Sampling in lotic reaches: FBILL index

METHODOLOGY

1  Select a river stretch that has not been flooded recently.

Samples should be taken in the central areas or at the edges at depths greater than 0.3 m.

2  Define exactly the river stretch to be sampled.

Sampling should be done a lotic zone; this is strictly necessary in this sampling protocol.

The river reach to be sampled should be 20 times as long as its width, with a minimum of 20 m and a maximum of 200 m (approx.)

In temporary rivers the sample should be taken in an area where the flow is independent of the substrate.

The selected stretch should be at least 50 m upstream of any bridge or any kind of river crossing.

In this zone three (if the river stretch is shorter than 100 m) or four (if more than 100 m in length) areas are selected. Each area should measure 2 m^², and between them they should include all the substrates and velocities of the lotic zone.

3 Sampling to be done in each of the 3 or 4 areas selected: As the sampling is qualitative, a representative sample should be obtained.

— Remove the larger stones from the net.

— If the stones are less than 10 cm in diameter, kick an area equivalent to 1 m and collect all the material disturbed, holding the net against the flow of the river.

Repeat the above in all the areas selected.

If the samples are to be identified subsequently in the laboratory, preserve them in 70% ethanol or 4% formaldehyde.

Remember that the net should have a mesh of 250µ (and the opening should have a diameter of at least 30 cm).

The net should be carefully cleaned between two consecutive sampling stations in order to prevent the presence of animals from the previous sampling.

4 Sorting, identification and counting

The sample may be examined in the laboratory or in the field. Field examination is recommended only when the observer has considerable experience in taxonomy.

— Wash the sample in water

— Place the sample in a white tray with somc water

Pick up the microinvertebrates. The larger ones may be taken directly with the tweezers; for the smaller ones use a stereoscope at 10x

— Identified animals are kept in vials with 70% ethanol and labelled

In samples with a large number of animals subsarnpling may be done, but a minimum ot 200 individuals should be sorted, identified and counted under the stereoscope.

The following abundance code should be used:

1 = 2 or fewer individuals;

2 = 3-10 indv;

3 = 11-100 indv.;

4 = more than 100.

Place the sample in a white tray with some water.

• Identify the animals directly with the naked eye or using a magnifying glass.
• Identification should proceed until no new families are detected.
• If the macroinvertebrates cannot be properly identified in the field the animals should be kept in vials and taken to the laboratory for correct identification.
• The following abundance code should be used:

  1 = 2 or fewer individuals;

  2 = 3-10 indv;

  3 = 11-100 indv.;

  4 = more than 100.

   

• Caution should be taken if the tray is full of litter. In this case the sample should be divided into several parts and each of them carefully examined for macroinvertebrates.

Steps to follow in order to calculate the index after sampling, sorting and identifying the macroinvertebrates.

Use the table in the following way:

1. Starting with input group A, check whether any of the families are present in any of the groups.

2. When you find a family belonging to one of the input groups, select the top or bottom line depending on the number of families found (in groups A, B and C only).

3. Finally, the taxonomic richness (total number of families) in the sample is used to determine the FBILL value.