Unlike terrestrial ecosystems, the temperature changes in aquatic ecosystems are not very sharp. The aquatic systems do not experience sudden changes in temperature in nature. Therefore, organisms living in aquatic ecosystems are not adapted to gross temperature changes. Also, oxygen occurs in aquatic ecosystems in the dissolved form. Can you imagine what will happen if the temperature of a water body is suddenly raised by artificial means? We will discuss here how hot water is generated in various human activities and how the release of heated water into oceans and seas affects the organisms inhabiting there.

In Unit 4, you read about the laws of thermodynamics. Energy, you know, is the ability to perform work. You are familiar with the concept of unidirectional flow of energy. The second law of thermodynamics can be stated in many ways including the following: No process involving an energy transformation will spontaneously occur unless there is degradation of energy from concentrated form to dispersed form. This when applied to generation of electricity will mean that electricity can be generated only after releasing a lot of waste heat. Thermal power plants produce superheated steam to generate electricity. After extracting usable energy from this steam, the left over hot water is let out into rivers, streams or oceans depending upon where the thermal power plant is located. We shall discuss the effects of releasing heated waters into oceans where the problem is acute.

Chemical industries, fossil fuel and nuclear power plants use a lot of water for Cooling purposes and return this used water to rivers, streams or oceans at a higher temperature. The siting of plants along the seacoast to take advantage of the marine waters has led to the perturbation of marine flora and fauna by heated water discharge. The hot water causes thermal pollution, decreasing dissolved oxygen in water which in turn adversely affects aquatic life. Nuclear power plants release 50 per cent of the generated heat to the coastal marine waters. Flora and fauna in the warm tropical waters live dangerously close to their upper limits of lethal temperature, particularly during the warm summer months. It requires only a slight deviation from this limit to cause a thermal stress to these organisms. Release of hot salty water, when coupled with wind system, alters the current and mixing patterns from offshore to onshore. This is more probable in tropical areas where the range of tides is quiet high.