In most places this is true. But the fens are a special case. When peat fen is drained the loss of water pressure allows the extremely porous peat to collapse and restructure, but it also exposes it to the air, causing wastage by oxidation.

This process of wastage is unique to peat soils, which are largely composed of organic matter. When peat is saturated, oxygen cannot reach it, so there is no biodegradation (which tangentially has led to the preservation of bodies such as Lindow Man). But when the peat is drained, biodegradation resumes and the peat evaporates, mostly becoming carbon dioxide.

The speed of this process can best be seen near Holme, where shrinkage was anticipated following the drainage of the fen and a post was driven into the underlying clay in 1851. Since then, some 4 metres of post have been exposed and the ground surface is currently falling by about 1cm a year. Given there was originally 6 metres of peat, it is estimated that all the peat will be gone in 80 years exposing the underlying clay.

So how much CO₂ does this produce? About 120 tonnes per hectare per year. This may not seem a lot but across the whole of the East Anglian fens, this adds up to some 1,000,000 tonnes of CO₂ per year!

Can and should we do anything about this? Well, over 50% of the original area peat has already disappeared (as shown below; the yellow area shows peat fen that has disappeared) so clearly we can do nothing about that.

But some 16,500 hectare of fen survive and much of this falls within our area. But more on that in the next post.