The effect of temperature on leaching and subsequent decomposition of dissolved carbon from inundated floodplain litter: implications for the generation of hypoxic blackwater in lowland floodplain rivers

MDFRC item.

Dissolved organic carbon export from floodplain litter during flood events is an important energy subsidy for lowland rivers. Temperature affects both the release and decomposition of dissolved organic carbon from floodplain plant litter. Unseasonally warm flood conditions have resulted in the release and consumption of carbon at a rate so rapid that water column oxygen has been depleted, causing the death of aquatic organisms upon exposure to this ‘hypoxic blackwater’. To date, there has not been a systematic investigation of the role of temperature on hypoxic blackwater dynamics. In a series of laboratory experiments, we investigated the temperature dependence of both leaching and decomposition of carbon from a common floodplain litter component in south-eastern Australia – the leaves of the river red gum Eucalyptus camaldulensis. The leaching rate increased with temperature and approximated Arrhenius kinetics. Additionally, the solubility of the leaf carbon increased substantially at temperatures above ∼ 25◦C. The rate of organic carbon respiration also increased with temperature, and the relationship with temperature was approximately linear. These data can be used to improve models for the prediction of hypoxic blackwater risk.