Waterborne loads of nitrogens and phosphorus to the Baltic Sea in 2005

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

Key message

In 2005 the total waterborne (riverine, coastal areas, and direct point and diffuse source) load of nitrogen entering the Baltic Sea amounted to 579 000 tons (part of the Russian data is missing, the real load probably about  620 000 tons), and total phosphorus load was 28 500 tons. The total runoff in 2005 was 15 500 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.

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 most countries at the same level as in the previous year. The reasoning behind this is that the riverine runoff also was almost equal to the runoff in 2004 (+7.4 %). Only phosphorus load from Lithuania halved (-48 %) from the previous year. This cannot be explained by changes in runoff, which decreased only by 3 %. Compared with the 10 year (1996-2005) average both nitrogen (-5 %) and phosphorus (-11 %) loads in 2005 were lower. This most probably reflects implementation of load reduction measures in catchment area. This theory is supported by the fact that the riverine flow (+7.4 %) was not in 2005  lower than the average of the foregoing period. It is also known that the load reduction measures are particularly efficient for phosphorus in municipal wastewater treatments plants, which for one is reflected in significantly larger decrease in phosphorus load.

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.

Figure 1. Direct inputs of Nitrogen (N_total, NH₄-N, NO_2,3-N) in t/a to the Baltic Sea and the river, coastal and direct point and diffuse source flow in m³/s of 1994-2005 of the 9 countries. (Note variable scales in the graphs) Click image to enlarge.

Figure 2. Direct inputs of Phosphorus (P_total, PO₄-P) in t/a to the Baltic Sea and the river, coastal and direct point and diffuse source flow in m³/s of 1994-2005 of the 9 countries. (Note variable scales in the graphs). Click image to enlarge!

Data 

Time series of direct inputs to the Baltic Sea of total nitrogen and total phosphorus including the river, coastal and direct point source flow in 1994-2005.

Table 1. Riverine, coastal and point source flow to the Baltic Sea of 9 countries in 1994-2005, m³/s

Table 2. Riverine, coastal and direct point and diffuse source inputs of N_total of 9 countries in 1994-2005 as totals, t/a.

*Note: Part of Russian nitrogen input data is missing.

Table 3. Riverine, coastal and direct point and diffuse source inputs of P_total of 9 countries in 1994-2005 as totals, t/a.

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 the 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 1994-2005 and harmful substances 1994-2005

6) Russian data includes also the reported data of the Kaliningrad Region.

Data Quality:

1) Methodology and frequency: variable, basically as agreed on the PLC-5 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 1994-2005 from the Kaliningrad region of Russia.

Nitrogen

Most of the data of 1994-2005 from the Kaliningrad region of Russia and Russian data of 1994-1999 and N_tot data of 2005 from the Gulf of Finland.

Phosphorus

Most of the data of 1994-2005 from the Kaliningrad region of Russia.

Lead

No data of 1994, 1996-1999, 2002-2003 and 2005 from Denmark, no data of 1995-1999 and 2001-2003 from Estonia.

Cadmium

No data of 1994, 1996-1999 and 2005 from Denmark, no data of 1995-1999 and 2001-2003 from Estonia, no data from Russia 2003.

Mercury

No data of 1994, 1996-1999 and 2005 from Denmark, no data of 1995-1999 and 2001-2003 from Estonia, no data of 1994-2005y from Latvia, no data from Lithuania of 1994-1998, 2000, 2002 and 2005 and no data from Russia 2004.

Analysis method of Mercury was changed in Finland  in 2000.

Missing data have been listed in table 7.

Table 7. Years of the missing data by parameter and country.

For reference purposes, please cite this indicator fact sheet as follows:
[Author’s name(s)], [Year]. [Indicator Fact Sheet title]. HELCOM Indicator Fact Sheets 2007. Online. [Date Viewed], http://www.helcom.fi/environment2/ifs/en_GB/cover/.

Last updated: 2.10.2007