Evaluating primary productivity, ripple effect and resilience of fluvial ecosystems: a new approach to assessing environmental flow requirement

Abstract. Productivity, ripple effect and resilience are characteristics of fluvial ecosystems. To evaluate these factors and develop new criteria for estimating environmental flow requirement (EFR), we propose a fluvial biomass model which calculates the amount of aquatic biomass accumulated through physical and climatic processes. Using this model, we introduce the indices of Contribution to Downstream Ecosystems (CDE) and Ecological Recovery Time (ERT) and apply them in the estimation of global EFRs. Average EFR values were estimated at 42 % of mean annual discharge. In comparison with previous global EFR estimates based on flow regime only, our model suggests 20 %–50 % higher values in monsoonal and savanna regions with high ecological richness, and in the lower reaches of large rivers in the higher latitudes where primary productivity is low and ecosystems largely depend on allochthonous biomass supply. The main advantage of our model is the ability to set variable EFRs within a river basin based on differences in ecological characteristics driven by climatic conditions and tributaries. Taking such longitudinal differences in EFR into account aids in developing integrated water allocation strategies by reflecting differences in water resource availability for humans within a catchment.