The Centre for Ecology & Hydrology's Prof Chris Evans writes about his work with peat bogs and leaky carbon

Chris Evans bog infographic

Much of the water we drink in the UK comes from our uplands, and a lot of this water is naturally brown. This is because it contains dissolved organic compounds leached from the soil, especially where – as is the case in many of our upland areas – that soil is peat. Water companies already invest large amounts of money and energy in removing these compounds during the water treatment process. 

But the trouble is, our upland waters have been getting browner – much browner. We know this because CEH and partner organisations in the UK Upland Waters Monitoring Network have been monitoring the quality of water in the upland lakes and streams of the UK for the past quarter of a century, during which time concentrations of dissolved organic carbon (DOC) have roughly doubled. 

This has increased treatment costs for water companies, and also increased the risks of toxic by-products, created by reactions between DOC and the chlorine compounds used in water treatment, entering water supplies. One solution to this problem is to invest in new water treatment processes, but another – which is being trialled by a number of water companies – is to try to reduce the amount of DOC leaching from the soils in the first place. 

Because many of the UK’s uplands have been historically degraded by human activities such as drainage, over-grazing and burning, the hope is that restoring them to a more natural state might reduce DOC losses to lower levels, which would reduce the need for expensive, energy-intensive water treatment processes. Such ‘nature based solutions’ are also appealing because of the other benefits they deliver – restoring the UK’s peat bogs will also enhance their biodiversity, reduce their greenhouse gas emissions, and possibly reduce flood risk in the rivers which drain then. So if investment in peat restoration by Britain’s water companies delivered not only better drinking water quality but also all these other benefits, it really would be win-win. 

So the multi-million pound question is, will it work? Unfortunately, the answer isn’t clear-cut. The brown elephant in the room is that DOC concentrations have been going up not only in reservoirs draining degraded peat bogs, but in lakes and rivers all over the UK uplands, in Scandinavia, in Central Europe and even in parts of North America. At the start of September I gave a talk at the International Water Association’s Natural Organic Matter conference in Malmö, and it was clear that the Swedes – and the Finns, and the Norwegians – have all the same challenges with rising water colour in drinking water supplies that we do. And we think we know why: acid rain. Back in the 1970s and 80s, sulphur pollution from coal burning power stations affected vast areas of Northern Europe. As well as killing fish and damaging forests, this pollution also changed the chemistry of the soil, making it more acidic. In effect, the soil got stickier – so more of the organic matter produced by plants and soils stayed in the soil, and less made it out into lakes and streams. 

Over the last 30 years, Europe has succeeded in reducing acid rain by well over 90%, to the immense benefit of our sensitive natural ecosystems. Unfortunately for the water companies, one of the consequences of this remarkable achievement has been increasing water colour. We can even see, using new techniques to reconstruct historical conditions using lake sediments, that DOC concentrations are returning to levels last seen in the 19th century, before the onset of acid rain. Of course, the Victorians had bigger health problems to worry about than the colour of their water, but (despite our love of DOC in the form of coffee or tea) it seems unlikely that the British population today would be happy to have brown stuff coming out of their taps. 

So does all this mean that the efforts of the water companies to reduce water colour by managing their catchments are doomed to fail? At risk of ducking the question, the answer appears to be yes, and no. Whatever anyone does, we are never going to go back to the clear (acidified) lakes and streams of the 1970s – we now live in a browner world. On the other hand, it seems very likely that poor management of our peatlands in the past has made matters worse, and that better management of them in the future could make things better.

At CEH, we are trying to understand these processes, and to develop models to predict how DOC may change in the future. We are also investigating whether other nature-based measures, such as reducing nutrient inputs to reservoirs, might reduce the problems that water companies face in treating water colour. If they can, then it would reduce the need for more concrete, chemicals and energy for water treatment, which in turn would mean lower costs for the water industry, and lower costs for customers, i.e. all of us. If this also happened to help restore and protect uplands that store carbon, support biodiversity and reduce flood risk, then it’s hard to argue that this would be anything other than a good thing. 


Tweets of Chris Evans presenting at the IWA Specialist Conference on Natural Organic Matter in Water - Malmö, Sweden (7-10 September, 2015)


Further information:

Prof Chris Evans' staff page

Carbon Catchments project page

External sites

The UK Upland Waters Monitoring Network 

Dissolved Organic Matter in Freshwater Ecosystems

Macronutrients Cycle Programme


Science areas: