2020, VOLUME 7 ISSUE 1Pages: 20-29
Co-existence of organic matter and live plant macrophytes under flooded soil conditions acidify sulfidic soil of acid sulfate soils
Patrick S. Michael
School of Biological Sciences, The University of Adelaide, Adelaide, SA 5005, Australia
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Acid sulfate soils (ASS) are formed under waterlogged or reducing soil conditions. These soils either contain sulfuric acid or have the potential to form it, in an amount that can have detrimental impacts on the environment. Under undisturbed soil conditions, the sulfidic soils are benign unless exposed to atmospheric oxygen which leads to oxidation and production of sulfuric acidity. In this study, the changes in pH, redox and sulfate content of sulfidic soil following addition of organic matter, establishment of plant macrophytes or turnover of organic matter from the plant macrophytes co-existing under flooded conditions was investigated. The results showed in the absence of plant macrophytes, organic matter addition induced ameliorative effects, whereas presence of plants macrophytes led to acidification. The reduction reactions of the added organic matter and the anoxia created by flooding were ineffective in reducing the amount of oxygen that was pumped into the rhizophore via the arenchymatous tissues. Under falling soil moisture regimes, e.g. during a drought event as a result of changes in climatic conditions, the presence of this type of plant species would aerate the reduced soil conditions. Aeration will then lead to oxidation of sulfides, producing sulfuric acid (H2SO4), which in turn will have negative impacts when released into the environment.