River Irwell
Manchester's most famous river, the River Irwell, flows down through north Manchester to become the Manchester Ship Canal. Salford is the twin city to Manchester and the River Irwell separates the city centre between the two. I'm involved in work on the River Irwell through the Salford Friendly Anglers, which is the oldest established fishing club in the world, and their efforts to improve water quality.
The Anglers' Monitoring Initiative on the River Irwell
Scientific update. Anglers Monitoring Initiative. 15th February 2012
Kick sampling for river bottom invertebrates
We have been coordinating a new study on water quality along the River Irwell since autumn 2011 as part of the Anglers' Monitoring Initiative run by the Riverfly Partnership.
The nymph stages of well-known river flies (mayflies, caddisflies, dragonflies etc) spend the first year or more of their lives living amongst the gravels of the river bed, before hatching out as the adult flies. Different species have different tolerances to pollution and the community composition of riverfly nymphs provides an excellent time-averaged indicator of environmental quality. The Environment Agency use a detailed scoring system for these invertebrates (the Biological Monitoring Working Party, BMWP, score) as part of their river monitoring. However, with resource limitations they are only able to take samples once a year and from just two sites on the River Irwell.
This is where we, the local community, can really make a difference. As part of the Salford Friendly Anglers, a group of us will be collecting monthly samples of riverfly nymphs from over a dozen sites distributed along the River Irwell. By analysing this data we will get a much more detailed map of the health of the River Irwell. Monthly monitoring will also act as a rapid warning system, with unseen pollution incidents being flagged up by changes in the invertebrate sample composition.
The core numbers we get feed back into the Riverfly Partnership's national Anglers' Monitoring Initiative. Beyond that, we are mapping all the data we collect to build up a spatial and temporal picture of the invertebrate community along the River Irwell using GIS (Geographical Information System) software.
Mapping data is available free from the UK Ordnance Survey in various standard GIS formats and it is onto such geographic data that we will mapping our results, using the open-source GRASS (Geographic Resources Analysis Support System) GIS software.
For AMI Recorders
The latest version of the data form for use with the kick sampling:
Excel version for data entry
PDF version ready to print and take out to the river
Send your kick sampling data to: our sampling HQ
All our team have been trained and certified as samplers through Riverfly Partnership training days.
What makes our data so invaluable is the frequency and coverage, which is orders of magnitude greater than the Environment Agency can achieve. For the samplers, please do not spend hours agonising over whether the nymph you are looking at is an olive or a blue-winged olive - what is important is the general picture of abundance spread across groups.
Guide to the invertebrate groups
Cased caddisfly
Distinguishing feature is the case carried by the nymph. Silk fibres hold together the materials of the case, which varied widely between species. The case may be formed of tiny stones or of various kinds of plant matter - some species even include a 'rudder' on the case made from a small twig (e.g. Halesus radiatus).
The caddis nymph inside the case has a segmented body with three pairs of legs, although you cannot see these features unless you remove the nymph from its case.
Caseless caddisfly
The three pairs of legs and paired tail-like legs at the rear are important features to identify a caseless caddisfly. Certain true fly larvae can look similar but have no legs; certain beetle larvae can look similar but do not have the tail-like legs at the rear.
One of the most common caseless caddisflies found on the Irwell is Rhyacophila dorsalis, which is unmistakable from its green colour.
Mayfly (Ephemeridae)
Mayflies have feathered gills along the side of the body, usually seven pairs, and a pair of wing cases that become more distinct as the nymph gets older and larger.
Blue-winged olive (Ephemerellidae)
The blue-winged olive (Serratella ignita) is up to 14 mm in length. One of the easiest distinguishing features is the clear banding of colours on the tails. If you have a live specimen, the blue-winged olive shows an unmistakeable 'donkey kicking' way of swimming - this clearly distinguishes it from the olives (Baetidae) that swim straight.
Stone clinger / flat-bodied up-wings (Heptageniidae)
The broad flattened bodies and large heads of the stone clingers, with eyes on top of the head, make these nymphs easy to identify in the field without needing a hand lens. In the Irwell we find lots of the yellow may dun Heptagenia sulphurea, which has pretty yellow and dark markings.
Olives (Baetidae)
These are slender nymphs with bodies tapering towards the rear. The gills along the side are plate-like and not feathery. Easily distinguished as live specimens from the blue-winged olives by the straight swimming motion (in contrast to the 'donkey kick' of the blue-winged).
Stonefly (Plecoptera)
Two tails and a lack of gills along the side of the abdomen distinguish the stoneflies. The two sets of wing cases are distinct and held out from the abdomen, in contrast to the related mayflies, stone-clingers and olives. The antennae are also long.
Freshwater shrimp (Gammarus spp.)
Small crustaceans up to 25 mm. Distinguish by the curved body, flattened side to side. Quite distinctive.
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