FRESHWATER RESEARCH CENTRE 
      
       SPECIALISTS IN AQUATIC RESEARCH AND TRAINING

Water Research Commission Project K5/1799: Water temperature and the ecological Reserve

Project leader: Dr Helen Dallas ( helen@frcsa.org.za)

Project Duration: April 2008 to March 2012 - Completed

Project team: Dr Nick Rivers-Moore (FRC), Mr Vere Ross-Gillespie (PhD student, UCT), Mr Bruce Eady (MSc student, UKZN)

WRC Report: Dallas HF & Rivers‐Moore NA. 2012. Water temperatures and the ecological Reserve. Water Research Commission Report KV 1799/1/12. Water Research Commission, Pretoria, South Africa.

Freshwater systems, both globally and within South Africa, are under pressure, and are amongst the most deteriorated and worst off systems, 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.  In summary, this project has: 

  • provided the models for simulating water temperatures in the absence of water temperature data;
  • automated the calculation of temperature metrics that facilitate the conversion of sub-daily temperature data into statistics that define a river’s thermal regime with respect to magnitude of water temperatures, frequency, timing and duration of thermal events;
  • identified thermally sensitive macroinvertebrate taxa that may be used as bio-indicators of thermal alteration;
  • identified key life history cues for selected macroinvertebrates in the context of water temperatures;
  • demonstrated the importance of maintaining thermal variability in river systems for aquatic macroinvertebrate community structure; 
  • generated a preliminary map of thermal regions that can provide an initial framework within which the thermal ecological Reserve is applied;
  • developed a thermograph that incorporates the natural range of variability and the concept of reference sites (and condition) with which an assessed (impacted) site can be compared, and the effect (if any) quantified; and
  • provided a decision tree for determining thermal ecological Reserve exceedance.

Conclusions and key messages

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.

Publications

Dallas HF.  2008.  Water temperature and riverine ecosystems: An overview of knowledge and approaches for assessing biotic responses, with special reference to South Africa. Water SA 34(3): 393-404. 

Dallas HF & Ketley ZA 2011.  Upper thermal limits of aquatic macroinvertebrates: comparing Critical Thermal Maxima with 96-LT 50 values. Journal of Thermal Biology 36: 322-327.

Dallas HF & Rivers-Moore NA 2011.  Micro-scale heterogeneity in water temperature.  Water SA 37(4): 505-512.

Dallas HF & Rivers-Moore N. 2012.  Critical Thermal Maxima of aquatic macroinvertebrates - towards identifying bioindicators of thermal alteration. Hydrobiologia 679: 61-76.

Rivers-Moore NA, Mantel S. & Dallas HF.  2012. Prediction of water temperature metrics using spatial modelling in the Eastern and Western Cape, South Africa.  Water SA 38: 167-176.

Eady BR , Rivers-Moore NA & Hill TR. 2013. Relationship between water temperature predictability and aquatic macroinvertebrate assemblages in two South African streams. African Journal of Aquatic Science. DOI:10.2989/16085914.2012.763110

Rivers-Moore NA, Dallas HF & Morris C.  2013.  Towards setting environmental water temperature guidelines: A South African example.  Journal of Environmental Management 128: 380-392.

Rivers-Moore NA, Dallas HF & Ross-Gillespie V. 2013.  Life history does matter in assessing potential ecological impacts of thermal changes on aquatic macroinvertebrates.  Rivers Research and Application 29:1100-1109.