Limnological Changes in the Review Trophic 7, State 3: 153-159 of Lake Niegocin after the Modernization of a Local Wastewater Treatment Plant 153 Changes in the Trophic State of Lake Niegocin after the Modernization of a Local Wastewater Treatment Plant Agnieszka Napiórkowska-Krzebietke, Małgorzata Wierzchowska, Barbara Błocka, Joanna Hutorowicz, Andrzej Hutorowicz, Bogusław Zdanowski Department of Hydrobiology, Inland Fisheries Institute, Oczapowskiego 10, 10-719 Olsztyn, e-mail: akrzebietke@infish.com.pl Abstract: The objective of this study was to evaluate the trophic state of Lake Niegocin as affected by the actions undertaken for the restoration and protection of this water body (modernization of a wastewater treatment plant in 1994). The study was conducted in the summer of the years 1986 to 2001. Changes in the concentrations of total phosphorus and chlorophyll, Secchi disc visibility and total phytoplankton biomass were analyzed. The values of trophic state indices of Carlson, TSI TP, TSI SD and TSI Chl, were also calculated. During the years 1986-1994 mean values of total phosphorus, chlorophyll and Secchi disk transparency were characteristic of strongly eutrophic waters. After the modernization of the wastewater treatment plant in Giżycko a much lower chlorophyll content and twofold higher water transparency enabled to classify Lake Niegocin as moderately eutrophic. However, phosphorus content was still in the range typical of strongly eutrophic waters. Changes in the trophic state of the analyzed lake were reflected in the mean values of TSI, which indicated eutrophy before 1995 and meso-eutrophy over the 1995-2001 period, as well as in almost twofold lower phytoplankton biomass. Key words: trophy, lakes, Carlson s trophic state index, phytoplankton, Secchi disc visibility Introduction Lake Niegocin (area 2600 ha, max. depth 39.7 m, mean depth 9.9 m) is located in the Land of the Great Masurian Lakes. Until the mid-1990s the lake received discharges of municipal waste. According to Vollenweider s criteria, phosphorus loading rates in this lake exceeded critical levels (Giercuszkiewicz- Bajtlik and Głąbski 1981, Giercuszkiewicz-Bajtlik 1990). The increase in eutrophy could be also caused by large-area biogene runoff from the agricultural catchment (74% of arable land) and water inflow from Lake Wojnowo and Lake Grajewko (Spodniewska 1979, 1986, Zdanowski and Hutorowicz 1994), heavily polluted by effluents from animal farms located in their direct catchments. The positive changes related to the modernization of the wastewater treatment plant in Giżycko included a considerable decrease in total phytoplankton biomass and a lower proportion of blue-green algae in biomass (Napiórkowska-Krzebietke and Hutorowicz 2006). The objective of this study was to evaluate the trophic state of Lake Niegocin as affected by the actions undertaken for the restoration and protection of this water body. Study area Lake Niegocin is located in the bifurcation region of the Land of Great Masurian Lakes, within which there is a watershed separating the drainage basins of the Vistula River and the Pregoła River (Mikulski 1966). Lake Niegocin and Lake Jagodne Małe with their direct catchments constitute the major axis of this area, which periodically may receive no surface runoff at all (Bajkiewicz-Grabowska 1991). Lake Niegocin receives water inflow from two neighboring lakes, Grajewko and Wojnowo as well as indirectly from the Staświnka River. Usually the water from Lake Niegocin flows to the south-west, to Lake Boczne, and then with the Pisa River to the rivers Narew and Vistula.
154 A. Napiórkowska-Krzebietke, M. Wierzchowska, B. Błocka, J. Hutorowicz, A. Hutorowicz, B. Zdanowski The principal land use within the direct catchment area of Lake Niegocin is agricultural in the 1980s arable land accounted for 74% of the total drainage basin (Giercuszkiewicz-Bajtlik 1990). At that time built-up areas accounted for 6.6% of the land use, while undeveloped land consisting of forest and water made up 17% and 1% of the land use, respectively. No considerable alterations to the land use were found in this area in the year 2000, and the observed small differences resulted from changes in agricultural use (Rocznik statystyczny..., 2001). In the 1980s and at the beginning of the 1990s the main point source of pollution affecting Lake Niegocin was the discharge of mechanically treated wastewater (117.9 kg P d -1 oraz BZT 5 2240 kg O 2 d -1 ) from the nearby town of Giżycko (31500 inhabitants). Other pollution sources were production plants, car washes and public facilities and utilities located within the direct catchment area of the lake. A potential pollution source was also the inflow of slurry-polluted water from Lake Grajewko and Lake Wojnowo (Cydzik et al. 1995). In 1994 the existing mechanical wastewater treatment plant in Giżycko was modernized by adding a biological treatment stage with chemical phosphorus Fig. 1. Sampling sites on Lake Niegocin: I near Giżycko, II near water inflow from Lake Grajewko, III near Wilkasy, IV near water inflow from Lake Wojnowo, V near water inflow from Lake Boczne. precipitation (throughput 14000 m 3 d -1 ). Since November 1994 treated wastewater has been discharged into Lake Grajewko, connected to Lake Niegocin by a short channel. Approximately 7000 m 3 d -1 of sewage was discharged during the years 2000-2001. According to the Provincial Inspectorate for Environmental Protection, mean pollutant concentrations in treated wastewater did not exceed the maximum permissible values specified in the water supply and sewage effluent discharge consent valid until 2003 (Różański 2001, 2002). In July 2001 the wastewater treatment plant in Giżycko got flooded after heavy rainfalls, which significantly reduced the treatment capacity of activated sludge. The normal operating efficiency of the plant was restored after two weeks. Over this time biogenic loads in the effluents discharged to the lake considerably exceeded the permissible levels (Analiza ścieków..., PWiK, 2000-2001). In addition, strong recreation and tourist pressure has always constituted a serious threat to Lake Niegocin. Methods The study was conducted in the summer (June, July, August) of 1986 to 2001 at research site I situated at a maximum depth (39.7 m), close to the town of Giżycko. In 2001 another four sites were established (II, III, IV and V) in the direct vicinity of probable point pollution sources (Fig. 1). Total phosphorus was determined by the molybdenum method, and chlorophyll (given as a sum of chlorophyll a and phaeophytins) was determined with a spectrophotometer, by the alcohol method, as described by Nusch (1980). Water visibility was measured using a Secchi disc. Phytoplankton biomass was calculated by cell volume measurement. Some results referring to phytoplankton biomass and chlorophyll content at research site I as well as to the environmental conditions of Lake Niegocin, obtained in 1986-2001, have already been partly published (Zdanowski et al. 1993, Zdanowski and Hutorowicz 1994, Napiórkowska-Krzebietke and Hutorowicz 2006). The significance of changes in water concentrations of total phosphorus and chlorophyll, Secchi disc visibility and total phytoplankton biomass was estimated using the Kruskal-Wallis test (independent group comparison test) and the two-sample Mann- Whitney test, at a significance level of 0.05 (Łomnicki 2002). A statistical analysis was performed using Statistica software (StatSoft, Inc..., 2000).
Changes in the Trophic State of Lake Niegocin after the Modernization of a Local Wastewater Treatment Plant 155 The values of trophic state indices of Carlson (1977), TSI TP, TSI SD and TSI Chl, were calculated based on the concentrations of total phosphorus and chlorophyll, and Secchi disc visibility. Results and discussion Mean total phosphorus content in Lake Niegocin in the summer of 1986-1994 was 0.242 mg l -1. Over the 1995-2001 period this value was about twofold lower (U = 10, p = 0.003, n = 20) (Fig. 2). Both before and after wastewater treatment plant modernization, the observed values were characteristic of strongly eutrophic waters according to the classification of trophy levels in temperate-zone lowland harmonic lakes, proposed by Hillbricht-Ilkowska and Kajak (1986) and Hillbricht-Ilkowska (1990) (as cited in Hillbricht- Ilkowska and Wiśniewski 1994). During the years 1986-1994 Secchi disc visibility varied from 0.5 to 2.6 m. The value greater than 2 was recorded twice only (in June). The other values corresponded to strongly eutrophic waters according to the classification of trophy levels in lowland harmonic lakes (Hillbricht-Ilkowska and Wiśniewski 1994). Low Secchi disc visibility readings in Lake Niegocin were also reported by Zdanowski et al. (1984, 1993) in 1976 (max. 2.8 m), and by Kufel (1998) and Kufel and Kufel (1999) in 1984-1996 (mean 1.6 m). Secchi disc visibility increased significantly (U = 24.5, p = 0.001, n = 28) (Fig. 3) over the 1995-2001 period, reaching even 4.5 m. The mean value noted after wastewater treatment plant modernization, i.e. Fig. 2. Arithmetic mean, standard error and standard deviation for total phosphorus content in Lake Niegocin in the summer, before (1986-1994) and after the modernization of the wastewater treatment plant in Giżycko (1995-2001) Fig. 3. Arithmetic mean, standard error and standard deviation for Secchi disc visibility in Lake Niegocin in the summer, before (1986-1994) and after the modernization of the wastewater treatment plant in Giżycko (1995-2001)
156 A. Napiórkowska-Krzebietke, M. Wierzchowska, B. Błocka, J. Hutorowicz, A. Hutorowicz, B. Zdanowski 2.6 m, is typical of moderately eutrophic waters (Hillbricht-Ilkowska and Wiśniewski 1994). In the summer before the modernization of the wastewater treatment plant in Giżycko (1986-1994), chlorophyll concentrations varied between 3.0 and 93.9 μg l -1 (Napiórkowska-Krzebietke and Hutorowicz 2006). According to the OECD classification of trophic state for inland waters, the maximal value corresponds to hypertrophic waters (Vollenweider 1989). A comparable chlorophyll content was observed over the 1976-1996 period (4.2-84.0 μg l -1 ) (Zdanowski et al. 1984, 1993, Zdanowski and Hutorowicz 1994, Kufel 1998, Kufel and Kufel 1999). In the summer after the modernization of the wastewater treatment plant in Giżycko (1994) chlorophyll content was almost twofold lower (U = 132, p = 0.009, n = 44) (Fig. 4). The maximal value (49.4 μg l -1 ), noted in 1995-2001 (Napiórkowska-Krzebietke and Hutorowicz 2006), was within the eutrophic range (Vollenweider 1989). The values recorded over this period were usually found to be typical of mesotrophic or moderately eutrophic waters (Hillbricht-Ilkowska and Wiśniewski 1994). The trophic state index of total phosphorus (TSI TP ) before wastewater treatment plant modernization (1986-1994) and in 1995-2001 ranged from 78 to 90 and from 62 to 82, respectively (Fig. 5). Fig. 4. Arithmetic mean, standard error and standard deviation for chlorophyll concentrations in Lake Niegocin in the summer, before (1986-1994) and after the modernization of the wastewater treatment plant in Giżycko (1995-2001) Fig. 5. Trophic state of Lake Niegocin in the years 1986-2001 based on the trophic state indices of Carlson (TSI Chl, TSI SD, TSI TP )
Changes in the Trophic State of Lake Niegocin after the Modernization of a Local Wastewater Treatment Plant 157 The pattern of changes in TSI SD was identical. Its values varied from 46 to 70, and from 38 to 54 before and after wastewater treatment plant modernization, respectively. The values of TSI Chl changed to a lower degree, i.e. from 41 to 75 in 1986-1994, and from 43 to 69 after 1994. The mean value of TSI, calculated based on the values of TSI TP, TSI Chl and TSI SD, indicated eutrophy (66) before 1995 according to Carlson (1977), Zdanowski (1999) and Håkanson and Boulion (2001), and meso-eutrophy (58) during the years 1995-2001. An improvement in water quality was also confirmed by a water cleanliness analysis performed by the Provincial Inspectorate for Environmental Protection. In 1984-1985 and 1990 Lake Niegocin was unclassified, while in 1993-1998 and 1999-2001 it was classified into water quality class III (Dorochowicz 1994, Cydzik et al. 1995, Wróblewska 2002). In 1991-1994 phytoplankton biomass in Lake Niegocin exceeded 8.0 mg l -1. According to Spodniewska (1978, 1979), this value is characteristic of eutrophic lakes in the Masurian Lakeland. According to the classification of lowland harmonic lakes, this value falls in the range noted in mesotrophic waters (Hillbricht-Ilkowska and Wiśniewski 1994). Positive changes in trophy levels resulting from wastewater treatment plant modernization were reflected in almost twofold lower phytoplankton biomass (mean 2.6 mg l -1 ) (KW-H(2,12) = 6.04, p = 0.049; Fig. 6) in the years 1995-1999 and 2000-2001. The composition of phytoplankton communities changed as well. Bluegreen algae, which dominated in the summer over the 1991-1994 period, were replaced by dinophytes (Napiórkowska-Krzebietke and Hutorowicz 2006). There were no statistically significant differences in the values of phytoplankton biomass and chlorophyll recorded at five research sites in the epilimnion of Lake Niegocin (KW-H(4,15) = 0.97, p = 0.915; Fig. 7), (KW-H(4,15) = 1.03, p = 0.906; Fig. 8). However, a tendency was observed towards intensive phytoplankton development at sites II and III, in the vicinity of potential pollution sources. A higher chlorophyll content was recorded at site II, near water inflow from Lake Grajewko. In July 2001, during wastewater treatment plant failure, untreated effluents were discharged to Lake Niegocin at this site. Conclusion The modernization of the wastewater treatment plant in Giżycko contributed to a considerable decrease in the concentrations of total phosphorus and chlorophyll in Lake Niegocin. A significant increase in Secchi disc visibility was also noted. The positive changes related to wastewater treatment plant modernization were also reflected in the values of trophic state indices of Carlson. Total phytoplankton biomass decreased in the summer after 1994. The development of planktonic algal communities in 2000-2001 was most probably affected by the high trophy of Lake Niegocin and the wastewater treatment plant failure in July 2001. In 2001, total algal biomass and chlorophyll concentrations at research sites located close to and at a certain distance from potential pollution sources were found to be comparable. Fig. 6. Total phytoplankton biomass (arithmetic mean, standard error and standard deviation) in Lake Niegocin in 1991-1994 (before the modernization of the wastewater treatment plant in Giżycko), in 1995-1999 (after the modernization) and in 2000-2001
158 A. Napiórkowska-Krzebietke, M. Wierzchowska, B. Błocka, J. Hutorowicz, A. Hutorowicz, B. Zdanowski Fig. 7. Total phytoplankton biomass (arithmetic mean, standard error and standard deviation) at five research sites on Lake Niegocin in 2001 Fig. 8. Chlorophyll concentration (arithmetic mean, standard error and standard deviation) at five research sites on Lake Niegocin in 2001
Changes in the Trophic State of Lake Niegocin after the Modernization of a Local Wastewater Treatment Plant 159 References Analiza ścieków 2000-2001. Oczyszczalnia ścieków w Giżycku. PWiK Sp. z o.o., Giżycko. Bajkiewicz-Grabowska E., 1991, Czy zaszły zmiany w położeniu działu wodnego w systemie Wielkich Jezior Mazurskich?, Pr. Stud. Geogr. 12: 269-278. Carlson R. E., 1977, A trophic state index for lakes. Limnol. Oceanogr. 22: 361-369. Cydzik D., Kudelska D., Soszka H., 1995, Atlas stanu czystości jezior Polski badanych w latach 1989-1993, Bibl. Mon. Środ., Warszawa, p. 636. Dorochowicz A., 1994, Stan czystości systemu Wielkich Jezior Mazurskich w latach 1982-1993, Biblioteka Monitoringu Środowiska, Suwałki. Giercuszkiewicz-Bajtlik M., 1990, Prognozowanie zmian jakości wód stojących. Instytut Ochrony Środowiska, Warszawa, p. 74. Giercuszkiewicz-Bajtlik M., Głąbski E., 1981, Predicting the pollution of Great Masurian Lakes from point and nonpoint sources, Ekol. Pol. 29: 361-374. Håkanson L., Boulion V. V., 2001, Regularities in primary production, Secchi depth and fish yield and a new system to define trophic and humic state indices for lake ecosystems. Internat, Rev. Hydrobiol. 86: 23-62. Hillbricht-Ilkowska A., Wiśniewski R., J., 1994, Zróżnicowanie troficzne jezior Suwalskiego Parku Krajobrazowego i jego otuliny stan obecny, zmienność wieloletnia, miejsce w klasyfikacji troficznej jezior, [in:] Hillbricht-Ilkowska A., Wiśniewski R. J. (eds), Jeziora Suwalskiego Parku Krajobrazowego: Związki z krajobrazem, stan eutrofizacji i kierunki ochrony, Zesz. Nauk. Człowiek i Środowisko PAN 7, Ossolineum, Wrocław-Warszawa-Kraków: 181-200. Kufel I., Kufel L., 1999, Spatial variability and long-term changes of the trophic parameters in the Great Masurian Lakes (Poland), Pol. J. Ecol. 47: 323-333. Kufel L. 1998. Chlorophyll-nutrients-Secchi disc relationships in the Great Masurian Lakes (north-eastern Poland), Pol. J. Ecol. 46: 327-337. Łomnicki A. 2002. Wprowadzenie do statystyki dla przyrodników, PWN, Warszawa, p. 263. Mikulski Z., 1966, Kształtowanie się działu wodnego na Wielkich Jeziorach Mazurskich, Prz. Geogr. 38(3): 381-392. Napiórkowska-Krzebietke A., Hutorowicz A., 2006, Longterm changes of phytoplankton in Lake Niegocin in the Masurian Lake Region, Poland, Oceanol. Hydrobiol. Stud. 35: 209-226. Rocznik Statystyczny Województwa Warmińsko-Mazurskiego, 2001, GUS, Olsztyn. Różański S. (ed.), 2001, Raport o stanie środowiska na obszarze województwa warmińsko-mazurskiego w latach 1999-2000: cz. I 1999 r., IOŚ-WIOŚ, Biblioteka Monitoringu Środowiska, Olsztyn. Różański S. (ed.), 2002. Raport o stanie środowiska na obszarze województwa warmińsko-mazurskiego w latach 1999-2000: cz. II 2000 r., IOŚ-WIOŚ, Biblioteka Monitoringu Środowiska, Olsztyn. Statistica for Windows (Computer Program Manual), 2000, Statsoft, Inc. Tulsa, OK: Statsoft, Inc., 2300 East 14 th Street, Tulsa, OK 74104, http://www.statsoft.com. Spodniewska I., 1978, Phytoplankton as the indicator of lake eutrophication. I. Summer situation in 34 Masurian lakes in 1973, Ekol. Pol. 26: 53-70. Spodniewska I., 1979, Phytoplankton as the indicator of lake eutrophication. II. Summer situation in 25 Masurian lakes in 1976, Ekol. Pol. 27: 481-496. Spodniewska I., 1986, Planktonic blue-green algae of lakes in north-eastern Poland, Ekol. Pol. 34: 151-183. Vollenweider R. 1989. Global problems of eutrophication and its control. Symp. biol. Hung., 38: 19-41. Wróblewska H., 2002, Influence of pollution from point sources on purity of Great Mazurian Lakes, Limnol. Rev. 2: 443-451. Zdanowski B., 1999, Eutrofizacja jezior Wigierskiego Parku Narodowego: zagrożenie i ocena, [in:] Zdanowski B., Kamiński M., Martyniak A. (eds), Funkcjonowanie i ochrona ekosystemów wodnych na obszarach chronionych, IRS, Olsztyn: 261-278. Zdanowski B., Hutorowicz A., 1994, Salinity and trophy of Great Masurian Lakes (Masurian Lakeland, Poland), Ekol. Pol. 42: 317-331. Zdanowski B., Hutorowicz A., Świątecki A., 1993, Zmienność wskaźników trofii i czystości wody wielkich Jezior Mazurskich, Zintegrowany Monitoring Środowiska Przyrodniczego, PIOŚ, Warszawa. Zdanowski B., Korycka A., Zachwieja J., 1984, Thermal and oxygen conditions and the chemical composition of the Great Masurian Lakes, Ekol. Pol. 32: 651-677.
160 A. Napiórkowska-Krzebietke, M. Wierzchowska, B. Błocka, J. Hutorowicz, A. Hutorowicz, B. Zdanowski