Learning outcomes Students should understand the following The environmental issues arising from the use of fertilisers. Leaching and eutrophication. Candidates should be able to analyse, interpret and evaluate data relating to eutrophication. Fertilisers Fertilisers are very effective but also have undesirable effects on the environment: • Reduced species diversity – nitrogen rich soils favour fast growing species (e.g. grasses and nettles) •Since nitrate and ammonium ions are very soluble, they do not remain in the soil for long and are quickly leached out, ending up in local rivers and lakes and causing eutrophication. Leaching Rain will dissolve soluble nutrients removing them from the reach of plant roots and eventually releasing them into watercourses. Very high levels of nitrates in drinking water can prevent efficient oxygen transport in babies and may be linked to stomach cancer. Leaching of nitrates can also harm the environment, leading to eutrophication. Eutrophication Oligotrophic - a lake that has a low level of nutrients. It has clear water and can support a small population of organisms. Eutrophic – a lake enriched with nutrients. The water is cloudy because of the presence of large numbers of algae and cyanobacteria. Eutrophication is a natural process that takes place over a long period of time. Eutrophication In the context of pollution "eutrophication" has come to mean a sudden and dramatic increase in nutrients due to human activity, which disturbs and eventually destroys the food chain. The main causes are fertilisers leaching off farm fields into the surrounding water course, and sewage (liquid waste from houses and factories). These both contain dissolved minerals, such as nitrates and phosphates, which enrich the water. Eutrophication fertilisers sewage (liquid domestic and industrial waste) minerals esp. nitrates minerals esp. phosphates eutrophication algal bloom competition for light consumers can't consume fast enough Limiting factor light dead plants dead algae detritus organic material The process of Eutrophication Limiting factor - minerals for light consume fast enough The process of Eutrophication cont. dead plants dead algae detritus more decomposers Limiting factor oxygen use up oxygen by aerobic respiration (increased BOD) aerobes die (invertebrates, fish, etc) anaerobic bacteria thrive. Release NH4, CH4, H2S Biochemical oxygen demand (BOD) This measures the rate of oxygen consumption by a sample of water, and therefore gives a good indication of eutrophication. A high BOD means lots of organic material and aerobic microbes, i.e. eutrophication. Aquatic ecosystems can slowly recover from a high BOD as oxygen dissolves from the air, but long-term solutions depend on reducing the amount of minerals leaching into the water. Reducing leaching can be achieved by applying inorganic fertilisers more carefully, by using organic fertilisers, by using low-phosphate detergents, and by removing soluble minerals by precipitation in modern sewage plants. As a last resort eutrophic lakes can be dredged to remove mineral-rich sediment, but this is expensive and it takes a long time for the ecosystem to recover. This has been done in the Norfolk Broads. Exam question (a) Why do plants need ions which contain nitrogen? (1) (b) (i)Explain why it is necessary for farmers to apply fertilisers to land that is used annually to grow a cereal crop. (2) (ii) Explain what is meant by the law of diminishing returns with respect to the application of artificial fertilisers. (2) (a) (b) (ii) (i) (i) protein / amino acid production 1 increased yields; replace ions taken in by crop; 2 increased application of fertiliser does not increase yields; therefore uneconomic 2 25 Nitrate concentration in reservoir 20 /mg per litre 15 125 Nitrate application to 100 farmland /kg per hectare 75 per year 10 50 5 25 0 1960 0 1965 1970 1975 Year 1980 1985 1990 Nitrate application to farmland Nitrate concentration in reservoir (c)The graph shows the relationship between nitrate application to farmland and the concentration of nitrate in a nearby reservoir. (i) Explain why there was an overall increase in the concentration of nitrate of nitrate in the reservoir between 1960 and 1990. (1) (ii)Suggest one explanation for the large fall in nitrate concentration in the reservoir between 1982 and 1984. (2) (d) Explain why there is concern at the amount of nitrates being leached into rivers, lakes and reservoirs. (4) (Total 12 marks) (c)(i) increased leaching as result of increased application (ii) Either increased rainfall (leading to increased volume of water flowing into reservoirs); increased volume leads to increased dilution of nitrate Or less rain; therefore more uptake by crop / less leaching (d) increased growth of plants / algae; (leading to) eutrophication; increase in microorganisms feeding on dead plants / algae; leading to deoxygenation; increased nitrate in drinking water; causing human illness 1 2 4  Task Read the application – Troubled waters- on p101 and answer the questions 1-4 Learning outcomes Students should understand the following The environmental issues arising from the use of fertilisers. Leaching and eutrophication. Candidates should be able to analyse, interpret and evaluate data relating to eutrophication.