history and plans Helena Gawrońska, Konstanty Lossow University of Warmia and Mazury in Olsztyn, Department of Environment Protection Engineering,

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1 Limnological Review 5 (2005) 6973 Restoration of the Domowe Lakes in Szczytno history and plans University of Warmia and Mazury in Olsztyn, Department of Environment Protection Engineering, Prawocheńskiego 1, Olsztyn Abstract: This paper presents the restoration project of the degraded Domowe Lakes in Szczytno. Changes of the water quality in years in both lakes were analysed and their present trophic condition was determined. Flushing/dilution was proposed as a restoration method for the Domowe Lakes. The basis for the project was on one hand the low water quality (continuously deteriorating in Lake Długie) and on the other the possibility to use underground water from nonoperational wells to flush the lakes, as well as the morphometric and hydrologic properties of the lakes, favourable for the proposed restoration method application. Key words: lakes, restoration, dilution/flushing, trophic state. Introduction Two lakes are situated within the city borders of Szczytno, namely Lake Długie (or Domowe DuŜe) and Miejskie (or Domowe Małe), both potentially valuable for recreation but also increasing the landscape and tourist value of the city. Unfortunately, the lakes location, as in the case of many other municipal reservoirs, became one of the reasons for their degradation (Lossow, Gawrońska 1998, Lossow et al., 1998, Lossow et al., 2004b). Both lakes function as receiving waters for storm run-off, and in the past also for domestic and industrial wastewater, which resulted in their considerable pollution (Drozd et al., 1974). Moreover, the excessive intake of the waters and the underground water by the industry of Szczytno, negatively influenced the trophic condition of the lakes. In effect, the water level dropped by nearly 1 m (Hydroprojekt, 1966). Therefore, yet in the 1960s, the need was discerned to restore the lakes and their functional value through renovation activities. The goal of this paper is to present the project of the Domowe Lakes restoration that was accepted for execution. The project was devised on the grounds of the authors conception. Object of the study The Długie and Miejskie Lakes are situated in the northwestern part of Szczytno, in the watershed of the Sawica, Omulew and Narew Rivers. With regard to the lakes hydrology they comprise closed reservoirs, although they interconnect by a 50mlong, periodically flowing canal. The only outflow can be found on the southeastern side of Lake Miejskie and that is the periodically flowing Domowy Canal, discharging to the Sawica River (Fig. Both 1). lakes are small and shallow. The area of Lake Długie is 62.1 ha, the max. depth 5.4 m, the mean depth 2.8 m, and the water bowl volume 1,749,000 m 3 (IRŚ 1969). The same para-

2 70 meters of Lake Miejskie are (respectively): 11.4 ha, 3.8 m, 2.2 m, and 255,000 m 3 (Drozd et al., 1974). With regard to the lakes protection and resistance to degradation, their main morphometric features are obviously unfavourable, an evidence of what is the high vulnerability to external impacts below the standard (Cydzik et al., 1992). Fig. 1. The Domowe Lakes in Szczytno: 1 13 storm run-off interceptor, I Domowy Canal Results and discussion Trophic condition of the Domowe Lakes The surveys of revealed a high pollution degree in both lakes (Drozd et al., 1974), although the values of the pollution indexes determined in Lake Miejskie were much higher (Tab. 1). The fairly advanced eutrophication was displayed mainly by the strong super-saturation with oxygen in the water layers (up to 150 % saturation) and by strong oxygen deficits near the (above 90%) or complete de-oxygenation, despite the dynamic (polymictic) type of the waters and lack of thermal stratification in the summer. The low water quality was also displayed by high water reaction during the growing season (exceeding ph 9), high content of organic substances (BOD 5 above 10 mg O 2 /dm 3 ), low water transparency (Sc approximately 0.5 m), and very high amounts of nitrogen and phosphorus compounds, especially in Lake Miejskie. All these pointed at the necessity to take decisive protective action (wastewater inflow cut-off) and restoration activities. Although most of the sanitary and industrial inputs were cut off in the past 30 years, the lakes continuously receive storm run-off (Fig. 1) without any preliminary treatment. Low Coli index (below 0.01), determined in 2003 by WIOŚ (the Voivodship Inspectorate for Environmental Protection) in Olsztyn (unpublished), indicates input of unidentified sanitary contaminants to Lake Miejskie. The authors research of 1995 and 2004 revealed (Tab. 1) that in both lakes the water quality was below the 3rd (lowest) water quality standard, assumed in Poland for evaluation of lake waters quality (Kudelska et al., 1994). However, it should be emphasised that in the past years the degree of water degradation in Lake Miejskie slightly decreased (possibly due to the gradual elimination of the pollution sources) while at the same time it incre-ased in Lake Długie, and eventually the water quality in both lakes became very similar (Tab. 1).

3 Restoration of the Domowe Lakes in Szczytno history and plans 71 Table 1. Range of variation of selection pollution indices in water of Domowe Lakes Indices Layer of Miejskie Lake Długie Lake water Reaction ph BOD mg O 2 /dm Chlorophyll a mg/m Mineral phosphorus mg P/dm nw 0.12 nw 0.49 nw Total phosphorus mg P/dm Ammonia nitrogen mg N/dm nw 0.02 nw Organic nitrogen mg N/dm Total nitrogen mg N/dm Chloride mg Cl/dm Visibility of Secchi disc m The data presented above point out clearly that renovation of the Domowe Lakes in Szczytno is not possible unless some restoration activities are performed. Former plans concerning renovation of the lakes in Szczytno The first projects aimed at water quality improvement in these lakes were prepared yet in the 1960s. The main goal was to raise the water table through water import from other drainage basins. In 1966, the Gdańsk Office of Hydroprojekt presented the conception of water table raising in both Domowe Lakes in Szczytno. The expected result was to enable water outflow from Lake Miejskie and dilute the polluted waters flowing to the Domowy Canal from the wastewater treatment plant (Hydroprojekt, 1966). Two conceptions were considered. The first assumed gravitational water input from the Wałpusza River through an open ditch directed to Lake Miejskie. The second considered the possibility to pump water from Lake Sasek Wielki or the Sawica River to Lake Długie. Both projects were abandoned in the conception phase. Nather (1978) proposed similar but more advanced solutions. His project assumed damming of Lake Sasek Wielki (in practice transformation into an impoundment lake), water drawing from the lake and transfer by pumping stations to Lake Długie. However, this would cause flooding and damage to large area surrounding the lake. This conception, alike other prepared in the next years, was never put into practice. The renovation project of the Miejskie and Długie Lakes in Szczytno Lossow and Gawrońska (1999) prepared in 1999 the brief fore-design concerning restoration of the lakes in Szczytno. However, it was not until 2004, that the organisational, technical and economic conditions were created for the project s execution. In the limnologic literature, the proposed renovation method is called dilution/flushing. To dilute the waters, the project assumes intake of the underground water from the Pleistocene aquifer. The water will be taken only from the non-operational wells in the Polska Street. The costs of the restoration will be covered by the City Hall in Szczytno. The conception of 1999 assumed elevation of the water table and dilution of the lake waters using a better quality underground water, which should eventually improve the trophic condition of the lakes. As Cooke et al. (1993) report, such goal can be achieved in two ways: (1) by reduction of the concentration of elements limiting production (dilution) and (2) by increase of the water exchange rate (flushing). However, significant water quality improvement can be expected only when a few conditions are met: the lake is of the polymictic type, inflow and outflow are located on the opposite

4 72 sides of the lake, high-quality water is available in large quantity, providing conditions for water exchange a few times throughout the year (Lossow 1998). Until present, the method has been rarely practised in the world (Klapper 1991). The reported example of lake flushing with river waters concerned Moses Lake, USA; water from other low-trophic level lake was used on Buffalo Pound, Canada; drinking water was applied on Green Lake, USA (Cooke et al., 1993). Effective flushing with underground water was practised only one time, i.e. on Lake Green, USA, using pre-treated drinking water (Oglesby 1969). In the case of the Domowe Lakes in Szczytno the underground water for flushing will not be treated. In accordance with the above conception, the restoration of the Domowe Lakes will be conducted in two phases. In phase I (2006 and 2007) the restoration will be conducted on Lake Miejskie; Lake Długie will be restored 2 years later. The project discussed below refers only to phase I of the resto-ration. The following sequence of the activities was proposed: Damming with a gate of the canal connecting Lake Miejskie and Lake Długie; Import of water from the non-operational wells to Lake Miejskie; Max. water damming in this lake, up to the datum of m above sea level; 2-year intensive flushing of the lake with underground water and discharge of the waters to the Domowy Canal. The devised technical project assumes import of underground water from the deep wells in the Polska Street and raising the water table in Lake Miejskie to the datum of m above sea level. Pipes hung under the water will conduct the water that flows out in the middle of the lake, partly through a fountain. The quantity of the imported water was determined for 120 m 3 /h. So assumed water import to the lake, at the bowl s volume of m 3, gives the theoretical water exchange of 410%. It should be noted that water damming to the assumed level, i.e. the level of the 1950s, will not threaten the constructions erected around the lake. It was also found out that the guaranteed water reserves for the water intake station would not be diminished. More details can be found in the water intake permit (GEO-KAT Sp. z o.o. 2004a) and in the technical project (GEO-KAT Sp. z o.o b). Flushing and dilution of the lake waters will be conducted under controlled conditions, which allows to determine the effectiveness of the method and to implement eventual modifications in the course of the restoration. In the case of the lakes in Szczytno, all previously mentioned criteria have been met, comprising the conditions for effective restoration with the described method. However, it is noteworthy that the multi-year input of pollutants can substantially limit the effectiveness of the restoration. It was displayed by the results of the chemical examinations of the sediments. Therefore, it was assumed that after flushing, additional restoration method would be applied, comprising phosphorus removal from the water and phosphorus fixing in the sediments (phosphorus inactivation). This method was successfully applied on two other lakes in Poland (Gawrońska et al., 2004, Lossow et al., 2004). In 2008 (phase II), the same restoration technique will be applied on Lake Długie and only then the flow between the lakes will be re-established. References Cooke G. D., Welch E. B., Peterson S. A., Newroth P. R., 1993, Restoration and management of lakes and reservoirs, Lewis Pub. (CRC Press. Inc.), Boca Raton FL. Cydzik D., Kudelska D., Soszka H., 1992, Atlas czystości jezior Polski badanych w latach , PIOŚ, Biblioteka Monitoringu Środowiska, Warszawa. Drozd H., Lossow K., Więcławski F., 1974, Morfometria i chemizm dwóch jezior w Szczytnie, Zesz. Nauk. ART. Olszt., 3, Gawrońska H., Lossow K., Grochowska J., Brzozowska R., 2004, Rekultywacja Jaziora Długiego w Olsztynie metodą inaktywacji fosforu. Mat. Konf. Nauk.-Techn. Ochrona i rekultywacja jezior. Grudziądz, GEO-KAT Sp. z o.o, 2004a. Operat wodnoprawny obejmujący zagadnienia związane z rekultywacją Jezior Domowych, GEO-KAT Sp. z o.o, Warszawa. Maszynopis. GEO-KAT Sp. z o.o, 2004b. Projekt techniczny rekultywacji Jeziora Domowego Małego w Szczytnie. GEO- KAT Sp. z o.o, Warszawa. Maszynopis. Hydroprojekt, Studium zaopatrzenia w wodę miasta Szczytna, Biuro Studiów i Projektów Budownictwa Wodnego Hydroprojekt Oddział w Gdańsku Maszynopis. IRŚ, 1969, Mapa batymetryczna. Kudelska D., Cydzik D., Soszka H., 1994, Wytyczne monitoringu podstawowego jezior, PIOŚ, Warszawa.

5 Restoration of the Domowe Lakes in Szczytno history and plans 73 Klapper H., 1991, Control of eutrophication in inland waters, Ellis Horwood, London. Lossow K., 1998, Ochrona i rekultywacja jezior, Teoria a praktyka, Idee Ekologiczne, s. Szkice, 13 (7), Lossow K., Gawrońska H., 1998, External input to Lake Wadąg effective and estimate loadings. Pol. J. Environ. Studies, 7(2), Lossow K., Gawrońska H., 1999, Koncepcja rekultywacji jezior: Długiego (Domowe DuŜe) i Miejskiego (Domowe Małe) w Szczytnie oraz jeziora Szczycionek, gm. Szczytno, UWM Olsztyn, Maszynopis. Lossow K., Gawrońska H., Tonder J.,1998, Kryteria wyboru optymalnej metody rekultywacji zbiorników wodnych na przykładzie Jeziora Wolsztyńskiego, Bad. Limnol., 1, Lossow K., Gawrońska H., Łopata M., Jaworska B., 2004a, Efektywność rekultywacji polimiktycznego jeziora Głęboczek w Tucholi metodą inaktywacji fosforu, Mat. Konf. Nauk.-Techn. Ochrona i rekultywacja jezior, Grudziądz, Lossow K., Gawrońska H., Łopata M., Jaworska B., 2004b, Selection criteria for restoration method on Lake Suskie, Limnological Review, vol. 4, Nather M., 1978, Zbiornik retencyjny na jeziorze Sasek Wielki i przerzut wody dla miasta Szczytna, Komunikat Informacyjny CBSiBW Hydroprojekt, Informator Projektanta Warszawa, Nr 3, 18. Oglesby T. T., 1969, Effect of controlled nutrient dillution on the eutrophication of a lake, In Eutrophication: causes, cosequences, correctives, Proceedings of a Symposium Nat. Acad. of Sciences. Washington D.C, Streszczenie Celem pracy jest przedstawienie przyjętego do realizacji projektu renowacji Jezior Domowych w Szczytnie. Jeziora Domowe (Miejskie i Długie) połoŝone są w północno-zachodniej części miasta. Są to zbiorniki niewielkie (pow. 11,4 ha i 62,1 ha) i płytkie (głęb. maks. 3,8 m i 5,4 m). Jeziora połączone są ze sobą kanałem o długości ok. 50 m. Jedyny odpływ, stanowi sztuczny Kanał Domowy (rys. 1), odprowadzający wody do rzeki Sawicy. Oba jeziora były w przeszłości wykorzystywane jako odbiorniki ścieków miejskich-i opadowych, a obecnie tylko opadowych (rys. 1). Spowodowało to bardzo silne ich zanieczyszczenie (tab. 1). Dodatkowym czynnikiem oddziaływującym niekorzystnie na stan troficzny, było stwierdzone juŝ w 60. latach XX wieku obni- Ŝenie poziomu lustra wody, nawet o jeden metr. Przeprowadzone w latach 1995 i 2004 badania wykazały, Ŝe mimo odcięcia większości ścieków, jakość wód obu jezior nie poprawiła się i wg kryteriów Kudelskiej i in. (1994) wody ich moŝna określić jako poza klasowe. Jedyną moŝliwością przywrócenia załoŝonej im funkcji rekreacyjnej jest ich rekultywacja. Biorąc pod uwagę warunki morfometryczne i hydrologiczne oraz moŝliwość wykorzystania wód plejstoceńskich z wyłączonych z eksploatacji studni do renowacji jezior zaproponowano metodę przepłukiwania/ rozcieńczania. Rekultywacja będzie prowadzona w dwóch etapach. W pierwszym etapie przewidziano przegrodzenie obu jezior, podniesienie poziomu wody i intensywne przepłukiwanie Jeziora Miejskiego. Ilość dostarczanej wody (120 m 3 /h) umoŝliwi czterokrotną jej wymianę w roku. NaleŜy jednak zaznaczyć, Ŝe wieloletnie wprowadzanie do jeziora zanieczyszczeń i ich odkładanie w osadach dennych moŝe w znacznym stopniu ograniczyć efektywność prowadzonej renowacji. W takim przypadku, po zaprzestaniu przepłukiwania niezbędne będzie zastosowanie dodatkowej metody rekultywacyjnej, polegającej na inaktywacji fosforu. W drugim etapie przewiduje się zastosowanie tego samego sposobu rekultywacji w Jeziorze Długim i dopiero wówczas przywrócenie połączenia między Jeziorami Domowymi.