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Eutrofication of water courses and degradation of water ecosystems

Intensive human activity on the shores of rivers and lakes, and in catchment areas significantly increases emissions of biogenous substances into Latvian lakes and rivers, and therefore into the Gulf of Riga and the Baltic Sea, thus accelerating the course of natural eutrofication.

Since the second half of the 1950s, the eutrofication rate in Latvia has increased significantly. Emissions of non-treated municipal wastes from towns and villages (main source of phosphorus) into surface waters, point and diffuse-source polluted run-off from the agricultural practices on collective farms, and incorrect and uncontrolled use of mineral fertilisers (main source of nitrogen) were the main reason for this increase, together with a lack of responsible management of water courses, their estuaries and adjoining coastal zones. Additions of nutrients from these sources not only increased the nutrient concentration discharged into the Baltic Sea, but also created huge storages of biogenous substances in waterplants and sediments that caused secondary pollution in inland waters.

About 5% of total freshwater watercourses discharge into the Baltic Sea comes from the territory of Latvia. This water, however, accounts for more than 10% of the total phosphorous load into the Baltic Sea and for up to 10% of the nitrogen load. Taking into account that the Baltic Sea is an almost closed, shallow sea with brackish water with an exchange rate of 30 years, the reduction of biogenous substances is of particular significance. Increase of the anthropogenic burden observed during the last decade has led to disturbances in the ecological balance and an acceleration of the eutrofication process in the Baltic Sea. Therefore, the solution of this problem has become a central issue in national environmental policies of the Baltic Sea states and on the level of the Baltic Sea region.

Latvia’s natural aquatic ecosystems have suffered severe damage due to ruthless and careless economic activity. Eutrofication is only one of the causes of degradation.

Major harm to Latvian natural aquatic ecosystems and habitats have been significantly harmed not only in their aquatic zones, but also in their littoral and riparian zones by hydro-construction and melioration activities. A classic example of this was the construction of the Daugava hydroelectric power station cascade, which destroyed natural biotopes in huge areas both in the Daugava, and its ancient river valley. Dams have completely blocked migratory paths for salmon, eel, and lamprey, since fish ladders were not included in the design of dams (except for Æeguma HEPP, where the fish ladder lost its significance after the construction of Riga HEPP downstream). Moreover, large numbers of plankton and baby fish perish when sucked through filters and into the turbines of power plants. Water plants, benthic organisms, fish spawn and baby fish are also often killed by water level fluctuations. The same problems can be observed to a lesser degree in small HEPPs, the reconstruction of which has started recently. Construction of the Daugava HEPP cascade has also created other serious environmental problems:

• washing away of the shores of watercourses in areas that have not been strengthened (50% of the total shore lengths);
• flooding, and fluctuation of groundwater level in adjacent territories;
• the formation of ice dams during spring floods on the Daugava at Jekabpils and Ogre;
• increased risks to Riga and to the levees and other protective structures around Ogre.

Another cause of destruction to Latvian aquatic ecosystems and biotopes was the campaign of the 50s and 60s to regulate and straighten small and medium-size rivers, during which a large number of small rivers were turned into ditches and canals. This destructive practice was amplified by widespread, and in many cases, poorly-planned and low quality land reclamation for agriculture and forestry. In 1986, the total length of regulated rivers was 2,814 km, but the total length of drainage ditches, regulating canals and trunk canals was 66,350 km. (For comparison, the total length of Latvian rivers is 37,500 km.) As a result, natural aquatic ecosystems were destroyed en masse and their self-purification potential was significantly diminished.

The problems of watercourse eutrofication and depletion of aquatic ecosystems in Latvia can be solved by a number of specific measures that are divided into two groups - cause-oriented measures and effect-oriented measures.

Cause-oriented measures:

Reducing the burden from household pollution. A group of measures that reduces mainly the phosphorous and nitrogen loads, at the same time limiting discharges of detergents, heavy metals, oil products and other dangerous substances into water.

This group of measures includes:

Improvement of household wastewater treatment/ management technologies and the technical condition and operation of sewerage networks. The main instruments for solution of these problems are policies supporting investments and loans; setting prices for water supply and wastewater services in accordance with the real costs of these services; improving the administration of water supply and wastewater services, which may also include change in ownership status.

Construction of new wastewater treatment facilities and expansion of sewerage systems. The above-mentioned instruments should be applied together with construction and expansion of facilities. An integrated approach would be of greatest benefit, which can be ensured by correct territorial planning (law ‘On territorial planning’) and a comprehensive EIA for choosing discharge sites and the most appropriate wastewater treatment technologies.

Water resource saving and reduction of consumption in the production, services and domestic sectors. This can be implemented by using instruments such as the Natural resources tax, pricing policy connected with use of water, as well as education of population (consumers), i.e. formation of public opinion.

Introduction of environmentally-friendly technologies and household products into the services and domestic sectors. Particular attention should be paid to custom duty policy, the certification of domestic chemical products, the use of the State Environmental Expertise, as well as the influencing of public opinion.

Reduction of diffuse pollution. A group of measures, the implementation of which would reduce diffuse emissions of biogenous substances (nitrogen, phosphorous, organic substances) into watercourses from agricultural lands and fertiliser storages, diffuse pollution from transport that enters watercourses as rainwater runoff from highways and roads, as well as air (local and transboundary) pollution.

This group of measures includes:

• reduction of agricultural pollution (see `Environmental impact of agriculture`);
• reduction of transport pollution (see `Environmental impact of transport`);
• reduction of air pollution (see `Transboundary pollution`);
• introduction of coastal protective belts and associated requirements;
• reorganisation, improvement and environmentally-friendly operation of melioration systems.

Reduction of industrial pollution. A group of measures for the reduction of toxic emissions from industrial sources.

This group of measures includes:

• introduction of environmentally-friendly technologies on the basis of the ‘best available technology’ and substitution principles. This can be achieved by the application of appropriate investment, loan and tax policies, customs duties on environmentally-unfriendly raw materials and production certification;
• treatment and pre-treatment of industrial wastewaters, as well as the practical utilisation or environmentally-safe storage of toxic sludge;
• practical utilisation or environmentally-safe storage of industrial wastes (see `Environmental impact of waste`).

Reduction of the hydro-technical burden. Theses are measures to mitigate the negative impacts of hydro-technical constructions on water quality and aquatic ecosystems, including the redrafting of regulations and standards for the design, construction and operation of hydro-technical installations, strengthening EIA requirements, guaranteeing fish migration paths, and the implementation of environmentally-friendly operational regimes.

Sustainable use of biological water resources, ensuring the interests of resource users, and avoiding the destabilisation of ecosystems and degradation of biotopes (see `Reduction of biodiversity`. and `Non-sustainable use of natural resources`).

Effect-oriented measures

A group of measures for the rehabilitation of natural watercourses and increasing the self-purification ability of aquatic ecosystems:

• restoring the natural course of straightened rivers;
• removal of heavily polluted sludge and sediment from the beds of watercourses;
• rehabilitation of overgrown lakes;
• maintenance of watercourses and their riparian zones (removal of sludge, harvesting of aquatic plants, regulation of overgrowth, restoration of benthic and littoral zone biodiversity, restoration of fish spawning and feeding grounds).

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Last updated: November 8, 1996. The information prepared by Valts Vilnitis: fuxis@varam.gov.lv