Katarzyna Kowalczewska-Madura

Trophic state of a lowland reservoir during 10 years after restoration

The restored Maltañski Reservoir was studied from its filling with water in 1990 till 2000. Total phosphorus, chlorophyll-a, and Secchi depth, as well as the Carlsons trophic state index (TSI) values based on those three parameters showed characteristic patterns of changes among seasons and years. Within each year, the lowest trophic state was usually observed in winter and the highest in summer. Because of the high loads of phosphorus received by the reservoir, this element did not limit primary production. TSI values calculated on the basis of total phosphorus were always markedly higher than calculated on chlorophyll-a and Secchi depth (similar to each other). The trophic upsurge phase lasted only a few months after the filling of the reservoir in 1990. Similar symptoms were observed after its refilling in the spring of 1993. The trophic depression phase lasted until the end of 1995. After that time a significant correlation between phosphorus concentration in the reservoir and in river waters flowing into the reservoir was observed. The successive phases of reservoir ageing, determined on the basis of phosphorus concentration, were not accompanied by changes in chlorophyll-a content. The influence of the top-down mechanism (biomanipulation effect) resulted in relatively low values of chlorophyll-a after the filling of the reservoir with water in 1990 and in 1993. As early as 1992 chlorophyll-a values reached a very high level and stayed at that level until the end of the study in 2000 (except for the short decline in 1993).

Functioning of the Lake Rusałka ecosystem in Poznań (western Poland)

Functioning of the Lake Rusałka ecosystem in Poznań (western Poland) Lake Rusałka is a shallow, artificial, strongly eutrophic reservoir. Thermal stratification is weak and comprises only about 8% of the bottom surface. In summer, the epilimnion is oversaturated with oxygen due to intensive phytoplankton growth (chlorophyll a up to 80.2 μg l-1), while conditions in the hypolimnion are anaerobic. The high concentration of ammonium nitrogen and low N:P ratio stimulated intense growth of cyanobacteria in the period from June to November. The domination of rotifers in the metazooplankton and low diversity and biomass of benthic macroinvertebrates was the cause of low top-down pressure of these organisms on the phytoplankton. The most advantageous restoration measures were identified to improve water quality and make the recreational use of the lake possible.

Models of phosphorus turn-over in a hypertrophic lake: the Lake Swarzędzkie case study

Models of phosphorus turn-over in a hypertrophic lake: the Lake Swarzędzkie case study Phosphorus cycling between components of the ecosystem of the hypertrophic Lake Swarzędzkie was studied in 2000-2003. The results of this study revealed considerable seasonal variation in phosphorus cycling. The main sources of phosphorus load in winter were the tributaries, whereas in summer internal loading prevailed. However, the most effective source of SRP (soluble reactive phosphorus) for phytoplankton primary production in summer was its excretion by organisms from the microbial loop. The share of this source in the total phosphorus pool was 38%, whereas internal loading contributed 23.7%, external loading 16.3%, and regeneration by metazooplankton 22%. This exerted a significant influence on the functioning of the whole lake ecosystem. Limiting both external and internal phosphorus loading is recommended to facilitate water quality improvement in the lake.

Zooplankton phosphorus excretion in Swarzędzkie Lake (Western Poland) and its influence on phytoplankton

Zooplankton phosphorus excretion in Swarzędzkie Lake (Western Poland) and its influence on phytoplankton Zooplankton phosphorus excretion was studied in Swarzędzkie Lake in 2000-2002. Phosphorus excretion rates were high from spring through autumn, but low in winter. The highest value, 203.7 μgP 1-1 d-1 (vertical profile mean), was recorded in June 2000. The mean rate was 26.6 μgP 1-1 d-1 and was 10 times greater for rotifers than for both cladocerans and copepods. In most months, the calculated phosphorus excretion rate was greater than the sum of tributary external phosphorus loading and internal bottom sediment loading. Nevertheless, the influence of the zooplankton phosphorus excretion rate on yearly phytoplankton abundance, biomass and chlorophyll a was not statistically significant. Yearly variance in phytoplankton variables was best explained by a canonical variable composed of internal loading and zooplankton phosphorus excretion (total redundancy 32.8%).

Phytoplankton composition and physicochemical properties in Lake Swarzędzkie (midwestern Poland) during restoration: Preliminary results

Abstract This paper presents the preliminary results of a study of the phytoplankton structure and dynamics and physicochemical properties of Lake Swarzędzkie in 2011. The subject of the study is a shallow, elongated, post-glacial lake located in western Poland. The surface area is 93.7 ha with a maximum depth of 7.2 m. Its poor water quality led to the implementation of chemical and biological restoration procedures in an attempt to improve it. The highest concentration of total nitrogen was 13.07 mg l-1 N. Secchi depth (SD) was low in the summer with a minimum value of 0.5 m in September. The most abundant group of phytoplankton were cyanobacteria, and the maximum value of chlorophyll a concentration was 278.0 μg l-1. The dominant species were Pseudanabaena limnetica and Aphanizomenon gracile. Cyanobacteria were the most abundant phytoplankton until November. Maximum diatom, cryptophyte, and chrysophyte density was noted in the spring, and the most abundant were Nitzschia acicularis, Cryptomonas marssonii, Rhodomonas lacustris, Erkenia subaequiciliata, and Dinobryon sociale. One-hundred and thirty-six phytoplankton taxa belonging to nine taxonomic groups were identified in Lake Swarzędzkie. The highest number of taxa was noted among chlorophytes (57 taxa), cyanobacteria (19), diatoms (16), and chrysophytes (12), while other taxonomic groups were represented by smaller number of taxa.

Phosphorus release from the bottom sediments of Lake Rusałka (Poznań, Poland)

Phosphorus release from the bottom sediments of Lake Rusałka (Poznań, Poland) Experimental research conducted on bottom sediments from the eutrophic Lake Rusałka (Poznań, Poland) indicated that the phosphorus release process has a significant influence on the functioning of the ecosystem. Internal loading was very intense in the deepest part of the lake, where it reached up to 29.84 mg m-2 d-1 P under anaerobic conditions. This part of the lake, however, was insignificant to overall internal loading. The highest loading was from the lake shallows, which covered 92% of the bottom area. Total mean annual loading to the ecosystem was 1214.5 kg year-1 P, i.e., 3.31 g m-2 year-1 P.

The bottom sediments of Lake Uzarzewskie - a phosphorus source or sink?

The bottom sediments of Lake Uzarzewskie - a phosphorus source or sink? Phosphorus release from bottom sediments studied in two zones of Lake Uzarzewskie differing in depth and water oxygenation displayed seasonal and spatial variability. The experiments indicated that the lake receives considerable internal loading, especially from the deeper, anaerobic, rarely-mixed part of the lake. Meanwhile, the shallow zone situated in the 0-3 m depth range, could be a sink for phosphorus during spring and a source during other seasons of the year. The total loading of phosphorus from the bottom sediments was over 950 kg year-1 P, and 83% of this amount originated from the deeper part of the lake. The mean release from this part was 24.89 mg m-2 d-1 P and the maximum in fall was 35.4 mg m-2 d-1 P.

Inorganic and methyl-mercury speciation in sediments of the Swarzędzkie Lake

Sediment samples were analysed for mercury and methylmercury content in different parts of the bottom sediment of Swarz ędzkie Lake, which were influenced by different external pollution sources. The results of determination with two methods of mineralization using two separate media (HNO3/H2O2 and HF) were compared. The accuracy of the studied methods was analysed using certified reference material IAEA 405 of river sediment. The recovery of mercury was satisfactory and ranged from 97.5 to 98.8%. Methylmercury compounds in the studied sediments were found in limited concentrations. Their concentrations ranged from 0.26 to 58.1 μg kg−1, i.e. 1.0–7.4% of the total mercury content. The depth profile displayed high values of both total and methylmercury content at a depth of 10–20 cm, related to the heavy pollution of the lake in the 1980s. Canonical analysis displayed the relationship of both total mercury and methylmercury concentrations with organic matter and phosphorus content in bottom sediments.

Internal phosphorus loading in selected lakes of the Cybina River valley

Internal phosphorus loading in selected lakes of the Cybina River valley The aim of this study was to assess the ability of bottom sediments to release or accumulate phosphorus. Ex situ experiments with the use of undisturbed sediment cores were done in 11 lakes situated in the Cybina River valley (Wielkopolska, Poland). Phosphorus release was observed both in aerobic and anaerobic conditions, however greater values were noted in the latter ones. Maximum values reached 41.4 mg m-2 d-1 P and 12.2 mg m-2 d-1 P in anaerobic and aerobic conditions, respectively.

Total phosphorus and organic matter content in bottom sediments of lake under restoration measures with iron treatment

Total phosphorus and organic matter content in bottom sediments of lake under restoration measures with iron treatment Rusałka Lake is a shallow, man-made, strongly eutrophicated reservoir, being a place of recreational activities for Poznan citizens. Restoration measures with the use of iron sulphate were conducted in years 2006-2007. Phosphorus and organic matter concentrations in lake sediments were analyzed in years 2005-2007 at two research stations (profundal and littoral) to determine its changes under the influence of restoration. Greater phosphorus concentrations were noted in profundal (max 1.55 mg P g-1 dry weight (DW)) than in littoral (max 0.98 mg P g-1 DW). An increase of P amount in sediment was observed after iron treatment. Among phosphorus fractions Res-P dominated, i.e. phosphorus biologically unavailable for organisms. Organic matter content reached 23.1% in profundal, while 14.8% in littoral. Its amount decreased in following years.