Movement of Light, Heat, and Chemicals in Water - Freshwater Ecology: Concepts and Environmental Applications - page 31

3 Movement of Light,
Heat, and Chemicals
in Water
Diffusion in Water
Light and Heating of Water
Summary
Questions for Thought
The movement of chemicals in water is a key factor to the survival and
growth of most aquatic organisms and central to the understanding of wa-
ter pollution. Light is the ultimate energy source for life on our planet.
Without light, energy would not flow through ecosystems and most bio-
geochemical cycles would stop. Light heats water, which ultimately leads
to stratification of lakes. The temperature and movement of water are tied
intimately to the rate at which chemicals move through the water.
DIFFUSION IN WATER
An insect detecting prey, algal cells acquiring nutrients, a fish breath-
ing, a contaminant moving through an aquifer, and a lake's seasonal heat-
ing patterns are all subject to the effects of diffusion of substances or heat
through water. Diffusion of heat and dissolved materials can be described
in a similar fashion, so both are described in general terms here.
Diffusion of chemicals is affected by many factors, including the con-
centration gradient between two points (distance and concentration differ-
ence), advective transport of water (water currents that move the chemi-
cals), temperature, size of molecules, the presence and structure of
sediments, and any direct movement of the chemicals by organisms. The
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