Week 4a- Water

Sources of elevated water temperatures can arise from urban road runoff and the use of water as coolants by power plants.  Most organisms will tolerant only a fairly narrow range of ambient temperatures.  The human body has a tolerance range of just 3°C, with 37°C an average "normal" temperature and hypothermia observed at <35°C and hyperthermia at 38°C.  Visible signs of stress may be observed outside the range of 35-38°C but there are also internal changes which may occur which are not observed.  

In aquatic systems, fluctuations in temperature are made worse by the change in oxygen solubility.  Remember that oxygen solubility increases with decreasing temperature.  Therefore the input of warm water to an aquatic environment can result in a decrease in oxygen concentration.  This has implications for the biodiversity of the system for two reasons.  Firstly, some organisms are more sensitive to fluctuations in oxygen concentrations than others and may either move to a more suitable environment or perish.  Adverse affects on cellular biology due to elevated temperatures is specific to each organism (larger organisms are generally more sensitive).  Secondly, anaerobic conditions encourage bacterial growth which may out-compete other species.

There is a degree of natural variation which includes:

• Diurnal variations
• Seasonal fluctuations

In addition, there are a number of anthropogenic sources which may causes issues with thermal pollution, including: