released. The added carbon clouds acidify the runoff water, and changes the local freshwater ecology with an impact on drinking water quality and fish production. Siltation from eroding peat can also be problematic for hydropower facilities. Soil subsidence and water regulation Subsidence (height loss) of drained peatlands has had a severe economic impact on agriculture, infrastructure and urban areas all over the world. As the water from the peatland is drained away, the peat body partly collapses under its own weight, the peat breaks down into smaller parts allowing it to stack denser, and the organic matter oxidizes, i.e. disappears into the air. The height loss through collapse happens quickly and is large (e.g. 30 cm per year), whereas oxidation is a slower but persistent process which is responsible for 1–2 cm subsidence per year in temperate areas (Erkens et al., 2016). In tropical regions, in the first five years after drainage, peatland subsidence is typically 1–2 metres. In subsequent years, it stabilizes to a constant 3–5

from their homes and provoked a partial shutdown of air transportation because of dense smoke covering thousands of square kilometres reducing visibility (Gilbert, 2010). Water pollution Peatland drainage also increases the release of carbon and nitrogen into the water (Charman, 2002; Holden, 2005). Degraded peatlands, eroded due to vegetation clearance, drainage, peat mining or gully formation, cause downstream water pollution. The dissolved and particulate organic carbon can significantly reduce water quality and affect the solubility, transport and toxicity of heavy metals and organic pollutants. Arsenic and lead contamination of drinking water from peatland erosion has been studied in the United Kingdom and may be especially problematic where these metals are concentrated in burnt ash (Rothwell et al., 2011; Clay et al., 2016). These heavy metals were originally deposited by industrial and vehicle emissions and are now slowly being


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