| Water
Pollution Detectives
2002 was seen as a very bad
year in as far as pollution is concerned. Many fish and other organisms
have died as a result of polluting industries. Why don’t you carry out
Pollution detective? Follow the following exercise and teach it to your
friends.
Concept
The enrichment of rivers and
streams by nutrients or organic pollution leads to changes in the minibeast
community. The diversity of these invertebrates can be used to monitor
pollution.
Context The presence
or absence (or better, the relative abundance) of minibeasts in rivers
can be recorded. The diversity and composition of the community sampled,
used in conjunction with a biotic index, allows the monitoring of pollution
levels in water and a comparison between the different sites and seasons.
Equipment
Appropriate nets.
You will also need: a white
sorting dish (a large margarine or ice cream tub is ideal)
Items for handling the catch:
plastic spoon-small pipette made from wide plastic tube
To make sorting and observation
of different creatures easier, try to find moulded plastic containers with
a number of sections (some food packaging may be suitable plastic egg cartons
or ice cube trays from fridges). Animals can now be taken from the main
white tray and separated.
Using it
Identify several running water
sites to compare. It is important to have some idea of the freshwater minibeasts
(invertebrates likely to be present in good, clear water in your area.)
There are some standard "scoring systems" available, but it is possible,
and perhaps better to construct your own. As a generalisation a list can
be made with the animals most susceptible to organic pollution at the top
and those most tolerant to pollution at the bottom i.e.
5 Insect nymphs e.g.
stonefly, mayfly, damsel fly
4 Adult insects e.g.
beetles and bugs
Some insect larvae e.g. caddis
fly larvae
3 Crustacea e.g. amphidos
2 Molluscs & Crustacea
e.g.
isopods
1 "Worms" including
leeches, and worm-like larvae e.g. bloodworms
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1. It is impo to identify a technique
of catching animals with a net depending on the size of the river.
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2. Record the presence or absence
of each animal or type of animal. It is not necessary to identify every
species accurately but useful to know for example the number of types of
mayfly.
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3. The greater the diversity,
the better the water quality. Also the higher the score (the more of the
types towards the top of the list) the better. You might record one stream
as a "5" and another as a "3" Or you could take into account all the groups
found on the highest scale. So a stream with two "5" animals would score
10 while a stream with a greater diversity of clean water animals (e.g.
four in category "5") would score 20.
Adapting it
To make the assessment more
realistic, take into account the relative abundance of each animal or group
scoring each into a broad category such as:
1=one animal only
2=between 2 and 10 animals
3=between 11 and 50 animals
4=between 51 and 100 animals
5=over 100 animals found in
the sample.
So two streams each "category
5" animals could be "5/1" and "5/5". Clearly the one with the greatest
total number of insect nymphs is likely to be cleaner.
Such studies lead on to asking
about sources of pollution. Where there is intensive agriculture or sewage
pollution, the levels of nitrate will be high. You can measure this with
chemically impregnated dipping sticks. As these are relatively expensive,
try cutting them vertically down the middle to double the sticks (it will
still be possible to read the colour changes against the graduated scale).
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