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Bog Water

Most of the water on a bog fell as rain not all that long ago, and has made its way fairly rapidly just below the surface through the thin layer of living vegetation. The peat under that surface layer of living vegetation is saturated with water, just like a sponge that will contract in a dry spell of weather to make sure that the overlying skin can itself remain saturated. Otherwise the water in that peaty sponge moves very slowly indeed.

So water is almost literally the life blood of a growing bog. The water is not all locked in peat. It lies at the surface of the bog in natural pools, and in man-made cuttings and drains.

The acid bog waters of raised bogs is characterised by having hydrogen (H⁺) as the dominant cation and sulphate as the main cation.

The high concentration of hydrogen ions (pH values are often below 4) is partly a product of acidification induced by the growth of species of bog moss or Sphagnum. The ionic composition of bog water shows quite strong geographical variation, reflecting variation in the solute concentrations in rainfall. Concentrations of sodium ions (Na⁺) are greater than in more continental bogs, reflecting maritime influence. In the more oceanic environments, particularly as one moves westwards across the countryside, the pH of bog water may increase slightly.

Bog water is clean and acid and not very high in nutrients, so it's not suitable for all forms of aquatic life. But there is a tremendous diversity of life forms surviving in the bog.

The base of the pools may be coated in slimy algae. Close examination of the material found reveals a tangle of fine threads of the alga called Spirogyra.

There are other kinds of algae in the water as well. Some of the darker green blobs are dense clusters of desmids. These are the single celled green algae that build up the food base on which the animals feed. There are dozens of different kinds of desmids. A few are shown in the drawing.

Even so, bog water is naturally low in nutrients, and many of the animals that live in the water depend on what comes in from the outside. The surface film of the water is like a web that tangles small unwary flying insects, and a bevy of small scavengers lie in wait for these windfalls. The most dramatic is the raft spider, which skulks in the vegetation at the edge of a pool with the tips of two of its legs resting gently on the water, alert for the slightest disturbance of the surface film. When prey arrives, it dashes across the water to capture it. It's a big creature - the biggest spider we have - but it's able to spread its weight so that the water can support it.

A more obvious member of this scavenging fraternity are the shiny whirligigs that scoot over the surface - they are the most accomplished swimmers in the habitat. Other creatures inhabiting the surface film of bog pools are pond skaters, water measurers and water crickets.

Dragonflies are often the top predators in bog pools, which, due to their acidity, lack fish. Many dragonflies are able to tolerate highly acidic conditions as larvae, favouring bog pools with Sphagnum. The dull brown nymph is fiercely carnivorous. It moults 12 times over a two to three year period before emerging from the pool as a young flying adult. In the water a range of mini-beasts occur including water scorpion, water louse, water spider, water beetle, caddis fly larva, mayfly larva, damselfly larva and water boatmen.

One of the most distinctive features of bog water is its brown colour and slight iron taste. The colour is due not so much to iron as to a mysterious mixture of chemicals from the peat. Bushmills claims that some of the unique and wonderful flavour of its whiskey is due to the blend of chemicals in its peaty water, which flows down from the bogs on the Antrim plateau.

There is often a lot of iron in the water, and there is a fascinating group of bacteria that use it to fuel their peculiar lifestyle. These bacteria add oxygen to the iron salts in the water, and that chemical reaction gives them the energy they need. A by-product of the reaction is an extremely fine grained deposit of rusty material, which you often see in drains around the bog. This is ochre, the first mineral substance exploited by mankind - as pigment, tens of thousands of years old. It used to form around iron-rich see pages on the growing bogs in the past, and the rusty deposits sometimes accumulated for centuries, forming substantial mounds of ochre. Bog iron ore was important: it made very fine steel, and it was especially suitable for gas purification and as a source of chemicals - which is where most of it went in the end, in the age of gas lighting.