A9. Sampling benthic invertebrate in deep rivers

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Figure 1 : Decision tree of the protocol for deep-river sampling. © Environment Agency 2017

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1 Objectives

Deep rivers aren’t a well-known environment because of the sampling difficulties. The aim of the following method is to know the macroinvertebrate community in these habitats not wadeable and unsuitable to use the kick-sampling methodology (see Unit-time invertebrate survey).

The key literature informing this page are:

2 Method summary

Figure 2 : Long-handled pond net. © Environment Agency 2017
Figure 3 : Yorkshire airlift sampler. © Environment Agency 2017

Deep water sampling has always been a challenge and several methods exist to perform it. It appears that only the Yorkshire Airlift sampler (Mackey, 1972) can give reliable abundance data. It is a sensitive and more accurate method for the wide and deep waters, additionally from being more cost-effective than other methods routinely used for monitoring. However, occupancy can be obtained by a variety of techniques including nets, grabs, dredges, freeze-corers, artificial substrates, light traps or several airlifts models.

To help managers in picking the most appropriate method, a decision tree Figure 1 has been designed to allow managers - considering the river characteristics – to choose between a conventional Pond-net, a Long-handled pond net, or an airlift sampling method.

The sampling method is guided by two river features: the average depth of three measurements taken at ¼, ½ and ¾ of the river width, and by the average width of the river. The pond net is recommended to sample shallow rivers of an average depth < 80cm (wadeable rivers) while the Long-handled pond net Figure 2 is more suitable for rivers > 80cm depth and <15m width (deep but narrow rivers). For rivers other than these two features (deep and wide rivers), Long handled pond nets don’t allow you to properly sample some deep habitats. Also, mid-channel benthos relative with their habitat proportion don’t provide reliable data, risking site misclassification and lowering habitat quality. It has to be discounted for this particular case and replaced by a vessel carried Yorkshire airlift sampler Figure 3 which is the unavoidable sampling tool (NS Share, 2006).

The Yorkshire airlift sampler is made with a 1.4m long and 10cm diameter plastic pipe with a right angle and a 45-degree angle bend on which is attached a collecting net. Air comes from an air supply cylinder and enters through the bottom of the pipe. The low density created by the air bubbles going up inside the pipe cylinder generate a bottom-up current due to the water flow entering the bottom of the device. Macroinvertebrates are washed away in this current and are trapped inside the net. The protocol to be accorded to the RIVPACS/RICT sampling method is 3 minutes of active airlift sampling of the main channel usually performed by one transect or several transects over habitats in proportion to their occurrence. It is followed by 1 minute of active marginal sampling with a conventional Pond net. Benthic fauna trapped in the net should be collected and stored in ethanol after the sample.

Techniques shouldn’t be combined within a single sample and the material characteristics of the Yorkshire airlift sampler have to be respected in order to get standardized samples usable in the RIVPACS/RICT database, which is advised to get a reliable analysis of your river and compare it with others. Indeed, future perspective could allow us to use the shallow water model for macroinvertebrates considering at the beginning the “deep river” criteria for the scores and also, because of these comparative results, reduce the number of deep-water reference site to assess to integrate the model.

All these information and protocol details can be found at :

3 Advantages

Long handled pond net

  • Allows a sample to be taken from the bank
  • Light material

Yorkshire airlift sampler

  • Most suitable, precise, and cost-effective, technique for sampling deep rivers
  • Samples collected with the airlift are comparable to a standard RIVPACS kick sample by achieving a sampling variance of less than 20% in all three metrics (BMWP, NTAXA, ASPT)
  • Airlifts work best on gravel or stony river beds
  • The high precision of Yorkshire pattern airlift samples presents an opportunity to counterbalance the increased costs of sample collection with a reduced sampling frequency

4 Disadvantages

Long handled pond net

  • Can be hard to move if the net is heavy when full

Yorkshire airlift sampler

  • Heavy material
  • Need a boat and material
  • Can become clogged by sampling material and bury itself if not well-managed
  • Can raise half brick and big material that can damage the net, less efficient on large boulders

5 Recommendations for methods application

Long handled pond net

  • If the long-handled pond net sampling overly disrupts the margins the 1-minute marginal sample should be taken first, and then the 3- minute long-handled pond net sample
  • Take care not to lose any of the sample when moving the net through the water column
  • Regularly check the frame, if it is bent it reduces its sampling efficiency
  • Use a 50cm deep net to avoid getting blocked by too much sediment
  • The pond net handle including frame should be 4 meters long and graduated to assist in measuring river depth
  • Empty the net bag once it becomes too heavy to easily move through the water, or at least after every minute of sampling
  • Where it is practical and safe to do so, the margins of both banks should be included in the marginal sample
  • Needs at least two people to undertake the sampling

Yorkshire airlift sampler

  • Sample of the margins can be performed by the airlift or by a long-handled pond net (record the device used)
  • Sometimes the streambed is not visible and sampling according to the habitat proportions present is impossible. In that case, the airlift sample should cover as many separate areas of river as is possible within the sampling area
  • Each airlift sample takes an absolute minimum of three minutes to collect, don’t count the time for repositioning the boat
  • Both the 3-minute airlift component and the 1-minute marginal component are pooled to form the complete airlift sample
  • Bounce the airlift gently on the river bed to prevent it digging in too deeply or becoming clogged
  • Find the Generic risk assessment and Safe systems of work, and health and safety aspects of airlift sampling document to prepare yourself and work safely

6 Cost

A manufactured Thames airlift costs around £2000 per unit, it should be approximately the same for the Yorkshire airlift sampler.

A Long handled pond net costs below £150 per unit.

7 Protocol and data analysis

Data analysis should include computation of water quality indices. The macroinvertebrate community can be assessed comparing its composition with environmental variables.

8 References

  • Davy-Bowker, J., Jones, J. I. and Murphy, J. F. (2014) Standardisation of RIVPACS for deep rivers: Phase I - deriving a standard approach to deep river sampling.
  • Environment Agency (2017) Freshwater macro-invertebrate sampling in rivers.
  • NS Share (2006) Review of methods for sampling invertebrates in deep rivers Final Report T1(A5.1) - 1.1.
  • Davy-Bowker, Jones and Murphy, 2014. Sampling benthic macro-invertebrates in deep rivers - "Standardisation of RIVPACS for deep rivers: Phase I - review of techniques for sampling benthic macro-invertebrates in deep rivers”
  • Mackey, A. P. (1972). An air-lift for sampling freshwater benthos. Oikos, 413-415. https://www.researchgate.net/publication/271810660_An_Air-Lift_for_Sampling_Freshwater_Benthos .