Effects of discharge regulation on slackwater characteristics at multiple scales in a lowland river

The spatial and temporal dynamics of physical habitat in rivers is driven by the interaction between channel morphology and discharge. However, little is known about how altered discharge affects the dynamics of habitat patches such as slackwaters. This study investigated the influence of discharge on the availability, stability, quality, and diversity of slackwaters in a southeastern Australian lowland river. The area, spatial configuration, permanence, and within-patch characteristics of slackwaters of two reaches in a regulated section and two reaches in a largely unregulated section of the river were compared. There was less slackwater area and it was less permanent at higher discharges and in the two regulated reaches than at lower discharges and in the largely unregulated reaches. Individual slackwaters were more homogenous in relation to within-patch characteristics in the regulated than in the largely unregulated reaches. However, variability in the spatial configuration of slackwaters and within-patch characteristics and diversity at the reach scale were not related to discharge. We suggest that channel morphology, rather than discharge, is the main driver of these characteristics.