Waterborne loads of nitrogen and phosphorus to the Baltic Sea in 2008

	Authors: HELCOM PLC-Group, the data consultant SYKE

Key message

In 2008 the total waterborne load (riverine, coastal areas, and direct point and diffuse source) of nitrogen entering the Baltic Sea amounted to 580 600 tons, and total phosphorus load was 25 300 tons. The total runoff in 2008 was 13 400 m³/s.

Results and assessment

Relevance of the indicator for describing developments in the environment

Eutrophication of the Baltic Sea is mainly caused by excessive inputs of nitrogen and phosphorus from the land-based sources. About 75% of the nitrogen and at least 95% of the phosphorus entering the Baltic Sea is waterborne (i.e. via rivers or as direct discharges into the sea). 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. This information, together with information from land-based sources within the catchment, is also crucial for being able to determine the priority order of different sources of nutrients for the pollution of the Baltic Sea as well as for 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 preliminary results of the fifth Baltic Sea Pollution Load Compilation (PLC-5), the largest share of the total inputs of both phosphorus and nitrogen into the Baltic Sea in 2006 originated from diffuse sources. Agriculture alone contributed about 80% of the reported total diffuse loads and the second largest anthropogenic source of nutrients originated from point sources, with municipalities as the main source. The data concerning loads for the year 2006 indicate that the general situation has not changed much from that of six years earlier in 2000 (PLC-4 Project). However, the role of agriculture may be somewhat more significant now as a result of increased implementation of nutrient removal measures in the municipal sector.

Both N and P fluxes vary significantly 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. 

The change in waterborne nitrogen loads figures from 2007 to 2008 show a decrease in input from all countries except for Estonia and Finland (Note that due to missing data for 2008 from Russia it is not possible to determin changes in Russian waterborne nitrogen inputs). These changes in loads correspond well with the changes in flow. When comparing waterborne phosphorus inputs in 2008 and 2007, there was no change, or a decrease, in load from all countries except for Estonia and Finland which experienced an increase due to greater runoff in 2008.  

Not all the changes in phosphorus loads, however, can be explained by river runoff. When comparing the 2008 waterborne loades to the 10 year average (1999-2008), waterborne nitrogen input load has decreased by about 12%, and phosphorus by almost 20%. The riverine, coastal and point source flow in 2008 was 10% lower than the 10-year flow average suggesting that a large part of the nitrogen and phosphorus reductions are due to hydrological variations. Nevertheless, total waterborne phosphorus inputs have clearly decreased, suggesting positive effects of the implementation of load reduction measures in catchment area. It is known that the load reduction measures are particularly efficient for phosphorus in municipal wastewater treatment plants. 

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 1994-2008 of the 9 countries. (Note variable scales in the graphs).

Figure 2. Direct inputs of Phosphorus (P_total-PO₄-P and PO₄-P) in t/a to the Baltic Sea and the river, coastal and direct point and diffuse source flow in m³/s of 1994-2008 of the 9 countries. (Note: variable scales in the graphs).

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 1994-2008.

Table 1. Riverine, coastal and point source flow to the Baltic Sea of 9 countries in 1994-2008, m³/s

Table 2. Riverine, coastal and direct point and diffuse source inputs of N_total of 9 countries in 1994-2008 as totals, t/a.

Table 3. Riverine, coastal and direct point and diffuse source inputs of P_total of 9 countries in 1994-2008 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, PO₄-P, N_total, NH₄-N, NO₂-N, NO₃-N and NO_2,3-N), concentrations of heavy metals (Cd, Pb and Hg) 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 (Wastewater treatment plants, industries and fish farms). From 2003 on also loads on direct diffuse sources have been collected. The 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.

The fractions in the nitrogen graph (Figure 1) have been calculated by deducting the reported loads of NH₄-N, and NO₂-N, NO₃-N, or NO_2,3-N as a sum, from the reported total nitrogen (N_total) load resulting in the fractions of NH₄-N, NO_2,3-N and organic nitrogen.

Apart from the above, in the table 2 only the reported total nitrogen (N_total) have been used not the sum of fractions.

In the phosphorus graph (Figure 2) total phosphorus load have been divided into two fractions P_tot and PO₄-P

As for the N_total, only the reported total phosporus (P_total) load have been shown in the table 3.

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: For the transboundary rivers, the following loads have been used:

River Tornio (Finland)/Torne älv (Sweden): in the Swedish data
River Narva (Russia and Estonia): in the Estonian data
River Oder (Poland and Germany): in the Polish data

5) Temporal coverage: nutrients 1994-2008 and harmful substances 1994-2008

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

Data Quality:

1) Methodology and frequency are variable, but the methods used have been 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 have been used for calculations.

2) Data are heterogeneous in space and time, which may cause some variation between the 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. Missing data have been listed in table 4.

FLOW

Russia:

-Data of 1994-1999 from the Kaliningrad Region (BAP)
-Data of coastal areas 1994-2008
-All data of 2008

Latvia: Data of coastal areas in 1994-2003 and 2007-2008.

Germany: Most of the data of 2008 (i.e. many rivers of Baltic Proper, all coastal areas and direct point sources).

NITROGEN

Russia:

-All data of 2008
-data of rivers in 1994-2003 and 2007-2008 from the Kaliningrad region
-data of 1994-1999, 2005, 2008 from the Gulf of Finland
-All data of coastal area 1994-1999, 2001-2007

Due to the missing Russian riverine N_total load to the Gulf of Finland in 2005, the difference between the calculated sum of Nitrogen fractions (Figure 1) and the reported N_total load (Table 2) in 2005 is evident. Only the total loads of direct point sources have been included.

Germany: Most of the N_tot, NH₄, NO₂₃, NO₂ and NO₃ data of 2008 of rivers, all data of coastal areas Direct point source data of 2007-2008 of N_tot, NH₄, NO₂₃, NO₂ and NO₃.

Poland: NH₄, (NO₂₃) and NO₂ data of 2008

In general, many countries have gaps in the point source data in different N-fractions (NH₄, NO₂₃, NO₂ and NO₃) over the years.

PHOSPHORUS

Russia:

-Most of the data of 1994-2008 from the Kaliningrad region of Russia.
-All data of 2008

Germany:

-Most of the data of 2008 (i.e. many rivers of Baltic Proper, all coastal areas and direct point sources).
-Point source data of 2007-2008

In general, many countries have gaps in the point source phosphorus data (P_tot, PO₄,) over the years.

LEAD

Denmark: data of 1994, 1996-1999, 2002-2003 and 2005-2008

Estonia: data of 1995-1999 and 2001-2003

Lithuania: data of 2007

Poland: data of 2008

Russia: data of 2008

CADMIUM

Denmark: data of 1994, 1996-1999 and 2005-2008

Estonia: data of 1995-1999 and 2001-2003

Poland: data of 2008

Russia: data of 2003 and 2008

MERCURY

Denmark: data of 1994, 1996-1999 and 2005-2008

Estonia: data of 1995-1999 and 2001-2003, 2007-2008

Lithuania: data of 1994-1997, 2002, 2006-2008

Latvia: data of 1994-2000 and 2002 and 2004

Poland: data of 2008

Russia: data of 2008

Sweden: data of 1994

Analysis method of Mercury was changed in Finland  in 2000.

Table 4. Years of the missing data by parameter and country.

For reference purposes, please cite this Baltic Sea Environment Fact Sheets as follows:
[Author’s name(s)], [Year]. [Baltic Sea Environment Fact Sheets title]. HELCOM Baltic Sea Environment Fact Sheets 2010. Online. [Date Viewed], http://www.helcom.fi/environment2/ifs/en_GB/cover/.

Last updated: 1 December 2010