English chalk streams are less healthy than we thought and are potentially even contributing to global warming, said Dr Mark Trimmer at a Science Media Centre press briefing today.
Dr Trimmer looked at a plant that covers up to three quarters of the surface of some streams and found that it helps methane generated in the sediment beneath the plants to escape into the atmosphere. "We found similar emissions to some UK peat bogs" said Dr Trimmer from Queen Mary, University of London. "This changes our perception of the health of the ecosystem and it indicates another disadvantage of agriculture."
Over 90% of the methane emissions from the river Frome in Dorset that reach the atmosphere do so via the stems of water crowfoot. The plant also causes a build-up of sediment from neighbouring farmland, which aids the production of methane by bacteria in the stream.
"Chalk streams are a British specialty habitat and a priority under the UK's Biodiversity Action Plan. They have a high status but there is growing concern about their ecological decline."
Dr Trimmer estimates that the total area of chalk streams in the UK is around 20 km2. The situation he observed in Dorset is likely to be widespread. More research is needed to understand methane emissions from chalk streams fully. "There is obvious climatic concern for any unquantified potential source of methane."