4.4G Water quality management (HL) Notes

Indicator Species

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, as they respond to changes in oxygen levels, pH, or toxic substances.

Pollution-Intolerant and Pollution-Tolerant Species

1. Intolerant Species

1. These species are sensitive to pollutants and require clean, oxygen-rich environments.
2. Their presence indicates unpolluted water with high dissolved oxygen content.

2. Tolerant Species

1. These species can survive in polluted, oxygen-poor waters with high organic matter.
2. Their dominance indicates heavily polluted environments or organic waste accumulation.

Advantages

1. Provides a long-term reflection of environmental conditions.
2. Cost-effective compared to chemical analysis.
3. Offers insight into the ecological impact of pollutants, not just their concentration.

Limitations

1. Populations can fluctuate due to natural factors such as temperature, predators, or seasonal variation.
2. Indicator species provide qualitative, not quantitative, data.
3. Different regions require locally adapted indicator species lists due to ecological differences.

Biotic Indices

1. A biotic index is a numerical expression that assesses 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 particularly useful for evaluating organic pollution.

How Biotic Indices Work

1. Sampling: Collect aquatic macroinvertebrates using methods like kick sampling or net scooping.
2. Identification: Identify species groups (e.g., stoneflies, mayflies, caddisflies, Tubifex worms).
3. Scoring: Assign tolerance values, higher for pollution-tolerant species and lower for intolerant ones.
4. Calculation: Use species presence and abundance data to produce a numerical value representing overall water quality.

The Trent Biotic Index

1. The Trent Biotic Index (developed in the UK) is a classic system for freshwater assessment.
2. It relies on identifying certain key macroinvertebrates, such as stoneflies, mayflies, caddisflies, freshwater shrimp (Gammarus), water hoglouse (Asellus), and Tubifex worms, and scoring sites based on which species are present.

Interpretation of Scores

1. High index (8-10): Clean, oxygen-rich water (presence of stoneflies and mayflies).
2. Medium index (4-7): Moderately polluted water (presence of caddisflies and shrimps).
3. Low index (0-3): Heavily polluted water (dominance of Tubifex worms and midge larvae).

How the Trent Biotic Index is Applied

1. Collect macroinvertebrates using kick sampling or a D-net.
2. Identify the organisms and record how many different types are found.
3. Assign tolerance scores based on pollution sensitivity.
4. Determine the index value using the chart or formula.
5. Interpret the score to classify the water quality.

Water Quality Index (WQI)

1. A Water Quality Index (WQI) combines multiple chemical and physical parameters into a single score, giving an overall picture of water health.
2. It simplifies data from several tests into one easily interpretable number.

Common Parameters

1. Dissolved Oxygen (DO): Indicates biological health.
2. Biochemical Oxygen Demand (BOD): Shows organic pollution levels.
3. pH: Measures acidity or alkalinity.
4. Turbidity: Indicates suspended solids and clarity.
5. Nitrate and Phosphate levels: Show nutrient pollution.