When a lake’s natural balance is shaken, the waters can be cleaned and restored to health. There are many ways to restore a lake. One of the most effective methods is chemical restoration.
A clear case of improvement, Lake Kirkkojärvi in Rymättylä, Finland, was restored in 2002 and 2005 and is according the southwest division of the Finnish Centre for Economic Development, Transport and the Environment, fit for swimming in 2011. The ecological state of the lake has been monitored since the early 1990s, and it has become established on a satisfactory level, while its state before the restoration was poor.
Chemical treatment and biomanipulation
The Kirkkojärvi commission was granted chemical treatment permits in 2002 and 2005. In addition to detailed water analyses before the treatment, the permits required the executors to remove dead fish and monitor environmental effects for two years after the treatment.
The project used liquid aluminum chloride to bind phosphorus from the water and the lake bottom into an insoluble form. The goals also included biomanipulation, i.e. removing the dense trash fish stock.
Clearing out accumulated phosphorus
The lake had suffered throughout the 1990s. Heavy blooms of blue-green algae appeared on the surface every summer, and the trash fish stock was larger than in any other lake evaluated in Finland. The bottom had high amounts of accumulated phosphorus.
As a result of the treatment, the waters cleared throughout. Water quality instantly changed from bad to excellent, remaining high until the winter of 2005 when the rains washed out high amounts of nutrients and solid matter from the surrounding fields to the lake. In 2005, the lake was treated with ferric sulfate, which binds phosphorus from the bottom sediment. Again, the results were positive.