The table below shows results from an investigation into fertiliser runoff. Students added different concentrations of nitrate fertiliser to identical tanks...
Question 1 Report
The table below shows results from an investigation into fertiliser runoff. Students added different concentrations of nitrate fertiliser to identical tanks of pond water containing the same number of algae and water fleas. After seven days they counted living water fleas and measured dissolved oxygen.
| Nitrate concentration / mg per dm3 | Dissolved oxygen / mg per dm3 | Living water fleas |
|---|---|---|
| 0 | 8.8 | 46 |
| 2 | 8.1 | 42 |
| 8 | 5.0 | 19 |
| 16 | 2.3 | 3 |
(a) Complete the conclusion: as nitrate concentration increases, the number of living water fleas __________ and dissolved oxygen concentration __________. [3]
(b) Explain why excess nitrate in river water can cause the reduction in dissolved oxygen shown in Table 1. [4]
(c) Design an investigation to compare nitrate pollution in water collected above and below a farming area. [6]
(d) Suggest two controls farmers could use to limit fertiliser entering a river. [2]
Answer Details
(a) As nitrate concentration increases, the number of living water fleas decreases and dissolved oxygen concentration decreases. The highest nitrate concentration gives both the lowest oxygen concentration and fewest living water fleas. [3]
(b) Nitrate ions are mineral ions used by algae and plants. Excess nitrate can cause rapid algal growth, an algal bloom. Algae block light, so submerged plants photosynthesise less or die. Decomposers break down dead organisms and respire, using dissolved oxygen, so oxygen concentration falls. [4]
(c) Collect equal volumes of water in clean labelled containers from several sites upstream and downstream of the farming area. Sample at the same time, or repeat on several dates. Measure nitrate concentration using a nitrate test kit or colorimeter. Repeat measurements at each site and calculate a mean. Keep sampling depth, distance from the bank and time of day consistent so that location is the main variable being compared. [6]
(d) Farmers could apply only the amount of fertiliser needed, avoid spreading before heavy rain, leave vegetated buffer strips beside the river, store slurry securely, or plant cover crops. Any two. [2]
Download The App On Google Playstore
Everything you need to excel in your exams
