A ten-year trajectory of change in a restored blanket peatland: implications for natural flood management

<p>The UK supports 15% of the world’s blanket peat cover but much of this vital resource is significantly degraded. In damaged peatlands runoff is quickly evacuated from hillslopes across bare peat surfaces and through erosional gullies, exacerbating downstream flooding. The restoration of damaged UK 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 significantly slow the flow of water in addition to providing other ecosystem service benefits. More recently, focus has shifted from stabilising eroding surfaces to the reintroducing <em>Sphagnum</em> moss as part of multi-benefit restoration initiatives.</p><p>This paper reports the results of long-term post-restoration monitoring on the Kinder Plateau in the southern Pennines of the U.K. Two sites were revegetated using lime-seed-fertiliser-mulch in 2011 and one of the 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 biogeomorphological changes spanning 10 years, showing the long-term trajectories of vegetation cover, runoff, sediment production, and water table.</p><p>The trajectories of recovery for different functions differ in form and rate. At both treatment sites, vegetation cover increases rapidly then slows as full cover is approached. Sediment production is quickly reduced to levels comparable to intact peatlands within two years and bare peat cover becomes negligible after ~7 years. Key runoff metrics (e.g. peak discharge and lag time) show similar immediate step changes as a result of increased surface roughness from the rapid vegetation expansion, followed by more gradual improvements as species richness develops through time.  The addition of gully blocking enhances the impact of re-vegetation alone, amplifying the step change, but there are no further benefits apparent in the longer-term trajectory. The introduction of <em>Sphagnum</em> provides further roughness, leading to marked increases in lag times and attenuation of runoff. There is also preliminary evidence that the Sphagnum inhibits surface drying, providing resilience to future climatic and anthropogenic stressors.</p><p>This study provides the first evidence that the reintroduction of <em>Sphagnum</em> in degraded headwater peatlands can provide additional Natural Flood Management benefits compared to standard restoration techniques aimed at stabilising eroding surfaces. We also show that water table recovery is not at odds with flow attenuation. We also note the importance of control assessing the impact of restoration interventions and the need for investment in longer-term (>10 year) monitoring to better understand the recovery of restored peatlands.</p>