18:15 〜 19:30
[MIS26-P07] タイ熱帯季節林小集水域における硫酸イオン起源の時空間異質性
キーワード：熱帯季節林, 渓流水, 硫黄動態, 硫黄安定同位体比, 大気沈着, 土壌水
In Southeast Asia an increase in emissions of sulfur (S) into the atmosphere may introduce new risks for the plant, soil and inland-water through acidification. However, the effect of the atmospheric S deposition on acidification by an increase in sulfate is poorly understood in tropical forests with possible S sources and processes in the internal cycle. S isotopic ratio (δ34S) could be a good indicator to identify the source of sulfate in soil and inland-water because only dissimilatory S reduction results in a large fractionation of S isotope. Our objectives are to clarify the spatial and temporal variability of δ34S in rainfall, throughfall, soil and stream water within the catchment and discuss the influence of the atmospheric S input on the stream in tropical forest.
Study catchment has been established at dry evergreen forest in Sakaerat silvicultural research station, northeastern Thailand. Anion-exchange-resin columns were installed for rainfall, throughfall, soil-water and stream-water through a year to collect and concentrate sulfate in the field. The sulfate retained in the resin was extracted by NaCl and precipitated as BaSO4. We determined 34S / 32S of the BaSO4 by mass spectrometer (IR-MS) and calculated δ34S (‰) using the reference material (Canyon Diablo Troilite). Annual weighted-mean δ34S was calculated from sulfate flux (kg ha-1 year-1) and δ34S in each period. We also determined δ34S by the concentration method for the water samples of rainfall and streamwater in some cases.
Annual weighted-mean δ34S and S deposition in rainfall were 4.1 ‰ and 6.4 kg ha-1 year-1, respectively. δ34S in stream-water was 4-5 ‰ higher than rainfall during late-wet and dry season, whereas δ34S in rainfall and streamwater was mostly comparable during early and middle wet season. In late-wet and dry season, δ34S in sub-soil water was particularly higher in the riparian zone near the outlet of the study catchment than in the area near the headwater and on the slope. Sulfate enriched 34S might be increased due to bacterial dissimilatory S reduction in late wet season and retained in the sub-soil during dry season, which could be a main source for the streamwater sulfate during base-flow periods. Meanwhile, in early and middle wet season, streamwater sulfate could be directly affected by atmospheric S input. These heterogeneity of internal S dynamics should be considered to examine the effect of atmospheric deposition on soil and inland-water ecosystems in tropical dry forest. The project is supported by the grant from APN (ARCP2012-18NMY-Sase: ARCP 2013 -13 CMY -Sase).
Study catchment has been established at dry evergreen forest in Sakaerat silvicultural research station, northeastern Thailand. Anion-exchange-resin columns were installed for rainfall, throughfall, soil-water and stream-water through a year to collect and concentrate sulfate in the field. The sulfate retained in the resin was extracted by NaCl and precipitated as BaSO4. We determined 34S / 32S of the BaSO4 by mass spectrometer (IR-MS) and calculated δ34S (‰) using the reference material (Canyon Diablo Troilite). Annual weighted-mean δ34S was calculated from sulfate flux (kg ha-1 year-1) and δ34S in each period. We also determined δ34S by the concentration method for the water samples of rainfall and streamwater in some cases.
Annual weighted-mean δ34S and S deposition in rainfall were 4.1 ‰ and 6.4 kg ha-1 year-1, respectively. δ34S in stream-water was 4-5 ‰ higher than rainfall during late-wet and dry season, whereas δ34S in rainfall and streamwater was mostly comparable during early and middle wet season. In late-wet and dry season, δ34S in sub-soil water was particularly higher in the riparian zone near the outlet of the study catchment than in the area near the headwater and on the slope. Sulfate enriched 34S might be increased due to bacterial dissimilatory S reduction in late wet season and retained in the sub-soil during dry season, which could be a main source for the streamwater sulfate during base-flow periods. Meanwhile, in early and middle wet season, streamwater sulfate could be directly affected by atmospheric S input. These heterogeneity of internal S dynamics should be considered to examine the effect of atmospheric deposition on soil and inland-water ecosystems in tropical dry forest. The project is supported by the grant from APN (ARCP2012-18NMY-Sase: ARCP 2013 -13 CMY -Sase).