Krystyna Kalinowska

Factors controlling bacteria and protists in selected Mazurian eutrophic lakes (North-Eastern Poland) during spring

BackgroundThe bottom-up (food resources) and top-down (grazing pressure) controls, with other environmental parameters (water temperature, pH) are the main factors regulating the abundance and structure of microbial communities in aquatic ecosystems. It is still not definitively decided which of the two control mechanisms is more important. The significance of bottom-up versus top-down controls may alter with lake productivity and season. In oligo- and/or mesotrophic environments, the bottom-up control is mostly important in regulating bacterial abundances, while in eutrophic systems, the top-down control may be more significant.ResultsThe abundance of bacteria, heterotrophic (HNF) and autotrophic (ANF) nanoflagellates and ciliates, as well as bacterial production (BP) and metabolically active cells of bacteria (CTC, NuCC, EST) were studied in eutrophic lakes (Mazurian Lake District, Poland) during spring. The studied lakes were characterized by high nanoflagellate (mean 17.36 ± 8.57 × 103 cells ml-1) and ciliate abundances (mean 59.9 ± 22.4 ind. ml-1) that were higher in the euphotic zone than in the bottom waters, with relatively low bacterial densities (4.76 ± 2.08 × 106 cells ml-1) that were lower in the euphotic zone compared to the profundal zone. Oligotrichida (Rimostrombidium spp.), Prostomatida (Urotricha spp.) and Scuticociliatida (Histiobalantium bodamicum) dominated in the euphotic zone, whereas oligotrichs Tintinnidium sp. and prostomatids Urotricha spp. were most numerous in the bottom waters. Among the staining methods used to examine bacterial cellular metabolic activity, the lowest percentage of active cells was recorded with the CTC (1.5–15.4%) and EST (2.7–14.2%) assay in contrast to the NuCC (28.8–97.3%) method.ConclusionsIn the euphotic zone, the bottom-up factors (TP and DOC concentrations) played a more important role than top-down control (grazing by protists) in regulating bacterial numbers and activity. None of the single analyzed factors controlled bacterial abundance in the bottom waters. The results of this study suggest that both control mechanisms, bottom-up and top-down, simultaneously regulated bacterial community and their activity in the profundal zone of the studied lakes during spring. In both lake water layers, food availability (algae, nanoflagellates) was probably the major factor determining ciliate abundance and their composition. In the bottom waters, both groups of protists appeared to be also influenced by oxygen, temperature, and total phosphorus.

Community structure of psammon ciliates in sandy beaches of lakes

Ciliate abundance and species composition were studied in the sandy beaches of six lakes of different trophic status (Poland). Samples of wet sand were taken in June 2007 from the euarenal (emergent sand), hygroarenal (sand wetted by lake waves) and hydroarenal (submerged sand) zones. The numbers of ciliates ranged from 105 to 2933 ind. cm−3 of sand and did not show any visible trend with lake productivity. In all the studied lakes, ciliates were much more numerous in the euarenal than in the hydroarenal. Small bacterivorous scuticociliates dominated in the euarenal, while Hymenostomatida, Cyrtophorida, Hypotrichida as well as Scuticociliatida comprised a significant part of the ciliate community in the hygro- and hydroarenal zones. There were positive correlations between ciliates and the concentrations of chlorophyll a and total nitrogen.

The Role of Planktonic Organisms in Urea Metabolism in Lakes of Temperate Zone - Case Study

ABSTRACT Although urea is the simplest N-containing organic compound ubiquitous in all aquatic environments, its role in N-nutrition of planktonic biota and relevance for eutrophication of freshwater ecosystems is still insufficiently defined and often bypassed. The dynamics of production of autochthonous urea as well as maximal potential net ureolytic activity (net URA Vmax) of phyto- and bacterioplakton were studied in mesocosm experiment and verified during the field studies conducted in the Great Mazurian Lake system (GMLS). Analysis of the obtained results revealed that the proteins were the main autochthonous urea precursors. Urea concentration in the studied mesocosms and in GMLS surface waters was positively correlated with flagellate, ciliate and crustacean biomass and, less evidently, with bacterial biomass (BB). In surface waters of GMLS net URA Vmax, similarly as urea concentrations, increased with their trophic status. Analysis of correlation of potential ureolytic activity with chlorophylla, (Chla) BB and L-leucine aminopeptidase activity (AMP) in lakes of different trophic status suggests that although both groups of planktonic microorganisms participated in urea decomposition processes, in eutrophic ones bacterial decomposition of urea is more evident. In highly eutrophic lakes excess of phosphorus induced higher nitrogen requirement resulting in the increase in protein decomposition rate. Intensified protein degradation resulted faster urea production, which finally induced higher ureolytic activity of planktonic microorganisms. In profundal waters of GMLS potential ureolytic activity was distinctly lower than in surface waters. This was caused by low temperature of hypolymnetic waters, inhibitory effect of hydrogen sulphide and lack of phytoplankton, which is known as a primary urea consumer.

Effects of zebra mussels on cladoceran communities under eutrophic conditions

The purpose of this study was to determine how zebra mussels affected cladoceran community structure under eutrophic conditions. We conducted a mesocosm study where we manipulated the presence of zebra mussels and the presence of large-bodied Daphnia (Daphnia magna and Daphnia pulicaria). We also conducted a complimentary life-table experiment to determine how water from the zebra mussel treatment affected the life history characteristics of the cladoceran species. We anticipated that small- and large-bodied cladoceran species would respond differently to changes in algal quality and quantity under the effects of zebra mussels. Large-bodied Daphnia successfully established in the zebra mussel treatment but failed to grow in the control. We did not observe positive relationships between food concentrations and cladoceran abundances. However, the phosphorus content in the seston indicated that food quality was below the threshold level for large-bodied cladocerans at the beginning of the experiment. We believe that zebra mussels quickly enhanced the phosphorus content in the seston due to the excretion of inorganic phosphorus, thus facilitating the development of large-bodied Daphnia. In conclusion, our results suggest that zebra mussels can alter the phosphorus content of seston in lakes and this can affect the dynamics of crustacean zooplankton.

Vertical distribution of the relic species Eurytemora lacustris (Copepoda, Calanoida) in stratified mesotrophic lakes

The aim of this study was to determine factors affecting the vertical distribution of Eurytemora lacustris in mesotrophic lakes (Wigry, Hańcza, Szurpiły; north-eastern Poland) during the summer stagnation. Eurytemora lacustris was found in all of the studied lakes, with the highest abundance (8 ind. L−1) in Lake Wigry. In Lake Szurpiły, E. lacustris has never been recorded before. The results of this study revealed that E. lacustris was most numerous in thermocline zones, suggesting that this species could temporarily tolerate warmer water and lower oxygen concentrations due to better food resources. During the study, it was found that a large part of the E. lacustris population had epibiont ciliates, in contrast to other species of zooplankton that did not have any epibionts. The improvement in the water quality of many deep lakes could lead to an increase in the abundance of E. lacustris. However, epibiont ciliates may be a threat for this species and may play a substantial role in determining the production, distribution, and community dynamics of E. lacustris.

Microbial and classic food web components under ice cover in eutrophic lakes of different morphometry and fisheries management

Abstract The thickness and duration of ice cover are strongly influenced by global warming. The aim of this study was to determine chemical (organic carbon, total nitrogen and phosphorus concentrations) and biological (nanoflagellates, ciliates, phytoplankton, rotifers, crustaceans) parameters under the ice cover in three eutrophic lakes (Masurian Lake District, Poland), differing in their morphometry and fisheries management. All the studied groups of organisms showed high variability over a short time. Taxonomic composition of planktonic communities, except for rotifers and phytoplankton, was similar in all lakes. Nanoflagellates were dominated by autotrophic forms, while ciliates were primarily composed of small oligotrichs and prostomatids. Nano-sized diatoms and mixotrophic cryptophytes were the most important components of phytoplankton and they formed an under-ice bloom in one lake only. Rotifers were mainly represented by Keratella cochlearis, Polyarthra dolichoptera and Asplanchna priodonta. Among crustaceans, copepods clearly dominated over cladocerans. Our research suggests that winter was a very dynamic period. In the under-ice conditions, pelagic organisms were strongly dependent on each other. The shallow lake and the deeper, small lake differed significantly in nutrient and chlorophyll concentrations, ciliate and phytoplankton biomass and the ratio of autotrophic to heterotrophic biomass. These results suggest that morphometric parameters may affect planktonic organisms during the ice-covered period.