3.3.3 Temperature All aquatic organisms have a fairly well-defined temperature tolerance range and this determines their distribution. Temperature affects the saturation concentration of dissolved oxygen (as seen in Table 2). An increase in water temperature will reduce the oxygen solubility as well as increase the metabolic activity of aquatic organisms. The combination of these two effects means that oxygen demand by organisms increases just when oxygen supply is being reduced. Coarse fish such as perc
3.3.1 Turbidity, colour and suspended solids As water runs off the land, there are some substances which do not dissolve but are taken along as
suspended solids. Then, depending on their sizes and the velocity of the river, the solid particles may settle out at a certain point or be carried on further. Quantities are affected by seasonal changes and tend to be higher in winter because of increased storm
runoff
due to higher rainfall and melting snow. The quantity of suspended solids (measured in g m<
3.3 Physical characteristics of natural waters A river's physical characteristics include: clarity/turbidity colour speed of flow/turbulence odour the presence of plants and macroscopic animal life. The physical characteristics are determined by location, geology and climate of the catchment area. In turn they influence the chemical and biological characteristics of the watercourse. The physical appearance m
3.2 Dissolved oxygen Organic and inorganic nutrients are the basic food supply essential for maintaining the plants and animals in natural watercourses. Equally essential to aquatic life is a supply of oxygen, needed for respiration. Oxygen dissolved in the water is also needed in the biodegradation of organic matter by aerobic (oxygen-consuming) bacteria. A measure of this
oxygen demand
can be obtained experimentally and is defined as the
biochemical oxygen demand
(BOD). The BOD i
3.1 Water, the medium of life The list of necessities for the provision of life includes various nutrients and water: water is one of the basic resources needed for the process of photosynthesis. Since it is an excellent solvent, water, even in its ‘natural’ state, is never pure H2O but contains a variety of soluble inorganic and organic compounds. Water can also carry large amounts of insoluble material in suspension. The amounts and types of impurities vary with location and time of year, and determine so
2.12 Summary The hydrological cycle is a complex process involving evaporation, transpiration, condensation, air circulation, precipitation, infiltration, surface run-off and percolation. Aquifers are an important source of fresh water supplying about one-third of the UK's potable water demand. Most of the world's water is present as saline water in the oceans. 2.10 Aquifers
Groundwater
is water that, after infiltrating and percolating through surface soils, flows into an
aquifer, an underground water-bearing layer of porous rock. About one-third of the UK's drinking water is drawn from aquifers. To permit economic development, an aquifer must be able to transmit large quantities of water from one point to another and therefore it must have a high permeability. The groundwater contained in aquifers is released from springs an 2.9 Percolation Movement of infiltrated water downwards through the zone of aeration (Figure 5) is known as percolation. The infiltrated water which does not remain held by capillary forces in the surface soils moves by the action of gravity through the unsaturated layers of soil or rock until it arrives at the water table. Here the percolated water joins the body of groundwater which seeps slowly to the sea. 2.8 Surface run-off In some inland drainage areas, all water is removed by evaporation and infiltration. However, precipitation not penetrating the land surface usually runs off the surface along defined channels which have been produced by geological processes, previous storms, or possibly by people. This accelerates the process. Its eventual destination is the ocean, except, of course, where it runs to inland seas such as the Dead Sea. It is in the runoff phase of the cycle that physical intervention by humans 2.7 Infiltration Entry of precipitation through the soil surface and on downwards, by gravity, is known as infiltration. The rate at which this process can take place is governed by the permeability (a measure of the ease with which water can flow through the subsurface layer) and by the existing degree of saturation of the soil. Infiltration can be impeded by outcropping impermeable rocks or by paved areas, and also by the presence of finegrained soils with a low permeability (such as clay). At certain times 2.2 Evaporation At an interface with the atmosphere, water changes its state from a liquid to a vapour in response to an increase in temperature caused by an external heat source. This temperature change is normally the result of solar radiation. The transfer of moisture into the air is called evaporation. The process is also controlled by the relative humidity, or level of vapour saturation, of the air. The greater the relative humidity of the air, the less likely it is that evaporation will take place for 2.1 Introduction The hydrological cycle, the continuous cycling of water between land, open water surfaces and the sea, either directly or indirectly, is an extremely complex process which has been known for a long time (Figure 1). The identifiable mechanisms of the cycle are complicated not only by the characteristics of air-water-land interfaces across which the cycle operates, but also by climatic factors which vary in both time and space. The various operations and mechanisms within the cycle are illustra References 4.2 New ways of thinking and acting: systems practice There are a wide variety of concepts and theories relating to management and managing. This unit is centred on the ideas and techniques that we believe define systems thinking, but it also draws upon concepts and theories from other areas where these are deemed to be useful. On top of this we see systems practice as requiring a readiness to use the experiential model of learning set out by Kolb, bringing theory and practice together in a meaningful way. It may be helpful to set out what 4.1 What it means to be good at managing What does it mean to be ‘good at managing’ and what part does systems thinking and practice play? One way to explore the first question is to ask what you know about your work that a school leaver, or someone fresh from university, would not know. Consider a senior secretary, for example, someone who clearly has a fair amount of managing to do, in our terms. Such a person must have certain basic skills and knowledge (in word-processing, filing, etc.) the foundation of which will have been 3 The acquisitive model of learning (Please refer to Reading 3: Models of the learning process, by Mary Thorpe) What happens when we learn? I shall explore three explanations, or models, of learning which attempt to answer this question. These three models have particular strengths and weaknesses. The point is not to choose between them, but to consider which one has the ‘best fit’ for different kinds of learning. The three models are introduced in turn, and each is followed by an activity that invites you to apply th 2.4 Using a variety of methods for effective study You may find it difficult at this stage to recognise what kind of activity would be most helpful for which parts of course study. In any case, people differ in what works best for them. The important point is to review the activities you are using for studying, particularly where you are setting yourself ambitious goals, or where you are finding things difficult. It might prove helpful to try out activities that you often avoid, or to ask other students how they study parts of the course that 2.2.2 Understanding Much more important than memorising, where academic study is concerned, is understanding. This is the kind of learning which requires a willingness by the learner to work with ideas and concepts, and a willingness to explore whether an idea has really been mastered or only partially grasped. Making mistakes can be a helpful stage in this kind of learning because the mistakes can reveal what it is that is not understood. It is when we put right, or sort out, such mistakes in understanding that 2 1 Different conceptions of learning (Please refer to Reading 2: What is learning?, by Mary Thorpe) Although we spend large amounts of our lives learning, intentionally and otherwise, it is quite unusual to spend any time thinking about what learning actually is. This reading gives you an opportunity to do so, and to consider whether how we choose to learn is always appropriate for what we are trying to learn. Spending time thinking about what learning is, how we define it and what it involves, is important for two reasons 3.1 Categories of fiction A genre is a particular type or category of fiction. It can apply to both the long and short form (Author(s):
Author(s):
