ACIDIFYING PROCESSES IN PEAT ON CULTIVATED AND FIRE-DAMAGED TROPICAL PEATLANDS

摘要

Previous study showed no significant change in terms of peat pH in a part of the study on the impact of agricultural practice and fire damage on peat characteristics. However, it was assumed that chemical processes associated with the pH state may shift in different modes. The present study monitored acidifying processes in peat on selectively logged peat forest, maize-cultivated peatland, and fire-damaged peatland. Single processes of all acidifying processes were quantified using input-output functions of ions contained in system components. The ecosystems studied were assumed to be a closed system such that the main input of ions was from rainfall and throughfall. Output flux was measured in soil solution collected by ceramic tube lysimeter. Acidifying processes of the top peat layer in all peatland types were dominated by dissociation of organic acids (73-94% of all processes), followed by nitrification (15.4%), and proton deposition (8.0%) in the maize-cultivated peatland. While in the fire-damaged peatland it was followed by retention of NH_4~+ (4.0%), nitrification (1.8%) and retention of Na~+ (0.6%). In the selectively logged peat forest dissociation of organic acids (85.1 %) was followed by retention of NH_4~+ (7.4%), retention of Na~+ and Mg~+ ions (5.6%), and nitrification (1.8%). During the study period of rainy season (December 2002-February 2003), acid loads were 1.32,0.80, and 0.71 kmol_c ha~(-1) in the top 10 cm peat layer in the maize-cultivated peatland, the fire-damaged peatland, and the selectively logged peat forest, respectively. The results showed that peat acidification in the rain-fed peatland resulted from a combination of acid deposition and internal transformation of organic acids and nitrogen, and biological accumulation of ions. Monitoring was also carried out in the 10-30 cm peat layer, which showed that the proportion of nitrification in acidifying processes was lower than in the top 10 cm peat layer. This implies that changes in chemical processes associated with the peat pH state was higher in the top peat layer.