Week 30 - Aquatic Organisms are Affected by Many Factors

Lesson 10

Read pages 386 - 389

Many human activities directly or indirectly affect the quality of water in an area. For example, industries and cities can dump toxic chemicals into a river. This type of pollution can have a detrimental affect on the biological community in the ecosystem.


Determination and measurement of pollution may be made in the following ways:

(a) By direct chemical analysis of the water.

(b) By the use of "indicator" organisms. The population of indicator organisms which, by close observation and experience, increase or decrease depending on the type and degree of pollution. For example, blood worms thrive in low oxygen levels. Scientists infer low oxygen levels if a lake has a high population of blood worms.
(c) Closely related to indicator species is the actual composition of the biological community. For example, a healthy pond may great biological diversity. That is, there is a variety of different species living the area. If the pond is polluted, the biological diversity of the ecosystem will decrease. That is, there will be fewer species living in the area. The remaining more tolerant species are usually experience a population explosion.
Healthy pond has great biological diversity which means:

• many species, but smaller population sizes of each species

Polluted pond has less biological diversity which means:

• fewer species, but larger population sizes of these species