Recultivation of Jelonek and Winiary lakes in Gniezno by inactivation of phosphorus in bottom sediments

PROJECT DESCRIPTION

BACKGROUND

Gniezno is situated in Gniezno Lake Region, the area in Poland with the lowest rainfall. Lakes Jelonek and Winiary are threatened by urban sprawl and for many years municipal household and industrial sewage drained into the lakes. The inflow of high loads of contaminants began in 19th Century and has resulted in the demise of vast numbers of fish in the lakes. The restricted potential for water exchange in the lakes has led to sedimentation and accumulation of suspended matter. Used for many decades as dumping sites for municipal sewage, the lakes have lost their capacity for self-purification and without action further degradation will occur.

OBJECTIVES

The main objectives of the Lake recult. in Gniezno project were to improve the water quality in the Jelonek and Winiary lakes, their purity condition and their biotope conditions. The project planned to demonstrate a re-cultivation method by inactivation of phosphorus in bottom sediments using coagulants directly administered to the bottom sediments and to disseminate this transferrable new methodology.

RESULTS

The main objective of the Lake recult. in Gniezno project was met: the quality of water improved substantially, and it is now possible to use the lakes for recreational activities. The reconstruction of the degraded lake banks not only secures the lake against infiltration of pollutants from storm water but also increased the landscape value of the lakes.

The project also achieved the following specific results:

Total phosphorus content in the water decreased to 0.047 mg P/dm3 in Winiary lake and 0.113 mg P/dm3 in Jelonek lake (the planned content was 0.1 - 0.2 mg P/dm3);

The water transparency increased: visibility of Secchi’s disc is 0.9 m in Jelonek lake and 2.9 m in Winiary lake (the planned value was 0.6 - 1.0 m);

The content of chlorophyll was reduced to 11.4 ppm in Winiary lake and to 51.5 ppm in Jelonek lake (the planned value was 15 ppm) in 2010 and to 19.8 ppm in 2011 (one year after the end of the project);

Blue-green algae have not been observed since inactivation of the phosphorus in bottom sediments (as planned).

The project demonstrated that the method of inactivation of phosphorus by application of coagulants directly to bottom sediments is an effective tool for the protection of shallow lakes, especially those located in cities and urban areas. It is a relatively cheap method that makes progress in a short period of time. The results of the project were publicised through press articles (local and national), TV coverage, school visits, posters and the construction of four noticeboards at the project sites. In addition, a national conference was held.

The project beneficiary recognises that the permanent monitoring of the lakes and their draining areas is necessary. Moreover, the beneficiary intends to implement the active conservation measures:

Seasonal elimination of reeds from the area of inflow to the Jelonek lake, which will take the biogenous stored in the reeds out in the lake;

Control of the fish stock, control catch of the selected fish species, which which will ensure a wide diversity of fish species;

Controlled mowing of water plants from the sites around the lakes devoted to recreation;

Control of macrophytes and their plantation if needed;

Campaign to prevent feeding of aquatic birds.

Finally, the project was a major step towards fulfilling the requirements of the Water Framework Directive (2000/60/EC). Among other goals, the directive aims to maintain inland sources of surface water in "good ecological condition". Currently the quality of water in the Gniezno's lakes can be considered in a good condition.

Further information on the project can be found in the project's layman report and After-LIFE Communication Plan (see "Read more" section).