Carbon Sequestration Potential in the Restoration of Highly Eutrophic Shallow Lakes

The primary goal of the study was to determine the quantity of carbon accumulated in shallow fertile water bodies that were restored after a long period of drainage. Massive drainage of mid-field water bodies took place in north-eastern Poland in the 19th century. Of 143 identified drained lakes (each of more than 1 ha before drying) in the Olsztyn Lakeland, 27 have been restored to their original state through natural rewilding processes or recovery projects. From among the variety of drained water bodies, 8 which have been naturally or artificially restored to their original condition 13 to 47 years ago, were the subject of a detailed study on carbon sequestration. The studied water bodies had high productivity, and they were classified as moderately eutrophic to extremely hypertrophic. An analysis of bottom sediments revealed that, after restoration, the examined water bodies have accumulated 275.5 g C m^-2 a^-1 on average, which is equivalent to 10.1 Mg ha^-1 a^-1 of carbon dioxide (CO₂) removed from the atmosphere. Results showed that the evaluated water bodies are effective carbon sinks. Most of the lakes drained in the 19th century are wastelands today, and they can be relatively easily restored to their original condition to create additional carbon sequestration sites. Lake restoration seems to be a cost-effective method both for carbon capture (as additional potential capacity as part of carbon dioxide removal (CDR) methods) and to support the sustainable use of agricultural areas. However, this second goal may be limited by the poor ecological status of such facilities.