Preliminary characteristics of the chemical composition of the toplayer. bottom deposits in Lake Dejguny (Mazurskie Lake District)

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1 Limnological Review 5 (2005) Preliminary characteristics of the chemical composition of the toplayer bottom deposits in Lake Dejguny (Mazurskie Lake District) Renata Brzozowska*, Julita Dunalska*, Bogusław Zdanowski** *University of Warmia and Mazury, Chair of Environmental Protection Engineering Prawocheńskiego 1, Olsztyn Kortowo **Institute of Inland Fishery in Olsztyn, Oczapowskiego 10, Olsztyn Kortowo Abstract: Lake Dejguny has the surface area of ha and the max. depth of 45 m, and is situated in the Mazurskie Lake District. The lake s study concerned the top layer (5 cm) of the bottom deposits, sampled from various lake zones (littoral, sublittoral, profundal). The sediments were characterised as mineral. Silica dominated by quantity in all collected samples (45 95% SiO 2 in dry weight, d.w.). Other elements, measured in the highest quantities, were collected from the deepest site in the lake. The content of organic matter was rather low ( % d.w.), such as the content of iron and aluminium (to 4.25% Fe 2 O 3 in d.w. and to 1.35% Al 2 O 3 in d.w.) whereas calcium and carbonates were determined in average amounts (to 12.15% CaO in d.w. and to 14.65% CO 2 in d.w.). The quantities of total nitrogen (N) and phosphorus (P) were low; only in the sediments collected from the deepest site in the lake they amounted to 1.38% N in d.w. and 0.9% P 2 O 5 in d.w. Key words: bottom deposits, organic matter, calcium, phosphorus, nitrogen. Introduction and goal of the study Bottom deposits comprise one of the most important elements of the lake ecosystem. They function as a storage of allochthonous and autochthonous matter. However, in certain conditions the function may change and sediments become a source of nutrients (Kajak, 2001; Wiśniewski, 1995, Wiśniewski, 1999) that may eventually deteriorate the lake s trophic condition. Recognition of the chemical composition of the top-layer bottom deposits, i.e. in direct contact with water, may give crucial information about the potential for phosphorus (the most important nutritive element) storage. Beside the so-called sorptive capacity, caused by the occurrence of iron, aluminium and calcium compounds, silt minerals and organic matter in bottom deposits (Golterman, 1998; Gomez et al., 1999; Sarazin et al., 1995; Wiśniewski, 1995), the processes of phosphorus fixation and release from bottom deposits are influenced by many factors with the most important being oxygen content in the near-bottom waters (Brzozowska et al., 2001; Cerco, 1989; Gawrońska, 1994). Extensive studies of Lake Dejguny, aimed at the trophic condition general assessment, were undertaken due to the conception to re-introduce in the lake the European whitefish (Coregonus albula (L)). As bottom deposits in the lake were never studied, their analysis comprised one of the elements of an extensive environmental study. Therefore, the goal of the survey was to recognize the chemical composition of the top-layer bottom deposits in the different lake zones (littoral, sublittoral and profundal). Material and methods Lake Dejguny, situated in the Mazurskie Lake District, north of the Sterławki Wielkie village, has the surface area of ha and the max. depth of 45 m (IRŚ, 1953; Fig. 1). According to Choiński (1991), the surface area of the water table is a little smaller,

2 12 Renata Brzozowska, Julita Dunalska, Bogusław Zdanowski i.e ha. The lake is an experimental object of the Institute of Inland Fishery in Olsztyn and the Fishery Technical School in GiŜycko. With regard to the fishery function, the lake has been classified as the European whitefish type. Fig. 1. Localization of the bottom sediments examination stations in Lake Dejguny.

3 Preliminary characteristics of the chemical composition of the top-layer bottom deposits The top layer of the bottom deposits (5 cm thick) was collected with a Kajak s tube sampler, from 6 sampling sites (located on two Profiles) and from different depths (littoral 1 m, sublittoral 4.5 m, profundal 16 m) and from the deepest site in the lake (45 m) (Fig. 1). Sampling was repeated 4 times (April, June, July, November 2004). Measurements in fresh sediment included water content and dry weight. After drying at room temperature, the sediments were powdered in a porcelain mortar and the material was used to prepare weighed amounts for next analyses. Total P content was determined according to the methods of Golachowska (1977). Other measurements were done according to the methods of Januszkiewicz (1978). Results and discussion The bottom deposits collected from different zones of Lake Dejguny varied in the macroscopic scale by the look and water content. The littoral sediments were sandy or gravel-sandy, with low water content (approx. 22% on average) (Tab. 1). As the depth of sampling increased, more water was measured in the samples (in sublittoral approx. 32% on average in site 2 and 26% in site 5; in profundal 45% in site 3 and 66% in site 6), up to over 90% in the deepest site of the lake (Tab. 1) where the sediments were more muddy. After drying out, the sediments were light grey. Table 1. Mean water content and dry weight of the bottom deposits from various sampling sites on Lake Dejguny Sampling site Water content (%) Dry weight (%) 1 (littoral) P1 Profile 2 (sublittoral) (profundal) (littoral) P2 Profile 5 (sublittoral) (profundal) Deepest site The dominant component of the bottom deposits from all sampling sites was silica, comprising on average from over 44% SiO 2 in d.w. in the deepest site to approx. 95% SiO 2 in d.w. in littoral (Fig. 2). Similar contents of silica were measured by Januszkiewicz (1970) in the sediments of the Kaszuby lakes and by other authors in eutrophic lakes (Gawrońska, 1987, 1994; Januszkiewicz, Samulowska, 1978). Fig. 2. Mean amounts of the bottom sediments components in Lake Dejguny examination stations (in % d.w.).

4 14 Renata Brzozowska, Julita Dunalska, Bogusław Zdanowski Organic matter was the second, as for cent contribution, component only in the sediments of the deepest site (site 7), i.e. on average a little over 18% d.w. (Fig. 2). In shallower sites its contribution was lower and varied from 0.5% d.w. (No 1) to 9.46% d.w. (site 6). The lowest content of organic matter was measured in the littoral sediments and the highest in profundal of both Profiles and in the deepest site. Such results confirm the observations by Januszkiewicz and Samulowska (1978) that the particles of the sediment organic matter can be easily pushed down the slopes of the lake bowl, moved in the same direction as the water masses, and sunk in the holes of the bottom. Organic matter deposition in the deepest sites is additionally favoured by lower water temperatures in profundal and the resultant lower rate of mineralization processes. Organic matter content in bottom deposits and mineralization processes occurring in the sediments, have an effect on the amount of the sediment nitrogen which results from the fact that organic form is quantitatively the largest fraction of the sediment nitrogen (Zdanowski 1983; Tomaszek, Czerwieniec, 1995; Van Luijn et al., 1999). The significant positive correlation between the amounts of organic matter and nitrogen (r = 0.942, n = 24, p = 0.01) in the sediments of Lake Dejguny indicates deposition of nitrogen mainly in the organic form. Total N was measured in the sediments in small amounts (from 0.09% N in d.w. sites 1, 3 & 4 to 1.38% N in d.w.) (Fig. 2). Likewise, a significant correlation was found between the contents of organic matter and total P (r = 0.956, n=24, p = 0.01) that may indicate the important role of organic matter in phosphorus deposition in the sediments. The lake is rich in organic matter, as confirmed by the elevated values of both dissolved (7.5 mg C/l on average) and particulate (1.5 mg C/l on average) organic carbon in the water, which could stimulate that process. Phosphorus can be also deposited in the mineral form: bound with calcium, iron or aluminium (Gawrońska, 1994; Kentzer, 2001). The contents of total P in the sediments of Lake Dejguny were low (from 0.67 mg P/g d.w. in littoral to 1.68 mg P/g d.w. in profundal). The sediments from the deepest site contained more phosphorus (approx. 4 mg P/g d.w.) (Fig. 2). Phosphorus binding with iron depends on the oxygen conditions in the near-bottom waters (Boström et al., 1988; Marsden, 1989). In the examined lake, in littoral and sublittoral, the oxygen conditions were good whereas in the near-bottom waters over the deepest site oxygen concentration in the summer dropped below 2 mg O 2 /l (to 0.2 mg O 2 /l in July). The latter was followed by an increase of phosphate concentration (to mg P/l) and total iron amount (to mg Fe/l) (IRŚ, unpublished). This may be the evidence of the unfavourable phenomenon of internal water loading with phosphorus. Iron content in the sediments (approx. from 0.6% Fe 2 O 3 in d.w. on average in site 1 to 4.25% Fe 2 O 3 in d.w. in site 7) (Fig. 2) should be considered as low in comparison with other lakes (Januszkiewicz, 1970; Januszkiewicz, Samulowska, 1978). Despite that, iron may play an important role in the processes of phosphorus fixing in the bottom deposits of the examined lake, as shown by the significant positive correlation between iron and total P (r = 0.903, n = 24, p = 0.01). The Fe:P molar ratio in the bottom deposits of Lake Dejguny varied between 4.1 and 15.7, and the highest values (usually above 10) regarded the profundal sediments in site 3 and site 6. Jensen and Anderson (1992) share the opinion that the Fe:P molar ratio above 8.3 is equivocal to the dominance of the fixing processes whereas Søndergaard et al. (1993) provide the hypothesis that the balance between phosphorus fixing and release occurs at the ratio of approx. 10. Lower values of the Fe:P ratio in the sediments of the deepest site in Dejguny (from 7.5 to 8.1) indicate the possibility for limited phosphorus fixing in the sediments by iron oxides and hydroxides. Aluminium, alike iron, is an element that bounds phosphorus. Phosphorus complexes with aluminium are resistant to changes in the redox conditions (Gawrońska et al., 2001). In comparison with other lakes (Januszkiewicz, 1970; Januszkiewicz, Samulowska, 1978), in the bottom deposits of Lake Dejguny aluminium was measured in low amounts (from 0.03% Al 2 O 3 in d.w. in site 2 on average to 1.35% Al 2 O 3 in d.w. in site 6). Despite the significant positive correlation between the contents of aluminium and phosphorus (r = 0.541, n = 24, p = 0.01), it seems that the quantity of aluminium is not important with regard to phosphorus binding in the bottom deposits. With regard to phosphorus, calcium is an important element of so-called sorptive complex of the bottom deposits. The main environmental factor having effect on phosphorus precipitation with cal-cium is water reaction. At ph phosphate ions precipitate as Ca 3 (PO 4 ) 2 (Golterman, 1998; Kent-zer, 2001). In Lake Dejguny water

5 Preliminary characteristics of the chemical composition of the top-layer bottom deposits reaction during the research oscillated between 7.4 and 8.5 (IRŚ, unpublished) which could favour the processes of phosphorus binding with calcium in the sediments. The quantities of calcium found in the top-layer se-diments (from 1.25% CaO in d.w. in site 1 on ave-rage, to 12.15% CaO in d.w. in site 6) (Fig. 2) should be considered as average (Gawrońska, 1987; Janusz-kiewicz, Samulowska, 1978). The significant corre-lation between calcium and total P (r = 0.746, n = 24, p = 0.01) in the examined sediments may confirm the role of calcium in phosphorus deposition. Carbonates were found to be a component occurring in the examined bottom deposits in higher quantities (from 0.90% CO 2 in d.w. in site 4 on average to 14.45% CO 2 in d.w.) (Fig. 2). The significant positive correlation between the content of calcium and carbonates (r = 0.914, n = 24, p = 0.01) confirms the thesis by Gawrońska (1987) and Januszkiewicz, Samulowska (1978) that calcium is depo-sited in lake sediments mainly in the form of carbo-nate. Other mineral components of the sediments, like magnesium or manganese, were detected in the examined sediments in low amounts The (Fig. top layer 2). of the bottom deposits of Lake Dejguny can be characterised as mineral. The quantities of the individual sediments components are similar in both examined Profiles. The dominant, as to quantity, component in the sediments in all sampling sites was silica. The amounts of organic matter and nutrients were rather small. The contents of the main components determining phosphorus deposition in the sediments were rather low (iron, aluminium, organic matter) or average (calcium), as compared to the sediments in other lakes. Calcium was deposited in the examined sediments mainly in the form of carbonate. The Fe:P ratio was not high either, although in the profundal sediments in sites 3 and 6, it was high enough for effective precipitation of phosphorus with iron in aerobic conditions. References Boström B., Andersen J. M., Fleischer S., Jansson M., 1988, Exchange of phosphorus across the sedimentwater interface, Hydrobiologia 170, Brzozowska R., Gawrońska H., Grochowska J., Lossow K., 2001, Nutrient release from the bottom sediments of the artificially aerated Lake Długie. Limnological Review, 1, Cerco C. F., 1989, Measured and modelled effects of tem-perature, dissolved oxygen and nutrient concentration on sediment-water nutrient exchange, Hydrobiologia 174, Choiński A., 1991, Katalog jezior Polski, Wydawnictwo Naukowe UAM, Poznań. Gawrońska H., 1987, Chemizm osadów dennych jeziora Mutek poddanego eksperymentowi sztucznego napowietrzania, Rocz. Nauk. Rol., H, 101, Gawrońska H., 1994, Wymiana fosforu i azotu pomiędzy osadami a wodą w jeziorze sztucznie napowietrzanym, Acta Acad. Agricult. Tech. Olst. Protectio Aquarum et Piscatoria, 19, Gawrońska H., Brzozowska R., Grochowska J., Lossow K., 2001, Effectiveness of PAX and PIX coagulants in phosphorus reduction in a lake laboratory experiments, Limnological Review, 1, Golachowska J., 1977, Prosta i szybka metoda oznaczania fosforu w osadach dennych jezior. Rocz. Nauk. Rol. H, 98, Golterman H. L., 1998, The distribution of phosphate over iron-bound & calcium-bound phosphate in stratified sediments, Hydrobiologia, 364, Gomez E., Durillon C., Rofes G., Picot B., 1999, Phosphate adsorption and release from sediment of brackish lagoons: ph, O 2 and loading influence, Wat. Res. 33 (10), IRŚ Olsztyn, 1953, Mapa batymetryczna i dane morfometryczne jeziora Dejguny. Januszkiewicz T., 1970, Skład osadów głębinowych grupy jezior na Pojezierzu Kaszubskim. Rocz. Nauk. Rol. 92-H-1, Januszkiewicz T., 1978, Studia nad metodą analizy współczesnych osadów dennych jezior, Zesz. Nauk. ART, Olsztyn, 187(8), Januszkiewicz T., Samulowska B., 1978, Chemizm współczesnych osadów dennych jeziora Wadąg k/olsztyna, Zesz. Nauk. ART, Olsztyn Ochrona Wód i Rybactwo Śródlądowe, 8, Jensen H. S., Anderson F. Ø., 1992, Importance of temperature, nitrate and ph for phosphate release from aerobic sediment of four shallow eutrophic lakes. Limnol. Oceanogr., 37, Kajak Z., 2001, Hydrobiologia limnologia, Ekosystemy wód śródlądowych, PWN, Warszawa. Kentzer A., 2001, Fosfor i jego biologicznie dostępne frakcje w osadach jezior o róŝnej trofii. Wyd. UMK, Toruń, Marsden M. W., 1989, Lake restoration by reducing external phosphorus loading: the influence of sediment phosphorus release, Freshwater Biology, 21, Sarazin G., cois Gaillard J.-F., Philippe L., Rabouille Ch., 1995, Organic matter mineralization in the pore water of a eutrophic lake (Aydat Lake, Puy de Dôme, France). Hydrobiologia, 315,

6 16 Renata Brzozowska, Julita Dunalska, Bogusław Zdanowski Søndergaard M., Kristensen P., Jeppesen E., 1993, Eight years of internal phosphorus loading and changes in the sediment phosphorus profile of Lake Søbygaard, Denmark, Hydrobiologia, 253, Tomaszek J. A., Czerwieniec E., 1995, Znaczenie procesu denitryfikacji dla bilansu azotu w ekosystemach wodnych. In: M. Zalewski (ed.), Procesy biologiczne w ochronie i rekultywacji nizinnych zbiorników zaporowych, Łódź. Van Luijn F., Boers P. C. M., Lijklema L., Sweert J. P. R. A., 1999, Nitrogen fluxes and processes in sandy and muddy sediments from a shallow eutrophic lake, Wat. Res. 33(1), Wiśniewski R. J., 1995, Rola zasilania wewnętrznego w eutrofizacji zbiorników zaporowych. Bibl. Monit. Środ. Łódź, Wiśniewski R., 1999, Próby inaktywacji fosforanów w osadach dennych i zahamowania zakwitów sinic w J. Łasińskim jako potencjalne metody rekultywacji, Mat. I Kraj. Konf. Nauk. Tech. nt. Postęp w inŝynierii środowiska, Polańczyk 30 IX 2 X, Zdanowski B., 1983, Ecological characteristics of lakes in north-eastern Poland versus their trophic gradient. Part IV. Chemistry of bottom sediments in 37 lakes. Ekol. Pol. 31(2), Streszczenie Obiektem badań było jezioro Dejguny (pow. 765,3 ha, gł. max. 45 m), połoŝone na Pojezierzu Mazurskim (ryc. 1). Podjęte badania osadów były częścią kompleksowych badań jeziora Dejguny, słuŝących do ogólnej oceny stanu troficznego. Ze względu na fakt, Ŝe dotychczas nie analizowano osadów dennych tego jeziora, celem badań było rozpoznanie składu chemicznego powierzchniowej warstwy osadów. Badaniami objęto warstwę osadów jeziora o miąŝszości 5 cm, pochodzącą z róŝnych stref jeziora (litoral, sublitoral, profundal). Próbki osadów pobierano czerpaczem rurowym Kajaka na siedmiu stanowiskach badawczych (ryc. 1). Osady pobrane z róŝnych stref jeziora róŝniły się między sobą stopniem uwodnienia i zawartością suchej masy (tab. 1) i miały charakter mineralny. Składnikiem dominującym ilościowo w osadach wszystkich stanowisk była krzemionka (45 95% SiO 2 w s.m.) (ryc. 2). Pozostałe składniki z reguły występowały w maksymalnych zawartościach w osadach pobranych z najgłębszego miejsca jeziora (st. 7). Ilości poszczególnych komponentów w osadach z obydwu profili badawczych były zbliŝone (ryc. 2). Zawartości materii organicznej były niewielkie (0,85 18,73% s.m.), podobnie jak ilości Ŝelaza i glinu (do 4,25% Fe 2 O 3 w s.m. i do 1,35% Al 2 O 3 w s.m.), a wapnia i węglanów przeciętne (do 12,15% CaO w s.m. i do 14,65% CO 2 w s.m.). Ilości azotu ogólnego i fosforu ogólnego były niskie, jedynie w osadach pobranych z najgłębszego miejsca jeziora zawartości sięgały do 1,38% N w s.m. i 0,9% P 2 O 5 w s.m. (ryc. 2). Stwierdzone wysoce istotne dodatnie korelacje pomiędzy zawartością materii organicznej i fosforu ogólnego (r = 0,956; n=24, p = 0,01), wapnia i fosforu ogólnego (r = 0,746, n = 24, p = 0,01), glinu i fosforu ogólnego (r = 0,541, n = 24, p = 0,01) oraz Ŝelaza i fosforu ogólnego (r = 0,903, n = 24, p = 0,01) mogą wskazywać na waŝną ich rolę w deponowaniu tego pierwiastka biogenicznego w osadach badanego jeziora. Pomiędzy zawartością wapnia i węglanów równieŝ występowała wysoce istotna dodatnia korelacja (r = 0,914, n = 24; p = 0,01), co potwierdza, Ŝe wapń odkładany jest w osadach badanego zbiornika głównie w postaci węglanu.