CHANGES IN THE QUALITY OF WATER IN BRDOWSKIE LAKE IN

J. Elementol. 2010, 15(4): 705 712 705 CHANGES IN THE QUALITY OF WATER IN BRDOWSKIE LAKE IN 1997-2006 Ryszrd Stniszewski, Józef Szoszkiewicz Chir of Ecology nd Environmentl Protection Poznñ University of Life Sciences Abstrct Most lkes in Polnd re shllow nd vulnerble to degrdtion mostly due to lke morphology nd lndscpe structure. Other fctors, like dischrged sewge, internl loding nd humn ctivities in the wtershed re lso importnt. During studies on Brdowskie Lke, wter smples were tken twice yer (spring nd summer seson) from the surfce lyer nd nlyses of soluble rective phosphtes, totl, nitrtes, conductivity, five-dy biochemicl oxygen demnd, chlorophyll, dry mss of seston nd were undertken. Brdowskie Lke is situted in Kujwskie Lkelnd nd its ctchment bsin covers bout 155.3 km 2. The littorl vegettion is dominted by reed bed with minor presence of other tx. The lke is very susceptible to degrdtion (morphology, griculturl lnds, housing) nd hs severl potentil sources of pollution, e.g. Noteæ River, nmeless strem nd summer houses. In generl, wter qulity of the lke ws better during the spring seson, especilly in terms of chlorophyll nd dry mss of seston concentrtions. In 1997- -2006, the level of conductivity ws very chngeble with the mximum vlues observed in 1999-2001. Significnt correltions between some prmeters in certin sesons of the yer were found, e.g. between chlorophyll nd during spring nd totl nd phosphtes in summer. The impct of wter level fluctutions on wter qulity prmeters, like totl nd chlorophyll ws observed. According to the results, the qulity wter in Brdowskie Lke is improving. After biologicl wstewter tretment plnt in the ctchment hd opened, the rte of slts flowing into the lke with sewge ws reduced. Key words: wter qulity indictors,, Brdowskie Lke, Kujwskie Lkelnd, Province of Wielkopolsk, wter level fluctutions. dr in. Ryszrd Stniszewski, Chir of Ecology nd Environmentl Protection, Poznn University of Life Sciences, Pi¹tkowsk 94C, 60-649 Poznñ, Polnd, phone: 8466522, e-mil: erstn@up.poznn.pl

706 ZMIANY JAKOŒCI WÓD JEZIORA BRDOWSKIEGO W LATACH 1997-2006 Abstrkt Wiêkszoœæ jezior w Polsce to jezior p³ytkie i podtne n degrdcjê. Jej g³ównym powodem s¹ n ogó³ morfologi zbiorników orz niekorzystn struktur u ytkowni zlewni. Inne czynniki, tkie jk dop³yw œcieków, ³dunek wewnêtrzny i dzi³lnoœæ gospodrcz, mj¹ równie istotne znczenie. Podczs bdñ Jez. Brdowskiego próby wody pobierno 2 rzy w roku (wiosn¹ i jesieni¹) z wrstwy powierzchniowej i wykonywno oznczeni tkich wskÿników, jk: fosfor rektywny, fosfor ogólny, zot zotnowy, przewodnoœæ elektrolityczn w³œciw, piêciodobowe zpotrzebownie tlenu, chlorofil, such ms sestonu i widzilnoœæ kr¹ k ego. Jezioro Brdowskie usytuowne n Pojezierzu Kujwskim m zlewniê o pow. ok. 155,3 km 2. Litorl zdominow³ trzcin, udzi³ innych tksonów roœlin jest m³y. Akwen brdzo podtny n degrdcjê (wrunki morfologiczne, du y udzi³ terenów wykorzystywnych rolniczo, zbudowni wiejskie) m wiele potencjlnych Ÿróde³ znieczyszczeni wody, jk np. rzek Noteæ, ciek bez nzwy, domki letniskowe z nieuregulown¹ gospodrk¹ wodno-œciekow¹ orz pobliskie zbudowni wiejskie. Zzwyczj jkoœæ wody by³ wy sz n wiosnê, szczególnie odnoœnie do stê eñ chlorofilu orz suchej msy sestonu. W ltch 1997-2006 poziom przewodnoœci elektrolitycznej by³ brdzo zmienny, mksimum przypd³o n lt 1999-2001. Stwierdzono istotne korelcje miêdzy niektórymi wskÿnikmi w zle noœci od pory roku, jk w przypdku chlorofilu i widzilnoœci kr¹ k ego wiosn¹ i fosforu ogólnego i fosfornów rozpuszczonych ltem. Zobserwowno wp³yw whñ poziomu lustr wody n niektóre wskÿniki jkoœci (fosfor ogólny, chlorofil ). Uzyskne wyniki œwidcz¹ o poprwie jkoœci wód Jez. Brdowskiego. Po uruchomieniu oczyszczlni œcieków w Poloniszu obni y³ siê np. poziom przewodnoœci elektrolitycznej, co œwidczy o ogrniczeniu dop³ywu ró nych soli do wód kwenu. S³ow kluczowe: wskÿniki jkoœci wody, fosfor, Jezioro Brdowskie, Pojezierze Kujwskie, Wielkopolsk, whni poziomu lustr wody. INTRODUCTION Most lkes in Polnd (bout 60%) re shllow. They often lie in lowlnds nd re susceptible to degrdtion mostly due to lke morphology nd lndscpe structure (CHOIÑSKI 1995). In shllow lkes, both nd volume of wter cn strongly ffect trophic conditions (HAKANSON 2005, STANISZE- WSKI et l. 2009). Other fctors tht influence wter qulity re dischrged sewge, internl loding, griculturl ctivities, industry, climtic conditions, vegettion structure, soil conditions, elevtion nd even longitude (HEATHWAITE 1995, SAPEK 1998, SŘNDERGAARD et l. 1999, NÕGES et l. 2003, HAKANSON 2005 nd others). The influence of some other fctors on Brdowskie Lke, such s inflow of wstewter from houses (the western shore), wstewter fter rinfll (the estern shore) nd from summer houses is difficult to ssess.

707 MATERIAL AND METHODS Wter smples were tken from surfce lyer of the lke twice yer (spring nd summer 1997-2006). The following nlyses were undertken: soluble rective phosphtes smples filtered using 0.45 µm pore size, Ascorbic Acid Method; totl Acid Persulfte Digestion Method; nitrtes smples filtered using 0.45 µm pore size, Cdmium Rection Method; conductivity electrometriclly; five-dy biochemicl oxygen demnd (BOD 5) Winkler method, summer only; chlorophyll ; dry mss of seston;. Wter qulity ws evluted in ccordnce with the regultions imposed by the Ministry for the Environment (Rozporz¹dzenie Ministr Œrodowisk 2008). Sttisticl evlution ws mde using the progrmme Sttistic (Sttsoft Inc. 2004). RESULTS AND DISCUSSION Brdowskie Lke is shllow lke (mximum of 5 m, verge of 2.2 m nd the ctchment bsin re of 155.3 km 2 ) situted in Kujwskie Lkelnd (the Noteæ River wtershed) nd covers n re of 198.2 h; its ctchment bsin covers bout 155.3 km 2 (Rport o stnie œrodowisk 2005). Due to its morphology nd lndscpe structure of the ctchment bsin (griculturl lnds 74%, housing 10%) s well s prevlence of rble lnds in the vicinity of the lke shores, Brdowskie Lke is very suseptible to degrdtion. Potentil sources of pollution re tributries (eg. the Noteæ River in the northern prt of lke, nmeless strem flowing from the south-western direction) nd summer houses on the western nd estern lke shore. Littorl vegettion is dominted by reed bed (clss Phrgmitete, Tx. et Preisg. 1942) with minor presence of perfolite pondweed (Potmogeton perfolitus L.) nd other plnt species from the clss of Potmete (Tx. et Preisg. 1942). Phytoplnkton is sometimes strongly dominted by blue-green lge, especilly during summer, when they cuse lgl blooms (STANISZEWSKI, SZOSZKIEWICZ 2000, Rport o stnie œrodowisk 2005, STANISZEWSKI et l. 2005). It is lke with good conditions for crp brem, whose the potentil

708 fish yield is bout 35 kg per 1 h, but other species like common blek, roch nd perch re lso present. In generl, wter qulity ws better during spring seson (Tbles 1, b). The highest concentrtions of totl in Brdowskie Lke were ob- Chrcteristics of ( mg P dm 3) ( µg Chl dm 3) (m) Dry mss of seston ( mg DMS dm 3) Soluble rective phosphtes ( mg PO4 dm 3) Nitrtes ( mg N-NO3 dm 3) Conductivity ( ms cm 1 ) selected wter qulity prmeters of spring mesurements Men vlues Tble 1 Brdowskie Lke in 1997-2006, Stndrd devition 0.08 0.04 24.69 12.42 0.97 0.40 10.40 5.31 0.11 0.06 0.09 0.07 0.714 0.227 Chrcteristics of ( mg P dm 3) ( µg Chl dm 3) (m) Dry mss of seston ( mg DMS dm 3) Soluble rective phosphtes ( mg PO4 dm 3) Nitrtes ( mg N-NO3 dm 3) Conductivity ( ms cm 1) selected wter qulity prmeters of summer mesurements Men vlues Tble 1b Brdowskie Lke in 1997-2006, Stndrd devition 0.10 0.05 39.83 15.79 0.79 0.16 17.85 7.73 0.17 0.10 0.08 0.11 0.685 0.267 BOD 5 (mg O2 dm 3) 5. 0 2. 0

709 Tble 1c Wter qulity ctegories of Brdowskie Lke in 1997-2006 evluted on the bsis of verge results (spring nd summer surveys) of totl, chlorophyll, nd conductivity in the surfce lyer of wter (five ctegories ccording to R ozporz¹dzenie Ministr Œrodowisk 2008) Yer 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 II IV IV II Conductivity The worst ctegory ssigned II served in summer 2005 but in spring they were lower (Tbles 1, b). nd dry mss of seston behved similrily. During the tests, ws sometimes lower thn 60 cm (spring 1998, summer 2003 nd 2005) nd once ws over 180 cm (182 cm, spring 2006), which ws ttrobutble to n unusully low concentrtion of chlorophyll in wter (4.28 µg Chl dm 3 ). Concentrtion of soluble rective phosphtes in lke wter rnged from 0.01 to 0.36 mg PO 4 dm -3 nd showed slightly incresing tendency with mximum in summer 2006. It ws prtilly relted to wter level fluctutions but it ws not sttisticlly significnt. The results showed, tht presence of nitrtes in surfce lyer ws generlly higher in spring before prt of nitrogen ws incorported in biomss of phytoplnkton nd mcrophytes. The highest concentrtions of nitrtes were observed in the yer 2003 during spring (bout 0.20 mg N-NO 3 dm 3 ) nd summer (0.40 mg N-NO 3 dm 3 ) mesurements were concentrtion of seston ws lso very high. Results obtined in summer surveys were very diverse nd it gve high vlue of stndrd devition for nitrtes (Tble 1b). In the yers 1997-2006 the conductivity of lke wters ws very chngeble. During spring the highest vlues (> 0 ms cm 1 ) were observed in the yers 1999-2001 nd the lowest in the yer 2006 (< 0.500 ms cm 1 ). According to summer surveys the highest vlue (> 0 ms cm 1 ) ws mesured in the yer 1999 nd very low in the yers 2002-2006, one yer

710 fter sewge tretment plnt in Polonisz hd strted-up (31 st of Mrch 2001). Conductivity showed positive but not sttisticlly significnt correltion with wter level fluctutions. Anlyses of biochemicl oxygen demnd were mde during summer period nd results rnged from 2.0 mg O 2 dm 3 to 8.0 mg O 2 dm 3. According to physico-chemicl prmeters from the yer 2006 the Brdowskie Lke wters cn potentilly fit stndrds of second ctegory of wter qulity. Tking into ccount ctul criteri, during t lest eight yers of surveys the sitution ws fr from this. Min problem ws low vlues of nd high conductivity (Tble 1c). Presence of significnt correltions between some trophic prmeters in certin yer seson were found (Tbles 2, 3). During spring seson strong correspondence between concentrtion of chlorophyll nd ws Brdowskie Lke liner correltion mong trophic prmeters for spring mesurements ( p < 0.05, N = 10) Soluble rective phosphtes Tble 2 the yers 1997-2006, Dry mss of seston 0.58-0.47 0.54-0.51 Soluble rective phosphtes -0.43 0.38-0.61 1.00-0.84* 0.62-0.50 Dry mss of seston * sttisticlly significnt Brdowskie Lke liner correltion mong trophic prmeters for summer mesurements ( p < 0.05, N = 10) Soluble rective phosphtes Tble 3 the yers 1997-2006, Dry mss of seston 1.00 0.70 * 0.61-0.64* 0.52 Soluble rective phosphtes 0.05-0.34 0.08-0.61 0.58 1.00-0.65* Dry mss of seston * sttisticlly significnt

found. In summer time reltions between totl nd phosphtes, totl nd wter clrity nd lso between nd dry mss of seston. Strong correltions between wter clrity nd trophic prmeters were found by other uthors in erlier studies (CARLSON 1977, MAN- DAVILLE 2000 nd others). In surfce wters of Brdowskie Lke the impct of wter level fluctutions on wter qulity prmeters ws not strong nd only in cse of trophic prmeters significnt correltions were found. Especilly in cse of chlorophyll concentrtion in spring (positive correltion) nd totl concentrtion in summer (negtive correltion) Tble 4. 711 Tble 4 Liner correltion between wter tble level nd trophic prmeters, spring (p < 0.05, N = 8) nd summer mesurements ( p < 0.065, N = 8), Brdowskie Lke in the yers 1999-2006 Wter tble spring Wter tble summer * sttisticlly level level significnt Soluble rective phosphtes Dry mss of seston -0.57-0.34 0.71 * -0.53 0.32-0.72* -0.70-0.09 0.44-0.63 CONCLUSIONS 1. Brdowskie Lke wters studied in the period 1997-2006 hve hd rther poor qulity but results from yers 2004 nd 2006 proved, tht ccording to physico-chemicl prmeters the lke hs potentil to chieve second ctegory of wter qulity. 2. Since the yer 2002 the decrese of wter conductivity hs been found nd it ws one yer fter strt-up of biologicl wste wter tretment plnt in lke ctchment, which probbly limited the rte of slts inflowing to lke with sewges. 3. Influence of wter level fluctutions on wter qulity prmeters ws observed but only in cse of totl concentrtion nd wter clrity it ws significnt. REFERENCES CARLSON R. E. 1977. A trophic stte index for lkes. Limnol. Ocenogr., 22(2): 361-369. CHOIÑSKI A. 1995. Physicl limnology of Polnd. Wyd. Nuk. UAM, Poznñ: 298 ss. HACH DR/2000. 2004. Procedure mnul 2004. HACH Compny USA, 798 ss.

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