IB Environmental systems and societies 4.4G Water Quality Management Notes

Indicator Species: Living Signposts of Water Quality

1. Indicator species are living organisms whose presence or absence reflects the quality of the environment they inhabit.
2. They provide biological evidence of pollution, responding to changes in oxygen levels, pH, or toxic substances.

Intolerant vs Tolerant Species

1. Intolerant species
   1. Need clean, oxygen-rich water, so their presence signals unpolluted conditions.
   2. Examples: stonefly nymphs, mayfly nymphs, and caddisfly larvae.
2. Tolerant species
   1. Survive polluted, oxygen-poor water, so their dominance signals heavy organic pollution.
   2. Examples: Tubifex worms, bloodworms, and rat-tailed maggots.

Advantages and Limitations

1. Advantages
   1. Provide a long-term reflection of environmental conditions.
   2. Cost-effective compared to chemical analysis.
   3. Show the ecological impact of pollutants, not just their concentration.
2. Limitations
   1. Populations fluctuate naturally due to temperature, predators, or season.
   2. They give qualitative, not quantitative, data.
   3. Different regions need locally adapted indicator-species lists.

Biotic Indices: Scoring Water Quality From Its Organisms

1. A biotic index is a numerical expression of water quality based on the presence and diversity of organisms with varying pollution tolerances.
2. It gives an indirect measure of water quality and is especially useful for evaluating organic pollution.

How Biotic Indices Work

1. Sampling: collect aquatic macroinvertebrates by kick sampling or net scooping.
2. Identification: identify species groups such as stoneflies, mayflies, caddisflies, and Tubifex worms.
3. Scoring: assign tolerance values, higher for tolerant species and lower for intolerant ones.
4. Calculation: combine presence and abundance data into a single numerical value for water quality.