Loss of intermediate flow states only evident when considering sub-daily
flow metrics in a major tributary in the Limpopo basin
Abstract
As the impacts of the anthropocene intensifies in rivers, 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 in an arid region of southern
Africa were quantified, focusing on the relation between daily and
sub-daily 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 has a
strong seasonal component, with significant decreases during the wet
season, not linked to long-term rainfall patterns. Flow variability has
increased over time, while 78% of sub-daily flow metrics were 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.