Search

The research was carried out on the flow-through Lake Mielenko (7.8 ha; 1.9 m), which also acts as a stormwater receiver. In 2015, a disposal for road salts was created in the lake’s catchment area. As a result of the inflow of salt-contaminated stormwater, there was a significant increase in the concentration of calcium (57 mg Ca/L), chloride (220 mg Cl/L) and electrolytic conductivity (790 µS/cm). Increased calcium concentrations in lake waters changed their hardness from low to medium-hard. The ecological effect of the change in hydrochemical conditions in Lake Mielenko is the Potamogeton crispus that grows abundantly in this reservoir, which prefer calcium-rich water. The overall aesthetics of the lake have deteriorated significantly, and the availability of water for recreation has also been limited.

The paper presents the results of the research on the restoration of the shallow Lake Domowe Duże in Szczytno (area 0.6 km2, average depth 3.4m). Restoration treatments were carried out in the years 2010-2012 and consisted in the inactivation of phosphorus using polyaluminium chloride. Technical restoration was supported by biomanipulation treatments consisting in stocking the lake with predatory fish. Water quality study were carried out before remediation and annually for a decade (2010-2019) during and after the application of coagulant. It was shown that the efficiency of removing excess phosphorus from water column was high (decrease from 0.23 mgP L-1 to 0.05 mgP L-1). The effects achieved during the coagulant application were maintained for 5 years after the end of the project. Currently, the phosphorus pool is still twice as low as before the treatments, but it is gradually increasing. The main external factor limiting permanent improvement of water quality is the open hydrological system and transport of biogenic matter by surface inflows draining anthropogenically transformed areas. Maintaining permanent improvement of water quality will require continuation of restoration measures.

This research concerns the restoration of the strongly eutrophied Lake Łajskie (Masurian Lake District, Poland) that received pollutants from the agricultural catchment. It is a shallow (max depth 7.4 m) and small (area 48 ha) reservoir with a wide profundal zone characterized by complete deoxidation in summer. Due to its important natural and social role, the lake has undergone a restoration process. Artificial oxygenation is the main method of improving water quality. Due to unfavorable morphometric conditions, the necessity to use multi-point aeration was assumed. An experimental installation based on eight reactors selectively oxygenating only the over-bottom waters was launched in 2019. In 2021, spatial studies of the effectiveness of aerators’ work were carried out at 96 measuring points grouped into 12-test fields around each reactor. The investigations were performed three times during the summer season. It was shown that, in the water of the deepest layers of Lake Łajskie, the oxygen concentration around all reactors increased to an average level of 1–2 mg L−1. The oxygenation efficiency was varied and related to the distance from the aerator and the location in relation to the direction of oxygenated water outflow. The results of the research indicate the legitimacy of designing multi-point oxygenation systems in the restoration of waterbodies degraded as a result of the impact of agriculturally transformed catchments.

Meromictic lakes are unique aquatic ecosystems that occur extremely rarely. The phenomenon of meromixis can result from both natural and anthropogenic factors. The aim of this study was to analyse thermal and chemical stratification in a small, deep (6 ha, H max = 24.5 m) lake. The evaluated lake had a typical summer thermal profile with a shallow epilimnion, a sharp thermocline, and a distinct monimolimnion layer in the hypolimnion, which was also maintained during circulation. The lake had a clinograde oxygen profile, with an oxygen deficit in the metalimnion and permanent anoxic conditions in the deeper layers, including during circulation. A redox zone was identified during summer stagnation. The monimolimnion formed a thermally isolated layer at a depth of around 15 m, and the chemocline was situated above the monimolimnion. In the chemocline, the EC gradient ranged from 61 to 77 μS·cm−1 per meter of depth in the summer and from 90 to 130 μS·cm−1 per meter of depth during circulation. EC was significantly correlated with Ca2+ concentration (r2 = 0.549). Chemical stratification, particularly with regard to organic matter distribution, was observed in the chemocline. The monimolimnion severely limited nutrient internal loading.

The efficiencies of the restoration of two lakes of varied morphometries and trophic states—meromictic, hypertrophic Lake Klasztorne Małe, and dimictic, eutrophic Lake Klasztorne Duże—with the use of the phosphorus inactivation method with sequential application of iron and aluminum compounds have been compared. The total dose of the agents applied for Lake Klasztorne Małe was 38 tons of PAX 18 (aluminum polychloride) and 14 tons of PIX 111 (iron chloride), and for Lake Klasztorne Duże, it was 74 tons of PAX 18 and 46 tons of PIX 111. After the application of the compounds, better efficiency of phosphate removal from the surface water layers was obtained in the case of the dimictic, eutrophic Lake Klasztorne Duże. The use of two doses of compounds did not lead to complete precipitation of phosphates from the bottom water layers of either lake. It is noteworthy that in the case of both lakes, inhibition of the internal loading process was observed. The obtained results for the Klasztorne lakes showed that the use of two types of compounds makes it possible to reduce the cost of restoration, and moreover, the dosing of iron salts in the coastal areas of the lakes ensures a higher level of ecological safety.

The study shows how water temperature, water hardness, and color of tank affect the swim bladder inflation effectiveness (SBIE) and survival in Eurasian perch larvae in controlled conditions. Three separate experimental rearings (in 50-L tanks) were conducted, where (1) water temperature (12 days, 3000 ind./tank; 15, 20, and 25 °C), (2) water hardness (12 days, 4600 ind./tank; 15 °C; and 5, 10, and 15°n), and (3) tank wall color (20 days, 25,000 ind./tank; tanks with black and white walls; 15 °C) constituted tested variables. During all of the experiments, the photoperiod was 24 h (24L:0D), and the intensity of light was 1500 lx at the water surface. In experiments 1 and 2, perch larvae were not fed and in experiment 3, from 5-day post-hatch (DPH), they were fed ad libitum with Artemia sp. nauplii. In experiment 1, the highest SBIE was observed for larvae reared at 15 °C (20.6 ± 1.1%) for 20 °C and 25 °C; the maximum SBIE was significantly lower (8.4 ± 2.9% and 13.0 ± 5.8%, respectively; p 0.05) in mortality of larvae and in final SBIE. The results of experiment 3 clearly suggests that the white tanks caused a significant (p

Lake restoration is a part of geoengineering, which is a useful tool for landscape management. The phosphorus inactivation method is one of the most popular lake restoration methods. Using chemical compounds for P binding is leading to the creation of sediment “active layer”, which should show higher P adsorption abilities, compared to non-modified sediment. Howewer, it provides rather little information, how long the modified sediment remains active, and whether it is effective in continuous P binding. Lake meromixis is not commonly observed phenomenon, and sediment located in monimolimnion area is subjected long term anoxia. Therefore, observation of “active layer” in a meromictic lake can give very important data about durability of restoration effects. The object of our study was meromictic Starodworskie Lake (5.57 ha, max. depth 24.5 m), located in Olsztyn Lakeland, Poland. In the past the analyzed lake was subjected to various restoration methods, and phosphorus inactivation method by alum use (1994–1995) was the last used treatment type. The mixing regime of this lake had changed from bradimictic (before and during restoration time) into durable meromictic (post-restoration period). The research made two decades after implementing of P inactivation showed the presence of “active” sediment layer 10–15 cm below sediment surface. This sediment layer showed much higher content of P bound to aluminum, compared to surficial sediment layer. P binding molar ratio was assessed and amounted to 16.1 straightly after restoration and 6.1 after 21 years. This fraction amounts were higher that the values noted before restoration (ca. 358% higher than in 1994) and during restoration (ca. 86% higher than in 1995), which was probably the effect of continuous phosphorus adsorption by “active layer” in post-restoration period.

The research presented in this work concerns the potential aluminum load of soft-water lake ecosystems as a result of performing chemical reclamation works. On a semitechnical scale, different doses of PAC-type aluminum coagulant (polyaluminum chloride) were tested. The required doses of coagulant (on average, 11 mg Al/L) were determined based on the amount of phosphorus that is bioavailable in the lake ecosystem. The research covered the lake water, near-bottom and interstitial water, and bottom sediments of five lakes with low alkalinity (0.4–2.5 meq/L) and low calcium contents (5–35 mg Ca/L). The experiments were conducted in situ for 2 years using mesocosms with a volume of approximately 20 m3. The effectiveness of the flocculation and sedimentation processes of coagulant flocs was closely related to changes in water pH caused by acidic coagulant application, and the corresponding transformation level ranged from 39.8 to 99.8%. In the waters of these lakes, where the alkalinity did not reach 1 meq/L, the coagulant used in doses adequate for intensive full-scale projects caused high water pollution with dissolved aluminum fractions (from 0.05 ± 0.01 to 4.67 ± 1.32 mg Al/L). In all lakes, the penetration of dissolved aluminum into the interstitial water of the bottom sediment was limited to the first 5-cm layer. After the application of coagulant, the aluminum content in the bottom sediments significantly increased in proportion to the amount of the PAC used (by 12–96% in terms of a 5-cm surface layer of sediment). Within 2 years of the research, solid fractions (flocks) of the coagulant moved to a depth of 5–10 cm below the bottom level. Due to high release rates of aluminum from the applied aluminum treatments, modifications to the treatment protocols are needed in soft-water lakes.

The research was carried out on Karczemne Lake, a water reservoir located in Kartuzy (northern Poland, Pomeranian Lake District). Monitoring of the water and bottom sediment of Karczemne Lake showed a very high level of contamination of the reservoir by a long-term inflow of untreated municipal sewage. The trophic status index of total phosphorus (TP) was unusually high at 101, and the TP content in the bottom sediments&mdash, 31 mg g&minus, 1 (dry weight)&mdash, was the highest value recorded worldwide in a lake. Based on the monitoring results, to achieve constant improvement of the water quality, we recommend a completely new, safe and economically justified method of bottom sediment removal and management. A very important aspect of this method is the prevention of uncontrolled sewage discharge back into the lake basin. Removed sediment with interstitial water will be pumped through a pipeline and transported to a sewage treatment plant. In the sediment mining field in which the sludge will be removed, the first phase of phosphorus inactivation will be carried out to chemically precipitate pollutants distributed in the water column as a result of sediment resuspension. After the deepening of the entire lake basin, the method of phosphorus inactivation will be carried out on the entire surface of the lake as the next stage of restoration. A supporting activity will be biomanipulation. Before the restoration is started, the municipal sewerage system will be modernized.

An annual assessment of the functioning of the filter systems filled with polypropylene and gravelite profiles, located in the river bed, to reduce total suspensions and biogenic compounds in the water before it was directed to the city lake was carried out. It has been shown that, due to poor maintenance and a small number of cleaning operations, the efficiency of the system has decreased considerably comparing to the period of correct operation. This was mainly related to the exhaustion of the ability to retain the main biogenic element – phosphorus. During the monitoring period the facility retained the ability to reduce organic pollutants, suspended solids and nitrogen.

The object of the study was Tyrsko Lake (area 18.6 ha, max. depth 30.4 m), located in the western part of Olsztyn (Olsztyn Lakeland). This lake is one of the clear water lakes in Olsztyn, but the progressive deterioration of water quality is observed during last years. The phosphorus concentration in the water-sediment interface, phosphorus fractions quantity and the amounts of components which can bind this element was investigated in the upper (0-5 cm) layer of deposits. The aim of study was the analysis the potential influence of bottom sediment on the lake water quality. The obtained results revealed, that bottom sediment of Tyrsko Lake can be classified as mixed, silica-organic type, with quite high content of iron (over 4% Fe in d.w.). The total phosphorus content was ca. 3.5 mg P g-1 d.w. on average. Phosphorus in bottom sediment was bound mainly with organic matter (NaOH-nrP fraction), which had over 50% share in TP. Easy mobile fractions (NH4-Cl-P and BD-P) together included ca 5% to 7 % TP only. The obtained results show, that bottom sediment of Tyrsko Lake can bind phosphorus quite effectively. Calculated internal mineral phosphorus loading during summer stagnation period was 10.9 kg P and it was lower that the assessed annual external phosphorus load (22.6 kg P y-1). The assessed annual phosphorus loading from both sources still was lower than critical load according to Vollenweider criteria. But due to the fact that internal loading phenomenon is occurring in the lake it should be taken into consideration that the lake water quality can deteriorate gradually during the longer time perspective. These findings should be taken into consideration in the future if the potential protection and restoration procedures will be developed.

The study was conducted on Lake Dlugie,a water body lying in Olsztyn, a town situated in northeastern Poland. From 1956 to 1976raw wastewater was discharged into Lake Dlugie and therefore heavy pollution was the reason for the total degradation of this lake. The concentrations of nutrients were very high in the bottom water layer (TN 22.89 mg L−1, TP 3.50 mg L−1). The mean concentration of chlorophyll an exceeded 60 μg L−1 on average and Secchi disc visibility was less than 1 m. The discontinuation of sewage discharge into the lake caused the saprotrophic state to transform into hypertrophy. Further improvement of the environmental conditions in the lake was possible only after the implementation of an appropriate restoration method. The restoration procedure of this lake began in 1987. The first stage involved an artificial aeration method, and the second stage consisted of a phosphorus inactivation method. The applied restoration methods led to the improvement of Lake Dlugie’s water quality. Even ten years after the restoration treatments ended, TP concentrations did not exceed 0.350 mg L−1, and TN – 3.0 mg L−1. Chlorophyll a contents oscillated in the range of 5–10 μg L−1, and Secchi disc visibility amounted to c.a. 4.5 m.

Artificial mixing and phosphorus inactivation methods using aluminum compounds are among the most popular lake restoration methods. Długie Lake (Olsztyńskie Lakeland, Poland) was restored using these two methods. Primarily, P precipitation and inactivation methods significantly increased the sorption properties of Długie Lake bottom sediment. Fifteen years after the termination of the restoration procedure, the alum-modified &ldquo, active&rdquo, sediment layer still has higher P adsorption abilities, which can limit P internal loading. Relatively low amounts of phosphates in the near-bottom water of Długie Lake, even in anoxia, as well as the fact that the assessed maximum sediment P sorption capacity is still higher than NH4Cl&ndash, P (labile P) and BD&ndash, P (Fe-bound P) sum (&ldquo, native exchangeable P&rdquo, ), confirm that hypothesis. Among the tested P adsorption models for the sediment, the double Langmuir model showed the best fit to the experimental data (the highest R2 values). This may indicate that phosphorus adsorption by the tested sediments most likely occurs through phosphate binding at two types of active sorption sites. P adsorption by the studied lake sediment during experiments was significantly connected to aluminum content in sediment. The research into the adsorption properties of sediment can be used as a tool for the evaluation of lake restoration effects.

The research covered three groups of lakes: urban lakes in Kartuzy in the East Pomeranian Lake District, a group of Barczewo lakes in the Olsztyn Lakeland, and a group of Leginy lakes in the Mrągowo Lakeland. The water bodies were evaluated in terms of water dynamics, oxygen saturation, mineral pollution, and trophic status. The lake complexes differed fundamentally in land-use types in the surrounding areas. The lakes from each group were different. Electrolytic conductivity was highest in urban lakes, especially in Lake Karczemne which has been a sewage receptacle for many years. In the group of urban water bodies, the trophic state index was highest in Lake Karczemne (TSI (SD) and (TP), within the limits of hypertrophy, R2 = 0.886). In this group of lakes, organic matter limited visibility (R2 = 0.943). In the lakes surrounded mainly by forests, TSI was lower and indicative of oligo/mesotrophy in Lakes Kierźlinskie and Dluzek. Lake Dluzek was characterized by extremely low electrolytic conductivity (43–87 μS cm−1). TSI (TP) exceeded the reference standards in all examined lakes. In eight water bodies, primary production was limited by nitrogen (TSI (Chl) – TSI (TN) > 0 and TSI (TN) – TSI (TP) < 0, TN/TP < 10), which promoted cyanobacterial blooms.

In order to determine the nutrient balance two groups of the lakes were selected: ten flow lakes, namely, Mielenko, Karczemne, Klasztorne Male, Klasztorne Duze, Paslek, Wymoj, Sarąg, Łeguty, Isąg and Suskie (located in Olsztyn Lake District and Kashubian Lake District), and ten non-flow lakes, namely, Czarne, Dlugie, Podkowka, Starodworskie, Sukiel, Track, Tyrsko, Kepijko, Paskierz and Podąbek (located in Olsztyn Lake District and in Ilawskie Lake District).

This study analyses the dynamics of organic matter and algae pigments in water of urban lakes subjected to various restoration techniques. Most of the lakes were restored with the inactivation method using coagulant PAX 18. One of them was supported with biomanipulation. Assessments of the organic carbon form content (POC, in suspension; DOC, dissolved form) and the chlorophyll and pheophytin concentrations were conducted. The ratios of individual parameters were then evaluated, and the relationships between these indicators were tested. It was found that decreasing primary production and the associated organic matter in a suspended form can improve self-purification processes in restored lakes. The decreasing POC after restoration leads to a reduction in the amount of DOC in the lake and determines the balance of production and decomposition. This improvement may initially be able to reduce the DOC content, mainly due to easily biodegradable compounds. The lower primary production supplies a lower content of hardly biodegradable compounds (when algae decay). After that, the amount of high-molecular-weight DOC can be reduced. The improved self-purification of the lakes was also reflected in a reduced chlorophyll/pheophytin ratio. There was no effective reduction of the organic matter content after the first restoration in polymictic lakes with high loaded biogens and organic matter (DOC) from the catchment.

The work presents the problems of revitalization of water reservoirs in Poland. Lakes are subject to the inevitable process of aging, but as a result of anthropopression, the processes of natural eutrophication have been repeatedly accelerated. The consequence of the supply of excess allochtonic matter to water reservoirs, with the passive character of these landscape elements, is their degradation manifested by a sudden deterioration of water quality. A number of methods for the renovation of natural water reservoirs have been developed. Methods involving the removal of excess nutrients outside the ecosystem are the removal of hypolimnion waters, removal of bottom sediments, flushing the lake bowl, and removal of seston, macrophytes, and fish. The second group of methods consists in reducing the amount of nutrients in the matter circulation in the lake. This includes artificial aeration of lakes, inactivation of phosphorus compounds, treatment of bottom sediments, or biomanipulation. Despite such diversification of existing ways of affecting the aquatic environment, both in Poland and in the world, it is rarely possible to obtain really good effects of the restoration measures undertaken. The most common reason for defeats is the failure to take into account the basic assumption of eliminating excess loads of pollutants reaching the lake from the catchment before commencing its reclamation. Poor effects are also caused by insufficient understanding of the functioning of the complicated lake ecosystem and incorrect selection of revitalization techniques according to the environmental conditions of lakes. Properly conducted reclamation requires collecting research results about the lake and its catchment, recognizing the conditions of the eutrophication process, impartial selection of methods, securing funds for all planned operations, and substantive supervision and monitoring which provides the basis for assessing effectiveness and possible adjustments in the project implementation.

The study was conducted on Dlugie Lake in Olsztyn, which for 20 years since the mid-1950s served as a domestic and storm wastewater receiver, which led to its complete degradation. The discontinuation of wastewater inflow in 1976 caused a change in the trophic state from saprotrophic to hypertrophic. Evident improvement of water quality was possible only after the implementation of proper restoration techniques. Dlugie Lake was subjected to artificial aeration with thermal destratification (1987–2000). After all opportunities to improve water quality in the lake by artificial aeration (low phosphorus sorption capacity of sediment) had been exhausted, it was decided that a phosphorus inactivation method using the coagulant PAX 18 be used (2001–2003). Before restoration, the nutrient concentration in the near-bottom water layer of Dlugie Lake was very high at 22.9 mg TN L−1 and 3.50 mg TP L−1. The average amount of chlorophyll a was ca. 200 μg L−1, and the Secchi disc visibility did not exceed 1 m. In 2017, 14 years after termination of the lake restoration process, the total phosphorus concentration at the bottom was 0.21 mg P L−1 on average, and the total nitrogen was 1.5 mg N L−1. The mean transparency of the water oscillated around approximately 5 m, and the amount of chlorophyll a was 1.86 μg L−1. Studies have shown that the most important step in reclamation is to prevent pollutants from entering the lake to the maximum extent possible and to use a combination of several reclamation methods as a matter of good practice. Stable environmental conditions have developed in the lake, and the values of chlorophyll a and the Secchi disk visibility indicate that the lake has reached a mesotrophic state.

Pseudomonas fluorescens and Aeromonas hydrophila bacteria are opportunistic pathogens that occur naturally in the aquatic environment and in the gut flora of healthy fish. Both species can pose a serious threat for fish that are highly sensitive to water pollution. The aim of this study was to determine the extent to which the amount of administered fish feed and fish biomass affect the distribution and abundance of Ps. fluorescens and A. hydrophila bacteria in a recirculating aquaculture system (RAS) during farming of European grayling (Thymallus thymallus L.) broodstock. A total of 68 water samples from the inflow, two rearing tanks and the outflow as well as 17 feed samples were collected and analyzed separately. Bacterial populations were analyzed by the culture-dependent method and a molecular method (fluorescence in situ hybridization, FISH) to detect culturable strains and viable but non-culturable strains, respectively. Fish biomass, feed and 16 water quality parameters (temperature, pH, concentration of dissolved oxygen, oxygen saturation, five-day biochemical oxygen demand (BOD5), total phosphorus, total organic phosphorus and nitrogen, orthophosphates, total nitrogen, nitrite and nitrate nitrogen, ammonia nitrogen, ammonium nitrogen, total suspended solids, and total organic carbon) were the explanatory factors. Statistically significant differences (RM-ANOVA, p ≤ 0.05) were stated in bacterial abundance in samples from the inflow, rearing tanks and the outflow. Water samples from the RAS were abundantly colonized by non-culturable Ps. fluorescens and A. hydrophila bacteria. Feed was not a source of bacteria, but a redundancy analysis (RDA) revealed that the amount of feed, fish biomass, BOD5, and total suspended solids and total organic carbon were positively correlated in both Ps. fluorescens and A. hydrophila. These parameters also influenced the distribution of both potentially pathogenic bacterial populations and contributed to the bacterial contamination of water in the RAS. Our results are particularly valuable for aquacultures that help to replenish wild stocks and rebuild populations of threatened species in natural aquatic environments.

Lakes along with their surroundings are an attractive landscape component that play an important role in recreation and relaxation. In Poland, the Great Masurian Lakeland, visited by a million tourists every year, is considered to be the most attractive lake area. However, tourist pressure has several negative effects which cause degradation of the water environment. The aim of this study was to determine the trophic state of Lake Mikołajskie which is a hub for sailing and motorboating traffic. Values of the trophic status index were calculated from the content of total phosphorus, chlorophyll a and Secchi disc visibility, according to the data from the Voivodeship Inspectorate for Environmental Protection. In summer, the concentration of total phosphorus was 0.019–0.042 mg dm−3 in 2013 and 0.022–0.055 mg dm−3 in 2014. The concentration of chlorophyll a was in the range of 8.3–45.0 μg dm−3 in 2013 and 8.9–22.0 μg dm−3 in 2014. The maximum visibility of Secchi disc reached 2.0 m (2013) and 1.8 m (2014). Based on the calculated, Lake Mikołajskie can be classified as a eutrophic lake. In order to protect lakes from degradation tourists should be educated about the rational use of surface waters and the surrounding catchment. However, it is not only the massive influx of tourists, but also the activity of residents (dictated by economic reasons) that contribute to the pollution of lakes. Therefore, the development of tourism and the economy of the whole region should be harmonious and balanced so that the natural resources can serve us and future generations for as long as possible.

The study was conducted on Lake Długie, located in the city of Olsztyn, which for 20 years received raw domestic sewage (400 m3 per day). After preliminary conservation operations, the lake was restored by artificial circulation and phosphorus inactivation methods. During artificial circulation, water temperature in the whole lake volume was equalized. The disconnection of the compressor stimulated the return to typical thermal parameters in the lake. Phosphorus inactivation did not affect the thermal regime in the lake. Artificial circulation caused an increase in the oxygen content in the whole lake, lowered the oxygen-depletion rate during stagnation, and shortened the duration of anaerobic conditions in the near-bottom waters. Phosphorus inactivation did not directly affect the content of oxygen. However, after the coagulant was added to the lake, the oxygenation of the water was further improved owing to the depressed photosynthesis caused by drastically reduced availability of phosphate for primary producers.

We investigated changes in the spatial distribution of phosphorus (P) and nitrogen (N) in the deep, mesotrophic Lake Hańcza. The raw data collection, supported by global navigation satellite system (GNSS) positioning, was conducted on 79 sampling points. A geostatistical method (kriging) was applied in spatial interpolation. Despite the relatively small area of the lake (3.04 km2), compact shape (shore development index of 2.04) and low horizontal exchange of water (retention time 11.4 years), chemical gradients in the surface waters were found. The largest variation concerns the main biogenic element – phosphorus. The average value was 0.032 at the extreme values of 0.019 to 0.265 mg L−1 (coefficient of variation 87%). Smaller differences are related to nitrogen compounds (0.452–1.424 mg L−1 with an average value of 0.583 mg L−1, the coefficient of variation 20%). The parts of the lake which are fed with tributaries are the richest in phosphorus. The water quality of the oligo-mesotrophic Lake Hańcza has been deteriorating in recent years. Our results indicate that inferences about trends in the evolution of examined lake trophic status should be based on an analysis of the data, taking into account the local variation in water chemistry.

This research deals with the impact of aluminum coagulants, used as a tool for the rehabilitation of water bodies, on changes in the phosphorus content in lakes with low alkalinity of water. Mesocosm scale experimental investigations in situ using polyaluminium chloride were carried out, based on five lakes with different levels of water buffering capacity (&lt, 1.0&ndash, 2.5 meq L&minus, 1). The research was accomplished using three coagulant doses (half a dose, a whole dose, and a double dose calculated for phosphorus inactivation in a lake ecosystem). The results were compared with the ones from the control mesocosms. The study was carried out in two consecutive years. It was shown that the effectiveness of phosphorus removal from a water column was related to the dose of the coagulant, pH value, and the content of organic compounds. The lowest treatment effectiveness was found for lakes, with the most severe symptoms for dystrophy, which were abundant with humic compounds. As the water alkalinity increased, so did the ability of the coagulant to adsorb phosphorus, while the ecosystem&rsquo, s load of aluminum in toxic forms decreased. Doubling the standard dose did not result in a noticeable improvement in the water quality. The results allow us to evaluate the chances of successful lake restoration by applying aluminum coagulants to natural water bodies which are susceptible to acidification.

The study was conducted on Długie Lake (area 26.8 ha, maximum depth 17.3 m), located in the town of Olsztyn, in north-eastern Poland (the Masurian Lake District). For 20 years starting in the 1950s, Długie Lake was used as a receiver of raw domestic and storm sewage in quantities oscillating between 350 and 400 m3 day–1. This led to complete degradation of the lake, known as saprotrophy. After some preliminary protective treatments in the catchment, the lake has been renewed by artificial aeration with thermal destratification and the phosphorus inactivation methods. Long-term reclamation of the reservoir has resulted in distinct and durable improvement of water quality. Before the restoration, the average phosphorus concentration in the surface water layer was 0.079 mg P L−1 and in the over-bottom water it reached 2.277 mg P L−1. The total phosphorus (TP) level also was very high, i.e. up to 3.5 mg P L−1. After the restoration, these values have declined to 0.001–0.017 mg P L−1 in the case of mineral P, and the current TP concentrations do not exceed 0.350 mg P L−1.

The study applied qualitative and quantitative phytoplankton analysis as a tool for determining algal community characteristics and identifying the directions and general trends of changes caused by the restoration of Lake Głęboczek through phosphorous inactivation before and during its application. The method applied in the studied lake aimed at reducing phosphorous availability through the chemical precipitation of its excess mineral forms in the water body and limiting their mobility in the bottom sediments. Restoration efforts led to shifts in the phytoplankton domination structure followed by the inhibition of blue-green algae development. In consequence, a significant decrease was recorded in the growth rate of the phytoplankton community.

Most of the inland lakes do not have up-to-datebathymetry. However, a significant progress in surveyingtechnologies creates a possibility to quickly and accuratelydescribe the underwater environment. Modern geodeticand global positioning techniques integrated with hydroacousticsystems provide a great opportunity to study thebottom shape with high resolution. Our study presentsa reliable methodology for investigation of bathymetryand morphometric parameters with the use of GNSS positioningtechniques and single beam echosounder. Theresearch was implemented on the deepest, glacial reservoirin the central part of European Depression - LakeHancza. Direct hydroacoustic and geodetic measurementscompleted by sediment study were conducted by the authorsin 2010-2013. After performing a field survey the DigitalElevation Model was constructed and the new bathymetricmap and morphometric card were elaborated. Themaximum depth was confirmed to be 105.55 m. The finalconclusions show that the available bathymetric data andmorphometric parameters of lakes are highly dependenton the research methodology used, the precision and accuracyof measurement techniques, proper water level determination,digital elevation model and bathymetric mapelaboration processes.

This paper presents the initial environmental effects of polyaluminum chloride application on the water quality of two connected, shallow urban lakes in the Mazurian Lakeland, Poland. The water quality of Lake Domowe Duże (62 ha, mean depth 2.4 m) and Lake Domowe Małe (11 ha, mean depth 2.8 m) in Szczytno did not improve after sewage discharge cutoff. Thus, local authorities decided to implement a restoration project involving the 3-year application of aluminum coagulant (26 g Al m−2) and manipulation of fish stocking. In 2010 and 2011, the first two stages of the project were conducted. After restoration measures, phosphorus concentration in water, chemical oxygen demand, chlorophyll ‘a’ and phytoplankton biomass decreased significantly compared to the control years. No long-term decrease of pH was obtained after aluminum application. Low concentrations of dissolved aluminum in a water column (below 0.2 mg L−1 during technical operations) did not show any negative effects on aquatic fauna.

Coagulation behaviour of polyaluminium chloride (PACl) was comparatively investigated in terms of the removal of turbidity and colour with surface water. The growth of flocs was also compared. The results show that the decrease in saturation and values of dissolved oxygen was ca. 20% for ALCAT and PAX 18 at both dosages and 15% for PAX XL 19H, respectively. The floc formation growth indicated that PACl coagulation occurred not only by charge neutralization but also by a form of sweep flocculation. Besides, flocs formed by ALCAT had better sizes than the flocs formed by PAX 18 and PAX XL19H. The rate of sedimentation was stable during coagulation with higher doses, and it was dependent on the substance used.

Sediments from hypereutrophic Lake Łajskie localized in northeastern Poland were examined on the basis of P-fraction. The sediments were collected at five sampling sites. In the investigated lake, the rank order of P-fractions was HCl-P > BD-P > NH4Cl-P > NaOH - nrP. The loosely sorbed phosphorus NH4Cl-P represented < 3% of the sedimentary inorganic phosphorus, while the reductant phosphorus (BD-P) ranged from 2 to 10%. The calcium bound phosphorus (HCl-P) showed considerable contribution (59-74%) to the sedimentary inorganic P-loads. BDP was the most reactive fraction in Lake Łajskie. Iron compounds and organic matter seem to play a significant role in regulating this labile P-budget.

The aim of this study was to determine the chemical composition of Lake Widryńskie bottom sediments (max. depth. 27.0 m, area 123.9 ha). The sampling of bottom sediments was conducted once, on 16 August 2010. Sampling was made in 10 specific areas. Among the 10 samples, 4 samples were taken from the littoral and sublittoral zones, while the rest were taken from the profundal zone. The dominant component of the sediments was silica and calcium carbonates were subdominant. Based on the survey, it was determined that silica occurred in greater numbers in littoral sediments, while in sublittoral sediments there was increased participation in the chemical composition of organic matter. The elements that build a capacity complex were a small percentage of the dry weight of sediment. Sediment from the vicinity of inflows contains higher amounts of silica, which confirmed the impact of the catchment on the chemical composition of sediments.

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.