UK GCSE level age ~14-16, ~US grades 9-10 Biology revision notes re-edit 23/05/2023 [SEARCH]

Surveying ecology : 8. Monitoring and analysis techniques - measuring abiotic factors, pollution, using living organisms as indicators of environmental changes - indicator species, pH, oxygen levels

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INDEX of biology notes on ecological surveying


(8) More on monitoring and analysis techniques - measuring abiotic factors - pollution

and using living organisms as indicators of environmental changes - indicator species

  • 1. Surveying using indicator species

  • Despite the presence of pollutants, some species of plants/animals can live in polluted air or water, but other organisms need clean air or clean water to survive and prosper.

    • Some organisms are particularly sensitive to changes in their environment and can be studied to monitor the effect of human activities on the environment - such organisms are called indicator species.

    • The absence or presence of these indicator species can be monitored and used as indicators of pollution e.g. so you can say much about whether a particular atmospheric or aquatic environment is relatively polluted or unpolluted.

    • So, these indicator specie, being quite sensitive to their environment, can used in environmental monitoring and hopefully control things to improve matters.

    • These pollution indicators may live ...

      • ... on surface exposed to air e.g. lichen on rocks/stone walls, blackspot fungus on roses,

      • ... live in water e.g. mayfly larvae, stonefly larvae, freshwater shrimps, bloodworms, sludgeworms.

        • ... and other organisms used to indicate levels or air or water pollution.

    • Methods of surveying using indicator species

      • (i) A simple survey might just consist of just seeing whether certain species are present or not.

        • This will tell you whether there is/is not pollution, but it can't measure how polluted a situation is.

      • (ii) You can employ some observational-catching technique to actually count the population of a species in a given area of land or volume of water.

        • Numerical data is better for estimations of levels of population and level of pollution, especially if you can repeat the survey at regular time intervals.

      • Pros and cons of using indicator species

        • Using indicator species is a relatively quick and simple way of indicating whether land, water or air is polluted.

        • Unfortunately, you cannot get an accurate value for the concentration of a pollutant e.g. this might need specialist chemical analysis.

        • The observations may be biased in a negative way due competition between species for he same food resources.

        • Therefore, sometimes it is better to use some non-living indicator methods - see section 4.

        • Below, in sections 2. and 3. I've described the use of a variety of living indicator species.

  • 2. Lichens can be used as air pollution indicators, particularly of the concentration of sulfur dioxide in the atmosphere.

    • Lichen

    • The cleaner the air in the environment, the more varied species, and the greater numbers of an individual species of lichen colonies are seen on rocks and stone walls. You would observe the 'cleaner air' effect if you surveyed walls all the way from a polluted town or city centre to some rural location away from roads well beyond the town or city boundary, and no doubt note the greater the numbers and variety of lichen growing on the walls the further you where from the town/city centre.

    • Therefore, lichen species can be used as quite a sensitive air pollution indicator i.e. low populations of a limited number of lichen species indicates polluted air, usually from sulphur dioxide (SO2).

    • Particular lichens are sensitive to poisonous sulfur dioxide (even in very low concentrations of SO2) from fossil fuel burning - road vehicle exhausts, power station chimneys etc.

    • Blackspot fungus readily grows on roses in relatively clean unpolluted air, but does not grow as readily in polluted air - the fungus is killed by the polluting sulfur dioxide. One advantage an urban gardener has over a country gardener!

  • 3. Invertebrate animals can be used as water pollution indicators and are used as indicators of the concentration of dissolved oxygen in water.

    • Lakes that are stagnant from overgrowth of algae (eutrophication from fertiliser run-off) become devoid of oxygen at lower levels because the decay bacteria use up the oxygen. This decreases invertebrate populations and animals that feed on them, like fish, also decline - so whole food-chains and complex ecosystems are disrupted.

    • If rivers become polluted from raw sewage spills or silage spills, the concentration of pathogens rise (extra food for them e.g. nitrate nutrients) and these microorganisms use up the oxygen, so all species needing oxygen decline - which is nearly everything!

      • Certain bacteria will thrive in these conditions and consume oxygen in the process.

      • Some aquatic invertebrate species actually thrive in low oxygen polluted water e.g. a high population of blood worms, rat-tailed maggots and sludge worms indicates very polluted water.

    • Particular invertebrate animals like the mayfly larvae and stonefly nymphs are sensitive to pollution, so their population size is a very good indicator of the purity of the water.

      • Mayfly larvae and freshwater mussels can tolerate slightly polluted water - just sufficient oxygen for them to survive.

      • Alderfly larvae cannot survive in polluted water - not enough oxygen for them to respire.

      • The above describes the effect of three levels of pollution - high, medium and low.

    • The less pollution in the lake or river water, the less the growth of algae/bacteria etc. and the more oxygen dissolve in the water (less used up), therefore the more mayflies and stoneflies hatched out for the trout! and more trout for the fisherman! BUT only in clean unpolluted water!

      • Knowledge and understanding of the process of eutrophication is not required.

  • 4. Environmental changes can be measured using non-living indicators (usually sensors - scientific instruments) to monitor factors such as oxygen levels in water, temperature, pH and rainfall.

    • You should understand the use of equipment to measure oxygen levels, temperature and rainfall, all of which are important indicators of environment change on land or in water and the bigger picture of global climate change.

      • Special meter probes can be dipped into water to measure oxygen levels, a bit like pH meter probes that measure pH (which is also an important indicator of relative acidity-alkalinity). A decline in aquatic oxygen levels as measured by an oxygen probe gives an immediate warning of pollution.

      • Temperature can be measured directly and very accurately with a mercury thermometer (being replaces on health and safety grounds), or, electronically using a thermocouple system. Average temperatures for the year, or seasonal averages, are important indicators of climate change. Both air and sea temperatures are monitored.

      • Specialised electronic instruments can automatically and continuously monitor air pollution levels of gases like carbon monoxide, sulphur dioxide and ozone levels in the atmosphere.

        • The data can be continuously fed, stored and analysed in computer systems for detailed analysis of air pollution patterns on a long-term basis, so a decline or an improvement in environmental conditions can be seen and its progress monitored.

        • You can follow pollutions levels of air pollutants from motor vehicles 24/7 in a city centre.

        • You can do the same with pH, oxygen level and temperature probes continually monitoring water systems like rivers.

      • Rainfall is easily monitored with a rain gauge, manually with a calibrated glass container (a bit like a measuring cylinder), or automatically by weighing the water collected with a sensitive balance. Like temperature, rainfall is an important aspect of regional climate data.

        • All of these monitoring systems can be fully automated these days and so 'automatic weather stations' can be set up in remote locations and data sent by radio to a weather centre or laboratory.

        • Satellites are being used to monitor several environmental factors eg decline of forests by burning and replace with cattle or crops, the area of ice/snow cover in arctic regions eg changes in the Greenland and Antarctic ice sheets. Even individual remote glaciers can be monitored - decline of some with temperature rise is concerning climate scientists studying global warming.

      • pH paper or pH meters can used to measure and monitor the relative acidity or alkalinity of water.

      • pH paper you might get in a soil testing kit.

You can measure the pH of a solution very accurately using a pH meter and a glass membrane pH probe. The pH meter is calibrated against a standard buffer solution of accurately known pH. You can test for acidity (pH <7) or alkalinity (pH >7) in rain water, river water etc. or water shaken with soil (after filtration or settling out). You can also use this instrument with a probe to measure water temperature too.



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