Grzegorz Wiśniewski

Assessment of multi-year (1956-2003) hypolimnetic withdrawal from Lake Kortowskie, Poland

Abstract Hypolimnetic withdrawal as a restoration method comprises the withdrawal of the nutrient-rich hypolimnion by a pipe directly to the outlet, thus replacing the surface outflow. The method was first applied to Lake Kortowskie in 1956 and continues today. The direct effects of hypolimnetic withdrawal can be observed in the near-bottom waters during the pipes operation (May-Sep). The treatment depends on the quantity of water withdrawn by the pipe. A high withdrawal rate increased the rate of hypolimnetic heating, diminished the water mass stability and shortened summer stagnation. Hypolimnetic withdrawal did not improve the oxygen conditions in Lake Kortowskie, although it shortened the duration of the anaerobic conditions near the bottom and diminished the spatial extent of oxygen deficiency. Increased release of phosphorus from the bottom deposits to the near-bottom water and finally the outlet via the withdrawal pipe has been observed, with a consequent impoverishment of the upper sediments. The amount of mineral phosphorus and ammonium nitrogen in the near-bottom water decreased independent of the withdrawn volume. The decrease of phosphorus and nitrogen during the pipes operation shows that hypolimnetic withdrawal removes nutrients released from bottom deposits so that the lake becomes less enriched in nutrients. Multi-year examination has confirmed that this process is the most positive feature of this restoration method. The restoration can be optimized by maximizing nutrient export and withdrawing throughout the summer stagnation (particularly in August and September), when nutrient concentrations near the bottom are maximal

Spatial variability of nutrients (N, P) in a deep, temperate lake with a low trophic level supported by global navigation satellite systems, geographic information system and geostatistics

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 km(2)), 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.

Comparison of coagulation behaviour and floc characteristics of polyaluminium chloride (PAX 18, PAX XL19H, ALCAT) with surface water treatment

Abstract 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.

Sediment phosphorus fractions in an urban lake and its usability for predicting of the internal loading phenomenon

The object of present study was Sukiel Lake (area 20.8 ha, max. depth 25 m), localised in north–eastern Poland (Mazurian Lake District), in Olsztyn city. The aim of this study was to analyse the phosphorus fractions in the sediments of two lake bottom zones - profundal (25 m) and sublittoral (7 m). Observed high P concentrations in the deposits of Sukiel Lake and quantitative domination of hard mobile P fractions (NaOH–TP, HCl–P and res–P) suggest that the sediments of Sukiel Lake are the effective trap for phosphorus and that limits excessive internal loading in this lake.

The use of expanded clay aggregate for the pretreatment of surface waters on the example of a tributary of Lake Klasztorne Górne in Strzelce Krajeńskie

Abstract The paper presents a proposal for the treatment of river water based on expanded clay (ceramsite). It is a lightweight mineral aggregate containing components relative to phosphorus adsorption (calcium, iron, manganese, aluminum). A pilot plant on a fractional technical scale was built on a nutrient rich (phosphorus up to 0.4 mg dm−3, nitrogen up to 10.0 mg dm−3), small (mean annual flow about 0.04 m3 s−1), natural watercourse (Młynówka River, a tributary of the Otok Channel, Noteć basin, the municipality of Strzelce Krajeńskie). The monitoring included quantitative and qualitative measurements of the water stream in 2014-2015. On the basis of the examinations, the calculated effectiveness of ceramsite filters in removing major contaminants from water was: for total nitrogen 5-6%, phosphorus 12-16%, and for suspensions 17-29%. The effectiveness of the treatment is highly influenced by hydraulic load, so this type application on a full-scale should occupy a sufficiently large volume. Taking into account simplicity of performance, ease of operation and low cost of construction and maintenance, such pretreatment plants based on expanded clay would seem to be a promising tool for the protection of surface waters in catchments of small rivers and streams.

BOTTOM DEPOSITS OF STRATIFIED, SEEPAGE, URBAN LAKE (ON EXAMPLE OF TYRSKO LAKE, POLAND) AS A FACTOR POTENTIALLY SHAPING LAKE WATER QUALITY

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 has been observed during recent years. The phosphorus concentration in the water-sediment interface, phosphorus fractions quantity and the amount of components which can bind this element was investigated in the upper (0–5 cm) layer of deposits. The aim of study was to analyze the potential influence of bottom sediment on the lake water quality. The obtained results revealed that the bottom sediment of Tyrsko Lake can be classified as mixed, silica-organic type, with a relatively 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 the bottom sediment was bound mainly with organic matter (NaOH-nrP fraction), which had over 50% share in TP. Highly mobile fractions (NH4-Cl-P and BD-P) together only included ca. 5% to 7% TP. The obtained results show that the bottom sediment of Tyrsko Lake can bind phosphorus quite effectively. The calculated internal mineral phosphorus loading during summer stagnation period was 10.9 kg and it was lower that the assessed annual external phosphorus load (22.6 kg). The assessed annual phosphorus loading from both sources was still lower than the critical load according to Vollenweider criteria. However, due to the fact that the 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 accounted for in the future if the potential protection and restoration procedures will be developed.

Productivity of lakes varying in water mass dynamics

Productivity of lakes varying in water mass dynamics The aim of the study was to reveal differences in the productivity of lakes varying distinctively in water mass dynamics, as shown by the examples of Lakes Track, Miodówko and Szeląg Wielki situated in the Olsztyńskie Lake District. The selected lakes are also characteristic for a high content of nutrients. The analysis of the obtained results has revealed that in the peak of the summer stagnation the productivity was the highest in the polymictic Lake Track. The content of chlorophyll a, which is a measure of primary production, in the Track waters reached the value of 123 mg m-3 whereas the water transparency measured as the visibility of a Secchi disc was below 0.6 m. The lowest primary production in the summer was observed in the bradymictic Lake Miodówko. The transparency of water in this lake was nearly 3 m while the content of chlorophyll a merely 1.7 mg m-3. Lake Szeląg Wielki, featuring the characteristics of a eumictic reservoir, in the peak of the summer period was noted for the average values of the analysed parameters (1.2 m water transparency, 40.3 mg m-3 chlorophyll a).