Role of temperature on the development of hypoxia in blackwater from grass

In eastern Australia the development of hypoxic blackwater/floodwater and its detrimental consequences are more common in summer than winter. This study examined the effect of temperature on the development of hypoxic conditions which was determined as biochemical oxygen demand (BOD) in floodwater when pasture grass (a source containing labile organic carbon) was inundated. Labile dissolved organic carbon (DOC) in blackwater is one of the main factors that contribute to the development of hypoxic conditions. Temperature plays a key role on the microbial mineralization of labile DOC and hence the development of hypoxic conditions. Prolonged flooding at different seasons (having different temperatures) was simulated in the laboratory by incubating fresh pasture grass cuttings with river water and soil at three different temperatures (20 °C, 27.5 °C and 35 °C) for 20 days. Although this study shows that elevated ambient temperatures can result in more rapid development of hypoxic conditions during the first week of flood peak, it is evident that blackwater formed at relatively moderate ambient temperatures (e.g. 20 °C) has a similar potential to deoxygenate the receiving water bodies, especially after one week's duration of flood peak.