© Acta hydrotechnica 21/35 (2003), Ljubljana
ISSN 1581-0267
87
UDK/UDC: 519.61/.64:546.49:556.55 Prejeto/Received: 7. 11. 2003
Kratki znanstveni prispevek – Preliminary scientific paper Sprejeto/Accepted: 30. 11. 2004
MODELIRANJE HIDRODINAMIKE IN TRANSPORTA ŽIVEGA SREBRA V
VELENJSKEM JEZERU – 1. DEL: ŽIVO SREBRO V JEZERSKI VODI
MODELLING OF HYDRODYNAMICS AND MERCURY TRANSPORT IN
LAKE VELENJE – PART I: MERCURY IN LAKE WATER
Jože KOTNIK, Milena HORVAT, Vesna FAJON, Martina LOGAR, Nives OGRINC
Velenjsko jezero se nahaja v Šaleški dolini, v eni najbolj onesnaženih slovenskih regij. Ve čja vira
onesnaženja sta dva: premogovna termoelektrarna v Šoštanju in Rudnik Velenje. Cilj te študije je
bil ugotoviti transport in distribucijo živega srebra v Velenjskem jezeru. V preteklosti so bile
posledice odlaganja premogovega pepela in odto čne vode z odlagališ ča pepela posebne kemi čne
zna čilnosti jezerske vode, kot so na primer visoke pH vrednosti (10–12) in visoka vsebnost težkih
kovin. Z uvedbo zaprtega kroga transportnega sistema pepela v letu 1995 se je kakovost vode hitro
popravila. Da bi ugotovili novejše vire živega srebra v Velenjskem jezeru, smo izmerili
koncentracije celokupnega živega srebra in metil-živega srebra na razli čnih okoljskih vzorcih (na
dotoku v jezero, na iztoku, v deževnici, sedimentu itn.). Rezultati so pokazali, da so glavni vir živega
srebra v jezeru jezerski pritoki in padavine. Koncentracije živega srebra in metil-živega srebra so v
jezerski vodi izredno nizke (celokupno živo srebro: 0,2–2,7 ng/L; celokupno metil-živo srebro: 20–
86 pg/L) in so primerljive z nekontaminiranimi jezeri po svetu. Koncentracije celokupnega in
metiliranega živega srebra smo merili na površini in na razli čnih globinah, ugotavljali pa smo
kroženje živega srebra, transport in kemi čne spremembe ter tudi za kalibracijo, preverjanje
matemati čnega modela za simulacije kroženja živega srebra v Velenjskem jezeru, kar bo
podrobneje opisano v 2. delu prispevka. V 1. delu podajamo le kratek povzetek o izotopski sestavi
jezerske vode ter vsebnosti Hg. Podatki o izotopski sestavi vode so bistvenega pomena za validacijo
in verifikacijo modela, opisanega v drugem delu.
Klju čne besede: živo srebro, metil-živo srebro, matemati čno modeliranje, sladkovodno jezero
Lake Velenje is located in one of the most polluted regions in Slovenia, the Šalek Valley. There are
two major sources of pollution: the coal-fired thermal power plant in Šoštanj (ŠTPP) and the coal
mine in Velenje. The aim of our study was to establish the transport and distribution of mercury in
the Lake Velenje. In the past, dumping of coal ash directly into Lake Velenje and drainage water
from the ash disposal site resulted in unique chemical characteristics of the lake water, such as very
high pH (10–12) and high concentrations of heavy metals. The introduction of a closed cycle ash
transport system in 1995 resulted in a very fast recovery of the lake water quality. With the aim of
establishing recent sources of mercury in Lake Velenje, total mercury and methylmercury
concentrations were measured in different environmental samples (lake inflows, outflow, rainwater,
sediments, etc.). The results show that the major sources of mercury in Lake Velenje are lake
inflows and wet deposition. Total mercury and methylmercury concentrations in the water column
are very low (total mercury: 0.2–2.7 ng/L; methylmercury: 20–86 pg/L) and can be compared to
other non-contaminated freshwater lakes. Total mercury and methylmercury concentrations were
measured at the surface and at different depths to establish mercury cycling, its transport and
chemical transformations, and for calibration and verification of a mathematical model for mercury
cycling simulations in Lake Velenje, which is in detail described in Part 2. In Part 1 only short
summary on lake water isotopic composition and Hg content is given. Data about isotopic
composition of lake water are essential for validation and verification of the hydrodynamic model
described in Part 2.
Key words: mercury, methylmercury, mathematical modelling, freshwater lake

Kotnik, J. et al.: Modeliranje hidrodinamike in transporta živega srebra v Velenjskem jezeru – 1. del: živo srebro v
jezerski vodi – Modelling of Hydrodynamics and Mercury Transport in Lake Velenje – Part I: Mercury in Lake Waters
© Acta hydrotechnica 21/35 (2003), 87–103, Ljubljana
88
1. UVOD
Onesnaženje zraka v bližini premogovnih
termoelektrarn vpliva na celotni ekosistem ter
tudi na človekovo zdravje. Sladke vode so
pomemben del katerega koli ekosistema.
Povišana koncentracija živega srebra v
atmosferi pretežno vpliva na vodna telesa, in
sicer neposredno z atmosferi čnim usedanjem
ali posredno z vtoki površinskih ali podzemnih
voda. Tretjino slovenske elektrike proizvajajo
premogovne termoelektrarne, med katerimi je
Termoelektrarna Šoštanj (TEŠ) najve čja, s
skupno proizvodnjo elektri čne energije 775
MW (slika 1). V tem prispevku posve čamo
pozornost  porazdelitvi živega srebra v
bližnjem Velenjskem jezeru. Obmo čje jezera
se namenja rekreativnim dejavnostim
(ribarjenja, plavanja itn.). Za ugotavljanje
vsebnosti in porazdelitve živega srebra ter
kroženja Hg v Velenjskem jezeru smo
uporabili dva pristopa.
1. INTRODUCTION
Air pollution in the vicinity of coal-fired
thermal power plants affects the whole
ecosystem as well as human health. Fresh
waters are a very important part of any
ecosystem. Elevated concentrations of
mercury in the atmosphere mainly affect water
bodies either directly through wet and dry
deposition or indirectly by surface and ground
water inflows. One third of Slovenian
electricity is produced by coal-fired thermal
power plants, among which the biggest one is
the Šoštanj Thermal Power Plant (ŠTPP) with
a common power of 775 MW (Figure 1). In
this work attention was devoted to mercury
distribution in nearby Lake Velenje. The lake
is considered to be a recreational resource (e.g.
fishing, swimming etc.). To establish mercury
levels and its distribution in Lake Velenje and
Hg cycling in the lake, two approaches were
used.
Slika 1. Karta Slovenije s Šaleško dolino.
Figure 1. Map of Slovenia with the Šalek Valley.

Kotnik, J. et al.: Modeliranje hidrodinamike in transporta živega srebra v Velenjskem jezeru – 1. del: živo srebro v
jezerski vodi – Modelling of Hydrodynamics and Mercury Transport in Lake Velenje – Part I: Mercury in Lake Waters
© Acta hydrotechnica 21/35 (2003), 87–103, Ljubljana
89
Z monitoringom smo želeli ugotoviti
nedavne vire in vsebnost živega srebra v
okolju. Izmerjene podatke smo nato uporabili
za modeliranje transporta živega srebra in
njegovo porazdelitev v Velenjskem jezeru.
Hidrodinami čni in transportni model smo
uporabili iz ve č razlogov. Prvi razlog je bil, da
je bilo zaradi visoke vrednosti pH jezero do
1995 biološko mrtvo. Po letu 1995 se je zaradi
nove transportne tehnologije pepela jezerska
voda zelo hitro popravila. Drugi č, Velenjsko
jezero je zaprt sistem, na katerega dotoki in
iztoki ne vplivajo bistveno, kar je poenostavilo
hidrodinami čne izra čune, modelno kalibracijo
in preverjanje. Poleg tega je velika koli čina
izmerjenih podatkov kakovosti jezerske vode
in zraka v okolici jezera zmanjšala napake, ki
bi jih v modelu povzro čale aproksimacije.
Dobro poznane so tudi meteorološke razmere
v okolici jezera. In nazadnje, na obmo čju je
prisotno to čkovno onesnaženje, ki je dobro
poznano in predstavlja razli čne stopnje
potencialne nevarnosti za okolje in človekovo
zdravje, tako posredno kot neposredno.
Ker postopke vzor čenja, analiti čne metode
in rezultate podrobneje opisujemo drugje
(Kotnik et al., 1999; 2001), tukaj podajamo
samo nekaj temeljnih rezultatov o vsebnosti
živega srebra v jezeru in na dotokih v jezero
(preglednica 1).
Through monitoring, we wished to establish
recent sources and mercury levels in the
environment. The measured data were then
used further for modeling of mercury transport
and distribution in Lake Velenje.
The application of a hydrodynamic and
transport model to Lake Velenje was done for
several reasons. First, until 1995, the lake was
biologically dead, because of very high pH.
After that year, ŠTPP's new ash transport
technology resulted in a very fast recovery of
the lake water quality. Second, Lake Velenje is
a closed system with very little influence on
water cycling from inflows and outflow, which
simplified hydrodynamic calculations, model
calibration and verification. In addition, lots of
measured data of lake water quality and air
quality in the surroundings of the lake reduced
errors that would have been introduced into
the model by approximations. Meteorological
conditions in the vicinity of lake are also well
known. Finally, there is a point source of
pollution, which is well known and which
represents a potential hazard to the
environmental and human health, both directly
and indirectly, through several mechanisms.
Since sampling procedures, analythical
methods and results are in more detail
described elsewhere (Kotnik et al., 1999;
2001) only some basic results about mercury
content in the lake and its inflows are given in
Table 1.
Preglednica 1. Koncentracija razli čnih vrst živega srebra na površini in v vodnem stolpu
Velenjskega jezera – pomladne in zimske razmere (v ng/L).
Table 1. Concentration of different mercury species in surface and water column
of Lake Velenje – spring and winter conditions (in ng/L).
Mesto – Location
Celokupni Hg –
Total Hg
Celokupni MeHg –
Total MeHg
Povpre čje v vodnem stolpu – Average in
water column (Lake I; n = 16)
1.24 0.6197
Dotok Lepene – Lepena inflow (n = 3) 2.68 0.0540
Dotok Sopote – Sopota inflow (n = 3) 1.36 0.0680
Lepena (n = 3) 4.34 0.1470
Sopota (n = 3) 2.29 0.1010
Pomlad – Spring
Iztok – Outflow (n = 3) 1.64 0.0390
Povpre čje v vodnem stolpu – Average in
water column (Lake I; n = 16)
0.97 0.025
Dotok Lepene – Lepena inflow (n = 3) 2.48 0.015
Dotok Sopote – Sopota inflow (n = 3 ) 1.90 0.030
Lepena (n = 3) 2.39 0.066
Sopota (n = 3) 1.00 0.005
Zima – Winter
Iztok – Outflow (n = 3) 1.42 0.005

Kotnik, J. et al.: Modeliranje hidrodinamike in transporta živega srebra v Velenjskem jezeru – 1. del: živo srebro v
jezerski vodi – Modelling of Hydrodynamics and Mercury Transport in Lake Velenje – Part I: Mercury in Lake Waters
© Acta hydrotechnica 21/35 (2003), 87–103, Ljubljana
90
Velenjsko jezero ima dva dotoka. Potok
Lepena priteka na vzhodni strani, poleg jeza,
ki Velenjsko jezero deli od Škalskega jezera.
Drugi dotok, potok Sopota, priteka v jezero s
severa. Oba prispevata okoli 12.000.000 m
3
vode letno (ocena in meritve ERICO Velenje).
Oba potoka sta dokaj majhna. Potok Sopota
izvira 4,5 km severno od pritoka v jezero. Te če
skozi podeželsko obmo čje, ki ga sestavljajo
ve činoma  pašniki, travniki in gozdovi. Ve čji
komunalni izpusti nanj ne vplivajo
neposredno. Tok potoka je hiter v celi dolžini
vodotoka. Povpre čni letni pretok, izmerjen na
dotoku v Velenjsko jezero, je 0,127 m
3
/s
(ocena in meritve ERICO Velenje).
Drugi dotok, potok Lepena, se nahaja na
vzhodni strani jezera. Izvira okoli 4 km proti
severovzhodu od vtoka v jezero, poleg
manjšega naselja Cirkovce. Nato te če skozi
Hrastovec. V povirnem delu na Lepeno
vplivajo komunalni izpusti iz prej omenjenih
naselij. Pred vstopom v Velenjsko jezero
priteka v manjše Škalsko jezer, ki ga od
Velenjskega jezera lo čuje umetni jez iz sadre,
odpadka procesa razžveplevanja zgorelega
plina v TEŠ-u. Iz Škalskega jezera te če potok
Lepena naprej v Velenjsko jezero. Med
Škalskim in Velenjskim jezerom je
ribogojnica, ki uporablja vodo iz Škalskega
jezera. V ribogojnici gojijo predvsem postrvi
in krape. Presežek vode iz ribogojnice se izliva
v Lepeno okoli 100 m gorvodno od pritoka
Lepene v Velenjsko jezero. Voda iz
Velenjskega jezera te če v reko Pako in tako
vpliva na kakovost re čne vode.
Velenjsko jezero ima tipi čne zna čilnosti
majhnega sladkovodnega jezera z zmerno
klimo. Ima mo čno termalno stratifikacijo med
poletnimi in zgodnjimi jesenskimi meseci in je
dobro mešano med zimskimi in zgodnjimi
pomladnimi meseci (slika 2). Zgodaj spomladi
je temperatura vode na vseh globinah približno
4 °C, zaradi pove čanega son čnega sevanja se
počasi za čne segrevati. Segrete višje vodne
plasti se zaradi vetra na površini nekaj časa
mešajo z globljimi, hladnejšimi plastmi, s
čimer se izena čujeta temperatura in z njo
gostota vode po globini.
Velenje Lake has two inflows. The stream
Lepena is on the eastern side near the dike that
separates Lake Velenje from Lake Škale. The
other, Stream Sopota, flows into the lake from
the north. Both of them contribute 12,000,000
m
3
 of water to the lake per year (measured and
estimated by ERICO Velenje).
Both are relatively small streams. The
Sopota stream has its source about 4.5 km
north of its inflow into the lake. It runs through
rural landscape, mostly consisting of pastures,
meadows and woods. It is not directly
influenced by larger municipal releases. The
flow is quite fast throughout the whole Sopota
bed. The average yearly flow measured at the
inflow into Lake Velenje is 0.127 m
3
/s
(measured and estimated by ERICO Velenje).
A second inflow, the Lepena stream, is
located at the eastern side of the lake. The
Lepena stream has its source about 4 km to the
northeast from its inflow into the lake, near a
small settlement called Cirkovce. It runs
through the settlement of Hrastovec. In its
upper reaches Lepena stream is influenced by
municipal releases from the aforementioned
settlements. Before entering into Lake
Velenje, it runs into the small Lake Škale that
is separated from Lake Velenje by an artificial
dyke made of gypsum, a waste product of the
desulphurisation process of flue gases in
ŠTPP. From Lake Škale, Lepena stream runs
further into Lake Velenje. Between Lake Škale
and Lake Velenje is a fish farm that uses water
from Lake Škale. At the fish farm, mostly trout
and carp are bred. Excess water from the fish
farm is released into the Lepena stream about
100 m upstream from the Lepena inflow into
Lake Velenje. Water from Lake Velenje flows
into the Paka River and influences the water
quality in that river.
Lake Velenje has typical characteristics of a
small freshwater lake in a temperate climate. It
has very strong thermal stratification during
the summer and early fall months, and is well
mixed during the winter and early spring
months (Figure 2). In early spring, the water
temperature at all depths is about 4°C and
begins warming due to the increase of the solar
radiation. The heated upper water layers mix
with the deeper, colder layers until the density
of the layers is equal.

Kotnik, J. et al.: Modeliranje hidrodinamike in transporta živega srebra v Velenjskem jezeru – 1. del: živo srebro v
jezerski vodi – Modelling of Hydrodynamics and Mercury Transport in Lake Velenje – Part I: Mercury in Lake Waters
© Acta hydrotechnica 21/35 (2003), 87–103, Ljubljana
91
0
2
4
6
8
10
12
14
16
18
20
22
24
26
28
30
0 5 10 15 20 25
Temperature (°C)
Depth (m)
S pring 1998
S ummer 1998
Winter 1999
Slika 2. Temperaturna stratifikacija Velenjskega jezera.
Figure 2. Temperature stratification in Lake Velenje.
6400 6600 6800 7000 7200 7400 7600 7800 8000
6200
6400
6600
6800
7000
7200
7400
7600
Lake Velenje
Sampling Locations
0 200 400 m
Sopota
Lepena
Outflow
A S H
L A N D F I L L
Lake I.
Lake II.
Lake III.
Location 1
Location 2
Location 3
Legend:
water
sediment
rain and snow
Recreation Area
air and water
S-1
S-2a
S-2b
S-3
S-5
S-6
S-7
20
40
60
Slika 3. Velenjsko jezero in odvzemna mesta.
Figure 3. Lake Velenje with sampling locations.

Kotnik, J. et al.: Modeliranje hidrodinamike in transporta živega srebra v Velenjskem jezeru – 1. del: živo srebro v
jezerski vodi – Modelling of Hydrodynamics and Mercury Transport in Lake Velenje – Part I: Mercury in Lake Waters
© Acta hydrotechnica 21/35 (2003), 87–103, Ljubljana
92
Ko pa je površinska plast (epilimnij;
globina 0–4 m) dovolj segreta, tako da
zaradi razlike v gostoti lahko plava nad
hladnejšimi plastmi (hipolimnij, pod 16 m),
se jezerska voda ne meša ve č. Navadno
vetrovi nimajo dovolj energije, da bi vodo
premešali do dna. Med dvema vodnima
plastema je tranzicijska plast vode, kjer
temperatura z globino hitro upada. Po
temperaturni stratifikaciji v pozni pomladi
veter meša le površinske plasti vode. Jezero
se ohlaja podobno, kot se segreva: jeseni se
površinska plast ohladi, medtem ko se
temperatura epilimnija in hipolimnija izena či.
Pri temperaturi 0 °C površinska plast
zamrzne, s čimer se prepre či mešanje vode
zaradi vetra.
2. VZOR ČEV ANJE IN ANALIZE
Odvzemne to čke okoli jezera in v jezeru
so bile izbrane tako, da bi se zagotovilo
detajlno predstavitev vsebnosti Hg, njegove
transformacije ter transport v razli čnih
okoljskih prostorih. Odvzemna mesta za
jezersko vodo, vodo na dotoku, sedimente in
padavine so prikazana na sliki 3.
When the surface layer (epilimnion; depth 0–
4 m) is heated enough so that it can, because of
density differences, float over the colder layers
(hypolimnium; below 16 m) the water in the
lake does not mix any more. Between the two
water layers is a transitional water layer in
which the temperature rapidly decreases with
depth. After temperature stratification in the late
spring, wind mixes only the surface water layer.
The lake cools in the same way as it is heated:
in fall, the surface layer is cooled, while
temperatures between the epilimnion and
hypolimnium become equal. At a temperature of
0°C the surface layer freezes, thus preventing
the mixing of water due to winds.
2. SAMPLING AND ANALYSES
The sampling points around and in Lake
Velenje were chosen in order to provide a
detailed representation of Hg content, its
transformations and transport in different
environmental compartments. Sampling
locations for lake water, water inflow, sediment
and precipitation are shown on Figure 3.
Vzorci jezerske vode so bili odvzeti v treh
sezonah: na koncu pomladi 1998 (za četek
maja 1998), v sredini poletja 1998 (za četek
avgusta 1998) in na koncu zime 1998/99
(konec februarja 1999). Vzorci so bili odvzeti
na 8 mestih: 3 mesta so bila v sredini jezera,
3 na jezerskem dotoku in iztoku ter 2 na
pritokih Lepene in Sopote. Na treh lokacijah
v sredini jezera je vzor čenje potekalo na
razli čnih globinah (0, 4, 8, 12, 16, 20, 24 in
30 m), ki so bile izbrane glede na
stratifikacijo vode.
Raztopljeno celokupno živo srebro in
metil-živo srebro, tako v raztopljeni obliki
kot partikularno, sta bila merjena takoj po
odvzemu. Celokupni THg je bil dolo čen s
tehniko CV AAS, in sicer po oksidaciji z
BrCl, redukciji z SnCl
2
 in ujetjem Hg
0
na
zlato (Horvat et al., 1996; Horvat et al.,
1991; Horvat, 1991). Reaktivno živo srebro v
vodi je bilo dolo čeno s tehniko CV AAS po
redukciji s SnCl
2
 in z amalgamacijo na zlato.
Koncentracije MeHg v vodi so bile dolo čene
s tehniko CV AFS, in sicer po solventni
Lake water samples were taken in three
seasons: at the end of spring 1998 (beginning of
May 1998), in the middle of summer 1998
(beginning of August 1998) and at the end of
winter 1998/99 (end of February 1999). Water
samples were taken at 8 locations: three
locations were in the centre of the lake, three at
lake inflows and outflow points and two within
the inflow streams of Lepena and Sopota. At the
three locations in the middle of the lake, the
samples were taken at different depths (0, 4, 8,
12, 16, 20, 24 and 30 m) that were chosen with
regard to water stratification.
Dissolved and particulate phases of total and
methylmercury in water samples were measured
immediately after sampling. Determination of
THg was performed by CV AAS following
oxidation with BrCl, reduction with SnCl
2
 and
trapping of the resulting Hg
0
 on gold (Horvat et
al., 1996; Horvat et al., 1991; Horvat, 1991).
Reactive mercury in water was determined by
CV AAS following reduction by SnCl
2
 and
amalgamation on gold. MeHg concentrations in

Kotnik, J. et al.: Modeliranje hidrodinamike in transporta živega srebra v Velenjskem jezeru – 1. del: živo srebro v
jezerski vodi – Modelling of Hydrodynamics and Mercury Transport in Lake Velenje – Part I: Mercury in Lake Waters
© Acta hydrotechnica 21/35 (2003), 87–103, Ljubljana
93
ekstrakciji in vodni fazi etilacije MeHg
(Horvat et al., 1993a; 1993b; Liang et al.,
1994).
Vse analitične metode so se redno
preverjale in izvajale v okviru kontrolnega
sistema kakovosti Odseka za znanosti o
okolju, Institut Jožef Stefan. Kakovost
analiti čnih meritev za analize Hg in
speciacija sta se preverjali z redno uporabo
certificiranih refere čnih materialov (CRM),
kot so DORM-1 (mišica trneža), DOLT-1
(jetra trneža) in IAEA-356 (onesnažen
morski sediment). Po drugi strani pa za
vodne vzorce certificirani referen čni
materiali za celokupno, reakcijsko in
metilirano živo srebro ne obstajajo, metode
pa so bile vseskozi preverjane s protokolom
US EPA (EPA Method 1631).
Izotopska sestava kisika v vodi je bila
dolo čena s standardno metodo, ki temelji na
ravnovesju med referen čnim CO
2
 pri 25 
o
C
za 24 ur (Epstein in Mayeda, 1953), kar je
bilo nato merjeno na masnem spektrometru
Varian MAT 250. Uporabili smo notranje
laboratorijske standarde (voda iz pipe –
Ljubljanski vodovod z δ
18
O = –9,34 ±
0,03 ‰ V-SMOW) za prepoznavanje
morebitnih odstopanj med pripravo vzorcev
ali instrumentalnih premikov med
ugotavljanjem kisikovega izotopskega
razmerja.
Postopek normalizacije za 
18
O:
normalizacijska ena čba je bila pridobljena iz
notranjih standardov, ki so bili merjeni v
zadnjih treh mesecih po postopku
programskega orodja za stabilne izotope
LIMS v. 7.0.
Za dolo čitev izotopske sestave devterija
(
2
H) je bila uporabljena redukcija vode na Cr
pri 800 
o
C za proizvodnjo vodikovega plina
(Gehre et al., 1996). Vodikov plin se nato
izmeri na masnem spektrometru Varian MAT
250. Uporabljeni laboratorijski standardi so
voda iz pipe in padavine: – 53,2 ± 1,4 ‰, –
32,4 ± 1,0 ‰, – 124,4 ± 1,2 ‰ V-SMOW.
Pred analizo se laboratorijske standarde v
serijah normalizira. Normalizacijsko ena čbo
smo pridobili po vsaj 25 meritvah po
delovnih standardih, in sicer po postopku za
stabilne izotope LIMS for Stable Isotopes v.
7.0.
water were determined by CV AFS following
solvent extraction and aqueous phase ethylation
of MeHg (Horvat et al., 1993a; 1993b; Liang et
al., 1994).
All analytical methods were regularly
validated and performed within a quality control
system of the Department of Environmental
Sciences, Jožef Stefan Institute. The quality of
analytical measurements for Hg analysis and
speciation was checked by the regular use of
certified reference materials (CRMs), such as
DORM-1 (Dogfish muscle), DOLT-1 (Dogfish
liver) and IAEA-356 (Polluted marine
sediment). As for water samples CRMs for total,
reactive and methylmercury are not extant,
methods were continuously validated by the US
EPA protocol (EPA Method 1631).
The isotopic composition of oxygen in water
was determined using the standard method
based upon equilibration with referenced CO
2
 at
25
o
C for 24 h (Epstein and Mayeda, 1953),
which was then measured on a Varian MAT 250
mass spectrometer. Internal laboratory standards
were used (tap water – Ljubljanski vodovod
with δ
18
O = –9.34 ± 0.03 ‰ V-SMOW) to
detect possible variations during sample
preparation or instrumental drift during the
oxygen isotopic ratio determination.
Normalization procedure for 
18
O: the
normalization equation was obtained from
internal standards measured over the last 3
months following the procedure in the software
LIMS for Stable Isotopes v. 7.0.
Reduction of water on Cr at 800
o
C to
produce hydrogen gas was used to determine the
isotopic composition of deuterium (
2
H) in water
(Gehre et al., 1996). The hydrogen gas is then
measured on a Varian MAT 250 mass
spectrometer. The laboratory standards used are
tap water and precipitation: – 53.2 ± 1.4 ‰, –
32.4 ± 1.0 ‰, – 124.4 ± 1.2 ‰ V-SMOW. The
laboratory standards are normalized in batches
before the samples are analyzed. The
normalization equation was obtained from at
least 25 measurements of working standards
following the procedure in the software LIMS
for Stable Isotopes v. 7.0.
The calibration of the δ
18
O and δ
2
H values
analyzed with respect to the international

Kotnik, J. et al.: Modeliranje hidrodinamike in transporta živega srebra v Velenjskem jezeru – 1. del: živo srebro v
jezerski vodi – Modelling of Hydrodynamics and Mercury Transport in Lake Velenje – Part I: Mercury in Lake Waters
© Acta hydrotechnica 21/35 (2003), 87–103, Ljubljana
94
Kalibracija vrednosti δ
18
O in δ
2
H,
analizirana v skladu z mednarodnimi
standardi, je bila izvedena z analizo
VSMOW, GISP in SLAP (‰ vrednosti) z
istimi postopki. Datum zadnje kalibracije je
januar 1999.
Rezultati δ
18
O in δ
2
H so prikazani kot
deviacije v ‰ od standarda V-SMOW
(Coplen, 1994). Natan čnost analize δ
18
O in
δ
2
H, ki je temljila na ponovljenih meritvah,
je bila ± 0,05 ‰ oziroma ± 1,0 ‰.
3. Hg V JEZERSKI VODI IN
SEDIMENTIH
Koncentracije celokupnega Hg (THg) in
celokupnega MeHg (TMeHg) (preglednica 1,
sliki 4 in 5) v Velenjskem jezeru so zelo
nizke v primerjavi z drugimi onesnaženimi
jezeri severne poloble (Kim in Fitzgerald,
1986; Henry et al., 1995b). Koncentracije Hg
in MeHg v površinskem sloju in vodnem
stolpu so primerljive s koncentracijami, ki so
bile izmerjene v neonesnaženih, oddaljenih
sladkovodnih jezerih severne poloble
(Meuleman et al., 1995; Henry et al., 1995b;
Leermakers et al., 1996). Delež metiliranega
živega srebra MeHg je 2,01–24,41%, kar
lahko primerjamo s podatki iz literature, ki za
sladkovodne sisteme navaja 1–12 % (Lee &
Iverfeldt, 1991) in 7–25 % delež (Bloom et
al. 1991).
Pri vzorcih, odvzetih spomladi, so bile
najvišje koncentracije celokupnega THg
ugotovljene pri površinski jezerski vodi pri
dotoku Lepene (2,68 ng/L), to pa smo
pripisali visoki vsebnosti partikularnega Hg
(75,5–81,8 %) v potoku Lepena.
Koncentracije THg v jezeru so se manjšale
od vzhoda (dotok Lepene) proti zahodu.
Najvišje vrednosti THg v vodnem stolpu so
bile v površinskem sloju (globine O–4 m).
Pod globino 4 m so se koncentracije THg
zmanjšale na vrednost 1 ng/L. Ve čina živega
srebra v vodnem stolpu je bila vezana na
(trdne) delce (50–60 %). Spomladi so bile
najvišje koncentracije TMeHg u gotovljene
na dotokih Lepene (54 pg/L) in Sopote (68
pg/L). Pove čano koncentracijo MeHg proti
jezerskemu dnu lahko pripišemo metilaciji
Hg v sedimentu in difuziji MeHg, ki prihaja
iz sedimenta v vodo nad njim (Sukhenko in
Vasiliev, 1995).
standards was carried out by analyzing
VSMOW, GISP and SLAP (‰ values) with the
same procedures. The date of the last calibration
is January 1999.
δ
18
O and δ
2
H results are reported as
deviations in ‰ from the V-SMOW standard
(Coplen, 1994). The precision of the analyses of
δ
18
O and δ
2
H based upon replicate
measurements was ± 0.05 ‰, and ± 1.0 ‰,
respectively.
3. Hg IN LAKE WATER AND
SEDIMENTS
Total Hg (THg) and total MeHg (TMeHg)
concentrations (Table 1, Figures 4 and 5) in
Lake Velenje are very low compared to Hg
concentrations in other polluted lakes of the
northern hemisphere (Kim and Fitzgerald, 1986;
Henry et al., 1995b). Hg and MeHg
concentrations in the surface layer and water
column are comparable to those reported for
unpolluted remote freshwater lakes of the
northern hemisphere (Meuleman et al., 1995;
Henry et al., 1995b; Leermakers et al., 1996).
The percentages of MeHg are between 2.01 %
and 24.41 % and are comparable to the literature
data, which report 1–12 % (Lee & Iverfeldt,
1991) and 7–25 % (Bloom et al. 1991) for
freshwater systems.
Of the samples taken during spring, the
highest THg concentrations were found in the
lake surface water at the Lepena inflow (2.68
ng/L) due to the high content of particulate Hg
(75.5–81.8 %) in Lepena Stream. THg
concentrations in the lake decreased from east
(Lepena inflow) to west. The highest values of
THg in the water column were in the surface
layer (0–4 m of depth). Below 4 m of depth, the
THg concentrations decreased to a value of 1
ng/L. Most mercury in the water column was
bounded to particulate matter (50–60 %).
The highest TMeHg concentrations during
spring were found in the Lepena (54 pg/L) and
Sopota (68 pg/L) inflows. The increase in MeHg
concentrations towards the lake bottom is due to
the methylation of Hg in sediment, and the
diffusion of the MeHg produced from the
sediment into the overlaying water (Sukhenko
and Vasiliev, 1995).

Kotnik, J. et al.: Modeliranje hidrodinamike in transporta živega srebra v Velenjskem jezeru – 1. del: živo srebro v
jezerski vodi – Modelling of Hydrodynamics and Mercury Transport in Lake Velenje – Part I: Mercury in Lake Waters
© Acta hydrotechnica 21/35 (2003), 87–103, Ljubljana
95
Slika 4. Vertikalna razporeditev razli čnih oblik živega srebra v Velenjskem jezeru v razli čnih letnih časih.
Figure 4. Vertical distribution of different mercury species in Lake Velenje during diferrent seasons.

Kotnik, J. et al.: Modeliranje hidrodinamike in transporta živega srebra v Velenjskem jezeru – 1. del: živo srebro v
jezerski vodi – Modelling of Hydrodynamics and Mercury Transport in Lake Velenje – Part I: Mercury in Lake Waters
© Acta hydrotechnica 21/35 (2003), 87–103, Ljubljana
96
Slika 5. Vertikalna razporeditev razli čnih oblik metil živega srebra v Velenjskem jezeru v razli čnih letnih časih.
Figure 5. Vertical distribution of different methylmercury species in Lake Velenje during diferrent seasons.

Kotnik, J. et al.: Modeliranje hidrodinamike in transporta živega srebra v Velenjskem jezeru – 1. del: živo srebro v
jezerski vodi – Modelling of Hydrodynamics and Mercury Transport in Lake Velenje – Part I: Mercury in Lake Waters
© Acta hydrotechnica 21/35 (2003), 87–103, Ljubljana
97
Poletne koncentracije THg v jezeru so bile
nižje kot pomladne (0,64–0,77 ng/L). V vseh
primerih je bila najnižja vrednost THg v
mezolimniju (0,03–0,12 ng/L). Odstotni delež
partikularnega Hg v vodnem stolpu je bil med
50 in 80 %. Koncentracije celokupnega MeHg
v površinskem sloju so bile najvišje pri dotoku
Lepene in so se znižale proti zahodnemu delu
jezera. Podobno stanje smo ugotovili pri
partikularnem MeHg. Raztopljeno MeHg je
bilo enakomerno porazdeljeno po jezerski
površini. Intenzivnejše koncentracije MeHg
poleti v primerjavi s pomladnimi so posledica
višjih letnih temperatur vode, s tem pa
intenzivnejših makrobiotskih aktivnosti ter
procesov metilacije, demetilacije in redukcije
v samem jezeru in pritokih.
Pozimi je bila najvišja koncentracija THg
izmerjena na dotoku Lepene (2,48 ng/L).
Ve čina živega srebra na tem mestu je bila
vezana na delce (75 %). V površinskem sloju
koncentracije Thg naraš čajo od zahodnega
proti vzhodnemu delu jezera. V vodnem stolpu
je vrednost THg naraš čala z globino, in sicer
od 0,9 ng/L na 1,4 ng/L. Najvišje
koncentracije TMeHg smo našli na dotoku
Lepene, in sicer v razponu med 15 in 35 pg/L.
Razmerje med partikularnimi in raztopljenimi
oblikami MeHg je bilo skoraj enako v
celotnem vodnem stolpu (0,4 do 2,7 %).
Celokupna koncentracija živega srebra je v
dotoku Lepene za spoznanje višja kot v jezeru
ali pri potoku Sopota (glej preglednico 1).
Višje koncentracije Hg in MeHg so lahko
posledica zna čilnosti prispevnega obmo čja
potoka Lepena. Lepena te če skozi ve č manjših
vasi, ki svoje komunalne odplake spuš čajo
neposredno v potok. Preden se Lepena izte če v
Velenjsko jezero, ta oblikuje manjše jezero
(Škalsko jezero). Voda iz Škalskega jezera se
uporablja za ribogojstvo in se nato vra ča v
Lepeno. Višje koncentracije THg v Lepeni so
verjetno posledica komunalnih odplak in
ribogojstva (i. e. fungicidi in pesticidi z
vsebnostjo Hg) v vaseh na povodju Lepene.
Koncentracija MeHg v potoku Lepena pa je
posledica biotske metilacije Hg v Škalskem
jezeru in dodatne biotske metilacije v
ribogojnici.
Najbolj informativni element vodnega sistema
za presojanje ravni stalne kontaminacije so
talni sedimenti. Temeljni sediment v
The summer THg concentrations in the lake
were lower than the spring concentrations (in a
range between 0.64 and 0.77 ng/L). In all
cases the lowest THg content was in the
mesolimnion (between 0.03 and 0.12 ng/L).
The percentage of particulate Hg in the water
column was between 50 and 80 %. The total
MeHg concentrations in the surface layer were
highest at the Lepena infow, and decreased
toward the western part of the lake. A similar
situation was also observed for particulate
MeHg. Dissolved MeHg was uniformly
distributed across the lake surface. The more
intense MeHg concentration peaks in the
summer compared to the spring are caused by
the higher water temperatures in the summer,
and with that more intense microbial activity,
methylation, demethylation and reduction
processes in the lake and its inflows.
In winter the highest THg content was
found at the Lepena inflow (2.48 ng/L). Most
mercury at that location was bound to
particulate matter (75 %). In the surface layer,
THg concentrations increased from the
western part to the eastern part of the lake. In
the water column, THg content increased with
depth from 0.9 to 1.4 ng/L. The highest
TMeHg concentrations were found at the
Lepena inflow. TmeHg concentrations were in
the range between 15 and 35 pg/L. The
proportion between particulate and dissolved
MeHg forms was almost the same all
throughout the water column (0.4 to 2.7 %).
Among inflows total mercury
concentrations in the Lepena Stream are
slightly higher than in the lake or in Sopota
Stream (see Table 1). The higher
concentrations of Hg and MeHg in the Lepena
Stream can be explained by the characteristics
of the Lepena Stream catchment area. Lepena
Stream flows through few small villages that
release their municipal discharges directly into
the stream. Before the Lepena Stream enters
Lake Velenje, it forms a small lake (Lake
Škale). Water from Lake Škale is further used
for fish-farming and returned back to the
Lepena Stream. Higher THg concentrations in
the Lepena are probably a consequence of
municipal waste discharges and farming
activities (i.e. fungicides and pesticides
containing Hg) in the villages of its catchment
area. MeHg in the Lepena Stream has its
origin in biotic methylation of Hg in Lake
Škale and additional biotic methylation at the
fish farm.
The most informative component of water

Kotnik, J. et al.: Modeliranje hidrodinamike in transporta živega srebra v Velenjskem jezeru – 1. del: živo srebro v
jezerski vodi – Modelling of Hydrodynamics and Mercury Transport in Lake Velenje – Part I: Mercury in Lake Waters
© Acta hydrotechnica 21/35 (2003), 87–103, Ljubljana
98
Velenjskem jezeru je premogov pepel, ki se je
v preteklosti odlagal v jezeru. V tistih delih
jezera, ki so zaprti za dotoke, sedimenti
vsebujejo ve č organskih snovi. Koncentracije
THg v vzorcih sedimenta iz odvzemnih mest v
Velenjskem jezeru so bile spremenljivih
vrednosti, od 53 do 166 ng/g (suhe teže). Višje
koncentracije THg so bile ugotovljene v
organsko bogatem sedimentu v bližini dotokov
v jezero. V globljih delih jezera, kjer sediment
ve činoma tvori premogov pepel, so bile
koncentracije THg dokaj nizke 71,5 ng/g, suhe
teže). Tudi koncentracije MeHg so bile višje v
organsko obogatenem sedimentu v bližini
dotokov v jezero kot v premogovem pepelu, ki
se je odlagal v globljih delih jezera. Najnižja
koncentracija MeHg je bila ugotovljena na
najnižji to čki jezera (0,05 ng/g, suhe teže).
Povišani koncentraciji THg in MeHg ob obeh
dotokih sta posledica sedimentacija organsko
obogatenih sedimentov iz potokov Lepene in
Sopote.
4. δ  18
O IN δ  2
H
Izotopi so atomi, katerih jedra vsebujejo
enako število protonov, a razli čno število
nevtronov. Izotopi istega elementa imajo
razli čne fizikalno-kemi čne lastnosti. Delimo
jih v dve temeljni skupini: na stabilne in
nestabilne (radioktivne) izotope.
Izotopsko sestavo ali razmerje med težjimi
in lažjimi izotopi istega elementa v spojini
izražamo z vrednostjo δ, ki je relativna razlika
med izotopsko sestavo vzorca in standardom.
Vrednost δ ponavadi izražamo v tiso činkah
(
0
/
00
):
systems, from the standpoint of estimating
their degree of stable contamination, is bottom
sediments. The sediment in Lake Velenje is
mostly coal ash deposited into the lake in the
past. In the parts of the lake close to lake
inflows, the sediment contains more organic
matter. The THg concentrations in sediment
samples from locations in Lake Velenje varied
between 53 and 166 ng/g (dry weight). Higher
THg concentrations were found in organic-rich
sediment close to the lake inflows. In the
deeper parts of the lake THg concentrations in
the sediment, which consisted mostly of coal
ash, the concentrations were relatively low
(71.5 ng/g, dry weight). MeHg concentrations
were also higher in the organic-rich sediment
close to the lake inflows than in the coal ash
that is deposited in the deeper parts of the lake.
The lowest MeHg concentration was found in
the deepest point of the lake (0.05 ng/g, dry
weight). Increased THg and MeHg
concentrations near both inflows are a
consequence of sedimentation of organic-rich
sediment from the Lepena and Sopota streams.
4. δ  18
O AND δ  2
H
Isotopes are atoms whose nuclei contain the
same number of protons but different numbers
of neutrons. Isotopes of the same element have
different physico-chemical properties. Isotopes
can be divided into two fundamental kinds:
stable and unstable (radioactive).
The isotopic composition, or proportion
between heavier and lighter isotopes of the
same element in a compound, expressed by the
value δ, which is the relative difference
between the isotopic composition of a sample
and a standard. Usually the δ value is
expressed in per mill (
0
/
00
):
1000 ⋅
−
=
standard
standard sample
R
R R
A δ ,( 1 )
kjer je A težji izotop in R = [] [ ]
1 2
A A , je
razmerje med koncentracijo lažjega [A
1
] in
težjega [A
2
] izotopa v spojini vzorca ali
standarda.
Delitev izotopov na dve snovi ali dve fazi
iste snovi z razli čnimi izotopskimi razmerji
imenujemo “izotopsko frakcioniranje”.
Temeljni dejavniki, ki povzro čajo izotopsko
where A is the heavier isotope and R =
[ ] [ ]
1 2
A A is the proportion between the
concentration of the lighter [A
1
] and heavier
[A
2
] isotope in a compound of sample or
standard.
The partitioning of isotopes between two
substances or two phases of the same
substance with different isotope ratios is called

Kotnik, J. et al.: Modeliranje hidrodinamike in transporta živega srebra v Velenjskem jezeru – 1. del: živo srebro v
jezerski vodi – Modelling of Hydrodynamics and Mercury Transport in Lake Velenje – Part I: Mercury in Lake Waters
© Acta hydrotechnica 21/35 (2003), 87–103, Ljubljana
99
frakcioniranje, so izotopske reakcije izmenjave
in kineti čni procesi, ki temeljijo predvsem na
razlikah v reakcijah, stopnjah izotopskih
molekul, ki jih povzro čajo razlike v masi, ter
na temperaturi.
S faktorjem frakcioniranja ( α) merimo
stopnjo izotopske frakcionacije med spojinami
in ga definiramo, kot sledi:
“isotope fractionation”. The main phenomena
producing isotope fractionation are isotope
exchange reactions and kinetic processes,
which depend primarily upon differences in
the reactions, rates of isotopic molecules
caused by their mass differences, and upon
temperature.
The fractionation factor is a measure of the
degree of isotope fractionation between
compounds, and is defined as follows:
B
A
R
R
B
A
B A
δ
δ
α
+
+
= =
−
1000
1000
,( 2 )
kjer je R razmerje koncentracije med težjim
in lažjim izotopom v spojini A in spojini B.
Poznavanje izotopske sestave vode nam
lahko pomaga pri ugotavljanju vira in sledenju
njegovih poti. Ko voda na primer izhlapeva s
površine morja ali jezer, se vodna para obogati
v lažjih izotopih H in 
16
O, saj ima H
2
16
O višji
parni/uparjeni pritisk kot H
2
HO in H
2
18
O. Med
odstranitvijo dežja iz vlažnih zra čnih mas se
ostanek vlage trajno siromaši v težkih
izotopih, saj je dež, ki zapuš ča sistem,
obogaten z 
18
O and 
2
H. Če se zra čne mase
premikajo proti polu in se ohlajajo, bo dodatni
dež, ki se tvori, vseboval manj 
18
O kot za četni
dež. V zmernih in vlažnih podnebjih je
izotopska sestava podtalnice in teko čih
površinskih voda podobna sestavi padavin v
obmo čju obogatitve (Gat, 1971). Ko voda
vstopi v jezero ali drugo obmo čje
izhlapevanja, lahko pri čakujemo, da se bo zelo
obogatila s težkima izotopoma 
2
H in 
18
O.
Rezultati meritev stabilnih izotopov δ
18
O in
δ 
2
H v Velenjskem jezeru so prikazani v
preglednici 2.
Na kisikovo izotopsko sestavo v vodnem
stolpu lahko vpliva ve č dejavnikov. V
naravnih pogojih, predvsem pa pri jezerih
srednje zemljepisne širine, vrednost δ
18
O
jezerske vode nikoli ne ostane konstanta.
Nasprotno, vrednost niha okoli vrednosti
stacionarnega stanja/stanja mirovanja,
ustrezujo č časovnim spremembam razli čnih
dejavnikov (temperature, relativne vlažnosti,
izotopske sestave skupnega dotoka in
atmosferi čne vodne pare).
where R is concentration proportion
between the heavier and lighter isotope in
compound A and compound B.
Knowledge of water isotopic composition
can help us to determine its source and trace
its pathways. For instance when water
evaporates from the surface of the ocean or
from lakes, the water vapor is enriched in
lighter isotopes H and 
16
O because H
2
16
O has a
higher vapor pressure than H
2
HO and H
2
18
O.
During removal of rain from moist air mass,
the residual vapor is continuously depleted in
the heavy isotopes, because the rain leaving
the system is enriched in 
18
O and 
2
H. If the air
mass moves poleward and becomes cooler, the
additional rain that is formed will contain less
18
O than the initial rain. In temperate and
humid climates the isotopic composition of
groundwater and flowing surface water is
similar to that of the precipitation in the area
of recharge (Gat, 1971). When water enters a
lake or other evaporative environment, it can
be expected to undergo extreme enrichments
in the heavy isotopes 
2
H and 
18
O.
The results of the δ
18
O and δ
2
H stable
isotope measurements in Lake Velenje are
shown in Table 2.
There are several factors that can affect the
oxygen isotopic composition in the water
column. Under natural conditions, particularly
for mid-latitude lakes, the δ
18
O value of lake
waters never remains constant. Instead, it
fluctuates around the steady-state value,
responding to seasonal changes of respective
parameters (temperature, relative humidity,
isotopic composition of total inflow and
atmospheric water vapour).

Kotnik, J. et al.: Modeliranje hidrodinamike in transporta živega srebra v Velenjskem jezeru – 1. del: živo srebro v
jezerski vodi – Modelling of Hydrodynamics and Mercury Transport in Lake Velenje – Part I: Mercury in Lake Waters
© Acta hydrotechnica 21/35 (2003), 87–103, Ljubljana
100
Preglednica 2. δ
18
O in δ 
2
H v Velenjskem jezeru in na dotokih (v 
o
/
oo
).
Table 2. δ
18
O and δ 
2
H in Lake Velenje and its inflows (in 
o
/
oo
).
Pomlad/Spring Zima/Winter
δ 
18
O δ 
2
H δ 
18
O δ 
2
H Mesto/Location
Globina
(m)/Depth
(m) [‰] [‰] [‰] [‰]
0 - 7,09 - 55,5 - 7,92 - 59,2
4 - 7,21 - 56,5 - 7,97 - 58,7
8 - 7,49 - 56,7 - 7,81 - 58,0
12 - 7,66 - 57,2 - 7,74 - 57,7
16 - 7,57 - 56,9 - 7,19 - 56,8
20 - 7,56 - 57,9 - 7,80 - 58,8
24 - 7,38 - 58,2 - 7,86 - 57,6
Jezero I/Lake I
30 - 7,34 - 57,7
0 - 7,83 - 57,2
4 - 7,84 - 56,8
8 - 7,83 - 56,6
12 - 7,89 - 57,3
16 - 7,78 - 56,8
20 - 7,82 - 56,6
Jezero II/Lake II
24 - 7,77 - 57,3
0 - 7,05 - 54,6 - 6,94 - 57,4
4 - 6,88 - 52,9 - 7,96 - 56,9
8 - 7,46 - 55,8 - 7,88 - 57,2
12 - 6,93 - 57,6 - 7,78 - 58,6
16 - 7,13 - 56,9 - 7,82 - 57,9
20 - 7,43 - 55,9 - 7,80 - 57,2
24 - 7,49 - 56,0
Jezero III/Lake III,
30 - 7,60 - 57,7
Dotok Lepene/Lepena inflow 0 - 7,34 - 57,8 - 8,95 - 62,9
Dotok Sopote/Sopota inflow 0 - 6,85 - 54,2 - 9,49 - 66,4
Odtok/Outflow 0 - 6,98 - 53,9 - 7,86 - 57,7
Lepena 0 - 8,98 - 62,1 - 9,53 - 65,2
Sopota 0 - 8,57 - 59,5 - 9,47 - 65,2
Amplituda sprememb zaradi letnih časov je
odvisna od specifi čnih podnebnih razmer
dolo čenega jezera, vendar je ponavadi nekje
med 1 in 2 ‰. V sezonsko stratificiranih
jezerih se aktivni volumen jezera spreminja z
letnim časom. Med poletno stratifikacijo je
izotopsko bogatenje jezera zaradi pove čanega
izhlapevanja omejeno na zgornjo, dobro
premešano plast (epilimnij). Zimski preobrat
pa zmanjša vrednost δ
18
O zgornjega sloja
zaradi mešanja z izotopsko lažjimi vodami
hipolimnija.
The amplitude of these seasonal variations
depends upon the particular climatic setting of
the given lake but is usually in the range of 1
to 2 ‰. In seasonally stratified lakes the active
volume of the lake changes with the season.
During the summer stratification, isotopic
enrichment of the lake water due to enhanced
evaporation is limited to the upper, well-mixed
layer (epilimnion). Winter turnover reduces
the δ
18
O value of the upper layer due to
mixing with isotopically lighter hypolimnion
waters.

Kotnik, J. et al.: Modeliranje hidrodinamike in transporta živega srebra v Velenjskem jezeru – 1. del: živo srebro v
jezerski vodi – Modelling of Hydrodynamics and Mercury Transport in Lake Velenje – Part I: Mercury in Lake Waters
© Acta hydrotechnica 21/35 (2003), 87–103, Ljubljana
101
5. ZAKLJU ČKI
V splošnem smo višje koncentracije THg v
vodnem stolpu našli v epilimniju, in sicer
zaradi vnosa raztopljenega in partikularnega
Hg na dotokih. V bližini odlagališ ča nismo
izmerili pove čanih koncentracij THg in MeHg.
Koncentracije THg in TMeHg v Velenjskem
jezeru so bistveno nižje od koncentracij Hg v
drugih onesnaženih jezerih severne poloble.
Velenjsko jezero ne predstavlja potencialnega
vira Hg in MeHg v človekovi prehranjevalni
verigi, četudi bi se jezero spremenilo v visoko
bioproduktivno jezero.
V drugem delu prispevka bodo
predstavljeni podatki o izotopski sestavi in
vsebnosti razli čnih zvrsti živega srebra v
pritokih in jezerski vodi, uporabljeni za
validacijo in verifikacijo hidrodinamskega in
geokemi čnega modela kroženja in pretvorb
živega srebra in njegovih spojin v Velenjskem
jezeru. Kon čni cilj raziskave so simulacije
razli čnih možnih scenarijev spreminjanja
vsebnosti Hg v jezeru.
ZAHVALA
Za finan čno podporo se zahvaljujemo
Ministrstvu za šolstvo, znanost in šport
Republike Slovenije.
5. CONCLUSIONS
Generally, higher concentrations of THg in
the water column were found in the
epilimnion, due to the input of dissolved and
particulate Hg from inflows. In the vicinity of
the landfill we did not find any elevated THg
or MeHg concentrations. THg and TMeHg
concentrations in Lake Velenje are very low
compared to Hg concentrations in other
polluted lakes of the northern hemisphere.
Lake Velenje does not represent a potential
source of Hg and MeHg in human food chain
even in case that it turns onto high
bioproductive lake.
Presented data on isotopic composition and
different Hg species in inflows and lake water
were further used for validation and
verification of the hydrodinamical and
geochemical model of Hg cycling and its
transformations in Lake Velenje that is
represented in second part. The final aim of
the study are simulations of Hg behaviour
under different possible scenarios.
ACKNOWLEDGEMENTS
We acknowledge the financial support of
the Ministry of Education, Science and Sports
of Slovenia for funding this work.
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Naslov avtorjev – Authors’ Addresses
dr. Jože Kotnik
Odsek za okoljske znanosti – Department of Environmental Sciences
Institut Jožef Stefan – Jožef Stefan Institute
 Jamova 39, SI-1000 Ljubljana, Slovenia
E-mail: joze.kotnik@ijs.si
dr. Milena Horvat
Odsek za okoljske znanosti – Department of Environmental Sciences
Institut Jožef Stefan – Jožef Stefan Institute
Jamova 39, SI-1000 Ljubljana, Slovenia
E-mail: milena.horvat@ijs.si
Vesna Fajon
Odsek za okoljske znanosti – Department of Environmental Sciences
Institut Jožef Stefan – Jožef Stefan Institute
Jamova 39, SI-1000 Ljubljana, Slovenia
E-mail: vesna.fajon@ijs.si

Kotnik, J. et al.: Modeliranje hidrodinamike in transporta živega srebra v Velenjskem jezeru – 1. del: živo srebro v
jezerski vodi – Modelling of Hydrodynamics and Mercury Transport in Lake Velenje – Part I: Mercury in Lake Waters
© Acta hydrotechnica 21/35 (2003), 87–103, Ljubljana
103
dr. Martina Logar
Odsek za okoljske znanosti – Department of Environmental Sciences
Institut Jožef Stefan – Jožef Stefan Institute
Jamova 39, SI-1000 Ljubljana, Slovenia
E-mail: martina.logar@ijs.si
dr. Nives Ogrinc
Odsek za okoljske znanosti – Department of Environmental Sciences
Institut Jožef Stefan – Jožef Stefan Institute
Jamova 39, SI-1000 Ljubljana, Slovenia
E-mail: nives.ogrinc@ijs.si