PART 7
Biological MonitoringIn the year 2001 the biological monitoring of agreed groups of aquatic or terrestrial fauna on both, the Hungarian and the Slovak side was carried out without changes. On the Slovak side it 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 plant communities. Moreover in 1999 the aquatic macrophyte observation was restarted 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 (e.g. similarity index of plant communities is not evaluated on the Hungarian side, evaluation of aquatic macrophytes differs on both sides, reed communities on the Slovak side are not observed as detaily as on the Hungarian side, the monitoring of Trichoptera, Ephemeroptera and Odonata on the Slovak side are based on aquatic larvae observation, while on the Hungarian side it reside in observation of imagines).
7.1. PhytocoenologyThe left side river branch system The monitoring area No. 2600 is situated upstream of the intake structure 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, due to the riverbed decrease and connected ground water level decreasing, were already observed since seventies of the twentieth century. This process became more intensive due to the significant decrease of ground water level and missing of floods after damming the Danube. In the present the terrestrial plant communities and fauna consist of mesohygrophilous species with wide ecological valence. In the last years stabilisation signs of plant communities at this level can be observed. Monitoring areas No. 2603 and 2604 are situated downstream of the intake structure and thanks to this the moisture relations have not changed significantly and high water level can be kept in the adjacent river branches. The only changes are floods, which were missing, but introducing artificial flooding reduced this. Terrestrial plant communities on the area No. 2603 were strongly influenced by cutting out the forest in 2001. This effect is much stronger than the influence of the waterworks. However, the observation in 2002 will continue on the original area planted by young poplars. According to monitoring results in 2001 the terrestrial plant communities on the area No. 2604 show signs of originality. Plant communities mainly consist of hygrophilous species and the presence of floodplain area indication species is permanent. Monitoring areas No. 2608 and 2609 are situated in a region where the backwater effect upstream the confluence of the tailrace channel and the Danube old riverbed eliminates the impact of waterworks. 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 on the area No. 2608 (changes in eco-indexes for light, temperature and continentality), which probably cannot be connected to the impact of Gabčíkovo structures. The plant community on the area No. 2609 is stabile, and corresponds to the regularly flooded wetland community. The area No. 2612 is located downstream the confluence of the tailrace channel and the Danube old riverbed, where the direct impact of the waterworks is minimal. The vegetation conditions of the observed poplar stand on this area are stable. The right side river branch system The Hungarian Party performs the monitoring of plant communities and reeds in summer period only. The vegetation period in 2001 was more reach in precipitation compared to the previous year. This was reflected on the flood-protected area by changes in the plant layer. Compared to the previous year plants were higher and the coverage larger. However, the decreasing tendency of the plant layer biomass on the observed areas in the floodplain with decreased ground water level (along the Danube river bed) had been confirmed in the year 2001 again. Decreases of hygrophilous species presence occur. According to phytocoenological surveys the reed stand at Kisbajcs has not changed the observation period, either in 2001. 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 shoreline vegetation is reach in species, accompanied by typical marshy species. The height and the density of reed blades are the highest one from among the observed areas. The reed stand at Malomszer is situated in a canal in which open water occurs in last years. The reed stand is stable and the density of blades in 2001 was higher than the average value of previous years. The outskirts of the reed stand at the Cvek shallow near Cikolasziget dried up and no open water was found. For this reason terrestrial plant dominate on this area. The reed stand at Dunakiliti was fired up and tilled in 2001. The monitoring area was destroyed.
7.2. Terrestrial molluscsThe left side river branch system The terrestrial molluscs’ community on the area No. 2600 in 2001 consist of mesohygrophilous species with wide ecological valence. The natural conditions on the area from the ground water level position and flooding point of view have became worse after diverting the Danube. However, this region was characteristic by continuous drying out already before this, due to the continuous deepening of the riverbed. Significant decrease of ground water level in this area after the diversion, because of strong drainage effect of the Danube, speeded up this process. At present the community has stabilised at mesohygrophilous level. Since 1997 the molluscs’ community on the area No. 2603 was under mutual impact of the Danube drainage effect and cutting out the neighbouring forest. The community mainly consisted of hemi-heliophytic and eurytopic species. In 2001 the willow stand on this area was cut out as well. However, removing of the tree layer has not been expressed yet. The monitoring will continue on the previously observed area, where young poplars stand growing now. The positive impact of introduced artificial floods on the terrestrial molluscs’ community on the monitoring area No. 2604 was proved in 2001 again. The monitoring results confirm the return of typical wetland molluscs’ community, which consist of polyhygrophilous and floodplain indicating species. The permanent increase of number and abundance of mesohygrophilous species with wide ecological valence on the area No. 2608 indicate the needs of hydro-technical solution of this region. The most important task is solving the water regime and enabling the regular flooding of this area. The monitoring area No. 2609 is situated at the confluence of the tailrace canal and the Danube old riverbed. The water regime and the moisture conditions remained unchanged. Typical marshy and wetland molluscs´ community was recorded on the area in 2001 again. Direct impact of the Gabčíkovo waterworks is not present on the area No. 2612. Similarly to previous years mainly mesohygrophilous forest molluscs species with wide ecological valence were recorded in 2001. The molluscs’ community on this area is stable. The right side river branch system The terrestrial molluscs’ community in the inundation area are intact. Recorded species in 2001 were present in previous years as well. Species occur abundantly; even the occurrence of the typical species Trichia striolata is not rare. The terrestrial molluscs’ community on the flood-protected area remained unchanged. The marshy and terrestrial species occur equally abundant. The future development of the communities depends on anthropogenic impact in the region.
7.3. Aquatic macrophytesThe growth rate, the composition and the amount of macrophytes were determined by the site-specific hydrological conditions, regulated water supply as well as by the temperature and light conditions. Monitoring of macrophytes in 2001 was performed on both Slovak and Hungarian side. The evaluation of recorded species on the Slovak side is done by the Braun-Blanquet method, while on the Hungarian side the Kohler index is used. The Danube In the Danube old riverbed only two Hungarian monitoring points are situated (No. 2 and 7). The monitoring area No. 2 is in the main riverbed where no macrophytes were observed before diversion the Danube, due to the water depth and flow speed. According to the Agreement in 2001, as in the previous years, during the vegetation period about 600 m3s-1 was released into the Danube old riverbed, because of what macrophyte community is not present henceforth. The monitoring area No. 7 is separated from the Danube old riverbed by shoreline vegetation (Salicetum triandrae). Due to intensive spreading of the scrubs the open water area decreased in 2001. The small shallow water rapidly became growth up. This was indicated by increase in abundance of aquatic (Elodea canadensis) and marshy species (Phragmites australis and Typha angustifolia). The left side river branch system As a consequence of the water supply to the river branch system the area around the monitoring site No. 2603 get much more amount of water. The macrophyte community on the monitoring area No. 2603 in the period after introducing the left side river branch water supply is stable but differs from the state before the water supply. The species diversity and abundance decreased due to higher amount of water flowing through the river branches. Macrophytes in mass occurrence are found only along the line structures, banks and at places protected before the strong flow. According to monitoring results of the last three years the macrophyte community in the dead arm on the monitoring area No. 2604 is similar to that in 1990-1991. The marshy lake is bordered by a reed stand of the association Phragmitetum communis; the open water area is almost fully covered by Ceratophyllum demersum. In littoral endangered aquatic and marshy species occur. However, the occurrence and abundance of respective species depend on hydroecophase spreading in the observed year. Macrophytes observation on the monitoring area No. 2608 was performed in shallow parts of the river arm, which was covered by water in 1990-1991. In present the macrophyte community development depend on ecophases present in respective years. During the large part of the vegetation period in 2001 only the limose ecophase was present (the ground water level directly influenced only the root system of plants). The community was created by species typical for dry arms, shoreline and littoral biotopes and alluvial meadows. The macrophyte communities observed on the monitoring area No. 2612, is henceforth rich in species and abundant. Very expressive is its zonation depending on the water depth in the observed parts of the river arm. The offensive spreading of Elodea nuttalii species was observed in 2001 again. The right side river branch system The water supply into the active floodplain was nearly equal during the vegetation period in 2001; discharges in 2001 were similar to discharges in previous years. High water depth was permanently characteristic at monitoring sites No. 4 and 9. Thanks to the favourable weather and light conditions the number of species and abundance of species taking roots increased in the Csákányi Danube river arm – site No. 9. Higher water depth and higher temperature in the Schissler river arm influenced favourably the algae growth, while the spread and abundance of macrophytes remained low. This situation resulted from creation of permanent connection between the Csákányi Danube and Schissler river arm. Hydrological conditions of the flood-protected area remained unchanged in 2001, due to permanent water supply. No extraordinary temperatures occurred, which limited the occurrence of thermophilous macrophyte species recorded in the previous year. Due to slower warming up of the water the thermophilous Hydrocharis morsus-ranae occurred in lower abundance. Some of the concomitant species were not recorded at all, which resulted in decrease of species number at monitoring site No. 8. However, the dominant floating leaved species reached the abundance similar to previous years. In the shallow marsh lake at Lipót – monitoring site No. 6, favourable changes were observed. Spreading of the original Nymphaea alba was observed, however the abundance of some other, previously typical species is lower, comparing to the period before damming the Danube.
7.4. Aquatic molluscsThe Danube The evaluation of the aquatic molluscs’ community in the Danube in 2001 is based on the data provided equally by the Slovak and Hungarian Parties (Slovak observation points at rkm 1841, 1817 and 1804, Hungarian observation points at rkm 1849, 1831, 1824 and 1816). Based on observations it can be stated that the molluscs community in the Danube is stable, a slight increase of abundance of species indifferent to the flow velocity was observed. However, the rheophilous species Ancylus fluviatilis, Lymnaea ovata and Bithynia tentaculata remain dominant. The species diversity and the abundance increase downstream. This can be explained by increasing diversity of existing biotopes. 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. Because of the connection of the river arm at monitoring site No. 2603 with the neighbouring water bodies high species diversity of the aquatic molluscs community is characteristic. The molluscs’ community in the year 2001 consisted of stagnicolous and indifferent species, present for the whole year. In the dead arm on the monitoring area No. 2604 low species richness and abundance of molluscs’ community was recorded also in the year 2001. The right side river branch system Relatively high species diversity was recorded in the right side river branch system. Danubian rheophilous species remain dominant, however the increasing abundance of some shell species indicates creation of river arm section with decreasing flow velocity and formation of muddy riverbed sections. The abundance of the frequently occurring molluscs species in the Mosoni Danube seems to be stagnant. All of the recorded species belong to the rheophilous species.
7.5. Dragonflies (Odonata)The left side river branch system The species composition of Odonata community 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 increase of rheophilous and semi-rheophilous species and decrease of species diversity have been recorded at observation site No. 2603. These changes are connected to changed water regime of most of branches – the water level increased and water began to flow. Results of previous two years indicate the partial recovering of the state before introduction of water supply. Rheophilous species were not recorded and the dragonflies’ community consisted of eurytopic species. The increasing tendency of stagnicolous species portion on the monitoring area No. 2604 was interrupted in the year 2001, even if the dead arm remained isolated. The dragonflies’ community consisted of eurytopic species. The above-mentioned composition without stenotopic species can indicate natural degradation of the dead arm too. The conditions in the river arm at monitoring site No. 2608 are not favourable for dragonflies’ community. Due to marshy bottom and absence of macrophytes no representative of dragonflies community have been recorded in the years 2000 and 2001. In spite of favourable conditions of the present biotope on the monitoring site No. 2612 only one individual of eurytopic dragonfly larvae was recorded. The right side river branch system The dragonfly communities of the respective types of biotopes developed differently under various human impacts. The species composition of floodplain area and shallow or deeper gravel pit mines on the flood-protected area has not changed significantly. The higher amount of water released into the Mosoni Danube did not influenced the dragonflies’ community composition. However, the increased amount of water in the previously slow flowing river branches on the flood-protected area altered significantly the previous conditions. Instead of typical rich stagnant water fauna species riverain species, with wide ecological valence, were recorded in 2001, which is indicated by decrease of species composition as well (observation site No. 22, Zsejke channel at Lipót).
7.6. Crustaceans (Cladocera, Copepoda)The Danube The stabilised conditions of the Danube old riverbed allow formation of stable composition of Cladocera community. Their species diversity was high last years and the relation between pelagic species and tychoplanktonic species is returning to the state before damming the Danube. However, in 2001 higher number of phytophilous Cladocera species was recorded due to higher emergent macro vegetation occurrence, which interrupted the above mentioned tendency. Rather high species diversity of Copepoda community in the Danube remained in 2001 too. The proportion between the euplanktonic and tychoplanktonic species is settled, however it differs from site to site on the observed stretch of the Danube. The left side river branch system In the year 2001 lower number of Cladocera species was observed in the river branch of monitoring area No. 2603, while the number of pelagic species was tiny. Tychoplanktonic species dominate in the medial and littoral of the river arm, which resulted from continuous decrease of euplanktonic species after introducing the water supply in 1993. The Copepoda species composition and abundance in the year 2001 remained unchanged, however differs from the composition in the period before introducing the water supply in 1993, when euplanktonic species occurred only. At present tychoplanktonic species dominate in medial and littoral of the river arm. The living conditions on the monitoring site No. 2604 are typical for paleopotamal. Spreading of submersed vegetation continues, because of what the conditions for euplanktonic Cladocera species became worse. Due to a mass occurrence of one pelagic species in 2001 euplanktonic species slightly prevailed over the tychoplanktonic species. The Copepoda community on the monitoring site was rich in species and abundant in 2001 again. No significant change have been observed in the medial of river arm, the euplanktonic species dominated, only fluctuation and changing of dominant species is recorded. However in the littoral of river arm slight domination of tychoplanktonic species was recorded for the first time in 2001. 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. In 2001 slight domination of tychoplanktonic Cladocera species was recorded in the littoral of river arm for the first time. This change of the community is probably connected with continuous isolation of the river branch from the main flow. The continuous overgrowing of the plesiopotamal on the monitoring site No. 2612 by macrophytes resulted in change of Cladocera community. In this community slow continuous replacement of euplanktonic species by tychoplanktonic ones is observed in last years. The quantity of tychoplanktonic species reached 71 %. The Copepoda community was stable in 2001, along with the dominance of euplanktonic species. The right side river branch system In comparison to the years 1999 and 2000 increase of species diversity was observed in Cladocera and Copepoda communities in 2001 at all of monitoring sites. The water temperature during the sampling in summer and autumn was unusually low, what can be the reason of low abundance of some Cladocera species, and relatively frequent occurrence of some meso-thermophilous species. The highest abundance of respective species was observed in the Schissler arm again, although the number of individuals in the summer was low because of algae growth and consequent high content of suspended solids. The pelagic Cladocera Bosmina longirostris and several phytophilous species were the most abundant. The number of species in the Csákányi and Zátonyi Danube river arms increased in 2001. The abundance of species of marshy biotopes with dense vegetation was high; some other phytophilous species were recorded. The species diversity in the Lipót marsh is stable; the most abundant species were Pleuroxus truncatus and phytophilous Sida crystallina.
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 flying imagines are monitored. The Danube Changes of ecological conditions in the Danube old riverbed resulted in changes in mayflies and caddisflies’ communities. The monitoring results on the Slovak side indicate continuous decrease of species diversity and abundance in previous years. In addition scrapers replaced filtrators continuously. In 2001 the Slovak Party have not recorded any larvae of mayflies’ community. However, the Hungarian Party describes in the impounded Danube river stretch a huge occurrence of mayfly of eutrophic water bodies, based on flying imagines observation (Caenis horaria, Caenis robusta). The typical species of large rivers, Heptagenia sulphurea, was not registered. The species diversity of caddisflies’ community in the Danube was low according to the results of the Slovak Party. Mainly filtrators composed this community, unlike the previous years. This change in the food chain can be considered as a positive one. The experts of the Hungarian Party recorded significantly higher number of species and number of individuals in 2001. According to their results caddisflies’ community rich in species settles the Danube. The left side river branch system The mayflies and caddisflies communities in the left side river branch system are generally characterised by decrease of species diversity and low number of individuals of species present. The mayflies’ community on the monitoring area No. 2603 was composed by stagnicolous and semirheophilous species. The species diversity and the abundance of species present are constantly low. The river branch used for the water supply is settled by rheophilous species in last years. The composition of caddisflies’ community is similar to the composition in previous years and consists of low number of species with low abundance. After the absence of caddisflies and mayflies species in the paleopotamal of the monitoring area No. 2604 some improvement have been recorded in 2001. Three mayflies species were detected, but only empty cases of caddisflies’ larvae were found. The natural overgrowing of the paleopotamal continues and it resumes in changes of the both communities. Moreover, the negative impact of high temperatures during summer time can result in extreme reaction of caddisflies and mayflies’ communities. After the absence of the only mayflies species in last year on the monitoring area No. 2608, larvae of stagnicolous species were recorded in 2001 again. Larvae with low abundance have been registered at all of the tree sampling. No representative of caddisflies’ communities were observed again. Similar situation was observed on the monitoring area No. 2612 as well. The mayflies’ community was represented by single stagnicolous species, with high abundance in autumn 2001. Caddisflies species were not found in 2001 again. The right side river branch system Different results in monitoring of caddisflies and mayflies on the Slovak and Hungarian side have been reached in the river branch system too. The species diversity and the abundance of mayflies’ species on the Hungarian side are significantly higher. The highest numbers are recorded on monitoring site at Mosoni Danube, near Feketeerdő. Huge occurrence of mayfly of eutrophic water bodies (Caenis horaria) was recorded in the Lipót marsh. On the other side the Ephemera vulgata species was repeatedly observed in the river branch system at Lipót and at Mosoni Danube. At Mosoni Danube a slow flowing and standing water species Ephemera glaucops was recorded for the first time. The caddisflies’ communities in the Szigetköz region are very rich, which is proved by high number of species and high number of individuals in samples. Sampling during favourable climatic conditions results in high species number both, along the Danube and along the water supply in river branch system. It can be stated that the dominance of species of oxygen rich biotopes with flowing water is generally very high.
7.8. Fish (Osteichtyes)The ichtyofauna monitoring on both sides is carried out by electro-fishing. The monitoring method used does not allow observing the ichtyocoenoses of deeper water bodies (first of all the deeper parts of the Danube) and cannot give complete results. The Danube The evaluation is based on Slovak observation results on monitoring areas No. 2600 and 2608 and Hungarian results observed on monitoring sites No. 10 and 11. In general it can be stated that the ichtyofauna community in the Danube is stable, no changes were recorded during last years. After diversion the Danube slight decrease in number of rheophilous species was recorded, which were replaced by eurytopic species. The species richness in the last years is at this level stable. The left side river branch system The ecological conditions in the river branch system at Bodíky (monitoring area No. 2603) have changed after introducing the water supply in 1993, however since than they are stable. The fish community is characteristic by high stability, with the dominance of eurytopic species. In spite of the continuous isolation of the paleopotamal on monitoring area No. 2604 quite rich in species and number of individuals ichtyocoenoses was recorded in 2001. The absence of extremely high temperatures during the summer months resulted in favourable composition of the fish fauna. The two partial monitoring sites of the monitoring area No. 2608 (upwards and downwards from the Foki weir) differ in their connection with the Danube. The monitoring site upwards Foki is during higher discharges connected with the Danube main riverbed. This resulted in rich species diversity and rather high number of individuals. Even if the highest abundance reach the eurytopic fish species, the presence of the rheophilous species remained. The monitoring site downstream of Foki weir lost its connection with the main riverbed after the diversion of the Danube. The ichtyocoenoses of this isolated site is relatively poor in last years. The occurrence of the rheophilous species, along with the dominance of eurytopic species, is minor and unstable. Even if in the year 2001 decrease of species diversity was observed on the monitoring area No. 2612, the fish community can be characterised as stable. The continuous decrease of species diversity during the observed period can be explained by absence of the connection between the river branch and the Danube main riverbed during the spawning time (it lost the spawning place function). In 2001 the limnophilous species Scardinius erythrophtalmus with the endangered species Misgurnus fossilis dominated. The further development of the site depends on the hydrological regime of the Danube. The right side river branch system 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. Two openings in the riverbank are enabling the fish migration between the river branch system and the river. The ichtyofauna of the monitoring site No. 9 – Csákányi Danube in the year 2001 consist of 8 fish species. Occurrence of rheophilous 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 rheophilous specie diminished, while phytophilous species appeared. Since 1995, after introducing the water supply by underwater weir in rkm 1843, reduction of aquatic vegetation and decrease of phytophilous species occurred. The reappearance of some rheophilous species reflects the partial reconnection of the river branch system with the main riverbed. The species composition in 2001 was stable; the species diversity was slight. Four years after connection the monitoring site No. 4 – Schissler arm with the Csákányi river branch 12 fish species was recorded in 2001. The species diversity was moderate; the eurytopic species Rutilus rutilus remained dominant. 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 2001 12 fish species were detected at monitoring site No. 12 - Gázfűi Danube, similarly to the previous years. Rutilus rutilus remained 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 limnophilous species, characteristic for wetland biotopes. Since 1998 the characteristics of fish community are stable and 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. The species diversity is increasing since 1994. Slowly flowing river arms and water bodies with stagnant water are settled by valuable limnophilous species, however sections with higher flow speed rheophilous species are occasionally detected, which are unusual to this kind of biotope. Sampling catches during the last three years were balanced.
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