Factors Controlling Deoxygenation of "Floodwater" Overlying an Acid Sulfate Soil: Experimental Modeling

An incubation experiment was conducted to simulate the effect of flooding onwater deoxygenation in acid sulfate soil floodplain systems. The originally oxygenated 'floodwater'could be deoxygenated immediately following 'flooding' and it is likelythat this was caused mainlyby decomposition of organic debris from the inundated plants. Deoxygenation eventually led to thedepletion of dissolved oxygen (DO) in the 'floodwater' and it is highly possible that this resultedin the transformations of ferric Fe to ferrous Fe, sulfate to hydrogen sulfide. and organic nitrogento ammonia (ammonification). The accumulation of these reduced substances allows the 'floodwater'to develop DO-consuming capacity (DOCC). When the 'floodwater' is mixed with the introducedoxygenated water, apart from the dilution effects, the reduced substances contained in the'floodwater' oxidize to further consume DO carried by the introduced water. However, it appears thatthe DO drop in the mixed water can only last for a few hours if no additional DO-depleted'floodwater' is added. Entry of atmospheric oxygen into the water can raise the DO level of themixed water arid lower water pH through the oxidation of the reduced substances.

An incubation experiment was conducted to simulate the effect of flooding on water deoxygenation in acid sulfate soil floodplain systems. The originally oxygenated 'floodwater' could be deoxygenated immediately following 'flooding' and it is likely that this was caused mainly by decomposition of organic debris from the inundated plants. Deoxygenation eventually led to the depletion of dissolved oxygen (DO) in the 'floodwater'and it is highly possible that this resulted in the transformations of ferric Fe to ferrous Fe, sulfate to hydrogen sulfide, and organic nitrogen to ammonia (ammonification). The accumulation of these reduced substances allows the 'floodwater' to develop DO-consuming capacity (DOCC). When the 'floodwater' is mixed with the introduced oxygenated water, apart from the dilution effects, the reduced substances contained in the 'floodwater' oxidize to further consume DO carried by the introduced water. However, it appears that the DO drop in the mixed water can only last for a few hours if no additional DO-depleted 'floodwater' is added.Entry of atmospheric oxygen into the water can raise the DO level of the mixed water and lower water pH through the oxidation of the reduced substances.