Distribution of macrophytes in different water-bodies (habitats) influenced by the Gabcíkovo hydropower station (Slovakia) – present status Helena Othelová 1 and Milan Valachovič 2 With 10 figures and 1 table in the text Abstract: The distribution of macrophytes in the Slovak reach of Danube is presented in three types of water bodies with different environments and management regimes: i) The Old Danube River (1839-1811 km), ii) the anabranch system iii), the seepage canal. The succession and content of aquatic plants changed depending on hydrological regime. The succession of macrophytes started in the Old Danube. Zannichellia palustris is the first hydrophyte that overgrows the river bed, which is covered by a thin layer of fine sediment. Temporary denuded pools on flat littoral zone provided favourable conditions for succession. The semi-natural anabranch system supported high biodiversity, where 24 species in three backwaters were recorded. Also the new artificial habitat of the seepage canal is species rich. Some of the rare and endangered species, such as Groenlandia densa, Hippuris vulgaris, Apium repens and Characeae found suitable habitats here. The distribution of neophyte, Elodea nuttallii increased rapidly in the Slovak part of Danube flood plain. 1 Institute of Botany, Slovak Academy of Sciences, Dúbravská cesta 14, SK-842 23 Bratislava, Slovakia, [email protected]. 2 Institute of Botany, Slovak Academy of Sciences, Dúbravská cesta 14, SK-842 23 Bratislava, Slovakia, [email protected]
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Distribution of macrophytes in different water-bodies (habitats)
influenced by the Gabcíkovo hydropower station (Slovakia) – present
status
Helena Othelová1 and Milan Valachovič2
With 10 figures and 1 table in the text
Abstract: The distribution of macrophytes in the Slovak reach of Danube is presented in
three types of water bodies with different environments and management regimes: i) The
Old Danube River (1839-1811 km), ii) the anabranch system iii), the seepage canal. The
succession and content of aquatic plants changed depending on hydrological regime. The
succession of macrophytes started in the Old Danube. Zannichellia palustris is the first
hydrophyte that overgrows the river bed, which is covered by a thin layer of fine sediment.
Temporary denuded pools on flat littoral zone provided favourable conditions for
succession. The semi-natural anabranch system supported high biodiversity, where 24
species in three backwaters were recorded. Also the new artificial habitat of the seepage
canal is species rich. Some of the rare and endangered species, such as Groenlandia densa,
Hippuris vulgaris, Apium repens and Characeae found suitable habitats here. The
distribution of neophyte, Elodea nuttallii increased rapidly in the Slovak part of Danube
flood plain.
1 Institute of Botany, Slovak Academy of Sciences, Dúbravská cesta 14, SK-842 23 Bratislava, Slovakia, [email protected]. 2 Institute of Botany, Slovak Academy of Sciences, Dúbravská cesta 14, SK-842 23 Bratislava, Slovakia, [email protected]
Introduction
Different aspects of the aquatic vegetation of the Danube flood plain were studied in
Slovakia . HEJNÝ (1960) provided a reputable source of information about auto-ecology
of aquatic and marsh plants and their localities. Phyto-sociological evaluations of aquatic
vegetation by Braun-Blanquet method were performed later by OTAHELOVÁ (1978, 1980),
OTAHELOVÁ, HUSÁK (1992), and ADAMEC et al. (1993), the latter also complemented with
ecophysiological studies. In recent years more papers relating to endangered species
appeared (OHRÁDKOVÁ 1998, OTAHELOVÁ 1998, OTAHELOVÁ, BANÁSOVÁ 1997).
However, detailed data of the spatial and temporal distribution macrophytes are absent.
These are very important, especially for the monitoring of changes caused by human
impact.
Construction of the Gabcíkovo hydropower station altered the hydrological regime
causing changes in the distribution of macrophytes, as well as in the vegetation along both
banks (RATH 1997, ŠOMŠÁK 1999). The aim of this study was to map the present
distribution of macrophytes along fixed sections and to prepare the foundations for future
monitoring. Quantitative values for macrophytes were compared with abiotic data and
some relationships between the distribution of plants and ecological factors were
observed.
Study area (Fig. 1)
The Slovak part of the Danube River is 172 km long. The mean discharge in Bratislava is
2,000 m3.s-1, the maximum and minimum flow rates are above 10.000 m3 s-1 and 570 m3 s-1
respectively. The most important tributaries are the Morava (March), Váh, Nitra, Hron and
Ipel (Ipoly).
The Danube flows through the Little Carpathians at the Devín Gate into the Danube
lowland (Podunajská nížina). The lowland relief characteristics typical of the fluvial plain
and lies between altitudes of 106 to 128 metres above sea level. This flattening of the
Danube’s gradient caused extensive aggradiation of a large amount of gravel and sand and
creation of a massive fluvial fan (flood plain) between Bratislava and Komárno during the
Quaternary period. The flood plain along the Danube represents a unique continental delta,
system of meanders and dead branches, a so-called "Inland delta”.
The territory has the warmest and driest climate of Slovakia (mean January temperatures
from -1 to -4 °C, July temperatures from 18.5 to 20.5 °C and the mean annual precipitation
from 0.55 to 0.6 m. The natural course of the Danube River in Slovakia has been strongly
influenced by human activities for two centuries. Since the early eighteenth century, free
meandering of the river was gradually limited by construction of the dykes. Thus, the wide
floodplain with its network of branches was reduced to a relatively narrow strip varying in
width from three to five kilometersm.
In the 1980´s work was started on the construction of the Gabcíkovo hydroelectric water
system which was completed in 1993. Diversion of the main stream into the bypass canal
began in October 1992. Presently, a discharge between 200 to 400 m3 s-1 is permanently
released through the weir in the Old Danube at river km 1851.7, where the Danube was
dammed. Compared with the original project, the mean monthly discharge (CHALUPKA
1998) was decreased about 83 %. The decreased flow caused succession of the macrophyte
vegetation in the Danube bed (ŠOMŠÁK 1999).
A semi-natural anabranch system surrounded by alluvial forest was preserved on the new
island between the Old Danube and the bypass canal. Owing to different management
regimes there are two distinguishable parts (sections) of this system.
The upper and middle part of the anabranch system on the left bank of the Old Danube
(Dobrohošt-Gabcíkovo section) has been fed with water from the bypass canal through a
special inlet structure since May 1993. The maximum capacity of the structure is 240 m3 s-
1, which makes it possible to simulate flood conditions in this system. The discharge of 30
m3 s-1 maintains water levels and moisture conditions in this region during the period of
vegetative growth. To improve the water balance and the distribution of flows throughout
the anabranches, cascades were rebuilt. Culverts and broad-crested weirs ensure flow
continuity and control water levels. To prevent the water from being lost to the Old
Danube, all contact points are blocked except the confluence of the main branch and the
river near Gabcíkovo. Thus water levels in the anabranches are presently higher than in
Old Danube (LISICKÝ & HOLUBOVÁ 1999). In case of the main branch, current speed
increased and the relationship between the drift, sedimentation and erosion changed. The
water level rose and the width of the arms increased. The banks became longer and less
straight and new pools with stagnant water appeared in depressions. The old main channel
of the Danube started to meander within the original riverbanks and the weirs provided
greater variability in water current. Since then, water level fluctuation has become
relatively low, with the exception of controlled flooding (KRNO et al. 1999). Relatively
good quality forest, with low defoliation, stands in the river branch system area between
Dobrohošt and Gabcíkovo which was controlled by supplying water to the within-dike
zone. The direct flooding has been manifested in the herbaceous vegetation by the
substitution of mesophilous and nitrophilous species by more hygrophilous and less
nitrophilous species (UHERCÍKOVÁ et al. 1999).
In the lower part of the anabranch system (Gabcíkovo-Sap section) the arms are not
artificially fed by water and are strongly influenced by the backward movement of water
from the confluence of the old river bed with the bypass canal (VRANOVSKÝ & ILLYOVÁ,
1999). The discharge rate varies and follows the pattern of the discharge rate at
Bratislava, and is also partially dependent s on the operation of the turbines (water level
fluctuation ca 0.5 m). Consequently, silt sedimentation has increased in this area and the
water level is slightly lower (KRNO et al. 1999). The area of the backwater represents
ideal conditions for the natural regeneration (successive development) of the willow
poplar communities (Salici-Populetum typicum, phragmito-caricetosum and
myosotidetosum) (ŠOMŠÁK 1999).
Canals are a new type of artificial aquatic habitat. On both banks of the bypass canal
seepage canals were built between July 1979 to May 1992. The researched seepage
canal is located on the right side of the bypass canal. Its total length is ca 20 km. It
follows its headwater section from Dobrohošt to the Gabcíkovo hydropower station,
where discharges into the tailrace section of bypass canal. The canal is fed by seepage
water from the Cunovo reservoir and the bypass canal. In times of high water in the
Danube, the water of the tailrace section of the bypass canal is released to the seepage
canal and it reached as far as Bodíky village. The lower sections of the canal gradually
reach widths between 2 and 7 m. The depth varies from 0.5 m to 6 m and the discharge
from 0.3 to 4 m3 s-1. The gradient of bed is 0.03-0.5%. A system of eight weirs controls
the water level. The bank is covered by the geo-textile, a 0.3 m thick coat of gravel-sand,
and by 0.2 m coat of humus.
The Danube floodplain in Slovakia has been protected since 1998 under the Act of the
National Council No. 287/1994 on Nature and Landscape Protection as a Protected
Landscape Area (PLA). This level of protection corresponds with Category V of the IUCN
classification. The upper part of the Žitný ostrov Island was declared a protected water
management area in 1978.
Material and Methods
A standardized method including field estimation as well as the data processing and
display methods was used for the evaluation of aquatic vegetation (KOHLER & JANAUER
1995). Aspects of dominance and characteristic types of hydrophyte distribution are
discussed by the use of numerical derivatives: distribution diagrams, relative plant mass
(RPM), means mass index (MMO, MMT) and a distribution ratio (d). Three types of
habitats influenced by construction of the Gabcíkovo hydropower complex were chosen
for the testing of the response to the water regime changes (Fig. 1):
1. The old main channel of the Danube River, now called ”Old Danube”- the Slovak side
lies between 1839 and 1811 river-kilometres. Length of the surveyed stretches was always
1 km in main channel. Length of stretches of another habitats depended on the vegetation
and environment. Numbering of stretches: 1-40. Date of survey: August 17-18, 1999.
2. Three ecologically different side arms in anabranch system on the left bank of the Old
Danube were surveyed from July to August 1999:
• Bodícka brána backwater - a parapotamon type of side arm, located in the Dobrohošť –
Gabcíkovo section. No. of stretches: 41-48.
• Královská lúka backwater- a plesiopotamon type of side arm, located in Dobrohošt –
Gabcíkovo section. No. of stretches: 49-52.
• Dedinský ostrov backwater – a parapotamon type of side arm, located in Gabcíkovo –
Sap section. No. of stretches 53-58.
3. The seepage canal on the right bank of the bypass canal. No. of stretches: 59-93. Date of
survey: July-August 1999.
All stretches were located by GPS and delineated onto a 1:25 000 scale map. For precise
location aerial photographs were used.
Results
A total of 42 species (36 vascular plants, 2 bryophytes, 4 algae) were found in the Danube
River and its flood plain area between 1839 and 1811 river kilometres (Table 1).
Old Danube River
Species List (Table 1, column 1)
The main channel of the Old Danube contained 18 species (17 vascular plants, 1
bryophyte).
Distribution Diagram (Figure 2)
The number of species in 40 stretches of 28 river kilometres of the main river channel and
12 pools on the left bank ranged between 0 and 10. The main channel was relatively poor
in terms of the number of species, predominantly 1(-2) species per kilometre. The upper
half of surveyed main channel had contiguous growth, but varying amount of Zannichellia
palustris. In the adjacent pools, an average of 4 species was recorded (max. 10), mostly
comprised of Elodea nuttallii, Potamogeton species, and Ceratophyllum demersum.
Relative Plant Mass (Figure3)
Submerged rhizophytes were the major growth form in the Old Danube River with
Z. palustris being by far the dominant species.
Mean mass Index and Distribution Ratio (Figure 4)
Potamogeton perfoliatus reached an MMO near 4 and Najas marina 3, but both have very
low MMT values and are absent from most of the length of the watercourse, indicating
their clumped distribution in Old Danube. Associated species had MMO values below 3.
Truly ubiquitous species were not found in any stretches with the exception of
Zannichellia palustris which attained a “d” value close to 0.5, whereas in all species “d”
values are below 0.2.
Anabranch system
Species List (Table 1, Column 2)
A total of 24 species (22 vascular plants, 1 bryophyte, 1 algae) was found in the three
backwaters surveyed.
Distribution diagram (Figure 5)
The three water-bodies were divided into 18 stretches and the accumulated length of the
survey stretches was ca 5.5 km. The length of relatively uniform survey stretches ranged
from 25 to 1000 m. The number of species varied from 4 to 11. With the exception of the
Královská lúka backwater, a long part of the arms had contiguous growth, but with
varying amounts of Elodea nuttallii. Its invasive distribution during previous years
especially in parapotamon tip of side arms was evident.
Relative Plant Mass (Figure 6)
Elodea nuttallii was the dominant hydrophyte. Subdominant species were Ceratophyllum
demersum, Potamogeton crispus and Myriohyllum spicatum with RPM value between
10-20 %.
Mean Mass index and Distribution Ratio (Figure 7)
The most abundant and ubiquitous species were E. nuttallii and Ceratophyllum demersum
in contrast to Salvinia natans and Nymphaea alba which had “clumped” distributions.
Seepage canal
Species list (Table 1, column 3)
25 species were recorded in this watercourse (Table 1). The majority of species were
common in the adjacent water bodies, but some currently occurred only here.
Distribution Diagram (Fig. 8)
The 19.8 km total length of the seepage canal was divided to 34 uniform stretches by
varying in length from 30 to 2100 m. The shortest stretches were usually in the weirs of
the section. The length of the majority of stretches varied from 300 to 800 m.
Relative Plant Mass (Figure 9)
Submerged rhizophytes were by far the dominant growth form. Only two stoneworts
Chara foetida and Ch. hispida reached RPM values between 10 and 20 %. RPM of other
species was less than 8%.
Mean Mass Index and Distribution Ratio (Figure 10)
Chara hispida, Ch. foetida, and Elodea canadensis reached the MMO values between 4
and 5. The distribution of Ch.hispida and Ch. foetida is middle-clumped. No truly
ubiquitous species were recorded, but 11 species had “d” values ca 0.5.
Discussion
The new hydrological regime of Danube River manifested itself in the succession of
plants in riverbed. From the point of view of the distribution of the macrophytes in Old
Danube it is possible to distinguish three reaches:
Theupper reaches impound (1839-1831 km) - In the main river channel only
Zannichellia palustris occurred most regularly. Elodea nuttallii was recorded here in only
one stretch of the main channel (1836 km) but the occurrence extends to the adjacent
oxbow. In the oxbow Ceratophyllum demersum and Z. palustris also grow. There are
also several semi-separated oxbows where Z. palustris occurred.
The middle reaches (1830-1820 km) - with the highest relative diversity of plant species
and habitats (anabranch system). Z. palustris continued to be dominant in the main
channel. Sporadic growths ofCeratophyllum demersum, Elodea nuttallii, and Ranunculus
trichophyllus occurred and created common communities in neighbouring oxbows.
Oxbows were relatively rich in macrophytes. The neophyte Elodea nuttallii dominated
but other species such as Zannichellia palustris, Potamogeton crispus P. pusillus, P.
pectinatus, Lemna minor and Myriophyllum spicatum were frequently present and in
varying amounts.
The lower reaches (1820-1811 km) -in these reaches the water level fluctuates, as they
are situated near the confluence with the new bypass canal. This influence is reflected in
the species composition. In left river bed Polygonum amphibium, Butomus umbellatus,
and Rorippa amphibia were recorded.These plants adapt to water level changes as
hydro-, limosal and terrestrial ecophases. Typical hydrophytes such as Elodea nuttallii
and Myriophyllum spicatum were sparse in the lower reaches. Mosses were found only in
one stretch (1813 rkm), within the Phragmites australis community. Cinclidotus riparius
(syn. C. nigricans) specifically and other common species of the Danube bank (cf. PIŠÚT
1981) were recorded in 2000 in 1811 km on a gravel deposit at the confluence with
bypass canal. Zannichellia palustris is typically absent from these lower reaches,
probably as a result of the high turbidity of the water. The last three kilometres near the
confluence of the Old Danube and new bypass canal were devoid of vascular plants.
RATH (1997) recorded a similar floristic spectrum while surveying the right bank
(Hungarian part) of the main channel of the Danube in stretches between 1826 and 1843
rkm in 1996. She recorded practically the same species structure (16 species) in similar
habitats. The frequency of Z. palustris and Elodea nuttallii has increased slightly over the
past three years.
The first hydrophyte, which overgrows riverbed of Danube River, is Zannichellia
palustris. During 1999 it had the highest distribution in the stretches surveyed. It created
a very low, thin carpet on the riverbed from 1838 to 1821 river kilometres, which is its
typical growth form in running waters. Z. palustris occupied stretches with low flow and
fine inorganic sediment. It was recorded also in adjacent oxbows where light conditions
were favourable. Relatively the most suitable conditions for succession of macrophytes
are on the flat littoral of the Old Danube along with the numerous oxbows and temporary,
ŠOMŠÁK, L. (1999): Flora and vegetation conditions of floodplain ecosystems. In: MUCHA,
I. (Ed.) Gabcíkovo part of the hydroelectric power project environmental impact
review. - Groundwater Consulting, Ltd., Bratislava, 241-246.
UHERCÍKOVÁ, E., PIŠÚT, P. & HAJDÚK, J. (1999): Changes flood-plain forests vegetation in
the permanent monitoring plots and vegetation succession on the Gabcíkovo
structures dikes. In: MUCHA, I. (Ed.) Gabcíkovo part of the hydroelectric power
project environmental impact review. - Groundwater Consulting, Ltd., Bratislava,
281-322.
VRANOVSKÝ, M. & ILLYOVÁ, M. (1999): Zooplankton in the Danube and its left side arm
system. In: MUCHA, I. (Ed.) Gabcíkovo part of the hydroelectric power project
environmental impact review. - Groundwater Consulting, Ltd., Bratislava, 167-174.
Tables:
Table 1
Total list of species in Inland delta of the Danube River (Slovakia)
Figure Captions:
Fig. 1.: Map of surveyed area –Slovak part of the Inland delta of the Danube River. Number
of stretches (Sampling sites) 1-93.
Fig. 2: Distribution Diagram of macrophytes / Old Danube
Fig. 3: Relative Plant Mass / Old Danube
Fig. 4: Mean mass Index and Distribution Ratio/ Old Danube
Fig. 5: Distribution Diagram of macrophytes / Anabranch system
Fig. 6: Relative Plant Mass / Backwaters
Fig. 7: Mean mass Index and Distribution Ratio / Backwaters
Fig. 8: Distribution Diagram of macrophytes / Seepage canal
Fig. 9: Relative Plant Mass / Seepage canal
Fig. 10: Mean mass Index and Distribution Ratio / Seepage canal
Table 1. TOTAL LIST OF SPECIES (1 Old Danube R., 2 Anabranchsystem, 3 Seepage canal )Locality 1 2 3No of survey stretch in map 1- 41- 59-
40 58 93
VASCULAR PLANTS Abbr. GF*Apium repens (Jacq.) Lag. Api rep saButomus umbellatus L. But umb saCallitriche cophocarpa Sendtn. Cal cop saCallitriche sp. Cal spe saCeratophyllum demersum L. Cer dem spEleocharis acicularis (L.) Roem. et Schult. Ele aci saElodea canadensis Michx. Elo can saElodea nuttallii (Panch.) H. St. John Elo nut saGroenlandia densa (L.) Fourr. Gro den saHippuris vulgaris L. Hip vul saHydrocharis morsus-ranae L. Hyd mor apLemna minor L. Lem min apLemna trisulca L. Lem tri spMentha aquatica L. Men aqu saMyosotis palustris ag. Myo pal saMyriophyllum spicatum L. Myr spi saMyriophyllum verticillatum L. Myr ver saNajas marina L. Naj mar saNuphar lutea (L.) Sm. Nup lut flNymphaea alba L. Nym alb flPolygonum amphibium L. Pol amp flPotamogeton crispus L. Pot cri saPotamogeton lucens L. Pot luc saPotamogeton nodosus Poir. Pot nod flPotamogeton pectinatus L. Pot pec saPotamogeton perfoliatus L. Pot per saPotamogeton pusillus agg. Pot pus saRanunculus circinatus Sibth.. Ran cir saRanunculus trichophyllus Chaix Ran tri saRorippa amphibia (L.) Besser Ror amp flSalvinia natans (L.) All. Sal nat apSparganium emersum Rehrmann Spa eme flSpirodela polyrhiza (L.) Schleid. Spi pol apTrapa natans L. Tra nat flUtricularia vulgaris L. Utr vul spZannichellia palustris L. Zan pal saNON-VASCULAR PLANTSAlge filamentosaea Alg fil spChara foetida A. Braun Cha foe saChara fragilis Desv. Cha fra saChara hispida L. Cha his saBryophyt sp. ??? saRiccia fluitans L. emend Lorb. Ric flu sp