Restoration of eroded blanket peatlands through revegetation and gully blocking is observed to also deliver significant natural flood management (NFM) benefits (reduce and delay floodpeaks). But ...there is a lack of clear understanding regarding how different catchment processes interact/counteract under each intervention scenario. We seek to provide more insight by rigorously calibrating TOPMODEL rainfall‐runoff model to different experimental catchments each representing an intervention scenario. Through numerical experimentation with the calibrated parameters, we estimate the impact‐magnitude of different processes. Our findings confirm the NFM benefits of these restoration‐focused interventions. In both interventions and in our largest storms, both the delay and reduced floodpeaks are primarily due to surface roughness reducing the floodwave speed thus thickening the overland flow; we conceptualize this as an increase in a “kinematic storage.” Impact of gully blocking in increasing kinematic storage is very significant and comparable to that of revegetation alone. Interventions' impact on “static storage” (interception + ponding + evapotranspiration) becomes important for smaller storms. Although interventions always increase lag times, they can be less effective in reducing peak magnitude when maximum rainfall intensity is sustained for durations longer than mean catchment delay. We propose two approaches to further increase catchment's static and kinematic storage. Finally, while our field‐scale numerical study contributes to the evidence‐base for NFM's effectiveness, it also provides a basis for modeling these interventions in the future. Such catchment‐scale numerical studies are necessary to extend our findings to spatial scales where flooding can cause socioeconomic damage, and to provide a tool for optimizing the distributed configuration of these interventions.
Key Points
Blanket peat restoration interventions significantly reduce flood risk to the downstream communities at risk
Revegetation and gully blocking of eroded blanket peat reduces flood risk primarily through increased surface roughness and not storage
Impact of gully blocking in reducing increasing “kinematic” surface storage is very significant and equivalent to revegetation alone
A diatom record from Moss Lake, Washington, USA spans the last 14,500 cal year and revealed Holocene climate change in the Pacific Northwest (PNW), including evidence for periodicities related to ...ocean-atmosphere teleconnections and/or variations in solar output. Three main climate phases were identified: (i) Late Pleistocene to early Greenlandian (until 10,800 cal year BP, spanning GI-1, GS-1), with a cold climate and low diatom abundance; (ii) early Greenlandian to Northgrippian (10,800–7500 cal year BP), shifting to a warmer climate; and (iii) late Northgrippian and Meghalayan from 7500 cal year BP onwards, with a cooler, moist climate. These climate shifts are in good agreement with the pollen record from the same core and other regional studies. Fluctuations in
Discostella pseudostelligera
and
Aulacoseira
taxa suggest climate cycles of different frequency and amplitude throughout the record. Spectral and wavelet analyses revealed periodicities of approximately 1400 and 400–500 years. We interpret the ~ 1400-year and ~ 400–500-year cycles to reflect alternating periods of enhanced (and reduced) convective mixing in the water column, associated with increased (and decreased) storms, resulting from ocean–atmosphere teleconnections in the wider Pacific region. The ~ 1400-year periodicity is evident throughout the Late Pleistocene and late Northgrippian/Meghalayan, reflecting high-amplitude millennial shifts from periods of stable thermal stratification of the water column (weak wind intensity) to periods of convective mixing (high wind intensity). The millennial cycle diminishes during the Greenlandian, in association with the boreal summer insolation maximum, consistent with suppression of ENSO-like dynamics by enhanced trade winds. Ocean–atmosphere teleconnection suppression is recorded throughout the PNW, but there is a time discrepancy with other records, some that reveal suppression during the Greenlandian and others during the Northgrippian, suggesting endogenic processes may also modulate the Moss Lake diatom record. The large amplitude of millennial variability indicated by the lake data suggests that regional climate in the PNW was characterised over the longer term by shifting influences of ocean–atmosphere dynamics and that an improved understanding of the external forcing is necessary for understanding past and future climate conditions in western North America.
Peatlands provide a range of ecosystem services but are sensitive to changes in climate and land-use, and many peatlands globally are degraded. We analyse a large-scale, unique and diverse dataset, ...collected over 15 years, as part of major landscape scale blanket peat restoration projects in the south Pennines, UK. Trajectories of ecosystem change after restoration were assessed by measuring key ecosystem responses including: vegetation cover and indicator species; water table, runoff, and water quality.
The reactions of these metrics vary in their behaviour, both in the timing of first response and the rate of change towards a new stable state. Re-establishment of vegetation is a key driver in rapidly reducing particulate carbon loss and attenuating stormflow, while over time biodiversity is improved by the return of native species, and water tables gradually rise. The phasing of these ecosystem service responses indicates that there are different characteristic timescales for the improvement of peatland functions, driven by both surface and subsurface processes. The rapid establishment of vegetation cover over two years, and its importance in improving a broad range of functions, signify it as a key milestone for reporting project success within typical funding timeframes.
This study supports the adoption of Lime-Fertiliser-Seed-Mulch restoration on eroding blanket peatlands globally. The trajectories developed are important to help guide practitioners of ecological restoration. Better understanding of the dynamics underpinning the slower response times of subsurface hydrological and biogeochemical function is identified as a key knowledge gap. An understanding of the limits of ecosystems recovery is important when target setting for restoration projects, especially where attaining pristine conditions is unachievable.
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•Ecosystem services show phased recovery following restoration in eroded peatlands.•Re-vegetation is key to reporting project success over short funding timeframes.•Results support wide-scale adoption of Lime-Seed-Fertiliser-Mulch restoration.
Atmospheric deposition of trace metals and metalloids from anthropogenic sources has led to the contamination of many European peatlands. To assess the fate and behaviour of previously deposited ...arsenic and lead, we constructed catchment-scale mass budgets for a degraded peatland in Northern England. Our results show a large net export of both lead and arsenic via runoff (282 ± 21.3 gPb ha−1 y−1 and 60.4 ± 10.5 gAs ha−1 y−1), but contrasting controls on this release. Suspended particulates account for the majority of lead export, whereas the aqueous phase dominates arsenic export. Lead release is driven by geomorphological processes and is a primary effect of erosion. Arsenic release is driven by the formation of a redox-dynamic zone in the peat associated with water table drawdown, a secondary effect of gully erosion. Degradation of peatland environments by natural and anthropogenic processes has the potential to release the accumulated pool of legacy contaminants to surface waters.
► The fluvial outputs of arsenic and lead in the degraded peatland are an order-of-magnitude greater than atmospheric inputs. ► The particulate phase dominates fluvial lead export, whereas the aqueous phase dominates fluvial arsenic export. ► Lead export is a primary effect of peat erosion, whereas arsenic export is a secondary effect of peat erosion.
Degraded peatlands can be significant sources of previously deposited arsenic and lead
Concentration depth profiles and inventories of solid-phase As, Sb, Pb, and Cu were determined in 210Pb-dated cores from an ombrotrophic peat bog in northwest England. Cores were collected from the ...peat dome and adjacent to an eroding gully. Down-core distributions of As, Sb, Pb, and Cu in the dome core are almost identical. The water table is close to the dome surface with only short-term draw-down. Under these conditions, As, Sb, Pb, and Cu are immobile, allowing the reconstruction of trends in historical contaminant deposition. The peak in atmospheric deposition of As, Sb, Pb, and Cu (4.59, 2.78, 147, and 26.7 mg m−2 y−1, respectively) occurred during the late 19th century. Stable Pb isotope ratios reveal that Pb deposition during this period was from indigenous and foreign sources. The mean water table is much lower at the gully edge, and there are pronounced interannual fluctuations. These conditions have not affected the integrity of the Pb and Cu records but have caused postdepositional mobilization and redistribution of As and Sb. Cumulative inventories show significant loss of As and Sb at the gully edge site. Long-term water table draw-down in ombrotrophic peat bogs has the potential to alter the geochemistry and fate of previously deposited As and Sb.
Upland peat soils are generally regarded as effective sinks of atmospherically deposited lead. However, the physical process of erosion has the potential to transform peat soils from sinks to sources ...of lead contamination. Lead input and fluvial lead outputs (dissolved
+
particulate) were estimated for a contaminated and severely eroding peatland catchment in the southern Pennines, UK. Lead input to the catchment is 30.0
±
6.0
g
ha
−1
a
−1 and the output from the catchment is 317
±
22.4
g
ha
−1
a
−1. Suspended particulate matter accounts for 85% of lead export. Contaminated peat soils of the catchment are a significant source of lead to the fluvial system. This study has demonstrated strong coupling between the physical process of erosion and the mobilization of lead into the fluvial system. The process of peat erosion should therefore be considered when estimating lead outputs from peatland catchments, especially in the context of climate change.
Erosion can transform peat soils from sinks to sources of lead contamination.
•DIN concentrations in waters of degraded peatlands are high.•Peatland restoration significantly reduces DIN leaching to upland freshwaters.•DOC and DON are closely coupled in waters draining bare or ...revegetated peatlands.
This study assesses the impact of peatland restoration on fluvial N dynamics of south Pennine headwaters (UK) using a space-for-time approach. We monitored dissolved nitrogen in catchment drainage waters at intact, bare, and early stage restoration peatland sites over a two year period (Jan 2013–Dec 2014). Our study demonstrates that peatland restoration is effective in reducing dissolved inorganic nitrogen (DIN) leaching to levels lower than, or comparable to, the intact peatland site despite the adoption of a restoration approach involving fertilizer application in the revegetation process. In comparison with the bare site, DIN leaching was ∼92% (10.2kgNha−1yr−1) lower at the restored site − where vegetation cover has been recently reintroduced. Whilst restoration increased the proportional significance of dissolved organic nitrogen (DON) when compared to the bare site, it was not to a level significantly different from what existed at the intact site. The results also reveal a strong positive relationship (P<0.001) between DON and dissolved organic carbon (DOC) at all the sites, suggesting similarity of source material. Nitrate decreased with increasing DOC concentrations across the sites, suggesting the influence of organic C supply on NO3− immobilisation. In all but the bare site, average DON concentration was low in winter, but high in summer, and DIN concentration exhibited a winter-high and summer-low pattern; although year-on-year variations in this seasonal pattern was observed mainly at the bare site. Overall, our study has shown that restoration/revegetation is effective in advancing ecosystem recovery of degraded peatlands. Understanding nitrogen behaviour and trajectories as peatland restoration moves beyond early phases will require long-term catchment-scale monitoring.
There is evidence that damaged peatlands can negatively affect the delivery of water related ecosystem services. There is interest in peatland restoration to meet different regulatory targets, ...including the Water Framework Directive (WFD). A comprehensive assessment of the economic benefits of restoration is missing. This paper synthesises hydrological and bio-geochemical knowledge on peatland restoration, as well as insights in the monetary valuation of water quality improvements in freshwater systems. This is used to identify challenges in valuing water quality related benefits from peatland restoration. The paper concludes that there is strong evidence for rapid ecological responses to peatland restoration related to reduced suspended sediment loads, and sufficient evidence that re-wetting will prevent further decline in water quality. Two main challenges arise for valuation: (1) incomplete evidence of effects of restoration on final ecosystem services and benefits, and (2) the spatial and temporal differences in peatlands’ responses. We suggest developing valuation scenarios on a case-by-case basis, using best available evidence of the changes associated with restoration described by a categorization of peatland status similar to the ecological status ladders developed for the WFD. These would need to be tested with the public and should include an element of uncertainty in services provision.
•There is strong evidence of rapid responses to restoration of suspended sediments.•Rewetting is expected to prevent further longer term declines in water quality.•There is incomplete evidence of effects on final ecosystem services and benefits.•Spatial and temporal differences in peatland’s responses affect potential valuation.•Way forward: Valuation based on status classifications and including uncertainty.
Peatland carbon stores are under widespread anthropogenic pressure, resulting in degradation and carbon loss. This paper presents DO14C (Dissolved Organic Carbon) dates from waters draining two ...eroded blanket peatland catchments in the UK. Both catchments are characterized by severe gully erosion but one additionally has extensive surface erosion on unvegetated surfaces. DO14C values ranged from 104.3 to 88.6 percent modern (present to 976 Before Present). The oldest DOC dates came from the catchment characterized by both gully and surface erosion and are among the oldest reported from waters draining temperate peatlands. Together with peat age‐depth data from across the peatland landscape, the DO14C ages identify where in the peat profile carbon loss is occurring. Source depths were compared with modeled water table data indicating that in the catchment where gully erosion alone dominated, mean water table was a key control on depth of DOC production. In the system exhibiting both gully erosion and surface erosion, DOC ages were younger than expected from the age of surficial peats and measured water tables. This may indicate either that the old organic matter exposed at the surface by erosion is less labile or that there are modifications of hydrological flow pathways. Our data indicate that eroded peatlands are losing carbon from depth, and that erosion form may be a control on carbon loss. Our approach uses point measurements of DO14C to indicate DOC source depths and has the potential to act as an indicator of peatland function in degraded and restored systems.
Plain Language Summary
Peatlands are the largest terrestrial soil carbon store, but are under widespread anthropogenic pressure, resulting in degradation and carbon loss. In this study of UK upland peatlands, we used radiocarbon dating of dissolved organic carbon (DOC) from waters draining eroded peatlands to identify the age of the carbon that has been lost. These dates are among the oldest reported from waters draining temperate peatlands. The dates combined with age‐depth data from across the peatland landscape allowed us to model where in the peat profile the carbon loss was concentrated. We compared these results with water table data and found that in the systems we studied, the type of peatland erosion that the system had experienced was an important factor controlling the age of carbon lost. The close association between radiocarbon age of carbon and water table suggested that radiocarbon dating of DOC might be a useful catchment scale proxy for water table, a direct measurement of the locus of carbon loss from the peat, and an effective measure of the overall “health” of the peatland ecosystem. The approach therefore has potential as a rapid method of assessing stabilization and restoration of intact peatland function.
Key Points
We present old 14C dates from waters draining eroded temperate peats, caused by deep C loss and low water tables in gullied peats
Novel approaches to dissolved organic carbon source identification indicate that water table drawdown and the nature of peat erosion influence loss of old carbon
Our method has potential as a rapid way to indicate peatland function and assess restoration success
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