The diagram in Fig. 1 shows a river landscape downstream from a hill farm. After heavy rain, brown water enters the river from a drainage ditch. A sewage wo...
Question 1 Report
The diagram in Fig. 1 shows a river landscape downstream from a hill farm. After heavy rain, brown water enters the river from a drainage ditch. A sewage works and a small town are also shown further downstream. Volunteers sampled aquatic organisms at three points, but the diagram, rather than a table, is their main field record. They found many mayfly larvae upstream and few below the sewage outlet. The local council plans a river restoration scheme.
(a) Which named organism shown in Fig. 1 is most likely to indicate clean, oxygen-rich water? [4]
(b) Outline four ways in which intensive farming can change river water quality. [4]
(c) Explain how untreated sewage can lead to a fall in biodiversity downstream. [5]
(d) Draw a labelled restoration plan for the river section in Fig. 1. Your plan should include methods that reduce pollution and improve habitats. [7]
Answer Details
(a) Mayfly larva [1]; it requires high dissolved oxygen [1]; it is sensitive to organic pollution [1]; its presence indicates relatively clean water [1]. (b) Any four: soil erosion adds sediment [1]; fertiliser adds nitrates/phosphates [1]; slurry/manure raises organic load [1]; pesticides can poison organisms [1]; drainage increases rapid runoff [1]; livestock may damage banks/add waste [1]. (c) Sewage adds organic matter [1]; decomposer bacteria feed on it and reproduce [1]; bacterial respiration uses dissolved oxygen [1]; oxygen-sensitive organisms die or move away [1]; fewer species and disrupted food chains reduce biodiversity [1]. (d) Award up to [7]: fenced livestock buffer [1]; vegetated riverbank strip [1]; wetland/settlement pond to trap sediment [1]; improved sewage treatment [1]; trees/native plants on banks [1]; riffles, woody material or varied channel habitat [1]; clear link to reduced runoff/pollution or increased shelter/spawning habitat [1].
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