Linking flow, water quality and potential effects on aquatic biota within the reserve determination process

Linking the potential effects of altered water quality on aquatic biota, that may result from a change in the flow (discharge) regime, is an essential step in the maintenance of riverine ecological funtioning. Determination of the environmental flow requirement of a river (as well as other activities, such as classifying the resource) is known in South Africa as determining the ''ecological Reserve''. This paper describes the philosophy behind the incorporation of water quality concerns in, as well as the constraints that are likely to be in operation during a Reserve determination. Three simple, predictive tools that have been developed for routine use in ecological Reserve assessments are described in this paper. Flow-concentration modelling can be used to predict the water quality that is likely to result from a given, prescribed flow regime. The Biotic Protocol attempts to provide an assessment of the likely implications of the predicted water quality for aquatic macroinvertebrates. Concentration time-series modelling can be used to rank complex flow scenarios with regard to potential consequences for water quality. Finally, a framework is presented for incorporating predictions of water quality and the implications for the aquatic biota in ecological Reserve assessments.