PART 7
Biological Monitoring
The biological monitoring of agreed groups of aquatic or terrestrial fauna on the Slovak side was performed on six complex monitoring areas. On these areas the phytocoenological observations were realised as well, which record the spring and the summer aspect of monitoring areas. Moreover in 1999 the aquatic macrophyte observation was started again. The same groups of fauna and flora, agreed in the frame of the joint monitoring, are monitored at 31 monitoring sites on the Hungarian side (Fig. 7-1). There are differences in some monitoring methods (observation of Trichoptera and Ephemeroptera groups, evaluation of aquatic macrophyte).
7.1. PhytocoenologyThe left side river branch system The monitoring area No. 2600 is situated upstream of the water supply to the left side river branch system, and the positive impacts of the water supply and artificial floods does not influences this area. Signs of continuous drying out of this monitoring area were already observed since seventies of the twentieth century. This process became more intensive due to the significant decrease of ground water level after damming the Danube. However, since 1996 signs of stabilisation of plant communities can be observed. Conditions on the monitoring area No. 2603 and 2604 after introducing the water supply and realising the artificial floods had been influenced positively. The impact of the Gabčíkovo waterworks in the region is not significant. However, the results of last years show that higher attention should be paid to the flooding regime in the future. Changes recorded on the area No. 2603 in the year 2000 are caused by anthropogenic interference to this area – cutting out the neighbouring forest stand. Several parameters on the area No. 2604 indicate changes in phytocoenoses in 2000. However, similar fluctuation of characteristics had already been observed during the monitoring period, and the data did not confirmed unambiguous tendency of changes in the phytocoenological community. Objective monitoring evaluation on this area will be more difficult in the next years, because of cutting the neighbouring forest in this year. Monitoring areas No. 2608 and 2609 are situated in a region with unchanged moisture conditions, created by the backwater effect upstream the confluence of the tailrace channel and the Danube old riverbed. However, the solution of the water regime in this region should not be underestimated. In the last years some signs of continuous change of the phytocoenological community could be noticed (changes in eco-indexes for light, temperature and continentality), which probably cannot be connected to the impact of Gabčíkovo structures. The forest community on the area No. 2609 is stabile, and corresponds to the regularly flooded wetland community. The vegetation conditions at the area No. 2612 are stable, the area is located out of the Gabčíkovo waterworks impact.
The right side river branch system The Hungarian Party performs the monitoring of plant communities (phytocoenological observation and leaf area measurements) and reeds in summer period. The vegetation period in 2000 was rather dry, which is reflected also in the vegetation monitoring results. Plants in the level E1 were significantly drier almost on every monitoring area. During the summer there were a lot of individuals found with twisted and dry leaves. Exceptions were the areas close to the arms supplied by water. The results of leaf area measurements document that on monitoring areas with decreased ground water level (along the Danube river bed) is the leaf area of trees smaller. The ground water level decrease and the absence of floods are demonstrated on willow stands, which requires regular flooding. According to phytocoenological surveys the reed stand at Kisbajcs have not changed in the observation period. Both the size and density of blades fluctuates from year to year with no particular tendency. The reed stand at the oxbow lake near Lipót preserved its homogeneous structure since the water supply has been introduced. The abundance and coverage of plant species of more terrestrial character, which are alien to this kind of vegetation, are low and remain restricted to the shoreline. The reed stand at Malomszer is stable and the density of blades is close to the average of previous years. The outskirts of the reed stand at the Cvek shallow near Cikolasziget dried up and no open water was found. These circumstances cause continuous decline of the reed density. The reed stand at Dunakiliti is similar to the Cvek shallow, but in the channel at the edge of the reed stand water occurs. The reed is healthy near the channel, but further away deterioration is evident.
7.2. Terrestrial molluscsThe left side river branch system The terrestrial molluscs observation results in 2000 on the area No. 2600 prove the stabilisation of this zoocenoses on mezohygrophilous level. This region was characteristic by continuous drying out before damming, due to the continuous deepening of the riverbed. Significant decrease of ground water level in this area after the damming, because of strong drainage effect of the Danube, speeded up this process. After cutting out the neighbouring forest the molluscs community on the area No. 2603 have changed slightly. In the year 2000 the hemi-heliophytic and eurytopic species dominate again. The positive impact of introduced artificial floods from the point of view of terrestrial molluscs was proved on the monitoring area No. 2604 in the year 2000 again. The monitoring results confirm the return of wetland mollusc community. Thanks to the improved hydrological condition the polyhygrophilous species dominate. The mollusc’s community is stable. The monitoring results of the terrestrial molluscs on the monitoring area No. 2608 prove the needs of hydro-technical solution in this region solving the water regime. Enabling the regular flooding of this area seems to be the most important. In the mollusc’s community on monitoring area No. 2608 significant occurrence of eurytopic species was detected. As a consequence of the unchanged moisture conditions the original terrestrial molluscs communities occur on the monitoring areas No. 2609 and 2612. Typical wetland mollusc community was recorded on the area No. 2609 again. The area No. 2612 is characteristic by stable terrestrial molluscs, with the dominance of eurytopic and hemi-hygrophilous species.
The right side river branch system The results on the monitoring site at Ásványráró did not show changes in species composition and abundance of the terrestrial molluscs community. No other data from the Hungarian side was included in the data exchange in 2000.
7.3. MacrophytesSimilarly to the previous years the growth rate, the composition and the amount of macrophytes were determined by the site-specific hydrological conditions, water supply, and temperature and light conditions. The evaluation of macrophytes observation in 2000 is based on observations on both Slovak and Hungarian side.
The left side river branch system As a consequence of the water supply to the river branch system branches the area around the monitoring site No. 2603 get much more amount of water. Macrophytes on the monitoring area decreased significantly comparing to the years 1990-1991. In mass occurrence they are found only along the line structures, banks and at places protected before the strong flow. According to the observation results in 1999 and 2000 the macrophyte communities in the dead arm on the monitoring area No. 2604 are similar to that in 1990-1991. Borders of the dead arm are covered by a reed stand belonging to the association Phragmitetum communis, the open water area is almost fully covered by Ceratophyllum demersum, with occurrence of some endangered species. Macrophytes observation on the monitoring area No. 2608 was performed in the shallow parts of the river arms, which were covered by water in 1990-1991. In 1999 they were without water and the development of the vegetation is typical for dry arm bed occasionally flooded by water. During the summer 2000 the depressions were covered by water, but in the autumn they dried up again. In the plant communities the species of alluvial meadows and shores dominate. The marshy parts of the monitoring area are still covered by the association Phragmitetum communis. In the year 2000 very rich macrophyte communities were observed on the monitoring area No. 2612, similar to records obtained before damming the Danube. However, probably because of climatic conditions offensive spreading of Elodea nuttalii species was observed.
The right side river branch system On the Hungarian side the growth of macrophytes is governed by the controlled water supply, however the weather conditions (lot of sunshine and record warm-up at the beginning of summer) also influences the yields and growth phases. Rather high discharges during the vegetation period did not allowed creation of the macrophytes community on the monitoring site No. 2 in Danube riverbed. Macrophytes were observed on the monitoring site No. 7, which is separated from the main riverbed, where species taking roots and species with flowing leaves were recorded. Hydrological conditions of the inundation area were determined by the ongoing water supply similarly to the previous years, while the air temperatures were higher. The characteristic species composition on the monitoring site No. 9 remained and consists of root-taking species. The retreat of the extension and the amount of macrophytes on the monitoring site No. 4 – Schissler arm – continued also in 2000. This is connected with the creation of permanent connection between the Schissler arm and the Csákányi Danube in 1997. Higher discharges and deeper water does not create favourable conditions for macrophytes development. As a consequence of extremely high air temperatures monitoring sites on the flood-protected area were settled by thermophilous macrophyte species, belonging to the slowly flowing and marshy biotopes, while no significant changes in their communities were recorded. Considering the species composition on the monitoring area No. 6 – Lipóti marsh, it can be stated that there are still certain differences in comparison with the previous state.
7.4. Aquatic molluscsThe Danube The evaluation of the aquatic molluscs community in the Danube is based on the data provided by the Slovak Party (monitoring areas No. 2600, 2608 and 2612). The aquatic molluscs communities in the Danube are relatively stabile, however a slight increase of species indifferent to the flow velocity was observed. The rheophile species Ancylus fluviatilis, Lymnaea ovata and Bithynia tentaculata remain dominant.
The left side river branch system The aquatic molluscs community in the river branch system on the Slovak side is monitored on areas No. 2603 and 2604. The parapotamal of monitoring site No. 2603 has heterogeneous character and is characteristic by high biodiversity of the aquatic molluscs community. The dead arm on the monitoring area No. 2604 is isolated from the other part of the inundation area, owing to what is the area characterised by low species richness also in the year 2000.
The right side river branch system The aquatic molluscs monitoring results refer to high species diversity of the existing biotopes.
7.5. Dragonflies (Odonata)The left side river branch system The species composition of Odonata communities on the Slovak side during the whole observation period is rather poor. After introducing the water supply in the left river branch system in 1993 the water regime of most of branches have changed. This is also the case of branches in the monitoring area No. 2603. In the observed river branch the water level increased and water began to flow. This biotope is settled by rheophile and semi rheophile dragonfly species, however in the year 2000 dominance of eurytopic species was recorded. The portion of stagnicolous species on the monitoring area No. 2604 increased also in the year 2000 and along with this a decrease of species diversity in dragonfly community was recorded. These changes refer to the continuous changing of the plesiopotamal to paleopotamal, which is partly caused by absence of strong floods. In the year 2000 in the dense macrophyte vegetation on monitoring area No. 2612 only five dragonfly species was found. In spite of favourable conditions of the present biotope is the dragonfly community characteristic by low species diversity, however in comparison to the previous year increase of diversity was observed.
The right side river branch system The dragonfly communities on monitoring sites No. 20 (Mosoni Danube at Mosonmagyaróvár) and No. 21 (shallow lakes at Rajka) are characteristic by high stability, while the abundance of observed species is permanently low. The dragonfly community of the marshy biotope on site No. 23 (Parti forest at Mosonmagyaróvár) develops according to the water availability in the respective year. The most expressive changes in the dragonfly community have been recorded on the site No. 22 (Zsejke channel at Lipót), where due to the changed hydrological conditions rather significant change occurred in the community.
7.6. Crustaceans (Cladocera, Copepoda)The Danube The Cladocera community in the Danube main riverbed in 2000 was characteristic by slight increase of species diversity. The tendency of returning the dominance of pelagic species in the medial continued, and is comparable to the state before damming the Danube. Favourable conditions for development of emergent macrovegetation continue in littoral, so phytophilous Cladocera species are represented significantly. Slight increase in Copepoda species diversity in 2000 in the Danube main riverbed has been observed as well, however the observation results show slight unusual dominance of tychoplanctonic species. The community species composition consists also of species typical for river branches.
The left side river branch system Along with the continuous high species diversity of Cladocera community on the monitoring area No. 2603, slight decrease of pelagic species composition have been recorded in the year 2000. The littoral is settled with phytophilous species. The Copepoda species composition on the area No. 2603 in the year 2000 remained unchanged, but it is different from that in the period before the damming – only euplanctonic species occurred. Current occurrence of original planktonic species was 43 %. The community in the littoral is stable, with the dominance of tychoplanctonic species. On the monitoring site No. 2604 continued the spreading of submersed vegetation in plesiopotamal in the year 2000. The Cladocera community remain very rich in species, however a mass occurrence of one pelagic species and tiny abundance of the other present species was recorded. The tendency of replacement the pelagic species by tychoplanctonic species, observed in previous years, was not confirmed in 2000. Rich in species and abundant Copepoda community, with the dominance of euplanctonic species, on the monitoring area No. 2604 occur during the whole observation period. Only fluctuation and changing of dominant species is recorded. For the whole observation period the Cladocera and Copepoda communities on the monitoring area No. 2608 are characteristic by high species diversity and dominance of euplanctonic species. It should be mentioned that continuous isolation of the river branch from the main flow probably would be observed also in the composition of these communities. However, no significant changes were recorded for the time being. Due to the continuous overgrowing of the plesiopotamal on the monitoring site No. 2612 by macrophytes slow continuous replacement of pelagic Cladocera by tychoplanctonic ones is observed. Similar tendency at Copepoda community had been observed in 1999, while in 2000 the euplanctonic species dominated.
The right side river branch system The Cladocera and Copepoda communities in the inundation area in 2000 were rather poor in species and mostly a decrease in abundance was observed too. The highest species diversity was recorded in the Lipót marsh and Schissler arm.
7.7. Caddisflies and Mayflies (Trichoptera, Ephemeroptera)There are differences in the mayflies (Ephemeroptera) and caddisflies (Trichoptera) taxocoenoses monitoring methods used by the Slovak and Hungarian Parties. On the Slovak side the larvae of caddisflies and mayflies living in the water are observed, while on the Hungarian side the imagines are monitored. The Danube There were gradual changes observed in the caddisflies and mayflies communities after damming the Danube. The changed living conditions caused that scrapers replace filtrators. Further decrease of characteristics was detected in communities poor in species and abundance and at the present they are near the detection limit in the Danube. Low number of species – mostly eurytopic – and low abundance has been detected on monitoring areas No. 2600 and 2603, while on areas No. 2608 and 2612 there were no species of the mentioned communities detected. Monitoring of mayflies in the Danube on the Hungarian side is performed at site No. 24 at Rajka and No. 26 at Szőgye, which is not directly influence by the damming. The changes in the communities on the observation site No. 24 are caused by mud sedimentation in the riverbed, along which a high abundance of mayflies is observed.
The left side river branch system The mayflies and caddisflies communities in the left side river branch system are generally characteristic by decrease of species diversity and low number of individuals of species present. Introduction of the water supply to the inundation area and accompanying increase of flow velocity in branches at the monitoring area No. 2603 is reflected in increase of rheophile and semirheophile species number of mayflies and caddisflies communities also in the year 2000. In the dead arm on monitoring area No. 2604 no species of mayflies was detected in the year 2000, only empty cases of caddisflies larvae were found. These negative changes are probably connected to changed of ecological conditions due to speeding up of natural growing old of the plesiopotamal related to changed flood and water level regimes. In the branch on the monitoring area No. 2608 there was no representative of mayflies and caddisflies communities observed, and the settlement of the monitoring area No. 2612 was very poor in the year 2000.
The right side river branch system The monitoring sites in the river branch system are characterised by high abundance of mayflies and generally changes were observed at monitoring sites influenced by the water supply. The caddisflies community in the right side river arm system, comparing to the species composition observed on the Slovak side, is rich in species. This is probably caused by the differences in the monitoring methods. The structure of the caddisflies community is changing after introducing the water supply and generally fluvial species dominate. Communities of oxygen rich biotopes develop in the inundation area of the Szigetköz. The prevailing part of the caddisflies community on the Mosoni Danube two species, the Agapetus laniger and Lepidostonum hirtum represent.
7.8. Fish (Osteichtyes)The ichtyofauna monitoring on both sides is carried out by electro-fishing. Since 1998 the Hungarian Party use a high power-output electro-fishing apparatus. However, the observation in the deeper water bodies (first of all from the Danube) cannot give complete results. The Danube Based on the observation on the monitoring areas No. 2600 and 2608 on the Slovak side and monitoring sites No. 10 and 11 on the Hungarian side the fish community in the Danube main riverbed seems to be stable. The ichtyofauna is rather rich in species, however higher number of eutrophic species was detected. At observation site No. 10 twelve species was recorded, from among the Rutilus rutilus and Neogobius kessleri dominate. In the period 1997-2000 21 species have been recorded on this site. At observation site No. 11 thirteen species was observed, from among rare and endangered species occurred as well (Hucho hucho, Barbatula barbatula, Sabajenewia aurata and Gymnocephalus baloni). The most abundant were Alburnus alburnus and Rutilus rutilus, while abundance of Neogobius kessleri was also significant. In the period 1997-2000 26 species was recorded at this observation site. Generally the rheophile species occur in low abundance, which may be caused by the method used.
The left side river branch system The ecological conditions on the river branch system at Bodíky (monitoring area No. 2603) have been changed after introducing the water supply, however since 1993 they are stable. Stabilisation of the condition was reflected in the stabilisation of fish community. Missing of occasional strong flooding of the plesiopotamal on monitoring area No. 2604 was reflected also in the fish species composition. In last years, as well as in 2000 low number of species and low abundance is observed. The species composition is characteristic for the ichtyofauna of dead arms. The two partial monitoring sites of area No. 2608 (upwards and downwards from the Foki weir) differ in their connection with the Danube. As a consequence of decreased water level in the main riverbed, the downward part lost its connection, which causes continuous decrease of species diversity and disappearing of rheophile species. The upward part occasionally communicates with the main riverbed and the fish community is rather rich in species and the species conserve their high abundance. The water regime on the monitoring site No. 2612 is not influenced by the operation of the hydropower station, however due to river arm separation from the Danube main riverbed there is no communication. In following years decrease of species diversity and dominance of limnophile and eurytopic species is recorded. In the last years, as well as in the year 2000 stabilisation of species diversity is characteristic, along with the dominance of eurytopic species.
The right side river branch system A dynamic regulation of the water supply and restoration of connection of river arms with the Danube main riverbed was enabled after putting the submerged weir into operation. The two openings in riverbank enable the fish migration between the river branch system and the river. The ichtyofauna of the monitoring site No. 9 – Csákányi Danube in the year 2000 consist of 7 fish species. Occurrence of rheophile species indicated the connection between the Csákányi arm and the Danube in 1992. During years 1993-1994, when insufficient water amount was supplied to the river branch system the rheophile specie diminished, while phytophillic species appeared. Since 1996, after introducing the water supply by underwater weir in rkm 1843, reduction of aquatic vegetation and decrease of phytophillic species occurred. The reappearance of some rheophile species reflects the partial reconnection of the river branch system with the main riverbed. In 2000 two new species have been detected (Gymnocephalus cernuus and Neogobius kessleri). Species diversity was moderate and Rutilus rutilus was dominant on this monitoring site. In the period between 1992-2000 19 species have been recorded. Since connection the monitoring site No. 4 – Schissler arm with the Csákányi river branch. Occurrence of 10 fish species was recorded in 2000. The species diversity was moderate; the Rutilus rutilus have been dominant. Between 1992-2000 19 fish species have been detected. In last years increase of species diversity can be observed and reappearing of species present before damming the Danube. The monitoring sites in the flood-protected area are situated at Gázfűi Danube and Lipót marsh. In the year 2000 11 fish species were detected at monitoring site No. 12 -Gázfűi Danube, similarly to the year 1999. Rutilus rutilus was dominant. Very abundant were the species Scardinius erythrophtalmus, Carassius carassius and Tinca tinca, characteristic for stagnant water bodies. The monitoring site is characteristic by moderate species diversity, consisting of limnophile species, characteristic for wetland biotopes. Since 1998 the characteristics of fish community is comparable to the results obtained before damming the Danube. After introduction of the water supply to the monitoring site No. 5 – Lipót marsh regeneration of ichtyofauna is observed. 10 species were detected in 2000, with the dominance of Rutilus rutilus. The fish community is characteristic by high species diversity, and some rheophile species were detected unusual to this kind of biotope. This reflects the permanent presence of through-flowing water in the oxbow lake. Occurrence of 22 fish species was proved between 1994 and 2000.
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