Volume 37 (2008): Issue 2 (June 2008)

Indices of microbial efficiency (expressed as oxygen consumption and carbon dioxide release) were determined in the water column of the meromictic Piaseczno Reservoir (in an opencast sulphur mine), which is rich in sulphur compounds. Phytoplankton abundances were low in both the mixolimnion (up to 15 m depth) and monimolimnion (below 15 m depth). In summer and winter, carbon dioxide release was 3-fold and 5-fold higher, respectively, in the monimolimnion than in the mixolimnion. Laboratory enrichments of the sulphur substrate of the water resulted in a decrease in oxygen consumption rate of by about 42% in mixolimnion samples, and in the carbon dioxide release rate by about 69% in monimolimnion samples. Water temperature, pH and bivalent ion contents were of major importance in shaping the microbial metabolic efficiency in the mixolimnion, whilst in the monimolimnion these relationships were not evident.

This paper describes the role of air masses in transporting iron to the coastal zone of the Gulf of Gdansk. Fe(II) concentrations in rainfall were measured between 19^th January and 30^th November 2005 in Gdynia, during which time they varied from 0.74 μmol dm^-3 to 97.45 μmol dm^-3. The relationship between iron concentrations and precipitation amount, including during preceding rainless periods, was calculated. The effectiveness of washing iron out of the atmosphere is described by the exponential function of precipitation duration.

Air masses arriving from west of the area transport terrigenous iron to the coastal zone of the Gulf of Gdańsk, while anthropogenic sources in Western Europe and Pomerania hardly affected the iron concentrations.

Populations of Chaetogammarus ischnus and Pontogammarus robustoides living in the middle part of the Włocławek Dam Reservoir (on the lower Vistula River, central Poland) were studied. The two species coexisted at offshore sites of the reservoir, with P. robustoides being much more abundant than C. ischnus. In samples collected from the bare bottom of the reservoir (sandy or covered by zebra mussel shells) and macrophytes a negative relationship between the two species was observed: C. ischnus occurred in high numbers in those samples in which abundance of P. robustoides was low. This phenomenon is postulated as resulting from the larger size and more predatory nature of P. robustoides, limiting the occurrence of C. ischnus.

Epiphytic algae occurring on submerged macrophytes were investigated as part of a study on the ecological status of a shallow macrophyte-dominated lake, Lake Skomielno, which has been used for recreation and fishery. Relatively high variability in biomass (DM) and chlorophyll a contents in epiphyton on particular plants was noted. Generally, the biomass of epiphytic algae was much higher in spring and autumn than in summer. In total, 335 taxa were found on the studied macrophytes with representatives of the Chlorophyta (143 taxa) and Heterokontophyta class Bacillariophyceae (131 taxa) dominating. The species composition of epiphytic algae was related to host plant and seasons, the highest species richness was observed on Stratiotes aloides in spring and on Potamogeton lucens in autumn. The Jaccard similarity index revealed differentiation of diatom communities between the macrophytes. Our data suggest that in the studied lake S. aloides and P. lucens can provide better habitat conditions for higher numbers of epiphytic taxa, abundances and epiphyton standing crop than Ceratophyllum demersum and Chara spp. can. The dominance of diatom species (e.g. Pseudostaurosira brevistriata (Grun.) Williams & Round, Achnanthidium minutissimum (Kütz.) Czarnecki, and Cocconeis placentula Ehrenb.) that are known as bioindicators of slightly alkaline, sufficiently oxygen-saturated and meso-eutrophic waters corresponds well with the physico-chemical parameters of Lake Skomielno.

This paper reports the results of studies of microbiological changes in the water quality of the Vistula and Brda rivers after the opening of sewage treatment plants in Bydgoszcz. The study involved determining the microbiological parameters of water quality. Based on the results obtained, it was found that the quality of the water in both rivers had improved decidedly after the opening of the plants, although an increased number of individual groups of microorganisms was found at the treated sewage outlet from one of the plants.

Lake Zbęchy is situated in the General Chłapowski Landscape Park, which is the model of a rural area that has been subjected to agricultural pressure for many years. Over a thirty-year period (1976-2006) serious changes in the plant associations of Lake Zbęchy have occurred. The maximal depth of plant occurrence decreased from 3.6 m in 1976 to 2 m at present. The area overgrown by submerged macrophytes decreased from 13 to 0.2 ha. The community of Nitellopsidetum obtusae that dominated the belt of submerged plants during the 1970s has entirely disappeared from the lake. The decreasing phytolittoral area in the lake is the result of progressive lake eutrophication and water pollution. The transformations of reed and sedge communities are of a partially natural and partially anthropogenic character. The ecological status of the lake has deteriorated significantly. The ecological state of the lake in 1976 was good according to the Water Framework Directive. Currently, it is sufficient, but the ESMI value of 0.21 only slightly exceeds that of a bad ecological state (0.20-0.00). The level of lake development in the succession process was between mature and aged in 1976; now it is classified as definitely aged.

The aim of the studies done in a shallow preliminary reservoir (western Poland) was to determine the intensity and seasonal variability of phosphorus release from bottom sediments. Ex situ studies were done using intact sediment cores taken in succeeding seasons at 3 research stations. The highest phosphorus loading was observed in spring (May and April), both in 2005 and 2006. The range of loading was between 23.7 and 66.6 mgP m^-2 d^-1. More intensive phosphorus release during warmer months was caused by microbiological decomposition of fresh organic matter, comprised of decaying filamentous algae from the previous vegetation season. Spatial variability resulted from differences in water depth between stations and in the biomass of filamentous green algae in 2005.

In 2001-2003, a survey was conducted of the effectiveness of restoration in the heavily eutrophic polymictic Lake Głęboczek, located in Tuchola. The application of the phosphorus inactivation method with polyaluminum chloride PAX 18 resulted in the complete removal of phosphates, and in a considerable (up to 50-60%) reduction of total phosphorus in the lake water. The sorptive capacity of the bottom sediments was enhanced after the restoration, particularly in the top layer (0-5 cm). An increase of the aluminum content and of mineral forms of phosphorus was observed, mainly the aluminum-bound fraction (at its greatest, by over 330%). The amount of mobile phosphorus in the sediments decreased by 40%. The evidence of the durable immobilization of phosphorus in the aquatic ecosystem was the limited phosphorus release from the bottom sediments. This was confirmed by a significant decrease of total phosphorus in the interstitial waters (from 4-6 mg dm^-3 to 2-3 mg dm^-3), and by a practically complete removal of phosphates from the near-bottom waters.

The use of natural or artificial water reservoirs by thermal power plants for cooling purposes alterswater ecosystems. Water ecosystems are mainly subjected to the abiotic influences of higher temperature and increased mixing. This study presents the thermal and oxygen conditions in a lake used for cooling water as well as the chemical changes occurring in it. There is a spatial differentiation in the temperature of the water surface over time periods (in summer and winter).

The vertical water temperature changes were definitely different from those of natural, unaffected lakes. Apart from a higher average water temperature, typical mixing and stratification periods were not observed. This apparently affected the dissolved oxygen conditions. The observed absence of a dissolved oxygen deficit resulted from the lack of a thermocline, which positively affected water quality. As a result, the two anthropogenic factors, i.e., the discharge of warm water and increased mixing, have flattened the negative effects on the lake. A new characteristic equilibrium for this lake was established. Single factors have been compensated for by this equilibrium. A relationship between temperature and biomass concentration was observed. The trophic state index (TSI) values permit classifying Rybnik Reservoir as a eutrophic lake.

Studies of benthic diatom communities in the surface sediments of the Swarzewo area of Puck Bay were carried out during 1998 and 1999 in order to assess water quality, and in particular the organic load. Among the 192 taxa identified, teratological forms of diatoms were recorded in 17 diatom species, primarily in the species Opephora mutabilis, Planothidium delicatulum and Fragilaria fasciculata. The number of teratological forms was significantly higher in sediments rich in organic matter, which had concurrent high concentrations of phosphorus and nitrite nitrogen compounds. The highest teratological diatom abundances were recorded in α- mesosaprobic conditions, especially during spring and summer. It is postulated that teratological diatom valves are indicative of poor water quality.