Water temperature and the ecological reserve

Estimating the thermal requirements of aquatic ecosystems in South Africa

Freshwater systems, both globally and within South Africa, are under pressure, and are amongst the most deteriorated ecosystems due in part to water abstraction, flow regulation and pollution. Successful implementation of environmental flow management requires taking cognizance of the full spectrum of flows together with thermal regimes, including their temporal and spatial variability. Water temperature is recognized as an important abiotic driver of aquatic ecosystems, and understanding the role that temperature plays in driving ecosystem change is important if effective management of thermal stress on aquatic ecosystems is to be achieved. Only through a foundation of fundamental research linking water temperatures and biotic response will the water temperature requirements for the ecological Reserve be met. This research project involved the collection of baseline water temperature data in a range of rivers in the Western and Eastern Cape, South Africa. The body of research in this project represents a considerable advancement in understanding thermal patterns in South African rivers, and how biota (individual species and aquatic macroinvertebrate communities) respond to thermal variability and stress. Understanding spatio-temporal thermal patterns in the Eastern and Western Cape provinces requires a multi-scale approach. Linking biotic response to thermal drivers is naive if mean temperature values only are used. Spot measurements of water temperatures are at best inadequate when used in conjunction with other data. Rather, understanding biotic responses to thermal regimes not only involves fundamental research on life histories of taxa, but also in relating these to the subtler statistics of a thermal regime. The collection and/ or modelling of sub-daily temperatures (mean, minimum and maximum values) is fundamental to describing thermal regimes relative to timing, frequency, duration and magnitude of thermal events.





Project Leader
Helen Dallas