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The rate of oxidation of peat soils is highly seasonal and varies with temperature and soil moisture content. Large variations in soil moisture content result in wet–dry cycles that can enhance peat degradation. Water‐table management plays a crucial role in controlling and damping the effect of these environmental factors. However, maintaining high ditch water levels in fields bounded by ditches does not guarantee a high field groundwater level. The effect of installing subsurface irrigation at different spacings on water table elevation was studied in a low‐lying peat grassland. The water table elevation data were compared against values predicted with a water balance model. In addition, greenhouse experiments were carried out on undisturbed soil core samples collected from the peat grassland as well as a low‐lying peatland under intensive arable faming to measure CO2 evolution under different water regimes. The field data from the peat grassland suggest that sub‐irrigation spacing as low as 10 m is necessary during summer periods to maintain groundwater levels similar to those in the ditches. Over the same period of observation, the difference in water level between the ditches and the non‐irrigated fields is as high as 0.7 m. Modelled outputs are in good correlation with the field observations, and demonstrate that simple water balance models can provide an effective tool to study the effect of water management practices and potential changes in subsurface conditions, climate and land use on water‐table levels. The measurement of CO2 emission from undisturbed peat soil columns shows that the rate of oxidation of soil organic matter from peat soils is highly seasonal and that drainage exacerbates the rate of peat mineralization.

Summary 1.The ecosystem approach and evaluation of ecosystem services is gaining increasing attention from scientists, practitioners and policy makers. An important part of this process is to establish the 'value' of the nature-conservation assets within an area. This value can then be compared with data for other ecosystem services to identify management priorities under different future scenarios. However, there is little consensus on how to perform such an evaluation. In this study, we assess seven methods of valuing nature-conservation interest and compare their utility. 2. Five agricultural land drainage schemes across lowland England were selected for study. The current land-use was determined and four different scenarios of future management were developed. The land-use and habitats predicted under each scenario were assessed using seven methods of determining value, namely: Ecological Impact Assessment method, reserve-selection criteria, target-based criteria, stakeholder-choice analysis, reserve-selection criteria guided by stakeholders, agri-environment scheme payments and contingent valuation. The first three methods derive values based on pre-defined priorities, the next two use stated preferences of stakeholders, and the last two methods derive monetary values based on revealed and expressed preference, respectively. 3. The results obtained from the different methods were compared. The methods gave broadly similar results and were highly correlated, but each method emphasized a different aspect of conservation value, leading to different possible outcomes in some cases. The advantages and disadvantages of each method were evaluated. 4. Synthesis and applications. As the ecosystem services approach becomes embedded in decisionmaking, ecologists are increasingly called upon to value the biodiversity of a site or to compare the value of different sites. This study has shown that seven different valuation methods, although all giving significantly correlated findings, resulted in seven different rankings of nature-conservation value for the 25 situations studied. This difference occurred in spite of the sites being of the same landscape type and occurring within the same country. The discussion concludes that each method has its strengths; monetary valuations are appropriate in some contexts, stakeholder preferences are paramount in others, but where objectivity is key, then assessment against independently defined criteria or targets should be the preferred method.