Euro-limpacs Deliverables


Report - response surface based on Monte-Carlo INCA in UK

Agencies responsible for the implementation of the Habitats Directive and Water Framework Directives need to be able to model the runoff of nutrients from land to waterbodies (river and lakes) to assess the hydrochemical and ecological response to eutrophication control measures, such as nutrient removal at Sewage Treatment Works (STWs) and land management changes. Both Directives require agencies to undertake such assessments at a catchment−scale. Water quality models are useful because they provide a method for testing our understanding of the factors and processes controlling water pollution, and quantitative estimates of how water pollution may be affected by climate−change and other drivers, such as land−management, atmospheric deposition and effluent discharges.

This report is concerned with the development of a Monte−Carlo version of INCA−P and the provision of a response−surface which relates changes in flow and in−stream total phosphorus concentration to the biomass of the macrophyte, Ranunculus penicilatus var. calcareous, commonly known as water crowfoot, and associated epiphytic growth. The model is applied to upper reaches of the River Kennet where a substantial data−set has been collated; the river is a major UK water resource typical of rivers in England which drain Cretaceous Chalk. The work presented is a ?proof−of−concept? and demonstrates that INCA−P can be applied successfully to generate a response−surface linking the physical, chemical and biological status of the stream. Preliminary results indicate that flow is a more important control on macrophyte biomass than total phosphorous concentration. If the flow is sufficiently high in the study reach (> 1.2 m3 s−1) then this could potentially negate the effects of a high (> 1 mg P l−1) total phosphorous input which would stimulate the growth of epiphytes; the high flow from up−stream dilutes the total phosphorous concentrations in the reach, and washes the growth of epiphytes from the system thereby reducing the inhibition of macrophyte photosynthesis.

Further work is required. The methodology should be coupled with a more clearly defined set of behaviour criterion to automatically remove ?non−behaviours? from the model result−set; such a set−up is equivalent to a likelihood−based uncertainty−analysis though it is based on matching observed behaviour in the system across a range of measures rather than a single ?goodness of fit? criterion. The climate and land−use scenarios must be defined rigorously; the current scenarios are arbitrary increments of the observed mean flow and total phosphorus concentrations. Changes in solar radiation and water temperature must also be included in the generation of the response−surface and its subsequent interpretation.

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