Mike Acreman

Classification of drainage basins according to their physical characteristics; an application for flood frequency analysis in Scotland

Abstract If the standardised floods at all sites within a given region are assumed to be samples from the same distribution, all data may be combined to yield an estimate of a regional dimensionless flood frequency relationship. The identification of these hydrologically homogeneous regions can be achieved on the basis of the physical characteristics of the basin which control the hydrological processes. Classification of the basins independent of the discharge data avoids the problems of regionalisation based on the highly variable, individual site estimates of flood frequency. Classification of the basins can be performed using the NORMIX multivariate clustering algorithm. The homogeneity of the basins can be tested using a likelihood ratio test of whether standardised data for all basins within a region may be adequately represented by a single regional flood frequency relationship. The method was applied to 168 basins in Scotland and five regions were identified, corresponding to physically reasonable basin types and all but one of which yield homogeneous distributions of flood frequency.

Environmental flows for natural, hybrid, and novel riverine ecosystems in a changing world

The term “environmental flows” describes the quantities, quality, and patterns of water flows required to sustain freshwater and estuarine ecosystems and the ecosystem services they provide. Environmental flows may be achieved in a number of different ways, most of which are based on either (1) limiting alterations from the natural flow baseline to maintain biodiversity and ecological integrity or (2) designing flow regimes to achieve specific ecological and ecosystem service outcomes. We argue that the former practice is more applicable to natural and semi-natural rivers where the primary objective and opportunity is ecological conservation. The latter “designer” approach is better suited to modified and managed rivers where return to natural conditions is no longer feasible and the objective is to maximize natural capital as well as support economic growth, recreation, or cultural history. This permits elements of ecosystem design and adaptation to environmental change. In a future characterized by altered climates and intensive regulation, where hybrid and novel aquatic ecosystems predominate, the designer approach may be the only feasible option. This conclusion stems from a lack of natural ecosystems from which to draw analogs and the need to support broader socioeconomic benefits and valuable configurations of natural and social capital.

The British river of the future: How climate change and human activity might affect two contrasting river ecosystems in England

The possible effects of changing climate on a southern and a north-eastern English river (the Thames and the Yorkshire Ouse, respectively) were examined in relation to water and ecological quality throughout the food web. The CLASSIC hydrological model, driven by output from the Hadley Centre climate model (HadCM3), based on IPCC low and high CO(2) emission scenarios for 2080 were used as the basis for the analysis. Compared to current conditions, the CLASSIC model predicted lower flows for both rivers, in all seasons except winter. Such an outcome would lead to longer residence times (by up to a month in the Thames), with nutrient, organic and biological contaminant concentrations elevated by 70-100% pro-rata, assuming sewage treatment effectiveness remains unchanged. Greater opportunities for phytoplankton growth will arise, and this may be significant in the Thames. Warmer winters and milder springs will favour riverine birds and increase the recruitment of many coarse fish species. However, warm, slow-flowing, shallower water would increase the incidence of fish diseases. These changing conditions would make southern UK rivers in general a less favourable habitat for some species of fish, such as the Atlantic salmon (Salmo salar). Accidental or deliberate, introductions of alien macrophytes and fish may change the range of species in the rivers. In some areas, it is possible that a concurrence of different pressures may give rise to the temporary loss of ecosystem services, such as providing acceptable quality water for humans and industry. An increasing demand for water in southern England due to an expanding population, a possibly reduced flow due to climate change, together with the Water Framework Directive obligation to maintain water quality, will put extreme pressure on river ecosystems, such as the Thames.

Ecological restoration of rich fens in Europe and North America: from trial and error to an evidence-based approach.

Fens represent a large array of ecosystem services, including the highest biodiversity found among wetlands, hydrological services, water purification and carbon sequestration. Land‐use change and drainage has severely damaged or annihilated these services in many parts of North America and Europe; restoration plans are urgently needed at the landscape level. We review the major constraints on the restoration of rich fens and fen water bodies in agricultural areas in Europe and disturbed landscapes in North America: (i) habitat quality problems: drought, eutrophication, acidification, and toxicity, and (ii) recolonization problems: species pools, ecosystem fragmentation and connectivity, genetic variability, and invasive species; and here provide possible solutions. We discuss both positive and negative consequences of restoration measures, and their causes. The restoration of wetland ecosystem functioning and services has, for a long time, been based on a trial‐and‐error approach. By presenting research and practice on the restoration of rich fen ecosystems within agricultural areas, we demonstrate the importance of biogeochemical and ecological knowledge at different spatial scales for the management and restoration of biodiversity, water quality, carbon sequestration and other ecosystem services, especially in a changing climate. We define target processes that enable scientists, nature managers, water managers and policy makers to choose between different measures and to predict restoration prospects for different types of deteriorated fens and their starting conditions.

Ecosystem services of wetlands: pathfinder for a new paradigm

Abstract Ecosystem services are natural assets produced by the environment and utilized by humans -- such as clean air, water, food and materials -- and contribute to social and cultural well-being. This concept, arguably, has been developed further in wetlands than any other ecosystem. Wetlands were historically important in producing the extensive coal deposits of the Carboniferous period; key steps in human development took place in communities occupying the wetland margins of rivers, lakes and the sea; and wetlands play a key role in the hydrological cycle influencing floods and river droughts. In this paper we examine three pillars that support the wetland research agenda: hydrology, wetland origins and development, and linkages to society. We investigate these through an overview of the evolution of wetland science and assessment of the wide range of topics relating to ecosystem services covered in this Special Issue. We explain the seminal change in how modern society values the benefits of natural ecosystems and highlight the pathfinder role that wetland research has played in the paradigm shift. Co-editors D. Koutsoyiannis and Z.W. Kundzewicz Citation Maltby, E. and Acreman, M.C., 2011. Ecosystem services of wetlands: pathfinder for a new paradigm. Hydrological Sciences Journal, 56 (8), 1341–1359.

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.

The changing role of ecohydrological science in guiding environmental flows

Abstract The term “environmental flows” is now widely used to reflect the hydrological regime required to sustain freshwater and estuarine ecosystems, and the human livelihoods and well-being that depend on them. The definition suggests a central role for ecohydrological science to help determine a required flow regime for a target ecosystem condition. Indeed, many countries have established laws and policies to implement environmental flows with the expectation that science can deliver the answers. This article provides an overview of recent developments and applications of environmental flows on six continents to explore the changing role of ecohydrological sciences, recognizing its limitations and the emerging needs of society, water resource managers and policy makers. Science has responded with new methods to link hydrology to ecosystem status, but these have also raised fundamental questions that go beyond ecohydrology, such as who decides on the target condition of the ecosystem? Some environmental flow methods are based on the natural flow paradigm, which assumes the desired regime is the natural “unmodified” condition. However, this may be unrealistic where flow regimes have been altered for many centuries and are likely to change with future climate change. Ecosystems are dynamic, so the adoption of environmental flows needs to have a similar dynamic basis. Furthermore, methodological developments have been made in two directions: first, broad-scale hydrological analysis of flow regimes (assuming ecological relevance of hydrograph components) and, second, analysis of ecological impacts of more than one stressor (e.g. flow, morphology, water quality). All methods retain a degree of uncertainty, which translates into risks, and raises questions regarding trust between scientists and the public. Communication between scientists, social scientists, practitioners, policy makers and the public is thus becoming as important as the quality of the science. Editor Z.W. Kundzewicz Citation Acreman, M.C., Overton, I.C., King, J., Wood, P., Cowx, I.G., Dunbar, M.J., Kendy, E., and Young, W., 2014. The changing role of ecohydrological science in guiding environmental flows. Hydrological Sciences Journal, 59 (3–4), 433–450

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.

Predicting the mean annual flood from basin characteristics in Scotland

ABSTRACT Flood data were assembled for 168 Scottish basins containing 3071 station-years of record. Multiple regression techniques were used to produce equations for predicting mean annual flood from physiographic and climatological basin characteristics. Mean annual rainfall (SAAR) gave better results than measures of extreme rainfall (M52D and RSMD). Percentage area of lake storage (LOCH) was found to be a better predictor than fraction of the basin draining through a lake (LAKE). Apart from SAAR and LOCH, the recommended equation requires the basin area (AREA), stream frequency (STMFRQ) and an index of the soil type (SOIL). Measures of average basin slope (AVES) and main stream slope (S1085) were not statistically significant. The standard error of the estimate of the predicted mean annual flood is 0.147. The equation has a coefficient of determination, R2, of 0.914 and appears robust over a wide range of basin types without requiring regionally derived multipliers or coefficients. No significant impro...

Trade-off in ecosystem services of the Somerset Levels and Moors wetlands

Abstract It is widely recognized that healthy ecosystems can provide considerable benefits to people, including food, timber, freshwater, protection from floods and much of what we call quality of life. A global review of these ecosystem services carried out as part of the Millennium Ecosystem Assessment (MEA) provided a framework for national and local studies. Using the MEA approach, this paper reviews the ecosystem services provided by the Somerset Levels and Moors wetland system in southwest England. This wetland provides a series of important services that are beneficial locally, regionally and globally, including grazing for cattle, carbon sequestration, flood water storage, recreation and archaeology. Some services are synergistic and reinforcing; for example, maintaining wet conditions supports wetland bird life that maintains biological diversity, attracts tourists, protects archaeological artefacts and reduces CO2 emissions; raising water levels to or above the ground leads to net greenhouse gas uptake by the wetland. Other services are potentially conflicting, for example raising water levels may reduce potential flood water storage and increase methane emissions. Comparison of the services of the wetland with those of drier habitats reveals for example that carbon sequestration, bird habitat provision and hay production is greater in wetlands, whilst grazing quality may decline and plant diversity may be reduced in the short term and distributions of disease vectors may be altered by wetland restoration through raising water levels. Management decisions affecting wetlands may necessitate a trade-off of ecosystem services. Editor Z.W. Kundzewicz Citation Acreman, M.C., Harding, R.J., Lloyd, C., McNamara, N.P., Mountford, J.O., Mould, D.J., Purse, B. V., Heard, M.S., Stratford, C.J. and Dury, S.J., 2011. Trade-off in ecosystem services of the Somerset Levels and Moors wetlands. Hydrological Sciences Journal, 56 (8), 1543–1565.