Trends of submerged vegetation transformation in well-preserved lakes with isoetids in NW Poland

The main objective of this study was to determine the changes in environmental conditions and vegetation structure that have occurred over nearly 30 years in well-preserved isoetid lakes under the influence of natural successional transformations, in the absence of direct human pressure on both the lakes and their catchment area. The research methodology was based mainly on non-invasive underwater work consisting of taking samples of plants and water. During the study period, the maximum depth of macrophytes decreased, from 10.5 to 7.5 m. The reason for these changes is a large increase in water color, decrease in water transparency and as a consequence of these changes, the light intensity of the water also decreased. The physical and chemical changes in the lake water have contributed to a pronounced remodeling of macrophyte communities primarily in the deep phytolittoral zones; there has been a complete elimination of bryophytes, especially those of the genus Sphagnum. Their habitats have been occupied by charophytes, primarily Nitella flexilis and Chara virgata. However, shallow water vascular plant communities (isoetids) have not been significantly transformed. Our research clearly shows that despite the lack of anthropogenic pressure on the lakes, far-reaching changes occur in the structure of macrophyte communities.