Short-term impact of peat drain-blocking on water colour, dissolved organic carbon concentration, and water table depth

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Water discolouration is a major management problem for UK water companies as a proportion of the supply relies on runoff from peat-covered catchments. Many peats have been drained using surface ditches but this has been shown to lead to more severe water discolouration. Drain-blocking is now actively encouraged in UK peatlands to promote peatland habitats and water companies are considering funding drain-blocking if water colour benefits can be demonstrated. However, there is concern that rewetting of the peat may lead to a sudden flush of water colour from the peat causing problems for water treatment works downstream. This study tested different drain-blocking techniques in an upland peat catchment and evaluated the impact of drain-blocking on water colour production immediately after drain-blocking. The study started sampling prior to the blocking of the drains and continued for 10 months afterwards. It was shown that drain-blocking significantly increased water tables in the vicinity of the drains. Drain-blocking approximately doubled water colour within blocked drains, a difference that was sustained across the entire study period. Whenever runoff occurred from a blocked drain it was always more discoloured than prior to blocking. However, during the 10 months following drain-blocking no catchment scale change in river water colour could be determined. No drain-blocking technique was demonstrably better or worse than any other with respect to water colour and percentage of time for which there was flow in the drain. Therefore, if more drain-blocking is undertaken then the most economical methods, using peat turves, should be adopted.