The study was carried on Lake Giłwa (100.8 ha, 9.4 m), in the drainage basin of the Giłwa and Pasłęka rivers. The data obtained in the study allowed the authors to classify Lake Giłwa as a water body belonging to the third stability degree according to Patalas (1960). As evidenced in the study, Lake Giłwa is a highly eutrophic reservoir. The lake waters were characterized by a high content of nutrients, up to 1.40 mg P·dm-3 and 12.47 mg N·dm-3. The high fertility of the lake was also exhibited by the values of BOD5 reaching 7 mg O2·dm-3, chlorophyll a content (73 mg·m-3) and low transparency — 0.7 m. In the peak of the summer, the stagnation oxygen profile is represented by a clinograde curve typical for eutrophic lakes, while carbon dioxide distribution in the water column is shown by a „reverse” clinograde curve, also typical for fertile reservoirs. The study has revealed that the water in Lake Giłwa is well buffered, as shown by the alkalinity values, 2.5-5.0 mval dm-3. Total hardness of the reservoir water varied from 157.1 to 278.8 mg CaCO3·dm-3, which is typical of hard water. The hardness was conditioned mainly by the calcium content. With the River Giłwa, the lake receives wastewater from the wastewater treatment plant in Gietrzwałd, which is manifested, for example, by the high values of electrolytic conductivity (321-476 µS·cm-1), indicating the degree of mineral pollution of the lake. Despite the wastewater input, the amount of chlorides is rather low, 20 mg Cl·dm-3 at the most.
Studied were the following lakes: Pasłęk, Wymój, Sarąg, Łęguty and Isąg, located in the nature reserve “Beaver Sanctuary on the Pasłęka River”. The hypothesis was that lakes located in a nature protection area are subject to eutrophication in a slow rate, however, the research did not confirm it. All lakes are very fertile, as shown by the concentrations of total nitrogen, total phosphorus, electrolytic conductivity and the high negative correlation between chlorophyll a and water transparency.In the peak of the summer stagnation oxygen profile is represented by the clinograde curve typical for eutrophic lakes while free carbon dioxide distribution in the water column is shown by a “reversed” clinograde curve, also typical for fertile reservoirs.
The study was carried out on a small (7.8 ha) and shallow (9.0 m) lake Mały Kopik, situated 9 km on south western from Olsztyn, drainage basin of Giłwa and Pasłęka rivers. The catchment area of the lake is 194.7 ha. Forests cover the most of the drainage basin area (64.2%), agriculture land comprises 28.7% (21% grass land and 7.7% arable land) and urban land - 7.1%. Lake Mały Kopik is not susceptible to degradation (III category), and drainage basin having a great potential for supplying matter to the reservoir, was included in basin category 4. The lake with its drainage basin belong to the 4th type of lake-drainage basin ecosystems. In such a system the natural eutrophication of the lake is expected to proceed at a fast rate. As evidenced in the study, lake Mały Kopik is highly eutrophic reservoir. The lake waters were characterized by a high content of nutrients, up to 0.673 mg P·dm-3 and 10.61 mg N·dm-3. The high fertility of the lake was exhibited also by the values of BOD5 reaching 7.5 mg O2·dm-3, chlorophyll a content - 50 µg·m-3, and low water transparency - 2 m.
Badania prowadzono na holomiktycznym Jeziorze Wulpińskim położonym w okolicach Olsztyna. Próbki pobierano w okresie cyrkulacji jesiennej 2007 r. i wiosennej 2008 r. nad głęboczkami obu jego zatok i porównano w danymi wcześniejszymi. Zbiornik składa się z dwóch części: eumiktycznej tomaszkowskiej (459 ha, 22 m) i bradymiktycznej barwińskiej (246 ha, 54,6 m) oddzielonych od siebie przesmykiem o długości ok. 60 m i głębokości 3,8 m. Podzlewnie obu zatok różnią się wielkością i sposobem użytkowania. Część tomaszkowska jest bardziej narażona na presję turystyczną i w 62,7% użytkowana rolniczo, natomiast w podzlewni barwińskiej pola i łąki stanowią 46,3%. Znalazło to odzwierciedlenie w uzyskanych wynikach badań: akwen tomaszkowski charakteryzowała niższa widzialność krążka Secchiego (1,5–1,75 m), wyższe stężenie chlorofilu a (23,25– –26,19 mg ∙ m–3) i feofityny (60,11–64,77 mg ∙ m–3), większa ilość materii organicznej allochtonicznej i wyraźna tendencja wzrostowa tego parametru w naddennej warstwie wód. W puli azotu ogólnego dominowała forma organiczna (85–99%).
A study was conducted on Wulpińskie Lake (706.7 ha, 54.6 m), located in north-eastern Poland. In the middle of the twentieth century, the lake began to be subjected to accelerated eutrophication due to excessive pressure from recreation and an inflow of sewage and pollution from leaky septic tanks and putrefactive reservoirs. The protective actions begun in the basin in 1996 resulted in a 77% reduction in phosphorus load and 28% reduction in nitrogen load. In 2008, mineral phosphorus and TP concentrations averaged 0.1 mg L⁻¹ and 0.16 mg L⁻¹, respectively, and the TN concentration was 0.84 mg L⁻¹. In addition, chloride and calcium concentrations declined and electrical conductivity subsequently decreased.
Badania prowadzono na niewielkim (10,5 ha) i płytkim (2,5 m) Jeziorze Gągławeckim (jezioro Gągławki). Jezioro posiada zlewnię o powierzchni 348,3 ha, w której największy udział mają lasy – 66,7%; grunty orne zajmują 18,9%, łąki i pastwiska 7,5% a teren zabudowany 2,9%. W wodach jeziora stwierdzono duże ilości biogenów, sięgające 0,285 mg P·dmˉ³ i 4,39 mg N · dmˉ³ oraz wapnia – 97,1 mg Ca·dmˉ³. Przyczyną wysokiej trofii tego zbiornika jest nadmierne jego obciążenie ze zlewni. Rzeczywiste ładunki biogenów spływające do jeziora przekraczają ładunki krytyczne wyliczone wg Vollenweidera. Niska jakość wód tego jeziora, przy wysokim obciążeniu ładunkiem zanieczyszczeń ze zlewni wskazuje na konieczność podjęcia działań ochronnych, polegających na zmniejszeniu obciążenia zewnętrznego.
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.
Our analysis deals with the land development and management for tourist and recreational purposes around Drwęckie Lake, a water body lying in the limits of the town Ostróda. A lot of tourists and residents in summer season can be attributed to the spatial management, a wide range of hospitality facilities and many opportunities to practice water sports and to hold mass events. Another aspect we analyzed was the influence that these various forms of development for tourism and recreation could have on the natural environment of Drwęckie Lake. To this aim, the shoreline burden indicator (K) values and the lake’s burden class were calculated. It has been concluded that both land and water shore zones are considerably loaded due to the densely developed space and increasingly intensive tourist and recreational activities. Current situation can lead to excessive degradation of the lake’s water and depreciation of the tourist value of the entire area.