1. LATVIJAS VIDES, ĢEOLOĢIJAS UN METEOROLOĢIJAS AĢENTŪRA © LVĢMA AQUATIC ECOSYSTEMS OF LATVIA T. Kolcova and I. Mikelsone

2. GENERAL INFORMATION 2 LATVIJAS VIDES, ĢEOLOĢIJAS UN METEOROLOĢIJAS AĢENTŪRA © LVĢMA T. Koļcova, I. Miķelsone Forests cover a total of 44% of the country, 10% consists of peat bogs, 2-3% is fresh water reservoirs, 38% is used for agriculture and 4% is taken up by towns, villages and roads. Latvia is situated in the North-eastern Europe on the coast of the Baltic Sea. It borders with Estonia in the north, Lithuania in the south, the Russian Federation in the east and Belarus in the southeast direction. The seacoast length is 494 km. The total land border is 1862 km. The coastal plain is mostly flat, but inland to the east the land is hilly with forests and lakes.

3. All rivers of Latvia discharge into the Baltic Sea or to the Gulf of Riga (part of the Baltic Sea). More than 12,000 streams are located in Latvia. Percentage of small rivers of a length of less than 10 km is 95%; only 17 are longer than 100 km. The drainage basins of large streams cover about 80% of the Latvian territory. Only the one river (Daugava River) has a length of more than 500 km. The lakes cover 1.3% of the Latvian territory. The total area of the lakes is about 1,000 km²; the number of the lakes amounts to 3,000. Most of them have an area of the water plane of less than 0.5 km². Latvian lakes are shallow with mean depth of 1-5 m, only 8 of them are deeper than 10 m. 3 LATVIJAS VIDES, ĢEOLOĢIJAS UN METEOROLOĢIJAS AĢENTŪRA GENERAL INFORMATION © LVĢMA T. Koļcova, I. Miķelsone

4. River basin district Number of river water bodies Total length of rivers (km) Surface area of RBD (km 2 ) RBD area comparing with total area of Latvia (%) Daugava668322,92727062,141,89 Lielupe333144,4318849,2713,70 Venta634972,76215625,2424,22 Gauja454234,95413050,9420,20 Total:20720675,07464587,55100,00 LATVIJAS VIDES, ĢEOLOĢIJAS UN METEOROLOĢIJAS AĢENTŪRA AQUATIC ECOSYSTEMS Any watery environment, from small to large, from pond to ocean, in which plants and animals interact with the chemical and physical features of the environment. Aquatic ecosystems of Latvia: freshwater ecosystems; estuarine ecosystems; coastal water ecosystems. © LVĢMA T. Koļcova, I. Miķelsone

5. LATVIJAS VIDES, ĢEOLOĢIJAS UN METEOROLOĢIJAS AĢENTŪRA FRESHWATER ECOSYSTEMS The main freshwater ecosystems of Latvia: - Daugava River basin; - Gauja River basin; - Lielupe River basin; - Venta River basin - © LVĢMA T. Koļcova, I. Miķelsone

6. LATVIJAS VIDES, ĢEOLOĢIJAS UN METEOROLOĢIJAS AĢENTŪRA © LVĢMA T. Koļcova, I. Miķelsone FRESHWATER ECOSYSTEMS: DAUGAVA RIVER BASIN GEOGRAPGY: The drainage basin of Daugava River stretches from the Valday Massive in the central part of European Russia to the Gulf of Riga and crosses the northeast of Belarus. The length of the basin is 700 km, the maximum width – 225 km. Total area covered by the Daugava basin exceeds 87 900 km², within Latvia – 24 700 km². The mean slope of Daugava River is 0,54 ‰. - Lakes cover around 3% of the Daugava basin area, mire – 7%. - - Biotops: forests (39%), pastures (14%), meadows (7%), wetlands (3%).

7. LATVIJAS VIDES, ĢEOLOĢIJAS UN METEOROLOĢIJAS AĢENTŪRA FRESHWATER ECOSYSTEMS: DAUGAVA RIVER BASIN © LVĢMA T. Koļcova, I. Miķelsone CLIMATE: The influence of Polar Maritime air masses of the North Atlantic origin gradually increases moving from the upstream to the downstream parts of the basin. - monthly avg. air temperature; - annual precipitation; - annual evapotranspiration – 450 mm; - snow cover duration 70-80 days, - ice cover formed in the upstream part at the beginning of December but in the downstream – at the end of December. -4,3°C (Jan.) -6,9 °C (Jan.) 16,9 °C (Jul.) 17,6 °C (Jul.) 800 mm 635 mm

8. LATVIJAS VIDES, ĢEOLOĢIJAS UN METEOROLOĢIJAS AĢENTŪRA FRESHWATER ECOSYSTEMS DAUGAVA RIVER BASIN © LVĢMA T. Koļcova, I. Miķelsone HYDROLOGY: The average density of river network is 830 m/km. There are 8 rivers longer than 100 km, and 6 lakes lager than 10 km² Hidrological regime: high spring flood, summer-autumn rainfall floods, summer and winter low flow periods, winter floods caused ice jump. Feeding: snow melt (50%), ground water (30-35%) and rainfall (15-20%). Mean annual Daugava River water runoff is 710 m³/s. 230 mm 280 mm 380 mm

9. LATVIJAS VIDES, ĢEOLOĢIJAS UN METEOROLOĢIJAS AĢENTŪRA FRESHWATER ECOSYSTEMS LIELUPE RIVER BASIN © LVĢMA T. Koļcova, I. Miķelsone The river basin area is 17 633 km², within Latvia – 8 750 km². The average slope of Lielupe River is 0,48 ‰. The river bed is much lower than average Baltic Sea level over a length of 100 km upstream from the mouth. -Lakes cover less than 1% of the Lielupe basin area, forest – 30% and mire cover 10%. -Karst area along the border. - the Memele River (Nemunelis in Lithuania) approx. 191 km in length of which 78 km in Lithuania, 29 km in Latvia and 84 km along the border, originates from the Aukstaitia heights. The river has two major branches; - the Musa River 164 km in length of which 140 km in Lithuania, 18km in Latvia and 6 km along the border, starts from the Tyrelis bog in Lithuania (87 m a.sl.)

10. LATVIJAS VIDES, ĢEOLOĢIJAS UN METEOROLOĢIJAS AĢENTŪRA © LVĢMA T. Koļcova, I. Miķelsone FRESHWATER ECOSYSTEMS LIELUPE RIVER BASIN CLIMATE: The influence of Polar Maritime air masses of the North Atlantic origin. - monthly avg. air temperature; -5,0°C (Jan.) and 17,0-18,0 °C (Jul.) - annual precipitation: 500-550 mm - snow cover duration: left bank - 88 days, right bank – 99 days; - ice cover formed at the middle of December. 550 mm 500 mm

11. LATVIJAS VIDES, ĢEOLOĢIJAS UN METEOROLOĢIJAS AĢENTŪRA © LVĢMA T. Koļcova, I. Miķelsone FRESHWATER ECOSYSTEMS LIELUPE RIVER BASIN HYDROLOGY: The average density of river network is 450 m/km. There are 8 rivers longer than 100 km, and 1 lake lager than 10 km² Hydrological regime: high spring flood, summer-autumn rainfall floods, summer drought and winter low flow period interrupted by thaws. Feeding: snow melt (50%), ground water (5%) and rainfall (45%). Mean annual water runoff is 110 m³/s. 150 mm 220 mm

12. LATVIJAS VIDES, ĢEOLOĢIJAS UN METEOROLOĢIJAS AĢENTŪRA © LVĢMA T. Koļcova, I. Miķelsone FRESHWATER ECOSYSTEMS GAUJA RIVER BASIN The river basin area is 8900 km², within Latvia – 7790 km², the river length is 460 km. The average slope of Gauja River is 0,50 ‰. Lakes and mire cover 1% of the Gauja River basin area, forest – 40%. The Gauja River basin starts from the small mire in Cesis administrative region on the high of 240 m a.s.l. The river basin middle and upper parts locate on the Vidzeme upland, and only lower riches cross the Gulf of Riga lowland.

13. LATVIJAS VIDES, ĢEOLOĢIJAS UN METEOROLOĢIJAS AĢENTŪRA © LVĢMA T. Koļcova, I. Miķelsone FRESHWATER ECOSYSTEMS GAUJA RIVER BASIN CLIMATE: The influence of Polar Maritime air masses of the North Atlantic origin. - monthly avg. air temperature: in the southeast part of basin -6,7 °C (Jan.) and 16,6 °C (Jul.), and in the lower part: -4,3 °C (Jan.) and 17,6 °C (Jul.); 700 mm 870 mm - annual precipitation: 700-870 mm - snow cover duration: 85-110 days; - ice cover formed at the beginning of December in the river upstream and at the middle of December in the downstream.

14. LATVIJAS VIDES, ĢEOLOĢIJAS UN METEOROLOĢIJAS AĢENTŪRA © LVĢMA T. Koļcova, I. Miķelsone FRESHWATER ECOSYSTEMS GAUJA RIVER BASIN HYDROLOGY: Feeding: snow melt (35%), ground water (35-40%) and rainfall (25-30%). Mean annual water runoff is 75,0 m³/s. The average density of river network is 390 m/km. There are 7 rivers longer than 100 km. Hydrological regime: high spring flood, summer-autumn rainfall floods, summer and winter drought. 360 mm 240 mm

15. LATVIJAS VIDES, ĢEOLOĢIJAS UN METEOROLOĢIJAS AĢENTŪRA © LVĢMA T. Koļcova, I. Miķelsone FRESHWATER ECOSYSTEMS VENTA RIVER BASIN GEOGRAPGY: The drainage basin of Venta River stretches from the lake Zvirgzas in Lithuania to the Baltic Sea nearby Ventspils city. The length of the river is 346 km, within Latvia – 176 km. Total area covered by the Venta River basin exceeds 11830 km², within Latvia – 7900 km². The mean slope of Venta River is 0,5 ‰. Lakes cover less than 1% of the Venta basin area, mire – 5%, forests – 20%.

16. LATVIJAS VIDES, ĢEOLOĢIJAS UN METEOROLOĢIJAS AĢENTŪRA © LVĢMA T. Koļcova, I. Miķelsone FRESHWATER ECOSYSTEMS VENTA RIVER BASIN CLIMATE: The influence of Polar Maritime air masses of the North Atlantic origin. - monthly avg. air temperature river downstream area is -2,7 °C (Feb.) and 16,7 °C (Jul.) bet upstream area –4,3 °C (Feb.) and 16,6 °C (Jul.); - annual precipitation: 700-750 mm - snow cover duration: 65-75 days; - on lower part of basin ice cover formed at the beginning of January bet in 30% of the observation period rivers don’t freeze. -2,7°C (Feb.) 16,7 °C (Jul.) -4,3°C (Feb.) 16,6 °C (Jul.)

17. LATVIJAS VIDES, ĢEOLOĢIJAS UN METEOROLOĢIJAS AĢENTŪRA © LVĢMA T. Koļcova, I. Miķelsone FRESHWATER ECOSYSTEMS VENTA RIVER BASIN HYDROLOGY: The average density of river network is 380 m/km. There are 3 rivers longer than 100 km and 1 lake lager than 10 km. Hydrological regime: high spring flood, autumn and winter rainfall floods and summer drought. Feeding: snow melt (55%), ground water (<10%) and rainfall (35%). In lower part of river basin mean annual water runoff is about 280 mm, in upper part 240-260 mm on the right bank and 280-300 mm on the left bank of Venta River basin. 240 mm 300 mm

18. LATVIJAS VIDES, ĢEOLOĢIJAS UN METEOROLOĢIJAS AĢENTŪRA © LVĢMA T. Koļcova, I. Miķelsone FRESHWATER ECOSYSTEMS GEOLOGY: All the rivers of Latvia, including the Daugava, Venta, Lielupe and Gauja River basins, can be divided into 3 types according to geological conditions: -rivers with carbonated riverbeds mainly composed of Devonian sediments: dolomite, clay, dolomite marlstone, and limestone ; -rivers with sandy riverbeds mainly composed of quaternary sediments: sand, sandstone, clay, sand-gravel, loam; - rivers with organic originated riverbeds composed of postglacial sediments: mainly peat.

19. LATVIJAS VIDES, ĢEOLOĢIJAS UN METEOROLOĢIJAS AĢENTŪRA © LVĢMA T. Koļcova, I. Miķelsone FRESHWATER ECOSYSTEMS GROUNDWATER The thickness of active water exchange zone range between 10 m in the Northern part of Venta River basin and 400 m in the Southern part of Venta River basin and the Eastern part of Daugava River basin. The main infiltration areas are located in the areas of higher altitude, namely in the Highlands of Rietumkursa, Austrumkursa, Ziemeļkursa, Idumeja, Vidzeme, Alūksne and Latgale. From there groundwater flows to the direction of the Baltic Sea, Riga Gulf and valleys of big rivers.

20. LATVIJAS VIDES, ĢEOLOĢIJAS UN METEOROLOĢIJAS AĢENTŪRA © LVĢMA T. Koļcova, I. Mikelsone FRESHWATER ECOSYSTEMS GROUNDWATER The main drainage areas of groundwater

21. LATVIJAS VIDES, ĢEOLOĢIJAS UN METEOROLOĢIJAS AĢENTŪRA © LVĢMA T. Koļcova, I. Mikelsone FRESHWATER ECOSYSTEMS The total catchments of fish and lamprey in Latvian priority waters exceed 80 % of the total catchments in Latvian inland waters. 23 fish species are reported in lake catchments statistics; only 8 of them may be regarded as economically significant: bream, pike, roach, pikeperch, tench, perch, Crucian carp and eel. Our rivers are used as spawning grounds by 5 economically significant species - salmon, sea trout, European smelt, vimba and river lamprey. It is estimated that there are about 100 000 anglers in Latvia There is a large number of species of aquatic flora and fish fauna in the Latvian aquatic ecosystems.

22. LATVIJAS VIDES, ĢEOLOĢIJAS UN METEOROLOĢIJAS AĢENTŪRA © LVĢMA T. Koļcova COSTAL WATER ECOSYSTEMS Seaward border of the Latvian coastal waters typically goes along the Latvian coast between isobaths of 10 and 15 m. The only exception is the coastal stretch between Kolka and Roja in the Riga Gulf, where a maximal depth of coastal waters reaches 25 m. The average depth of Latvian coastal waters is about 7 m, with the exception of Kolka – Roja stretch, where an average depth is 13 m. Bottom substrate of the Latvian coast consists of sand and gravel of different granulometric size, which is interrupted by more or less extensive aggregations of boulders and smaller stones and, at some places, by underwater exposures of limestone.

23. LATVIJAS VIDES, ĢEOLOĢIJAS UN METEOROLOĢIJAS AĢENTŪRA © LVĢMA T. Koļcova COSTAL WATER ECOSYSTEMS

24. LATVIJAS VIDES, ĢEOLOĢIJAS UN METEOROLOĢIJAS AĢENTŪRA © LVĢMA T. Koļcova, I.Mikelsone ESTUARINE ECOSYSTEMS The main Latvian estuarine ecosystem is located in the southern part of the Riga Gulf, in the vicinity of Daugava, Lielupe and Gauja river mouths. The 10% deviation from annual mean salinity is used as a criterion for establishing of boundary of transitional waters in the large river plume extending offshore. The average salinity of the Gulf of Riga surface layer is 5,26 practical salinity units; therefore the boundary of transitional waters is defined by 4,7 practical salinity units isohaline.

25. LATVIJAS VIDES, ĢEOLOĢIJAS UN METEOROLOĢIJAS AĢENTŪRA © LVĢMA T. Koļcova Area includes specific ecosystem shaped by the presence of the mixing zone. Presence of both freshwater and brackish water plankton and benthos species is characteristic there, as well as excess nutrients, dissolved and particulate organic matter, that originate in Daugava and Lielupe river basins. The average depth of the transitional water basin is 22 m, thus according to the mixing conditions it may be classified as “partially stratified”. The estuaries of Lielupe and Gauja Rivers usually freeze up at the middle of December, and ice cover period lasts 95 days an average. On Daugava River ice cover formation starts in the beginning of January bet is destroyed artificially. ESTUARINE ECOSYSTEMS

26. LATVIJAS VIDES, ĢEOLOĢIJAS UN METEOROLOĢIJAS AĢENTŪRA © LVĢMA T. Koļcova Type Salinity (PSU) Depth (m) Wave exposure Mixing Residence time (days) Substratum Ice cover (days) South-eastern exposed Sandy coast 6 < 18-20<30Exposed Permanently full <7 sand- gravel Irregular South-eastern exposed Stony coast 6 < 18-20<30Exposed Permanently full <7cobbleIrregular Gulf of Riga Sandy Coast 0,5 < 6<30 moderately exposed Permanently full <7 sand- gravel Irregular Gulf of Riga Stony Coast 0,5 < 6<30moderately exposed Permanently full <7cobbleIrregular COSTAL AND ESTUARINE WATER ECOSYSTEMS

27. LATVIJAS VIDES, ĢEOLOĢIJAS UN METEOROLOĢIJAS AĢENTŪRA © LVĢMA T. Koļcova Latvia marine monitoring program includes both sediments and biota: fish and molluscs. Contents of toxic substances in perch (Perca fluviatilis) and molluscs (Macoma balthica) are studied in the Riga Gulf. Contents of lead, cadmium, copper and zinc are determined in fish liver; contents of mercury in muscle, and all the abovementioned metals are determined in tissue of molluscs. ESTUARINE ECOSYSTEMS