Limnol. Rev., Volume 11, Issue 3 (September 2011) – 4 articles , Pages 97-132

The paper discusses the issue of plant overgrowth in the littoral zone of lakes. It presents the plant encroachment process and its environmental and economic consequences based on the example of selected lakes of the Wielkopolska Lakeland. In order to estimate changes of quantity in the riparian vegetation structure, historical records of changes of reed bed areas were compared with their present areas. Historical data included bathymetric plans from the 1960's created by the Institute of Inland Fisheries and information obtained from interviews with the inhabitants of settlements located in the vicinity of the studied lakes. Present-day boundaries of reed bed zones were identified using orthophotos, aerial photographs and in situ inspections. In the course of the field research, identification of plant species and estimates of plant condition in the studied stands were carried out. Obtained data combined with data on local hydrological-meteorological conditions, water quality and land use in the direct vicinity of lakes allowed the authors to determine the conditioning factors of riparian vegetation encroachment. The collected evidence allowed the authors to establish that in the last five decades, the area of reed beds around the studied lakes increased by an average of 15–20%. This process was usually accompanied by the encroachment of hydrophytic plants consequently leading to the shrinkage of supralittoral zones. In the last 20 years, these two phenomena intensified considerably, particularly during two low water periods noted during this period. However, the encroachment of riparian vegetation proceeded differently in the case of each lake and it was most protrusive in highly eutrophicated reservoirs and those with a history of permanent or long-term lowering of the water table. The qualitative structure of the studied plant communities was conditioned mostly by nutrient inflow and the type of growing medium. In large clean lakes and in zones of sandy lake bottom, the reed beds were dominated by the common reed (Phragmitetum australis). In smaller, polluted lakes and shielded bays of larger lakes with stagnant water, beside multi-species reed beds, floating-leaf hydrophytic macrophyte plants of the genus Nymphaea, tall stands of sedges and helophytes were observed. Full article

In the years 1991–2010 the water stages of 38 lakes in the Łęczna-Włodawa Lake District were observed. Water stage dynamics of the Łęczna-Włodawa lakes was varied. A multi-annual trend with seasonal water stage variability was clearly observable. Low water stages were observed in the years 1994–1996 and 2004–2005, whereas the highest water stages were reported for 2002 and 2010. The water stages of Lake Piaseczno, the deepest lake, were consistent with solar activity changes. Land improvement works in the Łęczna-Włodawa Lake District and black coal mining caused further local changes in the directions of flow of surface and underground water, as well as modifying the water stage regime of some of the lakes. Full article

The aim of the research was to determine the successional changes proceeding in the phytoplankton of a lake. The basis of the study was the analysis of long-term seasonal changes in the taxonomic structure and the estimation of the intensity of algal community development in phytoplankton of Lake Kortowskie. Seasonal changes in the phytoplankton taxonomic structure manifested themselves as a decreasing share of Bacillariophyceae in spring and autumn and Chlorophyta in summer phytoplankton. The retreating chlorophytes and the diatoms were replaced by blue-green algae, the increasing share of which caused a reduction in the stability of the remaining phytoplankton taxonomic groups, and consequently, taxonomic shifts and progressive development of the overall phytoplankton community in all phenological seasons. Intensive algal growth was observed in spring and lasted until late autumn. The highest phytoplankton biomass was always recorded in summer. Summer phytoplankton development was related to increased bluegreen algae domination, the massive growth of which was observed from spring to autumn. The development of the Cyanoprokaryota community had a negative impact on the diatoms, since the latter earlier disappeared from the biocenosis in spring and re-developed to a lesser degree in autumn. Full article

In the lakes Cheb and Słupino, located in the Wdzydze Landscape Park the quality of waters has been deteriorating in recent years. In the hydrologic year 2009 the quality of water was examined three times. Monthly measurements on the lake inflows and outflows were carried out 12 times to determine biogenic loads. In 2010 the supplementary measurements of biogenic loads were taken in the streams five times. According to Vollenweider's criterion, the loads of nitrogen and phosphorus compounds are too big, the heaviest to Lake Cheb. The discharge from the new sewage treatment plant is directed by the inflows into this lake. A similar situation takes place in the inflow to Lake Schodno. Paradoxically, in some catchments the construction of the sewage treatment plant may result in the deterioration of lake water quality. Full article