Sunday, March 18, 2012

How clean is the river? Pretty clean, according to the creepy crawlies!

This afternoon, mum and I spent some quality time together in celebration of Mothers Day - by counting macro invertebrates! (Not quite champagne in a jacuzzi, but anyhow...)

I'd borrowed a net and some books from the ecology lab at college, and so after a delicious, lazy brunch, I slipped on a pair of (leaky, as it turned out) chest waders, strolled down the River Field in the glorious Spring sunshine and hopped in the water to do a quick kick sample. It was shockingly cold and the current was strong, but I managed three samples before my soggy feet had had enough. Mum sat on the bank in the old armchair doing a David Attenborough with the camera. 

We tipped the lot into a bucket and brought it back up to the house. Priorities being what they are, we made a cup of tea, then sat down to try to identify them. We had no petrie dishes or pipettes, so improvised with teaspoons and ramekins - it seemed to work fine! 

Once the mud and silt had settled, we were amazed to see just how much diversity there was in the tray. Rivers are home to so much more than fish and these little creatures can tell us an awful lot about the quality of the water. Insects fall into two broad categories: those that have nymphs (like Mayflies, Stoneflies, Dragonflies and Damselflies) and those that have larvae (like Caddisflies, Midges and Alderflies); then there are the worms, beetles, molluscs, crustaceans and mites.

Some species are less tolerant to pollution than others, so each one - or 'Biological Indicator', as they're scientifically known - is gauged on the Biotic Index and awarded a number from 1 to 10 (the latter being the least tolerant). Adding these numbers up and dividing the sum by the number of species gives us an average value that we can use to describe the water's quality. 

At first, identifying them was fairly tricky, but with the help of the guide from the Field Studies Council, we soon figured it out, and spent a happy hour scooping out creepy crawlies with teaspoons and counting their tails, body segments and legs.

Here's a quick rundown of what we found, along with each species' value on the Biotic Index:

Freshwater Shrimp (6)
Caseless Caddisfly Larva (5)
Stonefly Nymph (10)
Flattened Mayfly nymph (10)
Cased Caddisfly Larva (7)
Swimming Mayfly Nymph (6)
Water Beetle (5)
Snails (3)

This gives us a Macro Invertabrate Biotic Index value of 6.5, which is - while not excellent - not bad either. I'm going to do this a couple of times over the summer to see how the picture changes and hopefully build up a water quality database. Though I might need a new pair of waders first...

Getting in!


Me picking out the weeds

Mum getting a closer look at a Freshwater Shrimp

My soggy waders

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