Recall How can we monitor air, water and soil pollution? Write down what BOD stands for and the definition. How can BOD be used to identify pollution? Learning outcomes You should all be able to: Describe an indirect method of measuring pollution levels. Most of you should be able to Explain an indirect method of measuring pollution levels – biotic index Explain how BOD can be used to assess pollution levels in water. Biochemical Oxygen Demand A measure of the amount of dissolved oxygen required to break down the organic material in a given volume of water through aerobic biological activity. Biochemical Oxygen Demand Amount of oxygen in the water required to decompose organic wastes (dead plants, leaves, grass clippings, manure, sewerage, food waste, etc.) Indirect measure of pollution Starter Analyse the diagram and explain what is happening. How can BOD be used to assess pollution levels? High BOD means low Dissolved Oxygen for plants / fish / invertebrates. High BOD = a lot of organic pollution Determined by number of organisms that are present and the rate or respiration. BOD indicates organic matter pollution How to measure BOD Take a sample of water Measure the oxygen level Place it in a dark place at 20°C for 5 days. After 5 days measure the oxygen again BOD = difference between 2 measurements. Source of pollutant BOD (mg dissolved oxygen needed l-1) Unpolluted river <5 Treated sewage 20-60 Raw domestic sewage 350 Cattle slurry 10,000 Paper pulp mill 25,000 Test yourselves Four factories discharge effluent containing organic matter into rivers. The table shows the volume of discharge into the river and the resulting biological oxygen demand. Factory Volume of Effluent / 1000 l day-1 BOD / mg l -1 A 14.0 27 B 1.0 53 C 3.0 124 D 0.8 33 1 Explain whether these pollution data are for point source or non-point sources. 2 Which pollution source, point source or non-point source is easier to regulate? Explain your choice. 3 Which factory is adding most to the BOD of the river into which it discharges? Indirect methods of measuring pollution BOD Abiotic factors Biotic factors Pollution Indicators What are pollution indicators? The organisms in polluted water tell you that there is something wrong. Examples of pollution indicators Lichens are plants that grow in exposed places such as rocks or tree bark. Air pollutants dissolved in rainwater, especially sulfur dioxide, can damage lichens, and prevent them from growing. This makes lichens natural indicators of air pollution. For example: bushy lichens need leafy lichens can really clean air survive a small amount of air pollution crusty lichens can survive in more polluted air no lichens air is heavily polluted with sulfur dioxide. Examples of pollution indicators Some invertebrates like bloodworms and rat-tailed maggots, are able to survive in polluted waters Examples of pollution indicators While others like mayfly nymphs and stonefly nymphs can only be found in very clean water. This is what happens when a stream or river becomes polluted 1. 2. 3. 4. 5. Pollutant is added, which kills some living things. Micro-organisms decompose them, they respire and use up the oxygen Lack of oxygen kills other organisms, but a few species stay alive As the water flows, oxygen levels gradually increase Other living things recover too. Sewage pollution and invertebrates Distance downstream from where sewage enters the river (m) What Invertebrates found (not drawn to scale) the water is like Oxygen levels Sewage enters here 010 Dark and cloudy v. smelly Chironomous larva rat-tailed maggot Falling quickly 10-100 Cloudy bad smell Tubiflex worm mosquito larva Very low Sewage pollution and invertebrates 100-200 Slight smell beginning to clear Flatworm caddis fly larva Gradually rising 200+ Clear Stonefly larva mayfly larva Back to normal Freshwater shrimp Stonefly nymph Stonefly nymphs prefer rocky, stony, or gravel bottoms in cool, well-oxygenated, swiftmoving streams or small rivers. Any effluent that reduces the oxygen content of the stream quickly kills the nymphs. Biological Monitoring Working Party (BMWP) = 10 Flattened Mayfly Nymph These are only found in very clean water containing lots of oxygen. They absorb oxygen from the water through their gills. They are primary consumers that eat plants and algae. BMWP = 10 Cased caddis Fly Larvae Caddisflies use silk (like butterflies) to build cases from gravel, twigs, needles, or sand. Different species build distinct cases, but they often lose them when removed from a stream. BMWP = 8 -10 Cranefly Larvae Up to four inches long with a Fleshy, plump, rounded segmented body Its digestive track (internal organs) can be seen moving back and forth as it crawls. No legs and the back end usually has several extensions or finger-like lobes. BMWP = 5 Flatworms 22 Flatworms are unsegmented worms with flattened bodies. Their flatness allows them to shelter beneath stones. Being flat increases the area of skin exposed to the water, which improves the flatworm's oxygen uptake. BMWP = 5 Freshwater Mite Tiny animals related to spiders. Up to 8mm. They have an oval body and 8 legs. Many are brightly coloured. BMWP = 4 Leeches Flat, Worm-like, segmented body. Many are scavengers or feed on other invertebrates. Suckers at both ends are used for attachment, feeding, and locomotion. They swim gracefully and quickly in an up-and-down motion. BMWP = 3 Red Midge Larvae (Bloodworms) These are sometimes called 'bloodworms' because of their bright red colour, but they are not worms at all. They are midge larvae. They eat dead organic matter and can tolerate very low oxygen levels. BMWP = 2 Tubifex Worms These are thread-like worms that live in the mud on stream bottoms. They are filterfeeders They can tolerate extremely low levels of oxygen and are therefore found in polluted water. BMWP = 1 This shows freshwater fauna as indicators of river pollution. Let’s do some monitoring of our own… Read the student instructions and divide the activities between the group – who will take what role? Make sure that you have all the necessary equipment. Visit areas A-D and decide which you think is the most polluted. Complete your results table and method as follows: Monitoring Pollution Roles: Julio = scribe, Emilia = rain analyst, Rodrigo = particulate analyst, Melanie = photographic investigator, Megan = Freshwater species investigator. pH testing of rain samples using UI paper Analysis of particulate levels using dust collector cards & hand lenses – given % cover score Research into lichens & analysis of photographic evidence – given score of present/absent/abundant Research into preferred habitats of freshwater species, and analysis of communities present 1. 2. 3. 4. Area pH of Rain Particulate % Lichen score Freshwater species present Rank 1-4 A B C D - Find source of pollution – traffic survey & check local industry - Lobby local council to introduce traffic calming measures - send leaflets to local industry to inform them of measures to reduce the pollution produced bushy lichens need leafy lichens can really clean air survive a small amount of air pollution crusty lichens can survive in more polluted air no lichens air is heavily polluted with sulfur dioxide.