Peatland burning, carbon and water colour
A 1,200 ha upland estate is managed for grouse shooting. Deep peat, averaging 2.5 m, underlies 70% of the area, and heather is burned in small rotational strips. A water company abstracts from a reservoir 6 km downstream. Dissolved organic carbon in the inflow has risen from 4.2 mg/L in 2012 to 7.8 mg/L in 2024, and the company spends £450,000 a year on coagulation and filtration. The estate proposes to stop burning and rewet 300 ha of drained peat by blocking grips. A conservation body supports the change, citing carbon storage and breeding waders. The estate owner warns that without burning, heather will become rank, wildfire risk will rise, and two full-time keeper jobs may go. The local planning authority must decide whether to approve the rewetting plan and a condition ending burning across the whole estate, or only on the rewetted area.
1. Explain how rotational burning can affect peat soils and the colour of the reservoir water.
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Burning removes the vegetation canopy and exposes the peat surface to rain, wind and sunlight. The blackened surface absorbs more radiation and can dry out, while the loss of Sphagnum reduces the peat-forming vegetation. Without a protective cover, peat particles are eroded into drainage channels, and exposed peat oxidises, releasing carbon. Burning can also damage the surface layer and reduce water retention, so the water table falls and decomposition continues. These processes increase dissolved organic carbon and fine particulate matter in runoff. The water company then has to remove colour and precursors before supply, which explains the rising treatment cost. The link is therefore a chain: burning changes vegetation and hydrology, peat erodes and oxidises, and carbon compounds enter the reservoir. The 4.2 to 7.8 mg/L rise in dissolved organic carbon is consistent with this mechanism, although other factors such as climate and drainage also matter.
2. Recommend whether the planning authority should require an end to burning across the whole estate or only on the rewetted 300 ha. Justify with reference to carbon, water and wildfire risk.
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A whole-estate ban would deliver the greatest carbon and water benefits because it removes the disturbance across all 1,200 ha, not just 300 ha, and prevents continued erosion from the remaining burned strips. However, the owner's warning about rank heather and wildfire is credible: if burning stops without grazing or cutting, fuel loads can build up and a severe wildfire could damage peat more than controlled strips. A conditional whole-estate approach is the best judgement. The authority should approve rewetting of 300 ha and require a phased end to burning, but only with a wildfire management plan, controlled cutting or grazing, and a monitoring programme. The two keeper jobs should be retained for management and monitoring. If the estate refuses these conditions, restricting the ban to the rewetted area is a weaker but safer fallback. The recommendation is therefore adaptive rather than a simple ban.
3. Design a five-year monitoring programme to test whether rewetting is working.
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Use paired treated and control plots: 300 ha rewetted and comparable drained peat elsewhere. Measure dissolved organic carbon and water colour at the reservoir inflow monthly, with before-and-after data and a control catchment if possible. Record water-table depth in dipwells, peat surface height and peat bulk density, and vegetation cover, especially Sphagnum. Use fixed-point photography and satellite or drone imagery to map bare peat and rewetting. Record wildfire incidents and fuel loads. Compare treatment costs with the £450,000 annual water-treatment bill. The programme should state success criteria in advance, for example a 20% fall in dissolved organic carbon and a rising water table after five years, and should report uncertainty rather than assuming that rewetting alone caused any change.