A simple model to quantify the potential trade-off between water level management for ecological benefit and flood risk

Throughout the world, historic drainage of wetlands has resulted in a reduction in the area of wet habitat and corresponding loss of wetland plant and animal species. In an attempt to reverse this trend, water level management in some drained areas is trying to replicate a more natural ‘undrained’ state. The resulting hydrological regime is likely to be more suitable to native wetland species; however the raised water levels also represent a potential reduction in flood water storage capacity. Quantifying this reduction is critical if the arguments for and against wetland restoration are to be discussed in a meaningful way. We present a simple model to quantify the hydrological storage capacity of a drainage ditch network under different water level management scenarios. The model was applied to the Somerset Levels and Moors, UK, comparing areas with and without raised water level management. The raised water level areas occupy 11% of the maximum theoretical storage but when put in the context of the recent severe flooding of winter 2013/2014 occupy only 0.6% of the total flood volume and represent an average increase in flood level of 7 mm. These results indicate that although the raised water level scheme does occupy an appreciable volume of the maximum possible ditch storage, in relation to a large flood event the volume is very small. It therefore seems unlikely that the severity of such large flood events would be significantly reduced if the current water level management for ecological benefit ceased

Wetland hydrological monitoring: overview and Boxford Water Meadows case study

The aim of this report is to provide the reader with the information required to make informed decisions about the best and most appropriate way to monitor a wetland site. To achieve this aim, the report has the following objectives: 1. To outline the need and purpose for monitoring. 2. To summarise the methods used to identify and categorise wetland types. 3. To describe the broad types of monitoring that may be undertaken. 4. To give detailed information about the range of wetland monitoring techniques available. 5. To provide guidance on how to select the most appropriate monitoring techniques. 6. To illustrate, using the Boxford wetland as a case study, how the techniques described in this report can be applied, and what challenges and solutions are encountered

TESSA: A toolkit for rapid assessment of ecosystem services at sites of biodiversity conservation importance

Sites that are important for biodiversity conservation can also provide significant benefits (i.e. ecosystem services) to people. Decision-makers need to know how change to a site, whether development or restoration, would affect the delivery of services and the distribution of any benefits among stakeholders. However, there are relatively few empirical studies that present this information. One reason is the lack of appropriate methods and tools for ecosystem service assessment that do not require substantial resources or specialist technical knowledge, or rely heavily upon existing data. Here we address this gap by describing the Toolkit for Ecosystem Service Site-based Assessment (TESSA). It guides local non-specialists through a selection of relatively accessible methods for identifying which ecosystem services may be important at a site, and for evaluating the magnitude of benefits that people obtain from them currently, compared with those expected under alternative land-uses. The toolkit recommends use of existing data where appropriate and places emphasis on enabling users to collect new field data at relatively low cost and effort. By using TESSA, the users could also gain valuable information about the alternative land-uses; and data collected in the field could be incorporated into regular monitoring programmes

Nutrient dynamics in a semi-natural treatment reedbed

Constructed wetlands are increasingly being used to treat polluted water and reedbeds in particular are widely favoured for removing nutrients from wastewater. Reedbed systems are generally considered cheaper to operate than their industrial counterparts, and have the additional benefit of providing valuable habitat which has the potential to support a wide range of wetland species. Whilst the nutrient removal rates of these systems may be monitored for a period following creation, there is a lack of long term monitoring and as a result there is a poor understanding of how removal efficiency changes with time. In addition, factors such as vegetation type, residence time and latitude of the reedbed all affect the nutrient removal rates. This work focuses on a treatment system at the Wildfowl and Wetlands Trust Reserve at Slimbridge in Gloucestershire, which receives a high nutrient load from the reserve’s bird populations. Recently collected hydrochemical data is compared to data collected shortly after the creation of the reedbed and show that comparing the inflow and outflow concentrations, the system currently reduces only ammonia concentrations; nitrate concentrations are unchanged and phosphorus concentrations increase. Potential management options that may improve removal capacity are discussed

Special issue – coastal dune slack hydro-ecology

Coastal dune slack wetlands exist at the interface between land and sea. They typically occur in the low-lying areas between dune ridges where the water table remains at or near the ground surface for some or all of the year. Like many wetland habitats, the hydro-ecological conditions provide a niche in which specially adapted species can exist. Notable dune slack species with European protection include the natterjack toad (Bufo calamita) and the fen orchid (Liparis loeselii). Dune systems are amongst the most dynamic of all habitats and dune wetlands can appear or disappear in timescales comparable to human lifespans as coastal processes deposit or erode the substrates upon which they form. It is these dynamic processes that create areas of bare sand suitable for development of early successional stages of dune vegetation whilst elsewhere in the dune system natural succession drives a progression towards more mature vegetation. Over time, anthropogenic pressures including afforestation, abstraction and addition of nutrients have resulted in a decline in the quality and extent of dune habitat such that the majority of humid dune slacks across Europe are now in unfavourable condition. Management to address these pressures and improve dune habitats is underway in many countries however the complex mix of natural and anthropogenic processes that influence dune wetlands is at times difficult to disentangle making it hard to identify the most suitable management practices at particular sites. Up to now effective management of these habitats has not been supported by a coordinated presentation of the relevant research. The establishment of multidisciplinary groups such as the UK Sand Dune and Shingle Network has proved effective in bringing together the range of expertise necessary to affect change. This special issue is the result of the second meeting of the network’s Sand Dune Hydrology Group which was held in Swansea in September 2013 with the intention of supporting effective habitat management through sound science

How effective are reedbeds, ponds, restored and constructed wetlands at retaining nitrogen, phosphorus and suspended sediment from agricultural pollution in England?

A high priority topic within the Department for Environment, Food and Rural Affairs (DEFRA) water quality programme is the mitigation of diffuse rural pollution from agriculture. Wetlands are often cited as being effective at reducing nutrient and sediment loadings to receiving waters. However, the research in this area is inconsistent, and whilst most studies have shown that both natural and constructed wetlands retain nutrients and sediments, others have shown that they have little effect, or even increase nutrient and sediment loads to receiving water bodies. DEFRA has commissioned a systematic review on the use of wetlands to mitigate N, P and SS inputs from agriculture to receiving freshwater in England. The review will encompass a comprehensive literature search on all available material on the subject, both published and unpublished within the British Isles. Specific inclusion criteria will be adhered to and a formal assessment of the quality and reliability of the studies will be undertaken. The data will then be extracted and a data synthesis undertaken. The review will inform an evidence-based policy that can be implemented by stakeholders

Review of hydrological issues on water storage in international development

Water is essential for all life is and occurs in various natural stores of the Earth’s hydrological cycle, including lakes, wetlands, rivers and aquifers. However, natural spatial and temporal variability in climate means that water of sufficient quantity and adequate quality is not always available for human needs (drinking, growing crops, generating power, supporting industry or maintaining ecosystem services, such as fisheries). Almost 900 million people lack safe and reliable water supplies. To meet the Millennium Development Goals we need to improve water availability. Future anticipated climate change and population increases will exacerbate this problem. Economic performance of countries is linked to their ability to cope with floods and droughts. Many countries, particularly in Africa have exploited little of their water storage potential restricting the development of hydropower production and irrigated agriculture. The World Commission on Dams (2000) concluded that large dams had made an important and significant contribution to human development by providing stable water resources and flood alleviation, but the social and environmental costs had, in too many cases, been unacceptable and often unnecessary. Large dams may be high risk under unstable political regimes and changing climates. In certain circumstances reservoir may release greenhouse gases. DFID supported the Dams and Development Project that provided guidance on how to implement the Commission’s recommendation, which included assessment of alternative options and improved stakeholder participation and environmental safeguards where dams are considered the best solution. Other organisations, such as the International Hydropower Association, the World Bank and IUCN also produced guidelines to make dams more sustainable, such as releasing sufficient water to maintain downstream ecosystems and their dependent livelihoods. Other water storage options include exploiting and enhancing natural storage, such as groundwater, managing catchments to maximise water yield, using virtual water, demand management, desalinsation and waste water reuse. Where dams provide the only option, networks of small dams may provide greater flexibility than single large dams. Based on a review focused on hydrological issues, we suggest 10 principles in developing storage that could contribute to a DFID policy. These are summarised as: 1. Undertake a full water resources assessment and implications for economic growth and poverty alleviation using best science and appropriate long-term data sets. 2. Undertake a full options assessment before selecting the most appropriate development solution. 3. Undertake a full life cycle analysis of the options including design, construction, operation, long term viability and decommissioning. 4. Assess flexibility and vulnerability to climatic variability and change including water availability and sedimentation using best science and appropriate data. 5. For schemes having trans-boundary nature implications, assess the political security and vulnerability issues and use benefits sharing 6. Calculate a full carbon balance for water storage options, especially hydropower, including a baseline survey of current conditions 7. Ensure that full safeguards are implemented including appropriate environmental flow releases and effective management to reduce health risks 8. Ensure that dams are multi-purpose, where possible combining irrigation, fisheries, public supply, power generation and flood management 9. Evaluate the relative merits of large single dams against a distributed networks of smaller dams to assess overall costs, flexibility in water management, exposure to climate change 10. Ensure that all proposed developments are part of an integrated catchment approach including developing appropriate laws and institutional capacit