual forest material into the peat 31,34,35 . This increases the load-bearing capacity of peat soils and improves the anchorage of OPs which allocate a relatively small proportion of total biomass to belowground root systems 11,[32][33][34] .…”