A total of 313 lakes with charophyte vegetation were identified based on the data presented in 1111 manuscripts under the shared title of “Assumptions for the fisheries management project in Lake (lake name)”, based on the results of an environmental inventory carried out by the Inland Fisheries Institute in 1953-1968. The lakes’ morphological characteristics were described, hydrophyte species that most frequently accompanied charophytes were identified, differences in summer water transparency were analyzed in 281 lakes with charophyte vegetation and the results were compared with the observations made in 657 other lakes, and the potential trophic state of lakes with charophyte vegetation was determined using Carlson’s trophic state index (1996). More than half (54%) of 171 dimictic lakes with charophyte vegetation were classified as mesotrophic and 31% as oligotrophic, whereas 50% of 110 polymictic lakes were classified as eutrophic, and 40% as mesotrophic. The frequency of taxa that contribute to the eutrophication (degradation) of water bodies, including Ceratophyllum spp. Myriophyllum spp. and Elodea canadensis, increased with a decrease in the percentage of charophytes in communities of submerged hydrophytes. Regardless of the proportion of charophytes in submerged hydrophyte communities, water in the lakes colonized by charophytes was more transparent than in the 659 lakes without charophytes. Water in many polymictic and dimictic lakes with charophyte vegetation, including lakes with a small contribution of charophytes, was more transparent than in lakes without charophytes, which suggests that charophytes are sensitive indicators of water quality and are components of ecological memory in aquatic ecosystems.
The possibility of doing a back assessment of the ecological status of a lake based on archival bathymetric maps indicating areas overgrown with rushes and aquatic vegetation was verified. This assessment was assumed to be in accordance with that performed with the official Polish macrophyte-based method for lake assessment (Ecological State Macrophyte Index, ESMI). The study was conducted on Lake Dobrąg located in the Warmian-Masurian Voivodeship (surface area - 108 ha, maximum depth - 27.9 m, mean depth - 11.6 m). It included the hydroacoustic distribution of submerged macrophytes along 85 evenly distributed belt transects (perpendicularl to the shore line), creating a bathymetric chart and maps of vegetation occurrence and identifying areas occupied by hydrophytes (Cmax) and the maximum depth of lake colonization (Z). Analogous data were read from archival bathymetric chart dating from 1964-1968. The values obtained were compared with the means (and their confidence intervals) of 83 stratified lakes in Poland in different ecological status classes. Analysis of changes indicated that the ecological status of the lake had deteriorated. In the mid-1960s, the status of the lake was less than “very good” while the current status borders between “good” and “moderate.” The results indicate that the proposed method could be useful when attempting to assess changes in ecological status using archival bathymetric charts showing areas overgrown with vegetation and the distribution of it in lakes.
Ciliates on the Macrophytes in Industrially Heated Lakes (Kujawy Lakeland, Poland)
The ciliate assemblage on the macrophytes was examined in 2005 during the vegetation period in the Konińskie Lakes which are heating by post-cooling waters from thermal electric plants. As a result of changed temperature regimen the alien thermophilic macrophyte Vallisneria spiralis is becoming increasingly common in the littoral zone. A total of 150 ciliate taxa belonging to 27 orders were found. Greater ciliate species diversity was found on architecturally complex, submerged forms such as Ceratophyllum demersum and Myriophyllum spicatum. By contrast the ciliate compositions on emergent macrophytes with simple architecture in their submerged parts, such as Typha, Sparganium, or Acorus, were less species rich. Despite the simple architecture of Vallisneria leaves, the ciliate diversity on them was high. The results show that replacement of native macrophytes by the alien form V. spiralis in heated lakes did not impoverish the ciliate diversity.