A plant nursery uses nitrate fertiliser. Drainage water from the nursery enters a river between sites U and D1.
Scientists measured nitrate concentration and dissolved oxygen concentration at four sites. They also used the same sampling method for 30 seconds at each site and calculated the mean number of two indicator species.
| Site | Position | Nitrate concentration in mg/dm3\text{mg}/\text{dm}^3mg/dm3 | Dissolved oxygen concentration in mg/dm3\text{mg}/\text{dm}^3mg/dm3 | Mean number of stonefly nymphs | Mean number of bloodworms |
|---|---|---|---|---|---|
| U | upstream of the outlet | 1.2 | 9.0 | 14 | 1 |
| D1 | 50 m downstream | 8.4 | 4.6 | 1 | 19 |
| D2 | 300 m downstream | 5.6 | 6.0 | 5 | 12 |
| D3 | 800 m downstream | 2.1 | 8.1 | 11 | 4 |
The scientists claim that nitrate from the nursery caused a reduction in water quality downstream of the outlet.
Evaluate the scientists' claim. Use the data in your answer.
109 exam-style questions on OCR GCSE Biology 6.1 Monitoring and maintaining the environment, covering 6.1.1 Field investigation of distribution and abundance, 6.1.2 Human interactions and biodiversity, 6.1.3 Maintaining biodiversity, and 6.1.4 Environmental change and distribution of organisms. Each one has a worked solution and a mark scheme showing where the marks go.