Human Activity`s Influence on Lake Arbi

Over the years man has strongly influenced Lake Arbi. For decades water has flowed into the lake from the fields, streets and households of the Moonuse Stream catchment area and even from the wastewater treatment ponds. Bathers also do have an impact. Thus, a lot of pollutants have accumulated in the lake, which act as fertilizers for the plants. Eutrophication has taken place and the lake has become hypertrophic. This process occurs without  human impact too, as the catchment nutrients from natural ecosystems also leach into the lake. Naturally, however, it takes a lake thousands of years  to reach the hypertrophic  state; due to human activity, decades. The consequences of eutrophication are algal blooms, a decrease in the water’s oxygen content, and overgrowth of the lake.

The consequences of  eutrophication for the lake ecosystem. Figure: Piret Vutt.

The condition of the lake has been improved by rehabilitation. As early as the 1970s gravel was transported to the muddy sediments near the shore. At the beginning of this millennium  some of the nutrient-rich mud was removed from the lake and spread on the shore at the song festival grounds, where  the swampy area was turned into a lawn. Sediment ponds were built on the most important inflows, and the streams were made more rapid by rocks, so the water became richer in oxygen. The sediment pond of the Moonuse Stream is next to this information board. The water level was lowered to make the shore path dry. It had been high due to the blockage in the outflow. The beach was rehabilitated. In 2020 a large platform was built above the water in the southeast corner of the lake.

The photo taken by the current song festival grounds in 1925 shows that a semi-natural meadow surrounded the lake. A sparse mire forest would probably grow naturally on the shores of the lake. The wet meadows on the shores of the lake are of conservation concern. The semi-natural communities are managed by mowing once a year in late summer or autumn. The  mown hay should be removed from the area to reduce the nutrient load and keep smaller meadow plants. Photo: photo database FOTIS in the National Archive.

Author: Liina Remm

Main photo: Ragnar Vutt