The identification and significance of chemicals released from decomposing barley straw during reservoir algal control

The presence of decomposing barley straw at c. 25 g m−3 in a disused water supply reservoir significantly reduced cyanobacterial and general phytoplankton activity compared with a control water body. Algal control was simultaneous with the release of a “cocktail” of phytotoxic chemicals, following both the initial immersion of the straw and then after a c. 3 month period of degradation in water. The toxicity of straw leachate to phytoplankton could be explained by the presence of toxicologically relevant levels of phenols and oxidised phenolics. Optimisation of the control of phytoplankton using barley straw is discussed with respect to observed environmental physicochemical conditions shown to favour the production of the more toxic oxidised phenoics under field conditions.