A ten-year trajectory of hydrological recovery in a restored blanket peatland

The UK supports 15% of the world’s blanket peat cover but much of this vital resource is significantly degraded. Damaged peatlands lose their hydrological integrity, depressing water tables and exacerbating downstream flooding as water is quickly evacuated from hillslopes across bare peat surfaces and through erosional gullies. The restoration of damaged peatlands is a major conservation concern, and landscape-scale restoration by revegetation and damming of gullies is extensive in areas of upland Britain. There is increasing evidence that the restoration techniques can raise water tables and significantly slow the flow of water in addition to providing other ecosystem service benefits. More recently, focus has shifted from stabilising eroding surfaces to reintroducing Sphagnum moss as part of multi-benefit restoration initiatives, but to date there is limited empirical data to evidence its impacts.

This paper reports the results of long-term post-restoration monitoring on the Kinder Plateau in the southern Pennines, UK. Two sites were revegetated using lime-seed-fertiliser-mulch in 2011 and one of these sites was also gully blocked in 2012 and had a further phase of restoration in the form of intensive Sphagnum planting in 2015. A third unrestored control site was also monitored. We present post-intervention trajectories spanning 10 years showing the long-term recovery of vegetation, water tables, runoff generation, water quality, and sediment production.

The trajectories of recovery for different functions differ in form and rate. At both treatment sites, vegetation cover and diversity increased rapidly then expansion slowed as full cover was approached. Sediment production was quickly reduced to levels comparable to intact peatlands within two years and bare peat cover became negligible after ~7 years. Key runoff metrics (e.g. peak discharge and lag time) showed similar immediate step changes as a result of increased surface roughness from the rapid vegetation expansion, followed by more gradual improvements as species richness developed through time.  The addition of gully blocking enhanced the short-term impacts of re-vegetation, amplifying the step change, but on longer timescales there were no additional benefits relative to the revegetation only site. Water tables recovered gradually at a constant rate and there is no sign of this slowing after 10 years. Water quality (DOC and colour) was highly variable throughout the study period and the long-term impact of restoration is inconclusive. The introduction of Sphagnum provided additional hydrological benefits, most notably through further increases in lag times and attenuation of runoff. There is also preliminary evidence that the Sphagnum provides resilience to surface drying.

This study provides the first evidence that the reintroduction of Sphagnum in degraded headwater peatlands can provide additional natural flood management (NFM) benefits compared to standard restoration techniques aimed at stabilising eroding surfaces. We also show that water table recovery does not counteract the benefits of flow attenuation. We emphasise the critical importance of control in assessing the impact of restoration interventions and the need for investment in longer-term (>10 year) monitoring to better understand the hydrological recovery of restored peatlands.