European Environment Agency (2005): Source apportionment of nitrogen and phosphorus inputs into the aquatic environment. EEA Report, No.7, 48p.

『水環境へ負荷された窒素とリンの汚染源別寄与割合』

Contents
Acknowledgements
『Executive summary
　Eutrophication is the excessive enrichment of waters with nutrients and the associated adverse biological effects, and it is still one of the major environmental problems across Europe. European waters are affected across the whole range from inland water bodies such as groundwater, rivers and lakes, to transitional and coastal waters and ecosystems in open seas. Eutrophication is caused by large anthropogenic inputs of the nutrients nitrogen (N) and phosphorus (P) to the aquatic environment from a range of societal sectors.
　During the last 10 years, the EEA has in its state of the environment reports and water reports presented results on the sectoral contribution of nitrogen and phosphorus to the pollution of the aquatic environment. The study aims at updating this information on the source apportionment of the total load of nitrogen and phosphorus to the aquatic environment on a large scale: country, large river basins, and sea areas.
　Source apportionment is the estimation of the contribution by different sectors to water pollution. In this study, the focus has been on the nutrients nitrogen and phosphorus from land-based activities to the aquatic environment, with the primary focus on the agricultural contribution.
　The overall approach has been to compile results from existing source apportionment studies for the assessment. Source apportionment results from the following sources have been used:
・international organisations such as transboundary river commissions and regional marine conventions;
・national and regional studies;
・research activities.
　The north-western part of Europe is generally well covered by source apportionment studies, but there is a shortage of information from the Mediterranean countries and some eastern European countries.
Key messages
・Run-off from agricultural land is the principal source of nitrogen pollution. Agriculture is typically contributing 50.80 % of the total load.
・The total area-specific load (kg N/ha per year) increases with increasing human activities, in particular with more intensive agricultural production in the catchments (Figure 1).
・For phosphorus, point sources such as households and industry still tend to be the most significant source. However, as point source discharges in many countries have been markedly reduced during the last 15 years, agriculture has sometimes become the main source.
・In regions with low population density and low percentage of agricultural land such as the Baltic Sea catchment, the area-specific phosphorus load is only one third of the load in densely populated regions in central and north-western Europe (Figure 2).
Nitrogen load in selected countries and catchments
・The total area-specific load of nitrogen (kg N/ha per year), illustrated by the area of the pie charts on Map 1, increases generally with increasing agricultural activity. The total area-specific load in the catchments/countries in north-western Europe is more than double (triple) than in the Nordic countries and Baltic States.
・For all countries and catchments examined, agricultural or diffuse losses (agriculture plus background) account for more than 60 % of the total load.
Phosphorus load in selected countries and catchments
・Similar to nitrogen, the total area-specific load of phosphorus (kg P/ha per year) is highest in countries and catchments with high population density and high share of agricultural land (Map 2).
・In countries/catchments such as Belgium and the Odra and Po catchments with high population density and without nutrient removal at the majority of wastewater treatment plants, point sources generally account for more than two thirds of the load.
Large European river catchments
・The total area-specific nitrogen load varies with a factor five for large European river catchments. There is a high area-specific nitrogen load in the agriculturally intensive catchments.
・There is a close relationship between the total area-specific nitrogen load and the surplus of nitrogen applied to agricultural catchments for large European river catchments (Figure 3).
・For most of the central European large river catchments, point sources account for the majority of the phosphorus load (Figure 4).
Trends during the past 30 years
・Discharges of both nitrogen and phosphorus from point sources have decreased significantly during the past 30 years, whereas the loss from diffuse sources has generally remained at a constant level (Figure 5).
・The change has been largest for phosphorus, where it has also resulted in the largest reduction in the total load due to the previously very high share of point source discharges.
・The loss from diffuse sources has become relatively more significant as a consequence of the reduced point source discharges.
　The changes are mainly due to improved purification of urban wastewater. In the Nordic and western European countries, purification is now very effective and eastern European countries are now following a similar development.
　Measures to reduce the nitrogen surplus on agricultural land are now beginning to show results in terms of a reduction in diffuse losses of nitrogen to water. For example, in Denmark, the nitrogen surplus was reduced by 34 % over the period 1989 to 2003 followed by a marked decrease in the marine nitrogen load (Andersen et al., 2004). However, due to a combination of processes affecting the nitrogen cycle in soil and water, the reduction in diffuse loading of the aquatic environment can be delayed by many years after measures have been implemented on land.
Outlook
　This study is the first step in a wider framework action dealing with the assessment of nutrient inputs from agriculture and other sources into water bodies of inland waters as well as transitional, coastal and marine waters and is seen in the context of ongoing EEA work on agriculture and environment.
　In order to assess the effectiveness of current policies and agreements and to identify gaps, it is essential to know how nutrient inputs are distributed across sectors. Results from source apportionment studies are therefore important in the policy formulation process and in monitoring the implementation of policies and the effectiveness of measures.
　To help achieve this, a European-wide source apportionment of nutrient loads could be carried out applying an appropriate source apportionment tool at regular intervals (e.g. every three to five years) for a representative part or for the entire network of stations within the Eionet-water network. This will establish time series of source apportionment for all the different regions across Europe.
　In the short term, the EEA aims at a spatially differentiated assessment of the agricultural share of the total nutrient input into the aquatic environment. Furthermore, the spatially differentiated assessment will address the relationship between agricultural activities in the catchments and resulting water quality of the rivers draining the catchments. Building upon this, the EEA intends to investigate the possible use of medium-scale models for European assessments, conceivably linked to more detailed modelling approaches in hot-spot areas.』


1　Introduction
2　Concept of source apportionment
　2.1 Eutrophication and sources of nitrogen (N) and phosphorus (P)
　2.2 Sources covered
　2.3 Different methods used in source apportionment studies
　2.4 Presentation of source apportionments
3　Information sources
　3.1 Load compilation and source apportionment studies for Europe's seas　
　3.2 Source apportionments at national level
　3.3 Source apportionments for river catchments
4 European source apportionments
　4.1 Coastal and marine areas
　　4.1.1 Nitrogen
　　4.1.2 Phosphorus
　　4.1.3 Regional differences in load and source apportionment to the two sea areas
　4.2 Countries
　4.3 Large river catchments
　4.4 Smaller catchments
　4.5 Large lake catchments
5 Sources of pollution　
　5.1 Background loss
　5.2 Agricultural diffuse loss
　5.3 Atmospheric deposition
　5.4 Rural population
　5.5 Point sources
6 Geographical differences
7 Temporal changes
8 What additional work on source apportionment is needed?
9 References
Annex 1 Data table for Maps 1, 2, 6.1 and 6.2
Annex 2 Bibliography on source apportionment (and load) for European seas
Annex 3 Bibliography on national source apportionment
Annex 4 Bibliography on European river catchment source apportionment studies


Figure 1 Source apportionment of annual nitrogen load


Figure 2 Source apportionment of annual phosphorus load


Figure 3 Total area-specific nitrogen load (before retention) by sources and nitrogen surplus in large river catchments using the Moneris model


Figure 4 Total area-specific phosphorus load (before retention) by sources in large river catchments using the Moneris model

〔European Environment Agency (2005): Source apportionment of nitrogen and phosphorus inputs into the aquatic environment. EEA Report, No.7, 48p.から〕


Map 1 Source apportionment of nitrogen load in selected regions and catchments


Map 2 Source apportionment of phosphorus load in selected regions and catchments

〔European Environment Agency (2005): Source apportionment of nitrogen and phosphorus inputs into the aquatic environment. EEA Report, No.7, 48p.から〕


Figure 5 Long time series of source apportioned load of nitrogen and phosphorus (kg/ha/year on y axes) in the period 1975-2003 (mixed approaches)

〔European Environment Agency (2005): Source apportionment of nitrogen and phosphorus inputs into the aquatic environment. EEA Report, No.7, 48p.から〕

Annex 4 Bibliography on European river catchment source apportionment studies

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