Lake Sauka Demonstration Site – LIFE GOODWATER IP.

The LIFE GoodWater IP project has brought together 19 Latvian organizations to jointly seek and implement solutions to improve the ecological status of Latvia’s surface waters.

The LIFE GoodWater IP aims to improve water quality in the long term in about 30% of rivers and lakes whose water quality has been identified as not being able to achieve good quality. We will do this by developing, adapting to Latvian conditions and implementing innovative management and governance measures. The project runs from 2020 to 2027.

Lake Sauka is a 718.2 ha lake located in the NATURA 2000 territory – in the nature park “Sauka”. The average depth of the lake is 5.1 m, but the maximum depth reaches 9.5 m.

Attēls

litātes elementi (Latvijas Universitātes Bioloģijas institūta pētnieku foto)

According to the classification of lakes, in accordance with the regulations of the Cabinet of Ministers No. 858, Lake Sauka corresponds to type 5 lake – a shallow clear water lake with high water hardness. The lake is flowing – the Klauce River and several streams flow into it, but the Dūņupe River flows out of the lake. In 1931-1934, by regulating the flowing Dūņupe, the water level of Lake Sauka was lowered.

ECOLOGICAL STATUS OF LAKE SAUKA

In order to determine the ecological status of Lake Sauka and the rivers in its catchment area, the LIFE GoodWater IP project studies various aquatic organisms – aquatic plants, phytoplankton (microscopic algae), zooplankton (finely dispersed animals), zoobenthos (aquatic invertebrates inhabiting the lake). ) and fish, as well as observations of physical and chemical parameters. The results of the study will be used to develop an ecosystem model to develop guidelines for improving the ecological status of lake water bodies at risk.

Elements of biological quality (photo by researchers from the Institute of Biology, University of Latvia)

Elements of biological quality are good bioindicators, as their species composition and abundance reflect different impacts on aquatic ecosystems over time.

PHYTOPLANKTONS

Phytoplankton are made up of microscopic algae and cyanobacteria (blue-green algae) that inhabit the upper water layers of a body of water, where sunlight shines and photosynthesis can take place. Lake Sauka is characterized by a high biodiversity of planktonic algae, as almost all algal compartments have been found in the lake. The current research results show that the phytoplankton of Lake Sauka is characteristic of good quality water bodies.

ZOOPLANKTONS

Zooplankton are made up of small animals scattered throughout the water. They are important water filters and an important link in the food chain, as they feed on the micro-organisms in the water but feed on other larger invertebrates and fish. The zooplankton species composition of Lake Sauka corresponds to eutrophic (nutrient-rich) waters.

View through a microscope of the zooplankton of Lake Sauka (photo by J. Paidere)

MACROZOOBENTOSS

Aquatic invertebrates (macrozoobenthos) inhabit the lake bed – burial in the soil, inhabit the topsoil, aquatic plants, wood and other substrates available on the bed surface. The highest number and density of macrozoobenthos species was found in the littoral of the lake up to a depth of 2.5 m, but the lowest – in the western part of the lake, where the peat substrate dominates.

All over the lake, sunken hornbills (Ceratophyllum demersum) are also common, which indicates eutrophication or an increased place of nutrients in the lake (photo by L. Grīnberga).

FISH

There are 17 fish species in Lake Sauka: stone carp, perch, ausle, ground squirrel, carp, reed, pike, tench, flounder, plum, roach, redfish, silver carp, spiderfish, vetch, pikeperch and catfish. Numerous and mass dominated by bream, roach, perch and plaice.

PHYSICAL – CHEMICAL INDICATORS

One of the most important parameters that help to assess the ecological quality of the lake is the concentration of nutrients – nitrogen and phosphorus – as well as water transparency. Measurements made in Lake Sauka show that the transparency, nitrogen (0.83 mg / l) and phosphorus (0.021 mg / l) concentrations correspond to good quality. Elevated phosphorus concentrations (0.097 mg / l) have been detected in the bottom layer, which indicates the amount of accumulated nutrients and can potentially affect the overall ecological quality of Lake Sauka.

Ecological quality of Lake Sauka and its inflowing and flowing watercourses (author: Latvian Center for Environment, Geology and Meteorology)

Elevated nutrient concentrations have been found in almost all ditches and rivers flowing into Lake Sauka, creating a risk of eutrophication in the future.

INTERESTING FINDINGS

Several fossil-shaped fruits of the floating lake nut (Trapa natans) have been found in Lake Sauka. Floating lake nut is a rare and endangered species in Latvia. It is a representative of the Tertiary period flora and thus a relic plant species. The lake nuts found in the lake are 3,500 years old. Lake Sauka is one of the 28 deposits where the fossil form of a floating lake nut can be found in Latvia.

Fossil form of floating lake nut (Trapa natans) (photo by I. Kokorīte)

Lake Sauka is also home to a specially protected aquatic plant species – the sea najada (Najas marina), which in Latvia is more characteristic of coastal lakes and lagoons, but so far rarely found in inland lakes, to which Lake Sauka also belongs.

INTERESTING FINDINGS

Fossil form of floating lake nut (Trapa natans) (photo by I. Kokorīte)

Naja Marina (photo by L. Greenberg)

In addition to rare and protected species, there is also an alien species in Lake Sauka – the variable mussel (Dreissena polymorpha), which forms overgrowth on a solid substrate, the lake bed and also mussels of local species, thus negatively affecting them.

Variable mussel (Dreissena polymorpha) (photo by I. Kokorīte)

HOW TO IMPROVE THE ECOLOGICAL QUALITY OF LAKE SAUKAS?

Various measurements are performed in several places in Lake Sauka and its estuaries to determine the compliance of quality indicators with the ecological quality of the lake, as well as potential sources of pollution. It is planned to create a lake ecosystem model to assess ecosystem functionality, as well as to select measures to improve quality and reduce nutrient runoff.