Effect of groundwater level fluctuation on soil respiration rate of tropical peatland in Central Kalimantan, Indonesia

Soil respiration (SR) rate was measured at the burned land (BL), the cropland (CL), the forest land (FL) and the grassland (GL) of a tropical peatland in Central Kalimantan, Indonesia from 2002 to 2011 for the purpose of analysis with a relation to the drying and rewetting. The SR rate was fitted with groundwater level (GWL) to the equation of log(SR) = alpha -beta x GWL using hierarchical Bayesian analysis where alpha and beta were regression coefficients classified by GWL changing directions (drying, rewetting and fluctuating), water-filled pore space (WFPS) ranges in topsoil (low 0-0.54, intermediate 0.54-0.75 and high 0.75-1 m(3) m(-3)), and land uses (BL, CL, FL and GL). SR rate (Mean +/- SD, mg C m(-2) h(-1)) was the significantly largest in the CL (333 +/- 178) followed by GL (259 +/- 151), FL (127 +/- 69) and lastly BL (100 +/- 90). In the CL, the significantly larger SR rate was found in the rewetting period than in the drying period in the high WFPS range. Also, the significantly steeper slope (beta) in the rewetting period was obtained in the high WFPS range than in the drying period. These results suggested that the rewetting of peatland enhanced the SR rate rapidly in the CL, and that the further rise of GWL decreased the SR rate. In contrast, the SR rate in the rewetting period was significantly smaller than in the drying period in the BL in the high WFPS range, because the BL in the high WFPS range was flooded in most cases. The SR rate in the rewetting period was not significantly different from the drying period in the FL and GL. All of beta were significant in the high WFPS range in all land uses, but not in the low-intermediate WFPS ranges, suggesting that GWL was not controlling factor of the SR rate when the GWL was deep due to the disconnection of capillary force under dry conditions. According to the results of correlation analysis of the alpha and beta, the a was significantly correlated with relative humidity, soil temperature and soil pH, suggesting that the a was enhanced by dry condition, high soil temperature and neutralization of soil acidity, respectively. The beta was significantly correlated with exchangeable Na+ and Mg2+ in the soil, but the reason was not clear. In conclusion, SR rate was enhanced by rising GWL with rewetting in the CL in the high WFPS ranges as well as by deepening GWL.