Waterborne inputs of nitrogen and phosphorus

	Authors: HELCOM PLC-Group, The Data Consultant SYKE Editor: Seppo Knuuttila, SYKE

Key message

In 2004 the total waterborne (including coastal areas) load of nitrogen entering the Baltic Sea amounted to 502 000 tonnes, and total phosphorus load was 22 500 tonnes. The total runoff in 2004 was 11 100 m³/s.

Results and assessment

Relevance of the indicator for describing developments in the environment

Eutrophication of the Baltic Sea is mainly caused by the excessive nitrogen and phosphorus loading from the land-based sources. About 75 % of nitrogen and at least 95 % of phosphorus enters the Baltic Sea as waterborne (i.e. via rivers or as direct discharges). The total catchment area of monitored rivers cover 97 % of the total Baltic Sea catchment area. Together with unmonitored rivers and coastal areas they comprised 96 % of the total waterborne N load entering the Baltic Sea in 2004 and 95 % of the total P load respectively. The rest originates from direct point (and direct diffuse) sources.

Policy relevance and policy references

Information on the waterborne inputs, including riverine inputs of nitrogen and phosphorus is of key importance in order to follow up the long-term changes in the nutrient load into the Baltic Sea. And also to be able to, together with information from land-based sources within the catchment, determine the priority order of different sources of nutrients for the pollution of the Baltic Sea as well as assessing the effect of measures taken to reduce the pollution load. Quantified input data is a prerequisite to interpret and evaluate the state of the marine environment and related changes in the open sea and coastal waters.

Assessment

Riverine nutrient load consists of discharges and losses from different sources within a river's catchment area, including discharges from industry, municipal waste water treatment plants, scattered dwellings, losses from agriculture and managed forests, as well as natural background losses and atmospheric deposition. According to the PLC-4 report diffuse load (mainly agriculture) contributed almost 60 % of waterborne nitrogen inputs and 50 % of phosphorus, respectively. As a result of improved treatment on industrial and municipal wastewater treatment plants nutrient discharges from point sources have reduced significantly between 1985 and 2000. However, the reduction targets for diffuse sources such as agriculture have not yet been fulfilled.

The figures for nitrogen and phosphorus load were in 2004 in many countries significantly higher compared to the previous year. The reasoning behind this is that both N and P fluxes vary considerably from year to year depending mainly on hydrological conditions. In periods of high runoff, nutrients are abundantly leached from soil, thus  increasing the loads originating from diffuse sources and natural leaching. To evaluate the change of pressure on nutrient supply to the Baltic region it is necessary to know the variability of runoff and normalize for this natural variability. To be able to evaluate the reductions of nutrient load made in the different sectors, comparable long-term data on riverine loads (since the early 1980s) should be available in order to prepare a proper trend analysis.

Incomplete data from some countries makes it difficult to draw further conclusions concerning the total N and P load into the Baltic Sea.

Figure 1. Total waterborne inputs of Nitrogen (N_organic, NH₄-N, NO_2,3-N) in t/year to the Baltic Sea during 2004 for the 9 HELCOM countries.  

Figure 2. Total waterborne inputs of Phosphorus (P_organic, PO₄-P) in t/year to the Baltic Sea during 2004 for the 9 HELCOM countries.

Figure 3. Time series of waterborne loads of Nitrogen (N_total, NH₄-N, NO_2,3-N) in t/year to the Baltic Sea and the river, coastal and direct point source flow in m³/s for the period of 1994-2004 of the 9 countries. (Note variable scales in the graphs)

Figure 4. Time series for waterborne loads of Phosphorus (P_organic, PO₄-P) in t/year to the Baltic Sea and the river, coastal and direct point source flow in m³/s for the period of 1994-2004 of the 9 countries. (Note variable scales in the graphs)

Table 1. Riverine, coastal and point source flow to the Baltic Sea of the 9 HELCOM countries in 1994-2004, m³/s.

Table 2. Riverine, coastal and direct point and diffuse source inputs of N_total of the 9 HELCOM countries in 1994-2004 as t/year.

Table 3. Riverine, coastal and direct point and diffuse source inputs of P_total of the 9 HELCOM countries in 1994-2004 as t/year.

References

HELCOM PLC data base

Meta data

Technical Information:

1) Data have been collected by the Contracting Parties of HELCOM and submitted to the Pollution Load Compilation database (PLC database). The data base is located in Finnish Environment Institute (SYKE).

2) Description of data:  The data are based on annual average concentrations (mg/l) of nutrients and their fractions (P_total, PO₄-P, N_total, NH₄-N, NO₂-N, NO₃-N and NO_2,3-N), concentrations of heavy metals (Cd, Pb and Hq) and mean flows (m³/s). The contracting parties have calculated the annual loads (t/a) of monitored and unmonitored rivers, coastal areas and direct point sources. From 2003 on also loads on direct diffuse sources have been collected. All these data have been pooled together as total loads to the Baltic Sea by country.

Monitored river loads and most of the point source data are based on measurements, and unmonitored river catchment, coastal area loads and direct diffuse loads on estimates, respectively.

3) Spatial coverage: drainage of the Baltic Sea of 9 riparian countries; Denmark, Estonia, Finland, Germany, Latvia, Lithuania, Poland, Russia and Sweden, including the drainages of the Baltic Sea in Belarus, Czech Republic, Norway, Slovakia and Ukraine. 

4) Transboundary rivers: To avoid double data reporting of the transboundary rivers, their loads have been included in as follows:

River Tornio (Finland)/Torne älv (Sweden): in the Swedish data

River Narva (Russia and Estonia): in the Estonian data

River Oder (Poland): in the Polish data

5) Temporal coverage: Nutrients 1994-2004 and Harmful substancies 1994-2004

Data Quality:

1) Methodology and frequency: variable, basically as agreed on the PLC-4 guidelines for monitored rivers daily flow and concentration regression or monthly flow and concentrations, and for unmonitored areas loads based on the surface area comparison with a similar monitored area.

2) Heterogeneous data in space and time and may cause some variation between years. Due to robust analysing methods in some countries reported loads might be too high.

Missing data

Only the missing data of all sources, i.e. monitored rivers, coastal area and direct point and diffuse sources, have been listed below. Therefore, more data may be partially missing.

Flow: No data of 2004 have been submitted from Russia and Latvia.

Nitrogen: No data of 2004 have been submitted from Russia and Latvia.

Phosphorus: No data of 2004 have been submitted from Russia and Latvia.

Lead: No data of 1994, 1996-1999 and 2002-2003 from Denmark, no data of 1996-1999 and 2001-2004 from Estonia, and no data of 2004 from Latvia and Russia.

Cadmium: No data of 1994, 1996-1999 from Denmark, no data of 1995-1999 and 2001-2004 from Estonia, no data from Russia 2002-2004, no data from Lithuania 2003-2004 and no data of 2004 from Latvia.

Mercury: No data on mercury from Latvia, no data of 1994, 1996-1999 from Denmark, no data of 1995-1999 and 2001-2004 from Estonia, no data from Lithuania of 1994-1998 and 2002, and no data from Russia 2004.

Missing data have been listed in table 4.

For reference purposes, please cite this indicator fact sheet as follows:

[Author’s name(s)], [Year]. [Indicator Fact Sheet title]. HELCOM Indicator Fact Sheets 2005. Online. [Date Viewed], http://www.helcom.fi/environment2/ifs/en_GB/cover/. 

Last updated 25 Nov 2005.