Contribution to the assessment of European River Basin Management Plans

3.1 Nutrients

3.1.1 Methodology

The GREEN model (Geospatial Regression Equation for European Nutrient losses; Grizzetti et al. 2012; Bouraoui et al. 2011) is used to predict annual loads of nitrogen (N) and phosphorus (P) from point and diffuse sources.

The model starts from inventories of point source emissions and diffuse emissions, aggregated at sub-basin level. Point source emissions are directly released to the stream network, whereas diffuse emissions are supposed to reach the stream network through runoff (surface and groundwater are lumped together), after a basin retention. The current version of the model does not account for retention of nutrients in aquifers and their lagged release to surface waters. While the problem is relatively straightforward with reference to specific river basins, research is ongoing about how to parameterize this process at pan-European scale.

In each sub-basin the model computes the nutrient load and the share of point and diffuse emissions, which are then transferred downstream, taking into account the retention occurring in the stream network.

Concentrations are obtained by dividing loads by appropriate streamflow discharges. One option is to use the annual average runoff, which can be estimated as the difference of annual precipitation and estimates of actual evapotranspiration from a Budyko-type model (Bouraoui et al. 2009; Grizzetti et al. 2012).

3.1.2 Spatial and temporal resolution

The spatial resolution of the model is the unit of the sub-basin, a portion of the river basin with average surface area of around 180 km² (HYDROEUROPE v1 Database: Bouraoui et al. 2011).

The model provides a yearly average load of N and P. This can be divided into load originated from different sectors: point sources, agriculture, atmospheric deposition or background.

3.1.3 Input

Point sources: inventories of wastewater treatment plant emissions, industrial emissions and from (currently, estimated from population connected to sewerage system and level of treatment - Eurostat data for year 2005)

Diffuse sources: mineral fertilizer and manure application rates, estimated by the CAPRI model⁶ (year 2005). Atmospheric deposition is included in the calculations (source: EMEP model). Emissions from scattered dwellings (estimated from population not connected to the sewerage system).

3.1.4 Preliminary assessment

The following figure shows example maps of N and P concentration (average for the year 2005) calculated with the current version of GREEN.



Figure –N (left) and P (right) concentration maps from GREEN (2005 average), accounting for point (below) and diffuse (above) sources separately.

3.1.5 Previous applications

1. 
   quantification of nitrogen and phosphorus loads to all European seas from 1985 to 2005, including an analysis of the effects of European policies on the water quality (Grizzetti et al. 2012);
   

2. 
   analysis of future scenarios of policies implementation at European scale (Bouraoui et al. 2014);
   

3. 
   assessment of risk of nitrogen water pollution on human health and aquatic ecosystem functioning (euthrophication) (Grizzetti et al. 2011; Leip et al. 2015);
   

4. 
   quantification of ecosystem services related to aquatic ecosystem (water purification in rivers) (La Notte et al. 2015; Liquete et al. 2015);
   

The results of this research have been used by the European Commission in the report on the implementation of the Nitrates Directive (European Commission 2007), and by the European Environment Agency in the Report on the Status of Environment 2010 (European Environment Agency 2010).

Recently⁷, GREEN has been benchmarked against MONERIS and SWAT models in the Danube, in the context of the assessment of nutrients for the Danube River Basin Management Plan (Malago et al. 2015) and against RiverStralher and SWAT models in the Seine river basin (Grizzetti et al. 2015).

3.1.6 Strengths

• 
  Robust estimation of annual nitrogen and phosphorus loads, concentrations and source apportionment
  
• 
  Cover all EU consistently, with high spatial resolution
  
• 
  Conceptually simple/transparent
  
• 
  Analysis at the river basin scale and sub-catchment scale
  
• 
  Can be used to test the effect of changes in nutrient inputs from various sources at different spatial location
  

3.1.7 Weaknesses

• 
  Statistical regression model that relies on measurements
  
• 
  Annual nitrogen and phosphorus load but not seasonal information
  
• 
  No memory, lag time estimation
  
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  No physical processes thoroughly represented
  

The resolution of the model, corresponding to sub-basins, does not allow comparison with individual water bodies. A criterion to aggregate reported pressures on individual water bodies for each sub-basin will have to be defined.

3.1.8 State of play

Indicators given by loads and concentration of N and P are available for Europe basedon model input updated to 2005 as a base year. Work is ongoing at the JRC to incorporate:

- updated estimates of nutrient applications from the CAPRI model (base year 2008, in future 2012 will be also available from CAPRI).

- update atmospheric deposition (year 2008-2010).

- increase the number of observations (water quality measurements) to calibrate the model (we are evaluating the possibility to use the EEA Waterbase)

Point sources (wastewater treatment plants, collected but untreated emissions, industrial emissions from E-PRTR) have been updated using the data available from EEA for the reporting year of 2010.

Nutrient concentrations should be interpreted in the light of appropriate environmental quality standards. Nutrient standards have been defined by Member States with reference to specific water body typologies, and will be taken into account as far as possible.