Ecologists investigate the rate of eutrophication in freshwater ecosystems by monitoring the maximum chlorophyll-a concentration (a proxy for algal density) in ponds. Their investigation shows that the eutrophication rate is faster when the Nitrogen to Phosphorus (N:P) ratio of the nutrient runoff is lower, resulting in a higher peak chlorophyll-a level:
The table below shows the mass of nitrogen and phosphorus per litre in runoff samples from three agricultural sources:
| Runoff source | Mass of nitrogen (mg/L) | Mass of phosphorus (mg/L) |
|---|---|---|
| Arable Field | 2.40 | 0.10 |
| Dairy Farm | 1.80 | 0.15 |
| Mixed Orchard | 1.28 | 0.08 |
Determine the Nitrogen to Phosphorus (N:P) ratio for each runoff source, and hence determine which source will cause the fastest rate of eutrophication, explaining your reasoning.
67 exam-style questions on OCR GCSE Biology 4.1 Ecosystems, covering 4.1.1 Cycling of materials in ecosystems, 4.1.2 Microorganisms in cycling materials, 4.1.3 The carbon and water cycles, 4.1.4 Factors affecting decomposition, 4.1.5 Levels of organisation in an ecosystem, 4.1.6 Abiotic and biotic factors affecting communities, 4.1.7 Interdependence and competition, 4.1.8 Trophic levels, 4.1.9 Pyramids of biomass, and 4.1.10 Efficiency of biomass transfers. Each one has a worked solution and a mark scheme showing where the marks go.