and the drainage basin role in the lake s eutrophication

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1 Limnological Review 5 (2005) Trophic condition of Lake Podkówka and the drainage basin role in the lake s eutrophication University of Warmia and Mazury in Olsztyn, Department of Environmental Protection Engineering Prawocheńskiego 1, Olsztyn-Kortowo Abstract: A small (6.92 ha) and shallow (6 m) lake was studied, situated in the north-western part of the Olsztyn city. The lake waters were characterized by a very high content of nutrients, up to mg P/dm 3 and 8.18 mg N/dm 3. The high fertility of the lake was exhibited also by the values of BOD 5 reaching 11.5 mg O 2 /dm 3, chlorophyll a content (28 mg/m 3 ) and concentrations of total organic carbon (TOC) oscillating between 12.4 and 17 mg C/dm 3. The reason for the high trophic status of the lake was excessive loading from the drainage basin. The actual nutrients loads to the lake exceeded the critical load level calculated according to Vollenweider (1968). Key words: eutrophication, drainage basin, nitrogen, phosphorus, external loading, allowable and critical loads of nutrients. Introduction Lake and its drainage basin create a natural landscape system which functions through transport of various forms of matter from the drainage basin and its accumulation in the reservoir (Bajkiewicz-Gra-bowska, 1999, 2002). The effect of constant input to water of the elements building organic matter is eutrophication which is the fastest in small and shal-low polymictic lakes surrounded by agricultural or urban land (Szyper The et main al., 1999, activity Szyper, hindering Kraska, the 1999). negative effects of eutrophication should be protection of lakes by cutting off the pollution sources executed by proper development in the drainage basins and on the lakes peripheries. Lake Podkówka is a small thaw reservoir situated among the moraine hills. The drainage basin in the beginning of the 1990s was dominated by wasteland (66.7%) with some fields, forests and bogs (Lossow, Gawrońska, 1993). In the past years, the use of the direct lake surroundings changed, as the land has been built up in nearly 50%. On the north and west of the lake some single-family houses can be found with the property land bordering with the lake. The number of houses increases every year. The goal of this study was to determine the trophic condition of the lake and the role of the drainage basin in the lake s eutrophication. Lake and drainage basin description Lake Podkówka s geographical location is 20 O 27 4 E, 53 O N; m above sea level (Mapa..., 1999). The first (and only) study of the lake was conducted by Lossow and Gawrońska (1993) and included the trophic condition determination, and bathymetric and morphometric properties determination. According to these authors, the parameters of the

2 94 lake are: 6.92 ha surface area, 6 m max. depth, 2.85 m mean depth, and 197,369 m 3 volume. The shoreline is little diverse (K 1.48) while the depth index of and the relative depth of indicate that the lake s bowl is strongly sunk in the ground. Based on own field studies and the topographic map studies it was concluded that the drainage basin of the lake is as small as 34.1 ha. The built-up land covers the most of the drainage basin (49.2%), waste-land comprises 30.3%, forests 9.1% and bogs 6.1%. On the north and west, the contiguous land is built-up with single-family houses; dense deciduous forest grows on the east, and waste-land makes the drainage basin on the south. Lake Podkówka has no surface inflows and outflows. Material and method The lake was surveyed in April 2002 through February Water for analyses was sampled from one sampling site, located in the eastern part of the lake, above the deepest (6 m) site (Fig. 1). Fig. 1. Bathymetric chart of Lake Podkówka

3 Trophic condition of Lake Podkówka and the drainage basin role in the lake s eutrophication 95 Temperature and oxygen content were measured each time the samples were taken, at every me-ter of the depth. Water samples were taken at 1 m under the water table and 0.5 m above the bottom. TOC content was determined in non-filtered samples. Dissolved organic carbon (DOC) was analysed after filtration through a 0.45 µm Millpore filter. Content of particulate organic carbon (POC) was found from the difference between TOC and DOC. The measurements were done with a TOC 5000 Schimadzu analyser, after prior acidification of the samples with 2M HCl to approximately 2 ph, to remove CO 2. Other chemical analyses of the water were done in accordance with the methods of Hermanowicz et al. (1999) and the Standard methods (1980). The surface area of the drainage basin was determined by demarcation of the watershed and planimetry work on the topographic map in the scale 1: The spatial nutrients run-off was calculated using the coefficients of Giercuszkiewicz-Bajtlik (1990) and Lossow and Gawrońska (1998). The static model of Vollenweider (1968) was used to calculate the allowable and critical loads levels of phosphorus and nitrogen. Results and discussion Lake Podkówka is a small reservoir with the edges in the north-west and east highly elevated, built-up or grown with deciduous trees. Wind penetration is therefore limited which is reflected by low water dynamics. The theoretical mixing depth of 2.64 m, calculated according to Patalas (1960a), points at the 4th degree of the static equilibrium. It was confirmed by the results of the studies of 2002; as soon as April, the thermal variability was noted in the water column and observed throughout the summer. Epilimnion was 3-m thick with the thermocline of the max. gradient 3.8 C/m. The intensity of water mixing and the degree of eutrophication influenced the oxygen settings in Lake Podkówka. In the surface water layers oxygen saturation ranged from 90 to 100%, with the extreme of 119% in some periods, indicating intensive production processes. They were accompanied by increase of reaction to ph 9.21 (Tab. 1), high concentrations of TOC 17.0 mg C/dm 3 (Tab. 1), BOD mg O 2 /dm 3, chlorophyll a mg/m 3, and low water transparency (0.7 m). In the deeper water layers, particularly near the bottom, oxygen was used up rather quickly, leading to total deficit in the peak of the summer stagnation. The reason were no doubt the intensive degradation processes of the matter produced in the lake and deposited in the bottom sediments. Table 1. Value ranges of the selected physico-chemical water parameters of Lake Podkówka, in various years Parameter Unit Layer Value surface Temperature C bottom Oxygen mg O 2/dm 3 surface bottom surface Reaction ph bottom Carbon dioxide mg CO 2/dm 3 surface bottom TOC mg C/dm 3 surface bottom DOC mg C/dm 3 surface bottom Nitrate mg N/dm 3 surface bottom Ammonium mg N/dm 3 surface bottom Total N mg N/dm 3 surface bottom Mineral P mg P/dm 3 surface bottom Total P mg P/dm 3 surface bottom BOD 5 mg O 2/dm 3 surface bottom Permanganate value mg O 2/dm 3 surface bottom Iron mg Fe/dm 3 surface bottom Manganese mg Mn/dm 3 surface bottom Many authors share the opinion (Zdanowski et al., 1992; Kajak, 1995) that trophic condition of a lake is reflected by the amount of phosphorus and nitrogen in circulation. The quantities of nitrogen and phosphorus in the waters of Lake Podkówka were very high, up to mg P/dm 3 and 8.18 mg N/dm 3 (Tab. 1, Fig. 2, Fig. 3), and dominated by the organic forms. Mineral phosphorus was practically not detected in the lake waters probably due to its utilization in the production processes. It was measured only at the end of the summer (Tab. 1, Fig. 2). Phosphates detected in the water in periods with strong oxygen deficits near the bottom were released from the bottom deposits. The process of internal loading with phosphorus from the bottom deposits was accompa-

4 96 nied by an increase of iron concentration to 10.2 mg Fe/dm 3 (Tab. 1). Fig. 2. Changes in phosphorus compounds content in Lake Podkówka waters Unlike mineral phosphorus, mineral nitrogen occurred continuously and its concentrations were very high (Tab. 1, Fig. 3). The quantity of the mineral forms of nitrogen was determined by ammonium and nitrate (Tab. 1). Large quantities of mineral nitrogen in the water throughout the growing season indicate on one hand large nitrogen resources in the lake but on the other, intensive mineralization and nitrification processes. Regarding the mineral nitrogen resources, Lake Podkówka can be classified as the poly type (Patalas, 1960b).

5 Trophic condition of Lake Podkówka and the drainage basin role in the lake s eutrophication 97 Fig. 3. Changes in nitrogen compounds content in Lake Podkówka waters Other parameters values are a sign of the advanced eutrophication processes (and the consequent high productivity of the lake); BOD 5 reached 11.5 mg O 2 /dm 3 (Tab. 1, Fig. 4), TOC throughout the growing season varied between 12.4 and 17.0 mg C/dm 3, water transparency was as low as 1.3 m on average (Fig. 5). With regard to the trophic state classification of Hillbricht-Ilkowska and Wiśniewski (1993), referring to water transparency, total P resources and chlorophyll a content, Lake Podkówka is a heavily eutrophic lake. According to the criteria given by Ku-delska et al. (1994) the lake water corresponds with the 3rd purity standard (average of 2.7 points). Fig. 4. Changes in organic matter (BOD 5 ) content in Lake Podkówka waters

6 98 Fig. 5. Changes in water transparency in Lake Podkówka No doubt, the fairly advanced eutrophication processes in Lake Podkówka are stimulated by the excessive input of nutrients from the drainage basin. The data presented in table 2 show that the total annual nitrogen and phosphorus load to Lake Podkówka, calculated according to Giercuszkiewicz-Bajtlik (1990), equals 23.3 kg of P and kg of N, or per unit surface g P/m 2 /year and g N/m 2 /year. According to the criteria of Lossow and Gawrońska (1998), the respective values are 20.9 kg P and kg N, or g P/m 2 /year and g N/m 2 /year. Table 2. Total annual nutrients loading to Lake Podkówka from the actual drainage basin and with regard to its present use-pattern Values calculated using unit run-off Values calculated using unit run-off External sources of pollution coefficients of Giercuszkiewicz-Bajtlik (1990) coefficients of Lossow and Gawrońska (1998) Phosphorus Nitrogen Phosphorus Nitrogen (kg P/year) (kg N/year) (kg P/year) (kg N/year) Spatial sources Atmospheric sources Total Allowable and critical loads levels to Lake Podkówka, calculated according to Vollenweider (1968), equal (respectively) g P/m 2 /year and g P/m 2 /year, or g N/m 2 /year and g N/m 2 / year. Comparison between the actual nitrogen and phosphorus loads and the values calculated according to Vollenweider (1968) allows to conclude that the loads exceed a few times not only the allowable but also the critical values, responsible for advanced eutrophication. Lossow and Gawrońska (1993) who examined Lake Podkówka more than 10 years ago described the reservoir as highly eutrophic. As evidenced in the study of 2002 the water quality deteriorated which together with the present high loading from the drainage basin shows the need to apply protective measures that would diminish the external loading. Taking into consideration the high vulnerability of this reservoir with no outflows (3rd water quality standard; Kudelska et al., 1994) to external impacts, farther development in the drainage basin may lead to total degradation of the lake. References Bajkiewicz-Grabowska E., 1999, Struktura fizycznogeograficzna układu krajobrazowego zlewnia jezioro i jej wpływ na tempo naturalnej eutrofizacji jezior, Funkcjonowanie i ochrona ekosystemów wodnych na obszarach chronionych, Wydawnictwo IRŚ, Olsztyn, Bajkiewicz-Grabowska E., 2002, Obieg materii w systemach rzeczno jeziornych, Uniwersytet Warszawski, Warszawa. Giercuszkiewicz-Bajtlik M., 1990, Prognozowanie zmian jakości wód stojących, Instytut ochrony Środowiska, Warszawa. Hermanowicz W., DoŜańska W., Dojlido J., Koziorowski B., 1999, Fizyczno-chemiczne badanie wody i ścieków, Arkady, Warszawa. Hillbricht-Ilkowska A., Wiśniewski R. J., 1993, Trophic differentiation of lakes the Suwałki Landscape Park (North Eastern Poland) and its Buffer Zone Present State, Changes Over Years, Position in thropic classification of lakes, Ekol. Pol., 41(1-2): Kajak Z., 1995, Eutrofizacja nizinnych zbiorników zaporowych, Biblioteka Monitoringu Środowiska, Łódź. Kudelska D., Cydzik D., Soszka H., 1994, Wytyczne monitoringu podstawowego jezior, Biblioteka Monitoringu Środowiska, Warszawa. Lossow K., Gawrońska H., 1993, Morfometria i chemizm wód jeziora Podkówka w Olsztynie z uwzględnieniem wpływu zlewni na zasilanie w związki biogenne, (maszynopis). Lossow K., Gawrońska H., 1998, External input to lake Wadąg Effective and estimate loadings, Polish Journal of Environmental Studies, vol. 7, No 2(1998), Mapa Topograficzna Polski, 1999, 1:10000, Olsztyn Osiedle Podleśna, cz. 40, Główny Geodeta Kraju. Patalas K., 1960a, Mieszanie wody jako czynnik określający intensywność krąŝenia materii w róŝnych morfologicznie jeziorach okolic Węgorzewa, Rocz. Nauk Rol., 77(B 1), Patalas K., 1960b, Charakterystyka składu chemicznego wody 48 jezior okolic Węgorzewa, Rocz. Nauk Rol., 77(B 1), Standard methodsfor examination of water and wastewater, 1980, American Public HealthAssociation, AWWA, WPCF, Washington D.C. Szyper H., Kraska M., 1999, Ocena zewnętrznego obciąŝenia związkami biogennymi jezior Drawieńskiego Parku Narodowego, Mat. III Konf. Nauk. Tech.

7 Trophic condition of Lake Podkówka and the drainage basin role in the lake s eutrophication 99 nt. Naturalne i antropogeniczne przemiany jezior, września 1999, Radzyń k. Sławy, Szyper H., Gołdyn R., Romanowicz W., ObciąŜenie jezior Wielkopolskiego Parku Narodowego związkami azotu i fosforu, Funkcjonowanie i ochrona ekosystemów wodnych na obszarach chronionych, Wydawnictwo IRŚ, Olsztyn, Vollenweider R. A., 1968, Scientific fundamentals of the eutrophication of lasek and flowing water, with particular reference to nitrogen and phosphorus as factor In eutrophication, Tech. report Organisation for Economic Cooperation and Development, Paris. Zdanowski B., Karpiński A., Prusik S., 1992, Warunki środowiskowe wód jezior Węgierskiego Parku Narodowego, Zesz. Nauk. PAN, 3, Streszczenie Badania prowadzono na niewielkim (6,92 ha) i płytkim (6 m) jeziorze Podkówka (rys. 1), połoŝonym w północno zachodniej części Olsztyna. Zlewnia tego jeziora jest niewielka, wynosi zaledwie 34,1 ha. Największy udział (49,2%) mają w niej tereny zabudowane, 30,3% zajmują nieuŝytki, 9,1% lasy, zaś 6,1% bagna. Całkowite roczne obciąŝenie jeziora Podkówka azotem i fosforem (tab. 2), wyliczone według kryteriów podanych przez Giercuszkiewicz-Bajtlik (1990) wynosi 23,3 kg fosforu i 275,6 kg azotu, co w przeliczeniu na jednostkę powierzchni daje ładunek równy 0,337 g P/m 2 /rok i 3,983 g N/m 2 /rok, zaś w oparciu o wytyczne podane przez Lossowa i Gawrońską (1998): 20,9 kg fosforu i 242,4 kg azotu, co w przeliczeniu na jednostkę powierzchni daje ładunek 0,302 g P/m 2 /rok i 3,502 g N/m 2 /rok. Ładunek dopuszczalny i krytyczny dla tego jeziora wyliczony wg Vollenweidera (1968) wynosi odpowiednio: 0,046 g P/m 2 /rok i 0,093 g P/m 2 /rok oraz 0,748 g N/m 2 /rok i 1,496 g N/m 2 /rok. Porównanie rzeczywistego obciąŝenia jeziora azotem i fosforem z ładunkami wyliczonymi wg Vollenweidera (1968) wykazało, Ŝe obciąŝenie to przekracza kilkakrotnie nie tylko wartości dopuszczalne, ale takŝe krytyczne powodujące przyspieszoną eutrofizację. Zawartości związków biogenicznych wodach jeziora Podkówka były bardzo wysokie, sięgające 0,498 mg P/dm 3 i 8,18 mg N/dm 3 (tab. 1, rys. 2, rys. 3). O ogólnej ich ilości decydowały głównie formy organiczne. W badanym zbiorniku stwierdzono takŝe wysokie wartości BZT 5, dochodzące do 11,5 mg O 2 /dm 3 (tab. 1, rys. 4), znaczną zawartość ogólnego węgla organicznego, wahająca się przez cały okres wegetacyjny od 12,4 do 17,0 mg C/dm 3 (tab. 1), jak równieŝ niską przezroczystość wody wynosząca średnio 1,3 m (rys. 5). Jak wykazały badania, jezioro Podkówka jest zbiornikiem silnie zeutrofizowanym, co przy wysokim obcią- Ŝeniu ładunkiem zanieczyszczeń ze zlewni wskazuje na konieczność zastosowania działań ochronnych, polegających na zmniejszeniu obciąŝenia zewnętrznego. W sytuacji wysokiej podatności zbiornika na wpływy z zewnątrz (III kategoria) (Kudelska i in., 1994) dalsza zabudowa obszaru zlewni moŝe przyczynić się do jego całkowitej degradacji.