Loss of intermediate-flow states only evident when considering sub-daily flow metrics in a major tributary of the Limpopo basin

As the impacts of the anthropocene intensifies, there is an increasing need to understand how these changes affect both daily and sub-daily stream flow variability, timing and flow quantities, as these are some of the most influential drivers of spatial and temporal dynamics of stream biota. In this paper, long-term changes in flow patterns of a strategic water source area (Luvuvhu catchment) in an arid region of southern Africa were quantified, focusing on the relation between daily and sub-daily flow and its potential impact on fish biota of the catchment. Long-term temporal trends in stream flow were modelled using generalized least squares (GLS), while sub-daily and daily mean flow of the same stations were compared using a suite of metrics. Periods of similar stream flow patterns were identified using K-means cluster analysis. A spreadsheet rule-based model was developed linking fish communities to streamflow patterns, providing a predictive framework for fish assemblage responses to stream flow classes. Long-term reduction in flow in the Luvuvhu catchment has a strong seasonal component, with significant decreases during the wet season, not linked to long-term rainfall patterns. The flow regime of the Luvuvhu river system has become more variable over time. Several sub-daily flow metrics were positively related to daily flow metrics. Oscillating flow conditions and the loss of intermediate-flow states may permanently exclude certain fish flow guilds. However, temporal partitioning is only evident when sub-daily metrics are considered, highlighting their importance for assessing ecological resilience.