Fayçal Bouraoui

Modelling diffuse emission and retention of nutrients in the Vantaanjoki watershed (Finland) using the SWAT model

Abstract The nitrogen and phosphorus natural removal in the Vantaanjoki basin (Finland) was modelled using the SWAT hydrological model, which simulates the water cycle and the movement and transformations of nutrients. The model was first calibrated and then validated. In a daily time step, the Nash–Sutcliffe coefficient for the simulations of flow, nitrogen and phosphorus loads ranges between 0.59 and 0.81 for calibration and from 0.43 to 0.57 for validation. The simulation of the whole Vantaanjoki basin over a period of 9 years (1989–1997) allowed an estimation of the annual average diffuse emissions and nutrient removal in the basin. Diffuse emissions predicted by SWAT were compared with those evaluated by traditional statistical methods, confirming the reasonable predictions of the model. The nitrogen and phosphorus load values measured at the final outlet were compared with the load reaching the surface waters, coming from both diffuse and point sources, obtaining an estimation of retention of 24% for total nitrogen and 51% for total phosphorus.

Sensitivity analysis of distributed environmental simulation models: understanding the model behaviour in hydrological studies at the catchment scale

Abstract The development of new hydrological simulation tools allows for the modelling of large hydrological catchments, with the aim of comprehensive management of the water resources, control of diffuse pollution processes, such as the fate of agricultural fertilizants and finally, with purposes of economical optimization of the crop yields as a function of the expected climate, the watershed characteristics and the socio-economical conditions of the region where the catchment is located. This paper describes the sensitivity analysis of a hydrological distributed model applied in one large European watershed by using a two-step procedure. Firstly, it allows for the consideration of a huge input parameter data set by using an implementation of the Morris screening procedure, eschewing the huge computational requirements arising from the necessary repetitive simulations. In the second step it provides quantitative estimations of sensitivity in terms of variance decomposition procedures based upon the FAST method for both the hydrological and the water quality determinants.

Nitrogen as a threat to European water quality

Grizzetti, B., Bouraoui, F., Billen, G., van Grinsven, H., Cardoso, A. C., Thieu, V., Garnier, J., Curtis, C., Howarth, R. W. and Johnes, P. (2011) Nitrogen as a threat to European water quality. In: Sutton, M. A., Howard, C. M., Erisman, J. W., Billen, G., Bleeker, A., Grennfelt, P., van Grinsven, H. and Grizzetti, B. (eds.) European Nitrogen Assessment. Cambridge University Press, UK, pp. 379-404. ISBN 9781107006126 Available at http://centaur.reading.ac.uk/20869/

Long term change of nutrient concentrations of rivers discharging in European seas

Cases of severe eutrophication are still observed in European surface waters even though tough regulation has been in place since the beginning of the 1990s to control nutrient losses and inputs in the environment. The purpose of this paper is to evaluate the evolution since 1991 of the quality of the water entering European seas in terms of the concentration of major nutrients (nitrogen and phosphorus), and to analyze the effectiveness of implemented national/international measures and EU legislation in reducing water nutrient pollution. Despite the reduction in large portions of the European territory of agricultural nutrient applications and nutrient point source emissions, the impact on water quality is limited. It is shown using two large river basins that this lack of response for nitrogen, and nitrate in particular, between the reduction of the nitrogen surplus and the recovery of water quality is partly explained by the lag time due to transfer of nitrates in the unsaturated and saturated zones and storage in the soils and aquifers. In order to monitor efficiently the impact of policy implementation on water quality, the Nitrates Directive and the Urban Waste Water Treatment Directive in particular, it is recommended to use long term permanent monitoring stations to be able to separate the impact of climate variability from that of policy implementation. It is also recommended to investigate and develop harmonized methodologies for estimating the lag time in order to come up with realistic estimates of response time of water bodies due to the implementation of measures.

Ensemble modelling of nutrient loads and nutrient load partitioning in 17 European catchments

An ensemble of nutrient models was applied in 17 European catchments to analyse the variation that appears after simulation of net nutrient loads and partitioning of nutrient loads at catchment scale. Eight models for N and five models for P were applied in three core catchments covering European-wide gradients in climate, topography, soil types and land use (Vansjø-Hobøl (Norway), Ouse (Yorkshire, UK) and Enza (Italy)). Moreover, each of the models was applied in 3-14 other EUROHARP catchments in order to inter-compare the outcome of the nutrient load partitioning at a wider European scale. The results of the nutrient load partitioning show a variation in the computed average annual nitrogen and phosphorus loss from agricultural land within the 17 catchments between 19.1-34.6 kg N ha(-1) and 0.12-1.67 kg P ha(-1). All the applied nutrient models show that the catchment specific variation (range and standard deviation) in the model results is lowest when simulating the net nutrient load and becomes increasingly higher for simulation of the gross nutrient loss from agricultural land and highest for the simulations of the gross nutrient loss from other diffuse sources in the core catchments. The average coefficient of variation for the model simulations of gross P loss from agricultural land is nearly twice as high (67%) as for the model simulations of gross N loss from agricultural land (40%). The variation involved in model simulations of net nutrient load and gross nutrient losses in European catchments was due to regional factors and the presence or absence of large lakes within the catchment.

Modelling mitigation options to reduce diffuse nitrogen water pollution from agriculture

Agriculture is responsible for large scale water quality degradation and is estimated to contribute around 55% of the nitrogen entering the European Seas. The key policy instrument for protecting inland, transitional and coastal water resources is the Water Framework Directive (WFD). Reducing nutrient losses from agriculture is crucial to the successful implementation of the WFD. There are several mitigation measures that can be implemented to reduce nitrogen losses from agricultural areas to surface and ground waters. For the selection of appropriate measures, models are useful for quantifying the expected impacts and the associated costs. In this article we review some of the models used in Europe to assess the effectiveness of nitrogen mitigation measures, ranging from fertilizer management to the construction of riparian areas and wetlands. We highlight how the complexity of models is correlated with the type of scenarios that can be tested, with conceptual models mostly used to evaluate the impact of reduced fertilizer application, and the physically-based models used to evaluate the timing and location of mitigation options and the response times. We underline the importance of considering the lag time between the implementation of measures and effects on water quality. Models can be effective tools for targeting mitigation measures (identifying critical areas and timing), for evaluating their cost effectiveness, for taking into consideration pollution swapping and considering potential trade-offs in contrasting environmental objectives. Models are also useful for involving stakeholders during the development of catchments mitigation plans, increasing their acceptability.

Description of nine nutrient loss models: capabilities and suitability based on their characteristics

In EUROHARP, an EC Framework V project, which started in 2002 with 21 partners in 17 countries across Europe, a detailed intercomparison of contemporary catchment-scale modelling approaches was undertaken to characterise the relative importance of point and diffuse pollution of nutrients in surface freshwater systems. The study focused on the scientific evaluation of different modelling approaches, which were validated on three core catchments (the Ouse, UK; the Vansjo-Hobøl, Norway; and the Enza, Italy), and the application of each tool to three additional, randomly chosen catchments across Europe. The tools involved differ profoundly in their complexity, level of process representation and data requirements. The tools include simple loading models, statistical, conceptual and empirical model approaches, and physics-based (mechanistic) models. The results of a scientific intercomparison of the characteristics of these different model approaches are described. This includes an analysis of potential strengths and weaknesses of the nutrient models.

The European Nitrogen Problem in a Global Perspective

Nature of the problem Reactive nitrogen has both positive and negative eff ects on ecosystems and human health. Reactive nitrogen is formed through the • use of fossil fuels releasing large amounts of nitrogen oxides into the atmosphere and through the production of ammonia by the Haber–Bosch process and using it in agriculture to increase our food, feed and fuel production. While the use of nitrogen as a fertilizer and chemical product has brought enormous benefi ts, losses of fertilizer nitrogen and combustion nitrogen to the environment lead to many side eff ects on human health, ecosystem health, biodiversity and climate.

Nitrogen flows from European regional watersheds to coastal marine waters

Approaches A comprehensive evaluation of net anthropogenic inputs of reactive nitrogen (NANI) through atmospheric deposition, crop N fi xation, • fertiliser use and import of food and feed has been carried out for all European watersheds. A database on N, P and Si fl uxes delivered at the basin outlets has been assembled. A number of modelling approaches based on either statistical regression analysis or mechanistic description of the processes involved • in nitrogen transfer and transformations have been developed for relating N inputs to watersheds to outputs into coastal marine ecosystems.

A long-term hydrological modelling of the Upper Guadiana river basin (Spain)

Abstract The Upper Guadiana catchment has experienced a change from wetlands to dry lands induced by human action. The Soil and Water Assessment Tool model, a soil water budget simulator for agricultural watersheds, was applied to this catchment. The ability of the model to represent the impact of groundwater withdrawals on the hydrological behaviour of the basin has been demonstrated, even if the details of some processes are not well represented from one year to another. This is probably due to a lack of sufficient rainfall data or information to model the influence of the reservoirs. An analysis of alternative scenarios has demonstrated the usefulness of the model for decision-making and the relevance of growing vines under semi-arid conditions instead of high water consumption crops to reduce water demand.