Jolanta Grochowska

Influence of restoration methods on the longevity of changes in the thermal and oxygen dynamics of a degraded lake

Abstract 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.

Durability of changes in phosphorus compounds in water of an urban lake after application of two reclamation methods.

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 m(3) 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 influence of different recultivation techniques on primary production processes in a degraded urban lake

The study was conducted in Lake Długie located in Olsztyn, the Masurian Lake District. In the 1950s and in the 1960s, Lake Długie was used for 20 years as a collector of raw domestic and storm sewage. This has led to complete degradation of the lake. After preliminary protection measures implemented in the catchment, the lake was restored by artificial aeration and phosphorus inactivation methods. Long-term recultivation of the reservoir resulted in a significant and long-lasting improvement of the water quality. Before restoration, the average concentration of organic phosphorus in the surface water layer amounted to 0.166 mg Porg l−1 and of organic nitrogen — to 3.0 mg Norg l−1. After restoration, these values decreased to 0.058 mg Porg l−1 and 2.0 mg Norg l−1. The results obtained eight years after the recultivation of Lake Długie are extremely interesting. The amounts of chlorophyll a did not exceed 7 μg l−1, water transparency remained at a depth of 2.9 m, and BOD5 did not exceed 2 mg O2 l−1. These observations show that during implementation of recultivation treatments, only chemical parameters of the water significantly changed, while biological elements reacted to the treatments with some delay.

Water Quality of Lake Ełk as a Factor Connected with Tourism, Leisure and Recreation on an Urban Area

Abstract Lake Ełk as an important element of the urban landscape is associated with tourism and active recreation and because of it with the economy of the town. Since 1999 the renovation method with the use of artificial aeration with simultaneous phosphorus inactivation and also as a biological filter – BIO-HYDRO structures were applied on the lake. This process was lasting 10 years and brought only a short-term improvement. At the same time, the shores of the lake were managed to develop of lake tourism: beach, swimming pool, tennis courts, a promenade, and two a water equipment rentals. The illuminated fountain, the road bridge and well – developed catering – accommodation base were made as well.

Variation of nitrogen forms in lakes with different intensity of anthropogenic pressure

Abstract The aim of this study was to compare the concentration of nitrogen and trace the dynamics of its changes in two lakes with different intensity of anthropogenic pressure. The dominant land use of Lake Paskierz catchment is built-up areas, while in Lake Sajmino, wasteland is the dominant land use. The total amount of nitrogen in Lake Paskierz ranged from 1.68 to 6.58 g Ntot m-3, while in Lake Sajmino it was from 1.03 to 1.84 g Ntot m-3. The organic fraction was a dominant form in the surface water layers of the examined lakes. A slightly different situation was found in near-bottom water layers of Lake Paskierz, where ammonium nitrogen was the dominant form in the summer stagnation. In other cases organic nitrogen was a dominant form in each of the reservoirs. Concentrations of nitrites and nitrates were low and did not affect essentially the overall amount of nitrogen in the studied lakes. Based on the results, it can be concluded that Lake Paskierz is overfertilized. The high concentrations of ammonia measured in near-bottom layers of the lake indicate that the internal supply may be a very important process affecting the trophic status. Lake Sajmino was characterized by significantly less nitrogen abundance, although the periodically increasing nitrogen concentration reveals the presence of adverse anthropopressure on the lake.

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.

A proposal of protection techniques in the catchment of a lake in the context of improving its recreational value

Abstract The study was carried out on Lake Rentyńskie (100.8 ha; 9.4 m) situated approximately 20 km to the west of Olsztyn, in the drainage basin of the rivers Giłwa and Pasłęka. The direct catchment area of the lake is 166.2 ha. Forests cover most of the drainage basin area (74%). As revealed in the study, Rentyńskie is a highly eutrophic reservoir. The lake waters were characterized by a high content of nutrients, up to 1.508 mg P dm-3 and 11.7 mg N dm-3. The high fertility of the lake was also evident in the values of chlorophyll a - 75.4 μg dm-3, and low water transparency - average 1 m. The total annual phosphorus and nitrogen load to Lake Rentyńskie, calculated according to Giercuszkiewicz-Bajtlik (1990) equals 759.0 kg of phosphorus and 31869.7 kg of nitrogen, or per unit surface 0.753 g P m-2 yr-1 and 31.611 N m-2 yr-1. Allowable and critical load levels to Lake Rentyńskie calculated according to the hydrological model of Vollenweider (1976) equal (respectively) 0.090 g P m-2 yr-1 and 0.189 g P m-2 yr-1. From a comparison between the actual phosphorus load and the values calculated according to Vollenweider it can be concluded that the loads not only exceed the allowable values by several times but also the critical values responsible for advanced eutrophication. The study showed that the River Giłwa, which flows through the reservoir, posed a major threat to the analysed lake . In order to improve the water quality in Lake Rentyńskie drastic protective measures should be taken in the basin of the River Giłwa, which is intensively used for agriculture, and also, at the point where the river enters the lake a special system to reduce the level of phosphorus compound concentrations should be set up.

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).