Joseph Holden

Artificial drainage of peatlands: hydrological and hydrochemical process and wetland restoration

Peatlands have been subject to artificial drainage for centuries. This drainage has been in response to agricultural demand, forestry, horticultural and energy properties of peat and alleviation of flood risk. However, there are several environmental problems associated with drainage of peatlands. This paper describes the nature of these problems and examines the evidence for changes in hydrological and hydrochemical processes associated with these changes. Traditional black-box water balance approaches demonstrate little about wetland dynamics and therefore the science of catchment response to peat drainage is poorly understood. It is crucial that a more process-based approach be adopted within peatland ecosystems. The environmental problems associated with peat drainage have led, in part, to a recent reversal in attitudes to peatlands and we have seen a move towards wetland restoration. However, a detailed understanding of hydrological, hydrochemical and ecological process-inter-actions will be fundamental if we are to adequately restore degraded peatlands, preserve those that are still intact and understand the impacts of such management actions at the catchment scale.

Peatland hydrology and carbon release: why small-scale process matters.

Peatlands cover over 400 million hectares of the Earths surface and store between one-third and one-half of the worlds soil carbon pool. The long-term ability of peatlands to absorb carbon dioxide from the atmosphere means that they play a major role in moderating global climate. Peatlands can also either attenuate or accentuate flooding. Changing climate or management can alter peatland hydrological processes and pathways for water movement across and below the peat surface. It is the movement of water in peats that drives carbon storage and flux. These small-scale processes can have global impacts through exacerbated terrestrial carbon release. This paper will describe advances in understanding environmental processes operating in peatlands. Recent (and future) advances in high-resolution topographic data collection and hydrological modelling provide an insight into the spatial impacts of land management and climate change in peatlands. Nevertheless, there are still some major challenges for future research. These include the problem that impacts of disturbance in peat can be irreversible, at least on human time-scales. This has implications for the perceived success and understanding of peatland restoration strategies. In some circumstances, peatland restoration may lead to exacerbated carbon loss. This will also be important if we decide to start to create peatlands in order to counter the threat from enhanced atmospheric carbon.

Piping and pipeflow in a deep peat catchment

Abstract Natural pipes are common in many upland blanket peats, yet little is known about pipe network morphology or pipeflow processes. Most information on soil piping comes from the shallow peaty podzols of the Welsh uplands, where monitoring suggests that pipes may be important contributors to streamflow. This paper presents information on piping and pipeflow from a deep upland blanket peat catchment in the Pennine Hills of Northern England. Pipe outlets are found throughout the soil profile ranging from the underlying substrate at ∼3-m depth to pipes which are within a few centimetres of the surface. Mean pipe diameters range from 3 to 70 cm; some pipes are over 150 m long. Slopes in the catchment are less steep than those usually associated with soil piping. Continuous flow records were obtained from 15 gauging sites on 8 separate pipes. The pipeflow response from deep blanket peat was found to be different to that reported in the shallow peaty podzols of the Welsh uplands; the distinction between ‘ephemeral’ and ‘perennial’ pipe types does not appear to be useful within the deep Pennine blanket peat. Response times from all of the pipes are short, even from pipes deep within the peat. At the same time pipes have a prolonged recession limb such that they maintain low flow for longer periods than most other runoff production processes within the catchment. Pipeflow contributes around 10% of the streamflow volume, but can at times contribute up to 30%. Soil pipes may, therefore, be far more important in some upland peat catchments than previous work has hitherto suggested.

Environmental effects of drainage, drain-blocking and prescribed vegetation burning in UK upland peatlands

Peatlands are important ecosystems for carbon (C) storage, provision of water resources and biodiversity. UK blanket peats represent 10—15% of those found worldwide. While many peatlands continue to be managed through artificial drainage and vegetation burning, it has long been recognized that local habitats and ecological diversity are strongly influenced by these practices. This paper reviews the hydrological, physicochemical and ecological effects of three widespread UK peatland management practices, namely artificial drainage, drain-blocking and rotational heather burning. Drainage and burning of peat often lead to altered runoff regimes, oxidation of organic matter, changes to C, nitrogen (N) and phosphorus (P) cycling, and increased metal and suspended sediment concentrations in streams relative to intact peatlands. Although artificial drainage is now rarely implemented on UK upland peats, a great number of historical drains remain, thus drain-blocking is increasingly being applied to restore many peatlands. In contrast, recent increases in the intensity and extent of rotational heather burning may result in further changes to peatland ecosystems. Relatively little is known about the environmental effects of rotational heather burning compared with drainage and drain-blocking management, and for all three of these management techniques there is scarce information on river ecosystem response. We hypothesize some likely effects of basin-scale drainage, drain-blocking and heather burning on stream ecosystems and illustrate these with a schematic model. Such a holistic consideration of peatland river basins is particularly timely with respect to the implementation of the EU Water Framework Directive.

Anticipating and managing future trade-offs and complementarities between ecosystem services

This paper shows how, with the aid of computer models developed in close collaboration with decision makers and other stakeholders, it is possible to quantify and map how policy decisions are likely to affect multiple ecosystem services in future. In this way, potential trade-offs and complementarities between different ecosystem services can be identified, so that policies can be designed to avoid the worst trade-offs, and where possible, enhance multiple services. The paper brings together evidence from across the Rural Economy and Land Use Programmes Sustainable Uplands project for the first time, with previously unpublished model outputs relating to runoff, agricultural suitability, biomass, heather cover, age, and utility for Red Grouse (Lagopus scotica), grass cover, and accompanying scenario narratives and video. Two contrasting scenarios, based on policies to extensify or intensify land management up to 2030, were developed through a combination of interviews and discussions during site visits with stakeholders, literature review, conceptual modeling, and process-based computer models, using the Dark Peak of the Peak District National Park in the UK as a case study. Where extensification leads to a significant reduction in managed burning and grazing or land abandonment, changes in vegetation type and structure could compromise a range of species that are important for conservation, while compromising provisioning services, amenity value, and increasing wildfire risk. However, where extensification leads to the restoration of peatlands damaged by former intensive management, there would be an increase in carbon sequestration and storage, with a number of cobenefits, which could counter the loss of habitats and species elsewhere in the landscape. In the second scenario, land use and management was significantly intensified to boost UK self-sufficiency in food. This would benefit certain provisioning services but would have negative consequences for carbon storage and water quality and would lead to a reduction in the abundance of certain species of conservation concern. The paper emphasizes the need for spatially explicit models that can track how ecosystem services might change over time, in response to policy or environmental drivers, and in response to the changing demands and preferences of society, which are far harder to anticipate. By developing such models in close collaboration with decision makers and other stakeholders, it is possible to depict scenarios of real concern to those who need to use the research findings. By engaging these collaborators with the research findings through film, it was possible to discuss adaptive options to minimize trade-offs and enhance the provision of multiple ecosystem services under the very different future conditions depicted by each scenario. By preparing for as wide a range of futures as possible in this way, it may be possible for decision makers to act rapidly and effectively to protect and enhance the provision of ecosystem services in the face of unpredictable future change.

How wetlands affect floods

It is widely recognised that wetlands play an important role in the hydrological cycle, influencing groundwater recharge, low flows, evaporation and floods. This has led to policies being formulated world-wide to conserve and manage wetlands to deliver these key services, especially flood risk reduction. Generic statements have often been published about wetland hydrological services but the term “wetlands” covers many land types, including wet woodlands, reedbeds, peat bogs, fens, and salt marshes. Each of these wetland types can have a hydrological function that is subtly different, making it difficult to generalise the flood reduction services of wetlands. In this paper we focus on two example wetland types (upland rain-fed wetlands and floodplain wetlands) to demonstrate why there are differences in flood functions both within and between wetland types. Upland wetlands generally tend to be flood generating areas while floodplain wetlands have a greater potential to reduce floods. However, landscape location and configuration, soil characteristics, topography, soil moisture status and management all influence whether these wetlands provide flood reduction services.

Overland flow velocity and roughness properties in peatlands

Overland flow is an important component of peatland hydrology. Hydrological models of peatlands are being developed that require estimates of flow velocity and its controls. However, surprisingly little is known about overland flow velocities in peatlands. Some peatlands have also been drained using open ditches, and these need to be incorporated into flow models. This paper presents field data on the velocity of overland flow and drain flow in upland peatlands. The relationships between flow velocity, vegetation cover, slope, and water depth are explored. Sphagnum provided a significantly greater effective hydraulic roughness to overland flow than peatland grasses. In all cases, a significant break in process occurred for flows with water depths of around 1 cm so that there were two components of the roughness curve. This is consistent with partial submergence theory for very shallow flows where resistance increases with depth as the soil surface first becomes fully submerged. While each surface cover type should be considered separately, the results also suggest that a first-order estimate of Darcy-Weisbach roughness and mean velocity can be based on a single parameter for each surface cover. This paper presents an empirical overland flow velocity forecasting model that can be applied to peatlands. The model combines the partially submerged component for flows with water depths below 1 cm with the fully submerged component for flows with depths up to 5 cm, which are representative of the depths of flows that occur across peatlands.

Restoration of blanket peatlands.

There is concern that ecosystem services provided by blanket peatlands have come under threat due to increasing degradation. Blanket peatlands are subject to a wide range of drivers of degradation and are topographically variable. As a result, many degradation forms can develop, including those resulting from eroding artificial drainage, incising gullies and areas of bare peat. Many degraded blanket peatlands have undergone restoration measures since the turn of the century. However, there has been little formal communication of the techniques used and their success. Using practitioner knowledge and a review of the available literature, this paper discusses the methodologies used for restoring sloping blanket peatlands. It then considers current understanding of the impact of restoration on blanket peatland ecosystem services. There is a paucity of research investigating impacts of several common restoration techniques and much more is needed if informed management decisions are to be made and funding is to be appropriately spent. Where data are available we find that restoration is largely beneficial to many ecosystem services, with improvements being observed in water quality and ecology. However, the same restoration technique does not always result in the same outcomes in all locations. The difference in response is predominantly due to the spatial and temporal heterogeneity inherent in all blanket peatlands. Peatland practitioners must take this variability into account when designing restoration strategies and monitoring impact.

Sediment and particulate carbon removal by pipe erosion increase over time in blanket peatlands as a consequence of land drainage

Land drainage is common in peatlands. Artificially drained blanket peat catchments have been shown to have a significantly greater soil pipe density than intact catchments. This paper investigates the role of surface land drains in the enhancement of soil piping in blanket peats. The density of piping was found to significantly increase in a linear fashion with the age of the drainage. Thirty-five years after drains were cut, slopes would be expected to have twice the density of soil piping than would an undrained blanket peat catchment. The rate of pipe erosion increases exponentially over time, so that particulate carbon loss from subsurface pipes is greatest where drains are oldest.

Priority water research questions as determined by UK practitioners and policy makers

Several recent studies have emphasised the need for a more integrated process in which researchers, policy makers and practitioners interact to identify research priorities. This paper discusses such a process with respect to the UK water sector, detailing how questions were developed through inter-disciplinary collaboration using online questionnaires and a stakeholder workshop. The paper details the 94 key questions arising, and provides commentary on their scale and scope. Prioritization voting divided the nine research themes into three categories: (1) extreme events (primarily flooding), valuing freshwater services, and water supply, treatment and distribution [each >150/1109 votes]; (2) freshwater pollution and integrated catchment management [100-150 votes] and; (3) freshwater biodiversity, water industry governance, understanding and managing demand and communicating water research [50-100 votes]. The biggest demand was for research to improve understanding of intervention impacts in the water environment, while a need for improved understanding of basic processes was also clearly expressed, particularly with respect to impacts of pollution and aquatic ecosystems. Questions that addressed aspects of appraisal, particularly incorporation of ecological service values into decision making, were also strongly represented. The findings revealed that sustainability has entered the lexicon of the UK water sector, but much remains to be done to embed the concept operationally, with key sustainability issues such as resilience and interaction with related key sectors, such as energy and agriculture, relatively poorly addressed. However, the exercise also revealed that a necessary condition for sustainable development, effective communication between scientists, practitioners and policy makers, already appears to be relatively well established in the UK water sector.