A Temporal Study of the Response of Aquatic Macroinvertebrate and Diatom Assemblage Compositions to Flow Intermittency and Absence in an Intermittent River, South Africa

Abstract

Flow is regarded by many aquatic ecologists as a key driver of river form and function, influencing a river's path through a landscape, creating and manipulating aquatic habitats and delivering nutrients and materials for productivity and growth. In intermittent rivers, however, flow is inconsistent and may stop for prolonged periods of time, causing a change in the equilibrium between process and form and creating what may appear to be an environment that is less healthy and intact than its perennial counterpart. Flow absence and intermittency creates unique disturbances that underpin the structure and function of intermittent rivers. The temporal scale at which these disturbance processes occur adds even further complexity, as dynamic feedbacks among system components mould the extent and intensity of various disturbances already set in motion by flow variability and absence. Despite this inherent and sometimes seemingly immeasurable complexity, there is an important and pressing need to understand the ecological dynamics of intermittent rivers to better inform decisions for natural resource management and environmental conservation purposes. The literature suggests that flow variability, intermittency and absence underpins the biotic potential and ecology of intermittent river environments, and whether perceived as negative or positive, are essential to the long-term integrity of intermittent river ecosystem.