Freshwater - State and impacts (Estonia)

Water quality of Estonian rivers

Municipal and industrial point-source pollution loads in Estonian rivers have decreased significantly since 1992: organic pollution, measured as BOD7, by 90 %, nitrogen by about 60 % and phosphorus by about 75 %. The decreases at the beginning of the 1990s were due mainly to the reduction in overall production activities. The further decreases since then are associated with the modernisation of production, construction and renovation of wastewater treatment plants, structured legislative drafting and increases in the pollution charge (http://www.keskkonnainfo.ee/publications/4263_PDF.pdf ).

Figure 1 shows the correlation between the decrease of total phosphorus concentrations in monitored rivers and the reduction of point-source pollution. In dry years, 1996 and 2006, a worsening of water quality due to less dilution can be observed. However, despite the decrease in the pollution load, the average phosphorus concentration in rivers has been quite different over the years. In several rivers high phosphorus concentrations occur during high-water and flood periods, which shows the dominant influence of diffuse loads, especially in south-eastern upland areas, where surface runoff of phosphorus is higher.

Figure 1. Municipal and industrial waste water phosphorus load into rivers and average total phosphorus concentration in Estonian rivers

 

The concentration of nitrogen in rivers depends mainly on the diffuse load and correlates quite well with the amount of precipitation for the year (Figure 2). The high nitrogen content in rivers at the beginning of 1990s was the result of intensive agriculture at the end of Soviet period. Since that time, the area of crop-land and the use of mineral fertilisers have fallen by nearly a factor of two. The number of animals, and as a result the amount of manure, have also been reduced. The average mean nitrogen content has increased, due mainly to steep increases in rivers with more considerable agricultural impact, despite these being in a minority (Figure 3). In the majority of Estonian rivers the increase has been quite moderate and the average nitrogen content varies around 2 mgN/l depending on hydrological conditions.

Figure 2. Dynamics of average discharges and content of total nitrogen in monitored Estonian rivers and use of nitrogen fertilisers

Figure 3. Annual average concentrations and trends of total nitrogen in rivers with considerable agricultural impact (15 rivers) and other rivers (43 rivers), river runoff and use of fertilisers

Assessment of the ecological status of Estonian surface waters

The assessment of the state of water bodies covers the period 2004-2008 and is based on the relevant national regulation (https://www.riigiteataja.ee/ert/act.jsp?id=13210253). The assessment is made in the framework of compilations of water management plans based on three groups of quality elements: biological, hydro-morphological and physico-chemical quality indicators. The main emphasis is on biological quality elements (http://www.keskkonnainfo.ee/publications/4263_PDF.pdf, pages 98-105). The methodology and results of the assessment are described in more detail in special report http://www.keskkonnainfo.ee/failid/vesi/pinnaveeseisund.doc.

Rivers

Water quality in monitored Estonian rivers is relatively good (Figure 4) and in most rivers it has no significant negative impact on biological quality. Generally high and good status of phyto-benthos, which mainly indicates the trophic level, confirms the good water quality. The main reason why the macro-invertebrates have a moderate or poor status in one sixth of water courses is hydro-morphological alterations caused by land drainage. Organic pollution from municipal and industrial wastewaters has decreased substantially and only impacts aquatic organisms in a few rivers.

Compared with other biota, the status of fish populations is worse. In about 30 % of monitored water courses the fish status is moderate or worse. In addition to land drainage – straightening rivers, lowering water level, sediment load, etc. – the main reason for this is the number of dams. In addition to man-made constructions, beaver dams also have a substantial negative impact on fish status, in particular trout, in smaller rivers and streams.

As the ecological assessment using current methodology has only been carried out for the first time, no reliable trends can be demonstrated, but comparison of single indicators for macro-invertebrates and phytobenthos indicate an improvement in their status in rivers, where water quality was the limiting factor 5-15 years ago.

Figure 4. Ecological status of Estonian rivers, streams and ditches 2004-2008

Lakes

The increase and intensification of agriculture in the 1970s and 1980s was the main reason for the rapid eutrophication of many lakes. Due to a decline in agriculture and implementation of water protection measures in the 1990s there has been a considerable improvement although there are departures from the general trend.

In 2004-2008, the status of 79 small lakes was assessed under the national monitoring programme (Figure 5). Despite a general reduction in pollution loads, about 20 % of lakes were classified as moderate or poor. The reasons for this are various and can be divided into past factors and current pressures. For several lakes, especially for those with a slow water exchange rate, past pollution from farms or municipal wastewater discharges or lowering of water levels are still the main reasons for their moderate or poor status. Currently, construction work or other human activities changing the landscapes on the edges of lakes have, in some cases, resulted in considerable pressures. For the soft-water light coloured lakes, which are the most sensitive, atmospheric deposition may be the reason for their only moderate status.

Figure 5. Ecological status of Estonian small lakes, 2004-2008

In addition to many small ones, Estonia has two large lakes: the transboundary Lake Peipsi with a surface area 3 538 km² and Lake Võrtsjärv with an area of 270 km².

The ecological status of Lake Peipsi has worsened in recent years. This is primarily due to eutrophication from an excessive phosphorus load. The percentage of blue-green algae relative to all algae has increased in the summer months, while diatom biomass has decreased. Algal toxin concentrations in the water have repeatedly exceeded the permitted limit values for bathing water. Due to the proliferation of algae, fish spawns have become muddy and fish reproduction conditions worsened. The ecological status of Lake Peipsi has therefore been assessed as moderate and the southern part of the lake, also called Lake Pskov, as poor.

Indicators of the status of the very shallow Lake Võrtsjärv depend significantly on the water level, which in recent years has been quite low. Its status was therefore assessed on the basis of data for the past 10 years. The combined rating of the ecological status of the lake on the basis of phytoplankton, macrophytes and water quality was deemed good. The major fluctuations in water level in recent years make it difficult to distinguish between natural and anthropogenic changes and thus reduce the reliability of the rating.

Status of groundwater

Estonian groundwater aquifers are divided into 15 groundwater bodies. The use of groundwater resources does not exceed the recharge of these and their quantitative status is therefore good. The only exception is the Ordivician Ida-Viru oil-shale basin groundwater body, which has been almost drained for oil-shale mining. The quantitative and chemical status of this groundwater body is bad and as long as oil-shale mining continues, good status cannot be achieved.

Due to the relatively low average share of agricultural land, diffuse agricultural pollution of groundwater does not pose a serious problem (Figure 6). The higher nitrate concentration in the Silurian-Ordovician groundwater bodies in East and West Estonia is caused by higher nitrate concentrations, as measured in monitoring wells of the Pandivere and Adavere-Põltsamaa Nitrate- Vulnerable Zone, where the share of arable land and the number of livestock is significantly above the Estonian average and the groundwater is only partly or slightly protected.

The total area of the Pandivere and Adavere-Põltsamaa Nitrate Vulnerable Zone is 3 250 km², or 7.5 % of the mainland area of Estonia, and can be divided into the Pandivere – 2 382 km² – and the Adavere-Põltsamaa – 667 km² – regions. In the past two decades, the nitrate concentration in groundwater has been significantly lower in the Pandivere than that in the Adavere-Põltsamaa region, but in recent years, the difference between the two regions has decreased considerably. While in 2000-2003, the annual average concentration of nitrates at all the monitoring points in the Pandivere region was 18 mg/l and in the Adavere-Põltsamaa region 45 mg/l, in 2004-2007 the respective indicators were 23 and 32 mg/l. In the Pandivere region, there was an increase in the nitrate concentration in two-thirds of the wells and a reduction in less than one-fifth. In the Adavere-Põltsamaa region, the number of wells where the nitrate concentration is decreasing, more than half the wells, exceeds the number where the nitrate concentration is increasing, approximately 40 %. Therefore, the earlier 2.5 times difference in the average annual concentration of nitrates in the two regions decreased in this period only to 1.4 times. It is also important to point out that the groundwater condition in the Nitrate Vulnerable Zone is not entirely due to nitrate pollution. In 2004-2007 the 50 mgNO₃/l level was exceeded in 23 % of the monitored wells but in 75 of the wells the mean nitrate concentration was 40-49 mgNO₃/l.

Figure 6. Content of nitrates (mgNO₃/l) in Estonian upper groundwater bodies

Drinking water in Estonia often fails to meet quality requirements because of the high natural content of iron, manganese and ammonium in groundwater. Although these substances affect the water’s taste, colour, and smell, they pose no direct threat to human health. In some parts of Estonia, the groundwater also contains excessive amounts of fluorine and boron. These natural properties of groundwater put additional requirements on drinking water purification facilities and raise costs, which increase the price of water for people.