The first primary objective of EUROHARP is to provide end-users (national and international European environmental policy-makers) with a thorough scientific 
evaluation of the nine contemporary quantification tools and their ability to estimate diffuse nutrient (N, P) losses to surface freshwater systems and coastal 
waters. Thereby facilitate the   
implementation of the EC Water Framework Directive.   
   
The second primary objective is to develop an electronic decision support system (tool-box) for the identification of benchmarking methodologies with 
respect to both costs and benefits, for the quantification of diffuse nutrient losses under different environmental conditions across Europe.    
   
EUROHARP will contribute substantially to improved comparability, transparency and reliability of the quantification of nutrient losses from diffuse 
sources, and thereby to improved efficiency of abatement strategies related to the implementation of e.g. the Nitrates Directive and the Water Framework 
Directive.      
   
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In recent decades, discharges of pollutants from waste water treatment   plants and industry have been successfully identified and in many cases   reduced, but 
assessing inputs of diffuse pollution from land, and the   degree of retention of pollutants, such as nitrogen and phosphorus,   within surface water systems 
is harder to achieve. A recent study has   compared different methods used to estimate diffuse pollution in river   catchments.     
   
 The EUROHARP project1 was a large scale comparison and evaluation of   contrasting nutrient pollution models used as policy support tools to   estimate river 
water quality. Accurate estimation of diffuse pollution,   such as nitrate and phosphorus, from agriculture is a major challenge.   Results need to be accurate 
and responsive to changes in land use and   land management to assess compliance with EU policy instruments, to   monitor trends in water quality, and to target 
mitigation measures in   time and space.     
   
 Contrasting types of modelling tools that predict river flows and   concentrations of pollutants were compared with measured data. Models   were chosen as 
examples of different approaches (process based,   semi-empirical, and conceptual) used as policy support tools in EU   Member States. Representative river 
catchments were chosen from 17   European catchments covering a range of climates (from north to south),   soils, hydrology, and land uses.     
   
 Results of the models EveNFlow and PSYCHIC showed that both were   capable of acceptable performance in modelling flows, nutrient   concentrations and loads 
in five out of six test catchment areas. In   the sixth area, in Greece, results were less accurate, due to   limitations in input data (rainfall, groundwater, point 
sources).   Accurate predictions of daily river flows were the primary factor   influencing the satisfactory prediction of nitrate and phosphorus   concentrations 
and loads. However, both models showed adaptability and   were capable of performing reasonably well when confronted with limited   or unknown data in the other 
five test catchments. The results   demonstrated that diffuse pollution tools can be applied to catchments   where climate and agricultural practices are very 
different to those in   the areas where such models were originally developed. This   adaptability demonstrates that some diffuse pollution tools have the   flexibility 
required for demanding and strategic policy support   purposes. Important generic principles for diffuse pollution support   which emerged from this work included: 
   
   
 Model selection should be governed by end-user requirements, taking   into account the availability of input data (e.g. screening tools may   be best suited 
to less complex approaches, whereas the system feedback   implicit in scenario modelling would benefit from adopting relatively   more complex approaches). 
  Modellers need to actively engage with catchment data managers to   ensure valid assumptions are made.   Comparison of the performance of the models evaluated 
in EUROHARP is   available from the project website: http://euroharp.org/diss/rep.htm,   and shows that no single model was consistently superior across all 
  catchments.