山形大学紀要（自然科学）第17巻第２号別刷
watersofLakeBaikalbeforeand after thethermalstratification development
Yasuhiro Satoh1,TakeshiSatoh1,YusukeTadaki2,YasunoriWatanabe2, HiroyukiUeno3,ToshiyaKatano3,Shin-ichiNakano3,KaoriAnbutsu4, MasakiKihira4,Osamu Mitamura4,Valentin Drucker5,YujiTanaka6,
Tetsuro Mimura7and Masahito Sugiyama8
Abstract
Solublereactivephosphorus(SRP),ammonia,nitrite+nitrateand Chl.a were measured in 24 surfacewatersfrom southern LakeBaikalin June2002,whilethose in 17 surfacewatersamplesfrom southern and partly centralLakeBaikalwere determined in Augustofthesameyear.Watertemperaturesindicated thatthesetwo monthswerebeforeand afterthethermalstratification development,respectively.
SRP and nitrite+nitratedecreased significantly and Chl.a,dominated by the
<10 μ m fraction,increased 3-fold from Juneto August,whileasimilarlow levelof ammoniawasrecorded in thesetwo months.Averagesand standard deviationsin Junewere0.18±0.04 μ moll-1forSRP,0.2±0.1 μ moll-1forammonia,3.3±0.7 μ mol l-1fornitrite+nitrateand 0.6±0.1 μ g l-1forChl.a.Thosein Augustweretracefor SRP,0.3±0.1 μ moll-1forammonia,0.4±0.1 μ moll-1fornitrite+nitrateand 1.7±0.5 μ g l-1forChl.a.TheseresultssuggestthatSRP and nitrite+nitrateweresupplied to thesurfacefrom deeperwatersby seasonalmixing and taken up by phytoplankton during thedevelopmentofthermalstratification.On theotherhand,thedistribution of ammonia in the surface water was independent from water movements, suggesting thattheammoniauptakeand regeneration wasin equilibrium atsuch a low concentrationsthroughouttheyear.
Nutrientand Chl.adistributionsin surfacewatersof LakeBaikalbeforeand after
thethermalstratification development
Yasuhiro Satoh1,TakeshiSatoh1,YusukeTadaki2,YasunoriWatanabe2, HiroyukiUeno3,ToshiyaKatano3,Shin-ichiNakano3,KaoriAnbutsu4, MasakiKihira4,Osamu Mitamura4,Valentin Drucker5,YujiTanaka6,
Tetsuro Mimura7and Masahito Sugiyama8 (Received February 16,2010)
(With 3 tablesand 2 figures)
1Faculty ofScience,YamagataUniversity,Yamagata,Japan
2Faculty ofScience,Tokyo Metropolitan University,Tokyo,Japan
3CMES,EhimeUniversity,Matsuyama,Japan
4SchoolofEnvironmentalScience,University ofShigaPrefecture,Hikone,Japan
5LimnologicalInstitute,Siberian Branch,Russian Academy ofScience,Irkutsk,Russia
6DepartmentofOcean Sciences,Tokyo University ofFisheries,Tokyo,Japan
7Faculty ofScience,NaraWomen'sUniversity,Nara,Japan
8GraduateSchoolofHuman EnvironmentalStudies,Kyoto University,Kyoto,Japan
Introduction
The water chemistry of Lake Baikal has long been studied by Russian scientists.A summary oftheirearlierstudieswasgiven in amonograph by Kozhov (1963), however, modern information on nutrients in Lake Baikal is limited.
Nagataetal.(1994)presented threeverticalprofilesforsolublereactivephosphorus (SRP) and nitrite+nitrate in southern Lake Baikal in late July 1992. SRP and nitrite+nitratewerealmostabsentin thesurfacelayer,increasing with depth up to 0.4 μ moll-1forSRP and 8 μ moll-1fornitrite+nitrateat50 m. Goldman etal. (1996)showed 11 verticalsectionsdown to 250 m forSRP and nitratefrom the southern end to thenorthern end ofLakeBaikalin July 1990.Thesouth basin was thermally stratified butthenorth basin wasnot,resulting in adramaticdifferencein nutrientdistribution from south to north: depletion ofnutrientsfrom thesurface layerin thesouth,whilevertically uniform and rich in thenorth. Watanabeand Drucker(1999)recorded phosphateand nitrite+nitratefrom thesurfaceto 50 m ata pelagicstation in thesouthern basin ofLakeBaikalin lateJuly 1992,showing that both nutrientswerealmostabsentfrom thesurface.SRP increased with depth to about0.3 μ moll-1at50 m and nitrite+nitrateto 7 μ moll-1. Dataon vertical profilesforSRP and nitratein southern LakeBaikalin March,Augustand October 1999 areavailablein Yoshidaetal.(2003).From theirprofiles,SRP in thesurface layerranged from almostzero in Augustand Octoberto 0.2 μ moll-1in March.
SRP increased to about0.3 μmoll-1below 50-100 m in allmonths.Nitratein the surfacelayervaried from almost0 μ moll-1in Augustto 5 μ moll-1in March.It increased to 5-6 μ moll-1below 100 m in allmonths. Averageconcentrations, 0.24±0.06 μ moll-1forammonia,0.04±0.02 μ moll-1fornitrite,0.34±0.08 μ moll-1 fornitrateand 0.02±0.01 μ moll-1fordissolved inorganicphosphorus,in 15 surface watersamplesfrom southern and partly centralLakeBaikalin August2002 are given in Kihiraetal.(2008).
Asshown above,someverticalprofilesofSRP and nitratein LakeBaikalare available. However, information on ammonia in the lake is extremely limited.
Furthermore, data on the basin wide horizontal distribution of nutrients is unavailableexceptforthe11 verticalsectionsby Goldman etal(1996)and the averageconcentrationsin Kihiraetal.(2008).Thepresentresultsprovidechanges in the horizontal distributions of SRP, ammonia, nitrite+nitrate and Chl.a in southern and partly central Lake Baikal in 2002, before and after thermal stratification development.
Materialsand methods
Twenty-fourbucketsurfacewatersampleswerecollected from southern Lake Baikalby scientistson board theRV ObruchevoftheLimnologicalInstituteSB RAS from 28 to 30 June2002 (Fig.1 upper).Similarly 17 samplesfrom southern and partofthecentralLakeBaikalwerecollected by scientistson board theRV Vereshaginoftheaboveinstitutefrom 24 to 31 Augustin thesameyear(Fig.1 lower). Watersampleswereimmediately filtered through pre-ignited Whatman GF/F glassfiberfilters(nominalporosity,0.7 μ m).Thefiltersand filtrateswere frozen on board ship in orderto carry outthechemicalanalysesin Japan.Chl.a wasdetermined by fluorometry (Model10-AU,TurnerDesigns,USA). Only a singleanalysisofChl.awasmadeateach station in JuneexceptforStn.24:
to evaluate the precision of the Chl.a analysis a four replicate analysis was Fig.1.Station locationsin LakeBaikalin June(upper)and August(lower)2002
