Soil carbon dioxide emissions from a rubber plantation on tropical peat

Abstract

Land-use change in tropical peatland potentially results in a large amount of carbon dioxide (CO) emissions owing to drainage, which lowers groundwater level (GWL) and consequently enhances oxidative peat decomposition. However, field information on carbon balance is lacking for rubber plantations, which are expanding into Indonesia's peatlands. To assess soil CO emissions from an eight-year-old rubber plantation established on peat after compaction, soil CO efflux was measured monthly using a closed chamber system from December 2014 to December 2015, in which a strong El Niño event occurred, and consequently GWL lowered deeply. Total soil respiration (SR) and oxidative peat decomposition (PD) were separately quantified by trenching. In addition, peat surface elevation was measured to determine annual subsidence along with GWL. With GWL, SR showed a negative logarithmic relationship (p<0.01), whereas PD showed a strong negative linearity (p<0.001). Using the significant relationships, annual SR and PD were calculated from hourly GWL data to be 3293±1039 and 1408±214gCmyr (mean±1 standard deviation), respectively. PD accounted for 43% of SR on an annual basis. SR showed no significant difference between near and far positions from rubber trees (p>0.05). Peat surface elevation varied seasonally in almost parallel with GWL. After correcting for GWL difference, annual total subsidence was determined at 5.64±3.20 and 5.96±0.43cmyr outside and inside the trenching, respectively. Annual subsidence only through peat oxidation that was calculated from the annual PD, peat bulk density and peat carbon content was 1.50cmyr. As a result, oxidative peat decomposition accounted for 25% of total subsidence (5.96cmyr) on average on an annual basis. The contribution of peat oxidation was lower than those of previous studies probably because of compaction through land preparation.

Factors affecting oxidative peat decomposition due to land use in tropical peat swamp forests in Indonesia

“…3d and 4e). Wakhid et al (2017) showed a clear relationship between GWL and PD in a nearby rubber plantation established using heavy machinery after peat compaction; their study site was located 25 km from ours. In their results, the CO2 efflux from PD increased linearly with decreasing GWL (r 2 = 0.94-0.98).…”

“…Then, to understand how the environmental factors affects CO2 fluxes, we compared the results from different types of land use under the same geophysical conditions. Wakhid et al (2017) recently reported both PD and SR for compacted peat in a rubber plantation only 25 km from our observation sites, enabling us to compare our results with data from a plantation. Finally, seasonal variation and annual CO2 emissions were estimated using empirical models.…”

“…Table 4. Comparison of annual carbon dioxide emissions from oxidative peat decomposition with previous studies using the chamber method (revised from Wakhid et al, 2017). Sundari et al (2012) showed the relationships between GWL and total SR at UF and DF using automated chamber data measured in [2004][2005].…”

Oil palm (Elaeis guineensis) production in Indonesia: carbon footprint and diversification options

“…Part of this variation may reflect genuine differences in local contexts but variations in methods and associated biases cannot be excluded. While chamber-based estimates(Wakhid et al, 2017) require…”

“…This recommendation byWösten et al (2008) has been used as a generic policy standard in Indonesia. The rate of CO 2 emissions of large-scale plantations has been widely studied(Page et al, 2011a;Carlson et al, 2015;Sumarga et al, 2016;Wakhid et al, 2017) but little is yet known of the subsidence and emission dynamics in the specific context of smallholder mosaic landscapes. Nonetheless, mandated groundwater levels for rewetted peat landscapes are applied to smallholder landscapes as well as plantations.…”