Purpose
Compare indicators of water quality from several sources and decide which supports the healthiest ecosystem.
Safety
Treat every water sample as contaminated: gloves on, no tasting, wash hands afterwards. Dispose of samples down the drain with plenty of running water.
Materials
- Water samples: tap, rainwater or pond, water with a pinch of fertiliser, water with a drop of dish soap
- pH strips, dissolved oxygen test kit, turbidity tube, thermometer
Procedure
- Label four sample cups. Do not open more than one at a time.
- Measure temperature first — it changes fastest once the sample is out.
- Measure pH, then dissolved oxygen, then turbidity.
- Record everything, including anything unexpected about smell or colour.
Data
| Sample | Temp (°C) | pH | DO (mg/L) | Turbidity (cm) | Notes |
|---|---|---|---|---|---|
| Tap | |||||
| Pond / rain | |||||
| Fertiliser added | |||||
| Soap added |
What "good" looks like
Most freshwater fish need dissolved oxygen above about and a pH between and . Trout are fussier than carp — tolerance ranges differ by species.
Analysis
- Rank the four samples from most to least able to support fish. Justify with numbers.
- The fertiliser sample models farm runoff. Explain, using The Nitrogen Cycle, why adding nutrients can lower dissolved oxygen.
- Name one thing your test could not detect that would still matter.
Hand in
- Data table
- Ranking with justification
- Answers to analysis questions
Curriculum connection
A1.2
apply a scientific experimentation process and associated skills to conduct investigations, making connections between their observations and findings and the scientific concepts they are learning
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B2.4
investigate factors and processes, including biodiversity, air and water quality, soil health, and succession, and explain how they contribute to ecosystem sustainability
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B2.5
explain the effects of various human activities on the dynamic equilibrium of ecosystems
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