Alkalinization and acidification of stream water with changes in atmospheric deposition in a tropical dry evergreen forest of northeastern Thailand

Abstract

Field surveys on atmospheric deposition and stream water chemistry were conducted in an evergreen forest in northeastern Thailand characterized by a tropical savanna climate with distinct dry and wet seasons. Atmospheric deposition of ion constituents by throughfall and stemflow was shown to increase in the beginning and end of the wet season, reflecting the precipitation pattern. The pH and electrical conductivity of stream water increased with alkalinity and base cation concentrations due to mineralization of organic matter by the first rain and retention of anions in soil during the start of the wet season. After initial alkalinization, the pH and alkalinity declined rapidly with the highest SO 4 2− concentration displayed in the middle towards the end of the wet season. The magnitude of peaks in SO 4 2− concentration (13.5-60.6 μmol c /L) reflects deposition during the first 2 months of the wet season (March and April) in respective years (60.8-170 mol c /ha). Release of SO 4 2− with H + , which is retained in soil during the early wet season, may cause acidification later in the season. The deposition and concentration of SO 4 2− declined over 6 years. However, the pH of stream water declined with increasing concentrations of SO 4 2− and other major ions. The release of materials accumulated in the ecosystem was facilitated by the decrease in SO 4 2− concentration/deposition and increased precipitation in the middle-late wet season. The retention-release cycle of SO 4 2− largely contributed to both seasonal and interannual variations in stream water chemistry in the tropical savanna climate studied.

Comparative physiology of canopy tree leaves in evergreen and deciduous forests in lowland Thailand

“…The accelerated development of agricultural land progresses forest fragmentation, resulting in vegetation changes particularly in the peripheral areas of the forest 49 . The amounts of sulfur oxides deposited from the atmosphere to plants and soil has been increasing in Thailand, resulting in changes in the chemical properties of forests 62 . Such enhanced anthropogenic influences and climate change may significantly impact the forest function and their habitat associations in future.…”

Strategic roadmap to assess forest vulnerability under air pollution and climate change

“…In Asia, much of the deposited atmospheric seems to be retained in forest soils (Duan et al, 2016; Sase et al, 2019), which may imply a future risk of soil acidification under changing climate. In fact, concentrations and pH of river waters are related to the S emission/deposition rate (Duan et al, 2011; Qiao et al, 2016; Sase et al, 2017, 2021). To understand the S cycle in forest ecosystems, targeted studies on deposition trend and changing climate are required (e.g., Mitchell & Likens, 2011; Sase et al, 2019, 2021; Vuorenmaa et al, 2017).…”