The macrophytes of lake Velenjsko Jezero, Slovenia – the
succession of macrophytes after restoration of the lake
Makrofiti Velenjskega jezera, Slovenija – sukcesija makrofitov
po restavraciji jezera
Zdenka MAZEJ1, Mateja EP[EK2
1 ERICo Velenje; Environmental Research and Industrial Co-operation Institute,
Koro{ka 58, 3320 Velenje, Slovenia; Tel.: +386 3 898 19 58; fax: +386 3 898 19
42; E-mail: zdenka.mazej@erico.si
2 Biotechnical Faculty, Department of Biology, Ve~na pot 111, 1000 Ljubljana,
Slovenia
Abstract. The macrophyte vegetation in the artificial lake Velenjsko jezero has
been monitored since 1996. The pH of the lake was around 12 up to 1994, when it
was remediated. After that macrophytes started to colonize a large proportion of the
littoral very quickly. The pioneer species, which appeared in the first survey year
(1996), were Chara sp., Nuphar lutea, Potamogeton crispus and Myriophyllum spi-
catum. Potamogeton crispus was the dominant species till 1997. In the following
years Najas marina and Potamogeton filiformis prevailed over other species in the
lake. Since the beginning of the colonization, the species composition had become
more heterogeneous and the quantitative relationships between the species varied
enormously. In the year 2004, 9 species were detected in the lake. While species
Najas marina, Potamogeton filiformis, Potamogeton lucens, Potamogeton nodosus
show positive development progress, in the last years minor appearance of Chara
sp., Potamogeton crispus and Najas minor was observed.
Key words: lake Velenjsko jezero, succession of macrophytes, species compo-
sition and distribution, relative plant mass, maximal depth colonization
Izvle~ek. Makrofite v umetno nastalem Velenjskem jezeru spremljamo od leta
1996. Vrednost pH jezerske vode je bila vse do leta 1994, ko so v Termoelektrarni
[o{tanj uvedli zaprti krog transportne vode, okoli 12. Vrednost pH je po tem ukre-
pu hitro padla na vrednost okoli 8. Makrofiti so postopoma pri~eli naseljevati
litoralno obmo~je jezera. Pionirske vrste v letu 1996 so bile Chara sp., Nuphar
lutea, in Potamogeton crispus. Potamogeton crispus je bila dominantna vrsta vse
do leta 1997. V naslednjih letih sta prevladali vrsti Najas marina in Potamogeton
filiformis. Od za~etka naseljevanja je prihajalo do velikih kvalitativnih in kvantita-
tivnih sprememb v vrstni sestavi in razporeditvi makrofitov. V jezeru je leta 2004
ACTA BIOLOGICA SLOVENICA
LJUBLJANA 2005 Vol. 48, [t. 1: 21-31
Sprejeto (accepted): 2005-09-27
stevilka 1_05.qxp  13.12.2005  12:32  Page 21
uspevalo 9 vrst. Medtem ko ka`ejo vrste Najas marina, Potamogeton filiformis, Potamogeton lucens
in Potamogeton nodosus pozitiven trend v razvoju, pa v zadnjih letih opa`amo manj{e pojavljanje
vrst Chara sp., Potamogeton crispus in Najas minor.
Key words: Velenjsko jezero, sukcesija makrofitov, vrstna sestava, distribucija makrofitov, rela-
tivna rastlinska biomasa, maksimalna globina naselitve
Introduction
The succession of submersed macrophytes in lakes is a complex process. Once they are estab-
lished, macrophytes have significant feedback effects on lake water quality and ecosystem health,
and are an important consideration in lake management (JEPPESEN & al. 1998). In lakes where con-
ditions favour development of high biomass of submerged aquatic vegetation over large areas, there
is potential for large-scale reductions in water column concentrations of nutrients and phytoplank-
ton, and increase transparency (JEPPESEN & al. 1998). Factors that influence the biomass and distri-
bution of submersed macrophytes both among and within lakes have been well studied. These fac-
tors include substratum character and water depth (WEISNER 1991), transparency (HUTCHINSON 1975,
NICHOLS 1992, MIDDELBOE & MARKAGER 1997, MAZEJ & GABER{~IK 1999, VAN DUIN & al. 2001,
BEST & al. 2001), water chemistry (PIP 1984, HASLAM 1987, PRESTON 1995, GERM & GABER{~IK
1996, GERM & al. 2003), temperature (PIP 1989, ROONEY & KALFF 2000), bottom slope (NICHOLS
1992), water level fluctuation and wave action (PRESTON 1995, ANDERSSON 2001), filamentous and
planktonic algae (URBANC-BER~I~ & al. 2002), grazing (JACOBSEN & SAND-JENSEN 1992, WEISNER &
al. 1997) and intra- and inter- species competition among macrophyte species (FOX 1992, AGAMI &
WAISEL 2002). The underwater light regime is one of the most important determinants of submerged
aquatic vegetation (HUTCHINSON 1975, NICHOLS 1992, BEST & al. 2001, VAN DUIN & al. 2001).
DUARTE AND KALFF (1986) asserted that within lakes, the morphometric variables of bottom slope
and community exposure are both negatively correlated with macrophyte biomass. In lakes, which
shelve rapidly, the density of plants on the shore of the lake falls very quickly. On the contrary, if the
shore is shallow and slopes gently, the belt overgrown by aquatic plants can be very wide (NICHOLS
1992).
Many macrophytes are tolerant to pH values between 10 and 11; higher values are destructive
(BOWES 1987). The pH of Lake Velenjsko jezero was around 12 until 1994, when reconstruction of
the fly ash system and introduction of a closed loop water cycle was made at the [o{tanj Thermal
Power Plant. The pH declined to around 8 and biota started to colonize the lake. Our study was
focused on aquatic macrophytes, an important group of primary producers, which provide conditions
necessary for fish, zooplankton and benthos in the littoral zones of lakes. Information on the distri-
bution and species composition of aquatic vegetation is necessary for management and understand-
ing of aquatic systems. We monitored the succession of species composition and abundance of sub-
mersed macrophytes after restoration measures in Lake Velenjsko jezero. Our method was based on
direct field observations along transects that enabled identification of the main environmental factors
influencing the appearance of macrophytes.
Acta Biologica Slovenica, 48 (1), 2005 22
stevilka 1_05.qxp  13.12.2005  12:32  Page 22
Materials and Methods
Description of the site
Velenjsko jezero is located in the [alek Valley, at an altitude of 366 m, with a surface 135000 m2
and a maximal depth of 54 m. It is an artificial lake resulting from mining activity. As a result of sub-
sidence, whole settlements, meadows and fields submerged and flooded. Up to 1983 fly ash slurry
from the [o{tanj Thermal Power Plant was transported by pipeline and emptied into Velenjsko jeze-
ro. It brought ash and calcium hydroxide to the lake, raising the pH of lake water to 12. Since 1983
the ash was used to build in embankments, but effluent with a pH around 12 remained the predom-
inant polluter of the lake until 1994. After reconstruction of the fly ash system and a closed loop
water cycle (October 1994), biota appeared in the lake again. It was recolonized by phyto- and zoo-
plankton, fish, macrophytes and other organisms. The pH of the lake is now around 8. The lake shore
is sparsely overgrown with emergent plants (e.g. Typha latifolia L., Phragmites australis (Cav.) Trin.
Ex Steud., Schoenoplectus lacustris (L.) Palla [Scirpus lacustris L.]); the major part of the lake shore
consists of bare areas, meadows and allotments. The littoral zone of the lake can be divided into three
main regions: the fairly steep western and south-western unstable shoreline, a north-eastern marshy
area, and the eastern and southern part of the lakeshore, which is used for sunbathing, walking, rid-
ing, bicycling and other recreational activities. Near the shore are allotments.
Macrophyte cover
The method of surveying the entire littoral from a boat, using depthmeter, view box and sam-
pling rake, was applied in the years 1996, 1997, 1999, 2000, 2003 and 2004. In the year 2003 sur-
veying of macrophyte community was carried out in detail. The littoral was checked every month
from June to September. The shoreline was divided into 25 sections of the length 200±2 m. Species
abundance in each section was evaluated according to KOHLER & JANAUER (1995) on a five level
descriptor scale (1 – very rare, 2 – infrequent, 3 – common, 4 – frequent, 5 – abundant, predomi-
nant). The evaluated quantity of plants is interpreted as mass index (MI), which is with »real bio-
mass« (PM) related with the function PM = MI3. Obtained data has been processed by standard
methodology, made in co-operation between the University teams of Hohenheim (Germany) and
Vienna /Austria) (KOHLEER AND JANAUER 1995). The Internet based description of the methodology
is accessible on the internet side www.midcc.at. From the data we can calculated two mass indexes;
MMO is the Mean Mass Index of the individual species with respect to the survey transects they
occur, MMT is the Mean Mass Index of individual species with regard to the full length of the lake
shoreline. The distribution ratio »d« of each species stands for MMT3/MMO3. Nearly similar and
high values of MMT and MMO (»d« value is near 1) reveal that a species is abundant and that it
occurred in almost all sections – the distribution of the species is homogeneous.
Zdenka Mazej, Mateja Ep{ek: The macrophytes of lake Velenjsko jezero... 23
MIi = Mass Index of species in transect i
Ali = length of transect i, where species occurred
GL = total length of lake shoreline
stevilka 1_05.qxp  13.12.2005  12:32  Page 23
The Relative Plant Mass (RPM %) was used to calculate the quantitative significance of indivi-
dual species in a section (PALL & JANAUER 1995).
PMxi = MIxi
3
RPMx = relative plant mass of species x
MIxi = for any transect i estimated mass of the species x
PMxi = plant mass of species x in transect i
Li = length of lake transect i
j = running index of the different species
Physical analyses of water:
Water transparency was measured with a Secchi disk. Temperature at 30 cm and pH were meas-
ured with a MultiLine P4.
Results
After restoration of the lake Velenjsko jezero, macrophytes, almost instantaneously, started to
gradually overgrow large surface of the littoral. In the Tab. 1, presence and relative abundance of dif-
ferent macrophyte species in lake Velenjsko jezero for the period 1996 – 2004 is presented. The pio-
neer species that appeared in the year 1996 were Chara sp., Nuphar lutea (L.) Sibth. & Sm. and
Potamogeton crispus L.. They colonized only a minor part of the littoral. Only three years later almost
the whole littoral was overgrown and the species composition had become more heterogeneous.
Changes in quantitative relationships between the species varied as well. Potamogeton crispus was the
dominant species till 1997. In the following years Najas marina All. and Potamogeton filiformis Pers
became the most abundant species in the lake.
Acta Biologica Slovenica, 48 (1), 2005 24
Species / Year of survey Abbrev. 1996* 1997 1999 2003 2004 
Jun Jul Sept Aug Jun Jul Aug Jun Jul Aug 
Chara sp. Cha sp 1 - - - - - - 1 1 1 
Myriophyllum spicatum L. Myr spi - 2 2 2 2 2 1 2 2 2 2 
Najas marina All. Naj mar - - - 3 4 1 3 4 - 2 4 
Najas minor All.  Naj min - - - 2 3 - - - - 1 2 
Nuphar lutea (L.) Sibth. Et Sm. Nup lut 1 1 1 1 1 1 1 1 1 1 
Potamogeton crispus L.  Pot cri 4 3 1 1 2 1 1 3 1 1 
Potamogeton filiformis Pers. Pot fil - 1 - - 1 2 3 3 3 3 3 
Potamogeton lucens L.  Pot luc - - - - 2 1 2 2 1 1 2 
Potamogeton nodosus Poir. Pot nod - - - - 2 1 1 1 1 1 1 
* Relative abundance of the species was not defined.
Table 1: Presence and relative abundance of different macrophyte species in lake Velenjsko jezero for the
period 1996 – 2004.
Presence: ♦ – present, – – not present. Relative abundance: a five level descriptor scale (1 – very rare, 2
– infrequent, 3 – common, 4 – frequent, 5 – abundant, predominant) (KOHLER & JANAUER 1995).
Tabela 1: Prisotnost in relativna abundanca posameznih makrofitskih vrst v Velenjskem jezeru v letih
med 1996 in 2004. 
Prisotnost: ♦ – prisotna – – ni prisotna. Relativna abundanca vrst: petstopenjska lestvica (1  = zelo redka;
2 = redka; 3 =zmerno zastopana; 4 = pogosta; 5 = prevladujo~a vrsta)  (KOHLER & JANAUER 1995).
stevilka 1_05.qxp  13.12.2005  12:32  Page 24
From the Fig. 1, where the distribution and relative abundance of different macrophyte species
around lake Velenjsko jezero is presented for August 2003, it is evident that Najas marina and
Potamogeton filiformis were the most abundant species in the lake in the late summer.
It can be seen from Fig. 2 that the quantitative relation among species during the growth season
varied enormous. Species Potamogeton filiformis was dominant in June, while Najas marina was the
predominant species in the lake in the late summer (RPM was 68.5% in August and 84.6% in
September). Other species were much less abundant.
Zdenka Mazej, Mateja Ep{ek: The macrophytes of lake Velenjsko jezero... 25
Figure 1. Distribution and abundance of different macrophyte species around lake Velenjsko jezero in
August 2003. The Lake was divided into 25 section with the length of 200±2 m. 
Slika 1: Distribucija in abundanca razli~nih makrofitskih vrst v Velenjskem jezeru avgusta 2003. Jezero
smo razdelili na 25 transektov dol`ine 200±2 m.
Figure 2. Relative plant mass (RPM %) throughout the season 2003 - Quantitative relation among
species during the growth season.
Slika 2: Spreminjanje razmerja v relativni rastlinski biomasi (RPM %) med razli~nimi vrstami makrofi-
tov od junija do septembra 2003.
stevilka 1_05.qxp  13.12.2005  12:32  Page 25
From the high »d« values, near 1 (Fig. 3) it is evident that Najas marina and Potamogeton fili-
formis overgrew most of the littoral in August and September, but the share of Potamogeton filiformis
was much smaller than that of Najas marina. The RPM of Potamogeton filiformis was only 25.2 %
in August and 8.2 % in September (Fig. 2).
Tab. 2 presents some physical characteristics of the water of lake Velenjsko jezero, in the years
1997, 2000, 2003 and 2004. The mean pH of the lake water was around 8 without any significant
variations. The mean Secchi disk transparency (Zs) was the highest in 1997, but in the next years it
decreased, while the mean temperature of the water increased.
Most macrophyte species colonized only shallow part of the littoral in 1997 (Tab. 3). This year,
species Potamogeton crispus reached the maximum depth of 3.5 m. Four species (Najas marina –
Zc = 4.0 m, Myriophyllum spicatum – Zc = 4.0 m, Potamogeton lucens – Zc = 4.0 m and
Acta Biologica Slovenica, 48 (1), 2005 26
0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1
Myr spi Pot fil Pot luc Pot nod Pot cri Naj mar Nup lut
Macrophyte species
"d
" 
va
lu
e Jun
Jul
Aug
Sept
Figure 3. The distribution ratio - »d« values (the ratio between MMT3 and MMO3) for different species
throughout the season 2003.  
Slika 3: Distribucijski kvocient - »d« vrednost (razmerje med MMT3 in MMO3) za razli~ne makrofitske
vrste preko sezone 2003.
Year Sechi disc 
transparency (m) 
Temperature (oC) pH P-tot. 
 (mg/l) 
N-tot.
(mg/l) 
1997 5.9 (4.2/9.0) 19.8 (17.8/21.3) 8.3 (8.2/8.7) 0.24 (0.13/0.44) 2.0 (1.47/2.57)
2000 4.5 (3.2/5.0) 22.2 (19.8/25.4) 8.4 (8.2/8.8) - - 
2003 4.6 (4.0/5.5) 23.4 (19.4/25.8). 7.8 (7.4/8.3) 0.1 (0.1/0.1) 1.3 (0.9/2.1) 
2004 3.7 (3.0/4.5) 21.7 (19.0/23.7) 8.2 (8.1/8.2) 0.1 (0.1/0.1) - 
Table 2: Mean physical and mean chemical characteristic of water in lake Velenjsko jezero averaged over
the period May to September in the years 1997, 2000 and 2003; average value (minimum value/maxi-
mum value).
Tabela 2: Povpre~ni rezultati fizikalnih meritev in kemijskih analiz vode v Velenjskem jezeru v ~asu od
maja do septembra v letih 1997, 2000, 2003 in 2004; povpre~je (minimalna/maksimalna vrednost).
stevilka 1_05.qxp  13.12.2005  12:32  Page 26
Potamogeton filiformis – Zc = 5.5 m) colonized the deepest part of the littoral in the year 2003. From
the data of the Table 3, negative relationship between Zs and maximum colonization depth (Zc) was
calculated – correlation coefficient Zs/Zc: r = – 0.59, n= 14.
Discussion
Lake Velenjsko jezero could be classified as meso-eutrophic according to the level of total phos-
phorus (OECD 1982, MAZEJ & GABER{~IK 1999), what offered good conditions for quick coloniza-
tion of macrophytes after restoration of the lake. Lake Velenjsko jezero, because of its original basin
shape, has a steep slope in its littoral along the majority of the lakeshore. This is the reason why only
a narrow area of shoreline is colonized by submersed macrophytes. ANDERSSON (2001) asserted that
the geomorphology of a lake basin is the primary factor affecting the structure of the interface zone
between land and water. The steepness of the lake margins is decisive for sediment stability along
slope gradients, which in turn influences the establishment of vegetation. The pioneer species, which
colonized only a minor part of the littoral in the year 1996, were Chara sp., Nuphar lutea and
Potamogeton crispus (MAZEJ 1998). Only three years later these species are not important compo-
nents of the littoral vegetation anymore. Chara sp. disappeared from the lake when other macrophyte
species overgrew the littoral in 1999, but it was detected in a very small quantity again in 2004. It is
known that Charophytes are pioneers among macrophytes, and colonize a new habitat very quickly
(PALMA-SILVA & al. 2002), but they are usually not competitive with angiosperms (BLINDOW 1992).
Nuphar lutea has remained more or less at the same abundance at the same location throughout these
years. Floating-leaved species may be expected to have a faster occupancy of areas with shallower
water and smaller fetches, and the development of the floating-leaved macrophyte community may
require years (REA & al. 1998). It has been reported (NICHOLS & SHOW 1986, BOLDUAN & al. 1994,
JIAN & al. 2003) that Potamogeton crispus and Myriophyllum spicatum are very invasive species,
which usually form a very dense population and establish large monospecific weed beds in many
lakes. However, this was not the case in lake Velenjsko jezero. Potamogeton crispus was the domi-
nant species till 1997. The life history of Potamogeton crispus differs from most other submersed
Zdenka Mazej, Mateja Ep{ek: The macrophytes of lake Velenjsko jezero... 27
Zs = 5.9 m  Zs = 4.6 m
Chara sp. 0.5 - 
Myriophyllum spicatum L. 3.0 4.0 
Najas marina  All.  2.0 4.0 
Najas minor All. 1.5 - 
Nuphar lutea (L.) Sibth. Et Sm. 2.0 2.0 
Potamogeton crispus L. 3.5 3.0 
Potamogeton filiformis Pers. 0.3 5.5 
Potamogeton lucens L. - 4.0 
Potamogeton nodosus Poir. - 2.0 
Table 3: Maximum colonization depth (Zc) of seven macrophyte species in 1997 and in 2003; Zs (mean
Secchi depth).
Tabela 3: Najve~ja globina uspevanja (Zc) sedmih makrofitskih vrst v letu 1997 in v letu 2003; Zs
(povpre~na Secchi-jeva globina).
stevilka 1_05.qxp  13.12.2005  12:32  Page 27
plants. Biomass production of Potamogeton crispus often reaches its maximum in early summer,
allowing it to avoid competition from other species in the habitat primarily because they are still in
the dormant state (TOBIESSEN & SNOW 1984). Young plants of Potamogeton crispus and
Myriophyllum spicatum overwinter, and then grow rapidly in the spring. In this respect, the two
species are similar (BOLDUAN & al. 1994). By early summer plants undergo senescence processes
and then remain dormant until autumn. It is known that Potamogeton crispus grows well in eutroph-
ic lakes, at low temperature and very low light intensities, being an important primary producer in
freshwater ecosystems, providing a good food source for herbivorous fishes (JIAN & al. 2003).
Grazing by fish, birds and invertebrates may be an important factor that limits development of plants.
Grazing sensitivity differs among submersed macrophytes (JACOBSEN & SAND-JENSEN 1992,
WEISNER & al. 1997), and it has been proposed that selective grazing affects species composition and
even succession (CRAWLEY 1983). It was ascertained that species of genus Potamogeton were signif-
icantly more heavily grazed by invertebrates (mean 4.2 % of leaf area) than non-Potamogeton species
(mean 0.8 % of leaf area) (JACOBSEN & SAND-JENSEN 1992). The grazing experiments made by
Weisner & al. (1997) also showed that non-Potamogeton species like Chara sp. and Myriophyllum
spicatum were not significantly affected by grazing. There are no data in the literature about her-
bivory on the species Najas marina, but we assume that this species is not tasteful food for herbi-
vores due to its fragility and its prickly shoots. Fragile shoots are easily broken and spread around
by the help of current, wind and birds. It might be the reason, that Najas marina predominates over
other species in lake Velenjsko jezero, including Myriophyllum spicatum. Myriophyllum spicatum
and Najas marina usually appear together in various natural habitats, where they compete with each
other. The result of studies (AGAMI & WAISEL 2002) showed that Myriophyllum spicatum was more
sensitive to intraspecific competition than Najas marina, and additionally the competitive effects of
Najas marina on Myriophyllum spicatum were stronger than vice versa.
Light availability affects both the biomass and community structure of phytoplankton and sub-
mersed vegetation (VAN DUIN & al. 2001, BEST & al. 2001). Although a significant positive correla-
tion between Secchi disc transparency and the maximum colonization depth of macrophytes has
been found in several studies (HUTCHINSON 1975, CHAMBERS & KALFF 1985, NICHOLS 1992,
MIDDELBOE & MARKAGER 1997, MAZEJ & GABER{~IK 1999), our study showed that transparency was
not the main factor which determined the depth distribution of macrophytes in lake Velenjsko jeze-
ro. The maximum colonisation depth of macrophytes is usually ascribed to light attenuation in the
water column and the minimum light requirement for growth (BLINDOW 1992), although other
parameters such as surface irradiance, hydrostatic pressure, water colour, temperature, grazing pres-
sure, substrate type and epiphyte loading can also affect maximum colonization depth (SAND-JENSEN
1989, VAN DUIN & al. 2001). Tall macrophytes (caulescent angiosperms and charophytes) compen-
sate for light limitation by shoot growth towards the water surface, so maximum colonization depth
is therefore independent of transparency (MIDDELBOE & MARKAGER 1997). Although mean Secchi
disc transparency was higher in 1997 than in 2003, the maximum colonization depth of macrophytes
(Potamogeton crispus) was only 3.5 m in 1997 and 5.5 m in 2003 (Potamogeton filiformis). The
results of ROONEY AND KALFF (2000) showed that angiosperms colonized deeper parts during years
characterized by an early warming of the water, independent of underwater irradiance. The year 2003
was very warm with high May air temperatures. The average temperature of lake water was 3.6 
o
C
higher than that in 1997. Since the majority of plants reproduce asexually, an earlier start to the grow-
ing season allowed plant communities more time for colonization.
Acta Biologica Slovenica, 48 (1), 2005 28
stevilka 1_05.qxp  13.12.2005  12:32  Page 28
Conclusion
The lake Velenjsko jezero has offered good conditions for development of macrophytes in less
than ten years. In this short period, species composition and the quantitative relationships between
the species varied enormously. Therefore further changes are expected in the coming years. We
assume that plant interactions might constitute the main controlling factor regulating the distribution
of macrophytes and coming projects should be oriented in studying plant interaction in grater detail.
Povzetek
Do leta 1983 je bilo Velenjsko jezero odlagali{~e pepela iz termoelektrarne [o{tanj. Od leta 1983
naprej so s sedimentacijo lo~evali pepel od transportne vode. Pepel so odlagali na deponijo, vodo pa
{e naprej ~rpali v jezero, kjer se je pH dvignil na okoli 12 in iz jezera so izginile vse oblike `ivljen-
ja. @e eno leto po uvedbi zaprtega kroga transportne vode leta 1994, kjer vodo ~rpajo nazaj in jo
ponovno uporabijo, se je pH na povr{ini jezera zmanj{al na 9, leta 1997 pa pH vode po celotnem glo-
binskem profilu ni presegal 8,7 in vanj se je po dalj{em obdobju spet za~elo vra~ati `ivljenje.
Vrstno sestavo in razporeditev makrofitov v Velenjskem jezeru spremljamo bolj ali manj redno
`e od leta 1996. Makrofiti so pri~eli po sanacijskih ukrepih zelo hitro naseljevati prazen litoral, saj
so bile nudene ugodne razmere – dosti hranil, podlaga za ukoreninjenje in ugodne svetlobne razme-
re. Velenjsko jezero je nastalo z ugrezanjem, zaradi ~esar se njegova obala na mnogih mestih zelo
hitro spusti v globino. To je tudi razlog, zakaj je z makrofiti pora{~en le ozek pas litorala. Pionirske
vrste, ki so se pojavile v prvem letu raziskav (1996) so bile Chara sp., Nuphar lutea in Potamogeton
crispus. Potamogeton crispus je bila dominantna vrsta do leta 1997. V naslednjih letih pa sta vrsti
Najas marina in Potamogeton filiformis prevladali nad ostalimi vrstami v jezeru. Chara sp. je bila
prisotna v zelo majhni koli~ini v jezeru le v letih 1996 in 1997, v naslednjih letih pa je v ob~asnih
pregledih litorala nismo ve~ zasledili. Zopet pa smo jo na{li na istem mestu v letu 2004. V vseh teh
letih je prihajalo do spremenjenega kvantitativnega in kvalitativnega razmerja med vrstami. V prvih
letih so makrofiti naselili predvsem del med ~olnarno in pritokom Sopote, medtem ko je bil del ob
deponiji nepora{~en. V naslednjih letih so se makrofiti raz{irili tudi v ostala obmo~ja litorala,
zmanj{ala pa se je njihova pojavnost tam, kjer se ka`e ve~ji vpliv zaledja – ob nasipu in na obmo~ju
pe{poti pod vrti~karskim naseljem »Kinte-Kunte«. Od leta 1996 pa do leta 2004 je {tevilo vrst iz 3
naraslo na 9. Medtem ko ka`ejo vrste Najas marina, Potamogeton filiformis, Potamogeton lucens in
Potamogeton nodosus pozitiven trend v razvoju, pa v zadnjih letih opa`amo manj{e pojavljanje vrst
Chara sp., Myriophyllum spicatum, Potamogeton crispus in Najas minor.
Le nekaj let je minilo od naselitve prvih makrofitov v jezeru, zato lahko pri~akujemo, da bo
pri{lo v naslednjih letih {e do dolo~enih sprememb in sicer tako v vrstni sestavi makrofitov kot tudi
v razporeditvi le-teh.
Aknowledgements
Authors thank to Prof. Dr. Alenka Gaber{~ik and Dr. Mateja Germ for valuable comments on the
manuscript.
Zdenka Mazej, Mateja Ep{ek: The macrophytes of lake Velenjsko jezero... 29
stevilka 1_05.qxp  13.12.2005  12:32  Page 29
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