Eutrophication

4.4.5  Eutrophication

Eutrophication including harmful algal blooms refers to artificially enhanced primary productivity in receiving water basins as a result of the increased availability or supply of nutrients. Data on nutrient and organic transport from the Republic of Belarus and the Russian Federation into Ukraine and ultimately the Black Sea provide the clearest evidence of the transboundary status of this issue. The transboundary status of the issue is shown in Table 4.1. A detailed causal chain showing the links between the immediate and underlying causes of this issue is shown in Figure 4.17.

Environmental impacts

The impacts of this issue are linked closely with those of a number of other issues including changes in the groundwater regime (Section 4.3.2), flooding events and elevated groundwater levels (Section 4.3.3) and modification and loss of ecosystems and ecotones (Section 4.5). The impacts of other water resource pollution issues in this section such as suspended solids, chemical pollution and microbiological pollution, (Section 4.4) are also closely linked.

Deterioration of water quality due to intensive algal blooms

Ukraine: Reduced flow circulation and extensive shallow-water sections in the reservoir chain have intensified the effects of water pollution in the Dnipro Basin. The most visible indication of pollution is the increased frequency of algal blooms related to high loads of nutrients (especially nitrogen and phosphorus) entering the Dnipro and its reservoirs.

Within Ukraine, the total area of shallow-water sections in the reservoir chain is 1,341 km². Of that, aquatic vegetation covers 480 km² with a total mass of over 300,000 tonnes/year. Higher aquatic plants (reed, rush, cattail, etc.) occupy approximately one third of the total shallow-water area. However, reduced water circulation and expansion of shallow-water sections frequently leads to (virtually annual) algal blooms, stimulated by high loads of nutrients (nitrates and phosphates) received by the Dnipro reservoirs. As a result of this, large quantities of dead algae fall to the bottom, representing a source of secondary pollution. Shallow-water sections are also conducive to siltation and swamping leading to the excessive growth of higher aquatic plants and blue-green algae.

Changes in species composition and productivity of indigenous fish species

Belarus: Acute and major changes in the condition of aquatic ecosystems have been associated with the construction of reservoirs in the Belorussian part of the Dnipro Basin. Flowing rivers have been converted into stagnant water bodies with altered flow and temperature regimes, resulting in changes in species diversity. Valuable indigenous species have disappeared and have been substituted by opportunistic species of low or no value.

Ukraine Commercial fish yield significantly increased by up to 20,000-23,000 tonnes immediately after the construction and filling of the reservoir chain. However, valuable fish species including sturgeon, herring, and sabre carp (Pelecus cultratus L.) have virtually disappeared since this period and currently only occur in the Dnipro Estuary. Semi-submerged vegetation thickets have intensively developed in the shallow-water sections over the course of the operational life of the reservoirs. The high density of this vegetation affects light and air penetration, causing anoxic conditions in the bottom water layer, thus reducing the fish spawning value of the ecosystem. Spawning and fattening areas in the Dnipro and its reservoirs have reduced 3-fold.

More information on changes in species composition in the basin can be found in Section 3.1.6 on nature reserves and protected areas and Section 3.3.2 (Review of the 2000-2001 field survey results).

Immediate causes

As with chemical pollution, the immediate causes of eutrophication in the Dnipro Basin can be grouped into two hierarchical levels. The first distinguishes the point and diffuse sources of nutrients together with the existence of extensive area of shallow-water sections in the Dnipro reservoirs (this cause relates specifically to the energy sector). The second more detailed level can be broken down into the following (also refer to Table 4.17):

- Operational discharge of liquids and gaseous effluents including cooling waters (point source);

- Emissions from storage of solid waste (point and diffuse source);

- Emissions from storage of liquid wastes (point and diffuse source);

- Runoff (point and diffuse source);

- Growth in the production of waste.

1. Operational discharge of liquids and gaseous effluents including cooling waters

Information on nutrient loads from point and diffuse sources in the basin (including organic matter and BOD) and the transboundary transport of pollution can be found in Section 4.4.1 (chemical pollution) and Section 3.3.2 (review of the 2000-2001 field survey results).

Figure 4.13 shows the nutrient load entering Dnipro Basin from the 3 riparian countries. Belarus is by far the greatest contributor of nutrients from point sources followed by Ukraine and Russia.

In Ukraine, discharges of cooling waters from nuclear and thermal power plants cause thermal pollution of cooling ponds which can potentially enhance the impacts of eutrophication. However, this has a limited transboundary effect.

2. Runoff

Of the total amount of nitrogen and phosphorus applied to agricultural land, about 20% of nitrogen and 5% of phosphorus reach the water bodies of the Basin with surface runoff.

In Belarus, agricultural soils contain phosphorus and nitrogen compounds at elevated concentrations. In 1989-1990, the annual nutrient load discharged into the surface waters of the Dnipro Basin from agricultural areas in Belarus was 21,200 tonnes of nitrogen and 610 tonnes of phosphorus. Figure 4.16 reflects the percentages contributed by various sources to the total nutrient load.

Figure 4.16 Total nitrogen and phosphorous load contributed by point sources from the 3 riparian countries in the Dnipro Basin

3. Extensive area of shallow-water sections in the Dnipro reservoirs.

The flow regulation ratio in the Dnipro Basin ranges from 2-3% in the Russian Federation and Republic of Belarus, to 22% in Ukraine. In the Pripyat River Basin within Ukraine, 1% of river flow is regulated in the Ubort River, reaching 11%-15% in the Ustia and Khomora Rivers.

The total area of shallow-water sections in the Ukrainian reservoir chain is 1,341 km². Of that, aquatic vegetation covers 480 km². Shallow-water sections with a depth of up to 2 m are reported to occupy over 19% of the total area of the Dnipro reservoirs (Table 4.13), affecting water use, recreational value and the ecological state. These sections represent an interface between the land and offshore waters of the reservoir, where various physical, chemical and biological processes affecting water quality are most pronounced. Being prone to swamping, shallow water sections impede access for fishing, recreation, and livestock watering and are also able to strongly affect the ecological state of the reservoir and riparian area under certain conditions, e.g. during flow variations, when water exchange with the offshore area is significant.

Table 4.13  Shallow-water sections in the Dnipro reservoirs

4. Growth in the production of waste

For details on the growth of waste production, refer to the immediate causes of chemical pollution (Section 4.4.1) and Sections 3.1.4 and 4.4.6 on mineral resources and solid waste pollution in the Basin.

Underlying sectoral causes

The underlying sectoral causes of this issue are very similar to those for chemical pollution (see section 4.4.1). They are mainly associated with resource uses and practices dominating the following sectors: agriculture, urbanisation and industry. Aquaculture, energy and transport contribute to a lesser degree. A list of the priority sectors for all issues is presented in Table 4.18 (Section 4.7)

A detailed causal chain reflecting the links between the immediate and underlying sectoral causes of this issue is shown in Figure 4.17 and a detailed description of terminology used in this causal chain is given in the definition of terms in Annex 2.

Priority inter-sectoral issues

Based on the causal chain in Figure 4.17, the priority sectoral resource uses and practices and the underlying political, economic and governance causes of this transboundary issue can be identified. These are shown in the Strategic Action Programme (SAP) decision making management tool (Figure 4.18).

The SAP decision making management tool shows the priority sectors for this issue (colour coded with the causal chain) together with three hierarchical levels of concern (shown in Section 4.3.1). Within each level the priority resource uses and practices and the underlying political, economic and governance causes for each transboundary issue are listed. These can either cut across all sectors (e.g. Lack of adequate finance) or be sector specific (e.g. incorrect use and storage of fertilisers and livestock-breeding wastes).

Justification for sectoral prioritisation

Agriculture is a major contributor to the nutrient load received by aquatic ecosystems in the Basin. High loads of nutrients enter the Dnipro and its tributaries with surface runoff from agricultural fields and livestock breeding sites causing the progressive eutrophication of aquatic ecosystems. In addition, non-compliant agricultural practices and illegal ploughing activities within the floodplain areas of the Basin, result in high levels of humus entering the water bodies of the Dnipro and its tributaries. This, together with progressive soil erosion is also a contributory factor.

Intensive fishing and aquaculture also contributes to eutrophication. These practices lead to the transport of exometabolites; artificial nutrition of the water; the application of mineral fertilisers to enhance growth of aquatic plants; and lime treatment to prevent diseases in fish. All these factors adversely affect water quality and enhance eutrophication of fish ponds and natural water bodies which receive return waters.

Another major contributing factor is the high nutrient load entering the water bodies of the Basin with municipal wastewater discharges and surface runoff from rural areas. Food processing and microbiological industries also produce effluents containing nutrients and organic compounds.

Energy and transport also encourage eutrophication, although in an indirect manner. In particular, damming and regulation of larger rivers has led to the expansion of shallow-water areas and the take-up and transport of nutrients and organic compounds from land flooded as a result of damming. This has caused intensive growth of blue-green algae and, consequently, reintroduced pollution into the Dnipro River.

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