Volume 17 (2017): Edizione 4 (December 2017)

Maximum depth of colonization (z_C) and total area covered by a population of Lobelia dortmanna, as well as underwater light regime were studied in 25 soft water lobelia lakes in north-western Poland. Variations in underwater light conditions among the lakes were described by Secchi disc depths (z_SD), and by attenuation coefficients of irradiance within photosynthetically active radiation range (K_d,PAR), and euphotic zone depths (z_EU) derived from photometric measurements conducted twice a year (in midspring and midsummer) during the period 2014–2015. Maximum depth of colonization of water lobelia ranged from 0.1 to 2.2 m (median z_C = 0.8 m; mean z_C = 1.0 m). Nine lakes showed the relative coverage of the littoral zone (RCLZ) by L. dortmanna to be greater than the mean value, which was 4.8%. Studies showed that light requirements of water lobelia increase when the maximum depth of colonization also increases. This pattern could be partially related to the greater energy needs of deeper growing individuals due to enlarged seed production and their incubation, and for the creation of much heavier inflorescences. Assessment of the light requirements of L. dortmanna along the depth gradient indicates that relative irradiance (percentage of subsurface irradiance of PAR) should be at the level of: (i) 47–50% (annual total of quantum irradiance 3083–3280 mol m⁻² yr⁻²) for plants growing within a depth range of 2.0–2.5 m; (ii) 44–47% (2886–3083 mol m⁻²yr⁻¹) for plants growing within a depth range of 1.5–2.0 m; (iii) 41–44% (2690–2886 mol m⁻²yr⁻²) for plants growing within a depth range of 1.0–1.5 m; and (iv) 34–41% (2230–2690 mol m⁻¹ yr⁻¹) for those growing in the littoral zone at a depth of between 0.5 and 1.0 m. In average conditions in the Pomeranian lakes, the maximum depth of colonization by L. dortmanna accounts for approximately a third of the Secchi disc depth and a fifth of the depth of the euphotic zone with irradiance of PAR at z_C equal to about 43% of subsurface irradiance. It has also been demonstrated that the light factor is a crucial one that limits the absolute maximum depth of lobelia population occurrence in Pomeranian lakes. The cleanest and most transparent lakes of this region have light attenuation coefficients (K_d,PAR) within the range of 0.35–0.42 m⁻¹, which corresponds to the maximum colonization depths of 1.8–2.2 m.

Lobelia lakes are valuable elements of the natural environment. They are characterised by low trophy, mainly in-forest location and a high transparency of water. However, similarly to other surface waters, they are subjected to increasing anthropogenic pressures, a good indicator of which is the level of surfactants, also called surface-active agents (SAAs). The aim of the study was to evaluate the intensity of anthropogenic pressures in 13 selected lobelia lakes and 14 streams in the catchments of these lakes in Northern Poland, based on SAA concentrations in the waters of these water bodies. We collected one water sample from each of these water bodies and determined the concentrations of cationic, anionic and non-ionic SAAs. We then compared the results with data concerning the ways in which these catchments and water bodies are used. While ionic (cationic and anionic) SAAs were found to be present in all the 27 samples (with concentrations ranging from 0.05 to 0.51 mg dm⁻³), non-ionic SAAs were identified in 17 of 27 samples (from 0.00 to 2.43 mg dm⁻³) with three samples largely exceeding the maximum concentration values reported by other authors. We concluded that SAAs are a real threat to the aquatic geoecosystems of lobelia lakes and that the pressures of tourism and leisure have the greatest impact.

Intensive and expansive human activity greatly accelerates the natural process of lake evolution. It is assumed that an increase in the rate of lake fertilization (often termed “eutrophication”) is the most common and most serious anthropogenic disturbance occurring in these aquatic geoecosystems. Lobelia lakes, one of the most valuable water bodies, are particularly exposed to this type of pressure. The article presents the trophic state of 13 lobelia lakes, located close to the Tricity area, in the northeastern part of the Kashubian Lakeland, which are not legally protected. These lakes represent different geoecosystems determining the rate of their natural evolution, and are subjected to various forms of anthropopressure (numerous summerhouses, fishing, waterside leisure and recreation). The trophic status of these lakes was assessed on the basis of the Carlson-type indices. The evaluation indicated that six of these lakes were in borderline mesotrophic-eutrophic state, and seven represented a significantly advanced eutrophic state.

The paper presents the results of an investigation of physical-chemical features of water as well as rotifer and crustacean abundance and diversity measures, relating to the taxonomic richness and species diversity index, in three lobelia lakes differing in trophic status and morphometric features. The main purpose of this study was to establish the diversity of zooplankton communities in the open water area of lobelia lakes, including extracting species common for each lake and also to find environmental predictors which are responsible for the development of zooplankton communities. Despite the fact that the three studied lakes are of the same origin, located in the same vicinity and have generally similar environmental factors, zooplankton community structure revealed a great variation in reference to species diversity (only ca. 20% of the species were common for all lakes) and particularly in inhabiting species. Obrowo Lake had the most diverse assemblages of both rotifers and crustaceans compared to Modre and Pomysko lakes. In the taxonomic structure species that are rare for the Polish fauna, such as e.g. Holopedium gibberum and Heterocope appendiculata, occurred. Even though the examined lobelia lakes are ecosystems that undergo varying human-induced impacts, they still remain taxonomically very variable aquatic ecosystems, containing rare species of very high ecological status. The observed symptoms of deterioration of water quality, reflected in the zooplankton biocoenotic features, showed that the best conditions were attributed to Obrowo Lake in comparison with the two remaining lakes – Modre and Pomysko. Total nitrogen and chlorophyll a concentration were decisive for the distribution of zooplankton species in Pomysko and Obrowo lakes, while in case of Modre lake water reactivity and conductivity were of higher impact.

Soft water lakes, or so-called lobelia lakes, which are inhabited by a specific vegetation composed of isoetids, have been subjected to intense research aimed at evaluating their condition and conservation status for many years in Poland. At the time of Poland’s accession to the European Union and the implementation of the EU Habitats Directive, these lakes were classified as natural habitat 3110. In accordance with the provision of the Habitat Directive a comprehensive methodology for monitoring and classification of the state of this habitat has been developed. Using this methodology, two monitoring trials (in 2009–2010 and again in 2016–2017) were carried out at 45 and 43 sites of the 3110 natural habitat, respectively. These studies confirm the high sensitivity of these poorly buffered aquatic ecosystems to all external influences, both natural and anthropogenic. The overall conservation status of the 3110 habitat in Poland showed a relatively high stability, with similar proportions of sites classified as favourable (FV), unfavourable inadequate (U1) and unfavourable bad (U2) between 2009–2010 (35%, 49% and 16%, respectively) and 2016–2017 (33%, 56% and 11%, respectively). Out of 43 sites examined in 2016–2017, 29 remained unchanged compared with the results of the previous survey concerning their overall status. Results of the monitoring research also allow for the observation and evaluation of mechanisms and directions of changes in the functioning of these ecosystems. Based on the experiences from two series of monitoring conducted so far, the methodology has been assessed as appropriate for the assessment of the conservation status of the 3110 natural habitat, however, some modifications and additions have been suggested.