Using Sea Water for Agriculture Aim: marking a text structure, using graphics in note-taking. 1. Pre-reading: Discussion on water supplies, fresh and sea water, arid areas in the world. 2. Scan the text 'Using Sea Water for agriculture' and label the margin brackets with the expressions at the bottom. 3. Compare your margin notes with 'simple graphics' 4. Read the article step by step: Paragraph 1,2 (focus on vocabulary) Match the given expressions with their definitions In the text, find the words that have the same meaning as the expressions on the handout Paragraph 3: Label the diagram 'Cheapest method of evaporation' and describe it to your neighbour. . " Paragraph 4: 'Arizona method' - flowchart To show how the process continues, use the arrows . 5. Complete the spidergram with the key points 6. Recapitulation: types of note-taking English for Biologists, MU Based on: Study Reading, Glendinning, E.H, Holmstrom, B, CUP, 1997 Hana Němcova Unit 6 The physical world Control of evaporation. and particularly of transpiration of water through plants, is obviously of crucial importance in all regions of the world where water is scarce. It is being investigated most thoroughly in connection with the use of sea water for agriculture. Sea water can actually be used as such for watering certain plants, on certain soils.^2() But it seems unlikely that it can be at all widely 5 used for growing plants useful for food. and it is not at all certain how long it can be carried on before the accumulation of salt in the lower parts of the soil makes it unusable. Most attempts to use sea water for agriculture depend on first removing the 10 excess salt. There are two basic methods of desalination. One depends on using a membrane which will allow the water to pass, but will hold back the salts (reversed osmosis). The other is distillation. that is to say water vapour or steam is produced and this. which does not contain salts. forms fresh water when it is condensed. The production of steam can be done by actually boiling the sea water or. more gently, by encouraging evaporation from the surface of sea water 15 which is warmed but not raised to boiling point. Both the membrane-filtering techniques and the boiling technique require large amounts of concentrated energy. They are essentially industrial processes of a very energy-consuming kind. The evaporation methods are much less demanding. and I will discuss them first. 20 The cheapest way of evaporating sea water is to use the heat of the sun. The sea water is run into shallow tanks of concrete or plastic. preferably with a black bottom which absorbs the sun's heat. The tanks. which are usually built long and narrow. are covered with a transparent roof with curved or sloping sides. The water in the tanks is warmed, evaporates, and the water vapour condenses again 25 on the cooler glass roof and runs down the sides to be collected in a trough at the bottom. Installations of this kind are already in use in many arid regions near the sea, from the coasts of Chile to the Aegean islands. It is a very satisfactory process provided one does not want too much water. It has mostly been used to provide drinking water. The quantities required for agricultural irrigation would 30 require enormous areas of tanks. A much more sophisticated low temperature evaporation scheme is being developed in Arizona.^21 The scheme involves using cold sea water which is pumped into the installation to aid the condensation of the water vapour which has been produced by hot sea water. Originally solar energy was used to heat the 35 sea water. but since any place that wanted to run such a scheme would certainly be generating its own electricity. probably with a diesel engine. use was later made of the 'waste heat' in the cooling water of the engine. They also introduced another improvement which is of very general application. The fresh water was used on plants grown in plastic greenhouses. A 40 large sheet of plastic is attached to a low brick or stone wall. and a small pump keeps the air pressure inside the plastic at about half a pound per square foot. above the air pressure outside. so the plastic is inflated, in the form of a long low sausage. The plastic is transparent to the sunlight which the plants need. while the water, led to the plant roots and transpired through their leaves. is trapped 45 inside and not allowed to escape back into the general atmosphere; it can be used again and again. Experimental plants of this kind are working in Arizona and Mexico. and a quite big one, planned to provide food for a sizeable population, is being built in the oil-rich Persian Gulf state of Abu Dhabi. There are quite a large number of areas in the world in which arid deserts come near 50 enough to the sea coast for developments of this kind to make important contributions to the world's food supply. Created by DPE, Copyright IRIS 2005 Created by DPE, Copyright IRIS 2005 2 ad paragraphs 1 and 2 Match the given expressions with their definitions: transpiration reverse osmosis distillation excess accumulation desalination investigation evaporation the separation of a liquid from a solid or another liquid by vaporization followed by condensation a change of state from liquid to vapour which can occur at any temperature up to the boiling point the evaporation of water vapour from plant leaves via tiny pores gradual increase in amount until there is a large quantity in one place a larger amount of something than is allowed or needed the salt removed from sea water so that it can be used in homes and factories separation of solute from a solution by causing the solvent to flow through a membrane at pressures higher than the normal osmotic pressure an (official) attempt to find out the reasons for something such as a scientific problem In the text find the words that have the same meaning as the expressions below: extremely important there is not enough of it available the top layer of the earth in which plants grow continue doing something have something inside or have something as a part takes a lot of energy needing a lot of ability, effort or skill