Biology Fieldwork

GCSE

Method

A frog in a pond

2. Method

Kick sampling in moving water

Kick sampling is suitable for shallow running water with a gravel or muddy bottom. The general idea is to dislodge the invertebrates from the river bed and trap them in a net. You can then take them out of the net for counting and identification. 

Hold a fine-mesh net in the direction that you are facing. This should be downstream of where you are standing. Use one foot to kick the bottom of the stream, dislodging the substrate in the direction of the net. Animals dislodged from the substrate will be washed into the net.

As sampling disturbs the substrate, always take the first sample at the lowest point upstream, then work back upstream.

Make sure you standardise:

  • The time you spend kicking at each site (e.g. 30 seconds)
  • The area of stream bed that you sample at each site

You could place a 50cm x 50cm quadrat on the stream bed, and only kick within the area of the quadrat. If the mouth of the net is smaller than the quadrat, you may need to kick more than once. By standardising the time spent kicking and the area disturbed, you can make a direct count of the density of invertebrates. If you standardise just the time spent kicking, you make a relative estimate of abundance only.

Sweep netting in still water

In still water such as a pond, or if the water is too deep to enter safely, stand on the bank and vigorously sweep a net in the water, ideally tracing out a figure-of-eight shape.

Make sure you standardise:

  • The time you spend sweeping at each site (e.g. 30 seconds)
  • The volume of water that you sample at each site

You could place a bottomless plastic dustbin in the water, to limit a known volume of water, and only sweep the net within the area of the dustbin. By standardising the time spent sweeping and the volume of water swept, you can make a direct count of the density of invertebrates. If you standardise just the time spent sweeping, you make a relative estimate of abundance only.

Identifying freshwater animals

Add some water from the stream or pond to a white plastic tray. Invert the net and empty the contents fully into the tray. After you have emptied the contents, wash the net through with pond or stream water before using it again.

Leave the tray to settle for about a minute. it will be much easier to identify the animals once you see them moving. Use a spoon or pipette to move different groups of animals into holding trays. Try to identify and count as many of the animals as you can use FSC freshwater invertebrates guide to aid identification.