ALBERT

Description: The freshwater ecosystems around the world are degrading, such that maintaining environmental flow (EF) in river networks is critical to their preservation. The relationship between streamflow alterations and, re- spectively, EF violations, and freshwater biodiversity is well established at the scale of stream reaches or small basins (∼〈100 km2). However, it is unclear if this relationship is robust at larger scales, even though there are large-scale ini- tiatives to legalize the EF requirement. Moreover, EFs have been used in assessing a planetary boundary for freshwater. Therefore, this study intends to conduct an exploratory evalu- ation of the relationship between EF violation and freshwater biodiversity at globally aggregated scales and for freshwater ecoregions. Four EF violation indices (severity, frequency, probability of shifting to a violated state, and probability of staying violated) and seven independent freshwater biodiver- sity indicators (calculated from observed biota data) were used for correlation analysis. No statistically significant neg- ative relationship between EF violation and freshwater bio- diversity was found at global or ecoregion scales. These findings imply the need for a holistic bio-geo-hydro-physical approach in determining the environmental flows. While our results thus suggest that streamflow and EF may not be the only determinant of freshwater biodiversity at large scales, they do not preclude the existence of relationships at smaller scales or with more holistic EF methods (e.g., including water tem- perature, water quality, intermittency, connectivity, etc.) or with other biodiversity data or metrics.