Freshwater - State and impacts (Slovenia)

Ecological quality of rivers

The first assessment of the ecological quality of rivers (Figure 1) in compliance with the Water Directive was carried out as part of drawing up the Water Management Plan (WMP). To begin with the assessment covered only bodies of water that had not been extensively changed through human encroachment.

The majority are in good ecological condition; more data is given in chapter d) - What is the 2020 outlook?

Ecological quality of lakes

The three biggest natural lakes have been assessed. Account has been taken of the biological elements of quality, general physical and chemical parameters and special contaminants, but not of fish, since as in the case of rivers, an evaluation methodology has not yet been formulated. Lake Bohinj has been classified as being in very good ecological condition, and Lake Cerknica as good. The reason for the moderate quality of Lake Bled is the excessive burden of nutrients.

Nutrients in rivers and streams

Slovenian rivers are fast-flowing, so they possess good oxygen conditions and few nutrients. The concentration of nitrates is slightly above the natural background, estimated at 1 mg N/L (4.4 mg NO₃/L). Average concentrations are lower than 10 mg NO₃/L, with higher amounts apparent in northeast Slovenia, although for the most part they do not exceed 40 mg. No major seasonal variations have been observed (VD10).

Eutrophication in lakes

Eutrophication, especially the accumulation of phosphorus in water, is a problem for the majority of lakes in the temperate climate band, which in Slovenia is only Lake Bled. Increasing the concentration of nutrients accelerates the growth of phytoplankton, which contribute to reduced translucency. At Lake Bled an improvement in quality, mainly the result of measures taken, has been observed. The average concentration of phosphorus, however, is much higher in artificial retention lakes in central and northeast Slovenia that lie in areas of intensive farming (VD07).

Groundwater quality

The water bodies most affected by human activity are in the northeast of Slovenia. A three-year data series indicates, with a high level of reliability, the poor chemical condition of the Savinja, Drava and Mura basins, and, with a low level of reliability, the eastern Slovenske gorice area. Of pesticides, the concentrations of atrazine are most commonly exceeded, although concentrations in groundwater are falling.

In karstic and fissure watercourses, which account for around 50 % of groundwater reserves, the groundwater is less burdened with pesticides and nitrates, owing to less intense settlement and sparser agriculture (VD06), (VD05). These water bodies have been assigned good chemical quality with a high or average level of reliability. The chemical state of groundwater (VD11) for the period 2006-2008 is shown in Figure 3.

Hazardous substances

The rivers and lakes are not burdened with hazardous substances. The assessment of the chemical condition for 2006-2008 indicates that only two bodies of inland water did not achieve good quality, owing to excessive concentrations of mercury and tributyltin compounds, respectively (VD12).

Acidification

Ammonia contributes to the eutrophication of water. It is estimated that that this comes primarily from the land – farming and poor sewage systems – rather than from the air, although there is a lack of any longer-term series of measurements that might confirm this view, nor is there a study on the proportion of nutrients entering water from the air.

Freshwater quantity

Only half the water that flows into or falls in the country is consumed, and one fifth of the groundwater. The use of groundwater for irrigation is almost negligible relative to the total consumption of water in Slovenia.

With an average precipitation level of 1,580 mm a year, and an outflow quotient of 54.5 %, the water balance in Slovenia is generally favourable. The average annual air temperature is rising, and there are pronounced differences in the spatial distribution of precipitation. In the 30-year water balance period 1971-2000 an 11 % increase in evaporation and a roughly 6 % lower surface run-off relative to 1961-1990 has been observed.

In 2006 aquifers carried a total of 922 million m³ of available groundwater, or around 460 m³ per inhabitant of Slovenia. A total of 21 % of the available quantities of groundwater was abstracted for consumption.

Drought

Since 1992, a total of seven summer droughts have hit agriculture. The drought accounted for 80 % of the total damage incurred from natural disasters in 2003. At least 15 % of the country’s surface area is threatened by a lack of water in the soil in summer months, most of all the Primorska region and northeast Slovenia. In observing climate change there has been a noticeable shift towards a serious lack of water in the interior of the country, too.

Water scarcity

The summer of 2003 saw the consequences of the uneven distribution of water resources in Slovenia, and in places also the weakness in the supply of drinking water, with a full 47,396 people. 2.4 % of the population, needing to be supplied with water brought in by tanker. Despite reserves in the Alps, the most favourable scenarios indicate that water shortages may be expected in the north-eastern parts of the country.

Floods

Floods threaten more than 3,000 km² or just fewer then 15 % of the country’s surface area. As much as half the flood zone is in the Sava basin, 40 % in the Drava basin and 4 % in the Soča basin. There is a threat primarily to flash-flood ravines, valley floors and, in many places, built-up alluvial plains. There is less extensive flooding from coastal tides and karstic flooding. In part of the flood areas grassland and pasture have been converted to cultivated land, and in some places flood areas have also been built on. In 1991 the area of usual flooding was home to 7 % of the population, a quarter of whom live in areas affected by major floods (PS01).

A rise in the sea level of 1 mm a year has been recorded. In the period 1960-2006, on 306 occasions the sea level reached the flood point of 300 cm above normal. Frequent sea flooding occurs mainly in the autumn and winter, and occasionally in spring, with the frequency increasing. The flood area is most extensive in the municipality of Piran, and in times of exceptional flooding, 2.5 % of the total population are threatened in coastal municipalities.

Decreasing groundwater levels

Estimates of the quantity of groundwater bodies provided by the hydrogeological service of the Slovenian Environment Agency (ARSO) point to a relatively good situation, although concern has arisen in recent years over the lowering surface level of certain parts of groundwater bodies. In the future, because of possible unfavourable developments owing to climate change, this phenomenon will be closely monitored.

Loss of wetlands

The most important preserved wetlands in Slovenia are flood meadows and wet grassland, which humans have created in part and help to preserve through extensive farming. They cover around 20,000 ha. In order to promote more intensive agriculture, drainage, regulation of watercourses and reinforcing of banks have destroyed wetlands in the central courses of rivers, for instance in Pomurje and the Vipava valley, and along the coast through the construction of transport infrastructure and urbanisation.

Loss of habitats/species

Activities, such as urbanisation, construction of transport infrastructure, tourism and industry have led to a loss of natural aquatic areas and coastal land, and with them a shrinking of the habitats of certain species of plants and animals.

Impacts on human health

Over the period 2004-2007 the quality of drinking water in Slovenia (VD08) did not significantly improve, either in terms of microbiology (ZD04) or chemical pollution. There was a favourable trend only in medium-sized and large supply areas. Supply of compliant and adequately healthy drinking water is enjoyed generally by 91 % of inhabitants who are supplied in large mains supply areas.