Soil carbon dioxide emissions from a rubber plantation on tropical peat

• Published in: The Science of the total environment Vol. 581-582; pp. 857 - 865
• Main Authors: Wakhid, Nur, Hirano, Takashi, Okimoto, Yosuke, Nurzakiah, Siti, Nursyamsi, Dedi
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.03.2017
• Subjects: Chamber method; Groundwater level; Oxidative peat decomposition; Soil respiration; Subsidence; Trenching; Oxidative peat decomposition; Subsidence; Soil respiration; Chamber method; Groundwater level; Trenching
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2017.01.035

Land-use change in tropical peatland potentially results in a large amount of carbon dioxide (CO2) 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 CO2 emissions from an eight-year-old rubber plantation established on peat after compaction, soil CO2 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±214gCm−2yr−1 (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−1 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−1. As a result, oxidative peat decomposition accounted for 25% of total subsidence (5.96cmyr−1) 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. CO2 efflux from peat soil through oxidative peat decomposition showed a clear seasonality in reverse parallel with groundwater level (GWL) from December 2014 through December 2015 during a strong El Ni no year (the left panel (a)). The strong linearity between soil CO2 efflux and GWL indicates that oxidative peat decomposition can be simply assessed from GWL (the right panel (b)). Each soil CO2 efflux is the mean of three trenching plots. [Display omitted] •CO2 efflux through peat oxidation was directly measured in a strong El Niño year.•Soil CO2 efflux showed negative relationship with groundwater level.•Oxidative peat decomposition accounted for 43% of total soil respiration.•Peat elevation varied seasonally in parallel with groundwater level.•The contribution of peat oxidation to subsidence was 25% on average.