Minet Country Park
Pond dipping
A Rocha Living Waterways has an interest in water quality.
(As we all have!)
A study of the life in water can tell us much about the quality of that water.
The ecology of water is of great importance to all of us. Frequent
pond surveys are being carried out.Without water we die, and with polluted water we fall sick with parasites & water-born diseases. While we would not wish to drink water containing abundant living creatures, the type of living creatures present can show us whether water is safe to drink - after we have filtered them all out! We do not recommend drinking pond water, however healthy the creatures are which flourish in it.
Pond dipping requires a net with a fine mesh, preferably smaller than 1 mm, and a white plastic dish. Microwave dishes are suitable. Sweep the net through the water and empty it into the dish with some pond water. Examine the contents with a magnifying glass. Dip near the surface, near the bottom, near reeds, & in open water.
WARNING:
Pond water is "dirty". You should wear plastic gloves while pond dipping, and should wash your hands before eating or drinking. It’s a good practice to carry sealed antiseptic wipes for cleaning hands.The table below shows how the creatures present indicate water quality. Creatures that can live in polluted water can also live in clean water.
Clean water
[4].
Mayfly larvae
|-----| 1 mm
Mayfly & stonefly larvae can only live in well oxygenated water. They have gills along their bodies for extracting air from the water.
* * * * * * * * * * * * *
Slight pollution
[3]
|-----| 1 mm
Freshwater shrimp
Caddisfly larvae & freshwater shrimps can tolerate slight pollution.
* * * * * * * * * * * * *
Bad pollution
[2]
Water louse & bloodworms (biting midge larvae) can tolerate dirty water.
|-----| 1 mm
Water louse (Asellus aqaticus)
This creature can walk out of water.
|--------| 1 mm
Blood worm (Midge larva) & daphnia
Notice the daphnia carry their eggs in their bodies.
* * * * * * * * * * * * *
Severe pollution, stagnant.
[1]
Drone fly larvae (rat-tailed maggots), & mosquito & gnat larvae obtain oxygen direct from the air at the water surface. They are not dependent on dissolved oxygen for life. Sludgeworms abound under conditions of pollution.
|-----| 1 mm
Mosquito (gnat) larva. Note its breathing tube at the tail.
Emerging from the pupa
* * * * * * * * * * * * *
Contaminated
[0]
No water life.
* * * * * * * * * * * * *
Algae will normally be abundant in healthy water, as it contributes to oxygenation of the water. Pond algae are usually free floating green plants, that can be seen through a microscope.
|---| 0.1 mm
These algae are from the Buckingham Palace Garden Lake
However, excessive "algal bloom" causes problems by blanketing light from the deeper parts of the pond. As it dies out, it smothers other life forms.
You will also see "water fleas" like daphnia & cyclops.
|-------------------| 1 mm
Daphnia in Spirogyra (blanket weed)
|--| 1 mm
Daphnia can be extremely abundant.
The damselfly larva is almost obscured.
|----| 1 mm
A hydra eating a worm.
|------------| 1 mm
Brown hydra
The most suitable microscopes for pond dipping have a linear magnification of 10-30 times. Do not use a cheap high power instrument. Such instruments are not suitable for examining living creatures, as they are too powerful. They need carefully prepared slides, & are likely to show excessive colour distortion.
A x10 magnifying glass is very suitable for looking closely at the creatures you can see swimming about.
