Nutrients released into the aquatic environment and deposited from the atmosphere constitute the immediate causes of eutrophication in the Baltic Sea region.
Figure 16 Nitrogen inputs to the Baltic Sea in 1995.
(Source: HELCOM 2001)
Aquatic nutrient loads
The nutrient load entering the Baltic Sea is assessed by the HELCOM Pollution Load Compilations (PLCs) (HELCOM 1987b, HELCOM 1993a, HELCOM 1998a, HELCOM 2004a). Rivers transport the majority of the nutrients from point and diff use sources to the Baltic Sea (Figure 16).
The reports of PLC-2 (HELCOM 1993a), PLC-3 (HELCOM 1998a) and PLC-4 (HELCOM 2004a) presented the sum nutrient load from point and diff use sources (from agriculture) that enter the Baltic Sea via rivers in the drainage basins, including both anthropogenic and natural (background) contributions. The latest pollution load compilation was
PLC-4, which also apportioned nutrients to their source. The following paragraphs are extracts from the PLC-4 Report (HELCOM 2004a).
The majority of nutrient losses and discharges into inland surface waters within the Baltic Sea catchment area are related to anthropogenic activities. In 2000 the discharges from point sources, the losses from diff use sources (e.g. agriculture, scattered dwellings, stormwater overfl ows) and natural background losses (natural losses from forest, wetlands and natural meadows) into inland surface waters within the Baltic Sea catchment area for total nitrogen and total phosphorus amounted to 82 2000 tonnes of nitrogen and 41 200 tonnes of phosphorus (Figure 17) (HELCOM 2004a). The major portions of the total nitrogen losses and discharges (58%) and the total phosphorus losses and discharges (53%) originated from diff use sources. Natural background losses and discharges from point sources for nitrogen amounted to 32% and 10% of the total losses and discharges entering inland surface waters within the Baltic Sea catchment area, respectively.
The corresponding fi gures for phosphorus were 27% and 20%.
The distribution of phosphorus and nitrogen load between the countries of the Helsinki Commission is presented in Figures 18 and 19 , respectively.
In 2000, the total riverine nitrogen load entering the Baltic Sea amounted to 706 000 tonnes (420 kg/km2). The bulk (81%) of this load was discharged by monitored rivers, with about 40% of the total load originating from the catchment area of the Baltic Proper Figure 15 Causal chain diagram illustrating the causal links for eutrophication.
Towns on the coast (61 000 tonnes)
Industry on the coast (15 000 tonnes) Issues
Impacts Immediate causes Sectors/Activities Root causes
Eutrophication
Aquatic nutrient load into the Baltic Sea
Aquatic load of nutrients from intensive agriculture:
Technology
- Inadequate adoption of modern agricultural technology Governance
- Inadequate integration of environmental and agricultural practices
Atmospheric deposition from energy production and transportation:
Population growth and urbanisation Transport
- Increased sea and road traffic Governance
- Ineffective laws and regulations to control emissions
- Lack of adequate transport policy Energy production
■ Loss of benthic fauna
■ Modification of ecosystems and ecotones
■ Toxic algal blooms
■ Oxygen depletion
Socio-economic:
■ Loss of recreational value
■ Cost of drinking water treatment
■ Infections, diseases and allergies
Transport
Aquatic load of nutrients from urbanisation:
Economy
- Lack of investment in wastewater facilities
Urbanisation - High urbanisation rate
CAUSAL CHAIN ANALYSIS 41
(HELCOM 2004a). Approximately 75% of the riverine nitrogen load in the Baltic Proper (286 000 tonnes, 525 kg N/km2) was discharged by the region’s three large rivers: Vistula (117 000 tonnes, 600 kg N/km2), Oder (53 600 tonnes, 450 kg N/km2) and Nemunas (46 830 tonnes, 480 kg N/km2). The second largest proportion of the total nitrogen load entering the Baltic Sea was 17% or 100 400 tonnes (230 kg N/km2), and was discharged from the Gulf of Finland catchment area, where the River Neva discharged 52 500 tonnes (195 kg N/km2) (HELCOM 2004a).
In 2000, the total riverine phosphorus load entering into the Baltic Sea amounted to 31 800 tonnes (19 kg P/km2). The majority (84%) of this load was discharged by monitored rivers, with up to 50% of the total load or 15 640 tonnes (29 kg P/km2) originating in the catchment area of the Baltic Proper (HELCOM 2004a). Approximately 83% of the load fed to the Baltic Proper, was discharged by the region’s three large rivers:
Vistula (7490 tonnes, 39 kg P/km2), Oder (3740 tonnes, 31 kg P/km2) and Nemunas (1 840 tonnes, 19 kg P/km2). Roughly 15% or 4 760 tonnes (11 kg P/km2) of the total riverine phosphorus load
Natural background losses (259 520 tonnes, 32%)
Losses from diffuse sources (484 090 tonnes, 58%)
Discharges from point source (78 640 tonnes, 10%)
Natural background losses (10 960 tonnes, 27%)
Losses from diffuse sources (22 040 tonnes, 53%)
Discharges from point source (8 220 tonnes, 20%)
Nitrogen:
822 000 tonnes
Phosphorus:
41 200 tonnes
Figure 17 Input of nitrogen and phosphorus to the Baltic Sea region.
(Source: HELCOM 2004a)
Figure 19 Distribution of total nitrogen load by country in the Baltic Sea region.
Note: Based on the source-oriented approach.
(Source: HELCOM 2004a)
Figure 18 Distribution of total phosphorus load by country into the Baltic Sea region.
Note: Based on the source-oriented approach.
(Source: HELCOM 2004a).
fl owing into the Baltic Sea came from the Gulf of Finland catchment area where the River Neva discharged 2 380 tonnes (9 kg P/km2).
The reported total nitrogen and total phosphorus aquatic discharges entering directly into the Baltic Sea from municipalities, industrial plants and fi shfarms amounted to 38 900 tonnes for nitrogen and 2 850 tonnes for phosphorus (HELCOM 2004a). The majority of the total nitrogen and total phosphorus direct discharges were produced by municipal wastewater treatment plants (MWWTPs) which accounted for more than 80% of both total direct nitrogen and total direct phosphorus discharges. Direct discharges from industry constituted 16% of the total direct nitrogen discharges and 14% of total direct phosphorus discharges into the Baltic Sea. Direct nitrogen discharges from industry into the Bothnian Bay and the Bothnian Sea are similar to the direct total nitrogen discharges from MWWTPs. The direct total phosphorus discharges from industry to these regions are about 3 times higher than the corresponding MWWTP discharges, while the direct discharges from fi sh farms are insignifi cant.
Atmospheric nutrient deposition
The deposition of nutrients from the atmosphere to the Baltic Sea is not directly linked to atmospheric emissions in the Baltic Sea region but depends largely on transboundary pollutants from adjacent areas.
The atmpospheric deposition of nitrogen into the Baltic Sea increased gradually during the 20th century, and was at its highest in the mid-1980s.
From 1985 to 1995 the atmospheric deposition was reduced by 10-25%.
The mean annual deposition of total nitrogen to the Baltic Sea between 1985 and 1995 was 320 000 tonnes/year (HELCOM 1998b). Figure 20 shows the deposition of nitrogen oxide (NO3-N) and ammonia (NH4-N) into the Baltic Sea in 1998. It should be noted that 12-20% of the overall nitrogen deposition to the Baltic Sea comes from shipping (HELCOM 2002).