Researchers at the Institute of Biology of the University of Latvia found several specimens of the fossil forms of the floating lake nut (Trapa natans) in Lake Sauka in November. Floating lake nut is a rare and endangered species in Latvia. In the last 85 years in Latvia, only the floating lake nut deposits were known only in Klaucāni, Priekulāni, Pokrata and Bancāni lakes.
Floating lake nut is a representative of the tertiary period flora and, consequently, a relic plant species in Latvia, which is included in the 1st category of the Latvian Red Data Book, as well as the Cabinet of Ministers Regulation No. 396 “Regulations on the List of Specially Protected Species and Restricted Uses of Specially Protected Species” in Annex 1 “List of Specially Protected Species”. The range of the walnut covers Central and Eastern Europe, the Mediterranean, South and East Asia. It is imported into North America and Australia and there are no natural soils. In Latvia, lake nut is found on the northern border of its distribution area. The plant is found in waters that are poor in calcium carbonates but rich in organic matter.
Floating lake nut is an annual aquatic plant of the lake nut family with a 1-2 m long, flexible stem, which is held in the bottom of the lake by the nut of the previous year, from which it grew. A rosette of floating rhombic leaves forms above the water at the end of the stem. The plant blooms in July, August. The flowers open in the mornings only for a few hours and after pollination they settle into the water, where in autumn ripe 2.5-4.5 cm wide and 2-3 cm high stone-shaped nuts with 2 or 4 sharp and shriveled growths, which are woody cup teeth. Fruits ripe in autumn peel off the stem, sink and anchor in the lake mud. Lake nut fruit can retain germination for up to 10 years, elsewhere in the literature even 45-50 years are mentioned.
In the last 85 years, only three floating lake nut deposits in Klaucāni, Priekulāni and Pokrata lakes (Andrušaitis, 2003) were known in Latvia. These are the northernmost lake nuts in Europe. It is believed that the plant in Lake Bancāni has been introduced from Lake Priekulāni during the last 20 years, possibly with the help of waterfowl (Sušķo et al., 2018).
Data from paleobotanical studies of sediments show that lake nut has grown in shallow water bodies in the territory of Latvia several thousand years ago, and its macro-remains and pollen have been found in the sediments of lakes of previous interglacial eras (Kalnina et al. 2007). 20th century At the beginning of the 1940s, 10 deposits of lake nut fossil fruits were known, then now their number together with fossil pollen deposits has increased to 27 (Kalniņa et al., 2018). Work is currently underway to determine the age of the peanut fossil forms found in Lake Sauka.
The research of the Institute of Biology of the University of Latvia in Sauka Eszter is taking place in the LIFE GOODWATER IP project, the aim of which is to improve the quality of Latvian risk water bodies. From 2020 to 2027, the project is implemented by nineteen organizations in Latvia under the leadership of the Latvian Environment, Geology and Meteorology Center.
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