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|Title:||Chapter 10. The Impact of the Changing Climate on the Supply and Recycling of Nitrate|
|Authors:||GEORGE Glen D.; JARVINEN Marko; NOGES Tiina; BLENCKNER Thorsten; MOORE Karen|
|Publisher:||Springer Science+Business Media B.V.|
|Type:||Articles in periodicals and books|
|Abstract:||A high proportion of the nitrogen found in lakes and rivers is present in the form of nitrate. The concentration of nitrate in many surface waters has increased over the last forty years (OECD, 1982; Roberts and Marsh, 1987; Johnes AQ1 and Burt, 1993). The main source of nitrate is diffuse drainage from agricultural land (Vinten and Smith, 1993) but point sources can be important in populated areas (Jarvey et al., 1998). In 1991, the European Union introduced the Nitrates Directive (91.676) to protect waters from pollution by nitrate leached from agricultural land. Over the years, a number of scientific projects have been funded to provide strategic support for this directive. These include the Euroharp project (www.euroharp.org) that compared budgeting methods and the INCA project (www.rdg.ac.uk/INCA) that developed a new simulation model. A number of approaches have been used to quantify the factors influencing the transfer of nitrate from terrestrial to aquatic systems. These include budget calculations (Reynolds et al., 1992; Johnes, 1996), process-based models (Wade et al., 2002; Tipping et al., 2006) and statistical analyses (Hirsch et al., 1982, Easterby, 1997). Most budget based studies rely on measurements acquired over short periods of time (Johnes and Burt, 1993). The accuracy of such estimates depends on the frequency of sampling and the reliability of the hydrological measurements. The modelling approach is, potentially, more powerful but requires detailed information on the hydrology of the catchment and the nature of the soil. Moore et al. (Chapter 11, this volume) describe the application of a simplified model (GWLF) which combines a realistic hydrology with an export coefficient method for estimating the flux of nitrate. This model is a good example of the ¿fast and frugal¿ approach recommended by Carpenter (2003) and has proved effective at simulating both the observed and the projected variations in the flux of nitrate at a number of CLIME sites. The statistical approach is less sophisticated but can be used in situations where there is not enough data to support either budget calculations or modelling studies. In this chapter, we use a statistical approach to investigate the effects of longterm changes in the weather on the supply and recycling of nitrate in a number of different lakes. Since the supply of nitrate to most of these lakes increased during the period of investigation, the raw time-series have been de-trended to focus on the effects associated with short-term (inter-annual) changes in the weather. The chapter includes an analysis of the large-scale climatic features that influence these variations and discusses the practical implications of the patterns observed in the different regions.|
|JRC Directorate:||Sustainable Resources|
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