Surveying ecology :
and analysis techniques - measuring abiotic factors, pollution, using living organisms as indicators of environmental changes
- indicator species, pH, oxygen levels
Doc Brown's Biology exam study revision notes
There are various sections to work through,
after 1 they can be read and studied in any order.
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
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
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
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.
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,
Methods of surveying using indicator species
(i) A simple survey might just
consist of just seeing whether certain species are present or not.
(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.
Pros and cons of using
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
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
indicators, particularly of the concentration of sulfur dioxide in the
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.
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
3. Invertebrate animals can be used as
water pollution indicators
and are used as indicators of the concentration of dissolved oxygen in
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
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
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!
|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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