Chapter 7

The biological monitoring of agreed groups of aquatic and terrestrial fauna and flora is carried out on six complex monitoring areas on the Slovak side. The same groups of fauna and flora, agreed in the frame of joint monitoring, were monitored at 23 monitoring sites on the Hungarian side in 2010 (Fig. 7-1). The list of the complex monitoring areas on the Slovak side and monitoring sites on the Hungarian side is given in Table 7-1. From the methodological point of view differences in some monitoring methods existed during the monitoring on both sides. Some differences at present result also from gradual introduction of evaluation according to the Water Framework Directive, which is not in the same state on the Hungarian and Slovak sides.

Table 7-1: The list of complex monitoring areas and monitoring sites in 2010

No.

Name

Locality

M o n i t o r e d g r o u p s

Macrozoobent.

Zoopl.

Slovak side – complex monitoring areas

B-6

2600

Dobrohošť – Dunajské kriviny

●

B-9

2603

Bodíky – Bodícka brána

●

B-10

2604

Bodíky – Kráľovská lúka

●

B-14

2608

Gabčíkovo – Istragov

●

B-15

2609

Sap – Erčéd

●

B-18

2612

Kľúčovec – Sporná sihoť

●

Hungarian side – monitoring sites

28a

B-01

Dunasziget – forest

●

28b

B-02

Dunasziget – meadow

●

B-03

Halászi – forest Derék

●

B-04

Lipót – Gombócos closure

●

H-04

Dunasziget – Schisler arm

●

H-05

Zátonyi Danube

●

5, 6

H-06

Lipót – Lipóti marsh

●

H-07

Danube, rkm 1828

●

H-08

Zátonyi Danube

●

H-09

Dunasziget – Csákányi Danube

●

H-10

Danube, rkm 1833

●

2, 11

H-11

Danube, rkm 1839

●

H-12

F-31

Zátonyi Danube, Gázfűi Danube, rkm 28,5

●

F-26

Kisbodak – Pálfi island, forest

●

F-27

Rajka – forest Felső

●

F-28

Novákpuszta – Nováki channel

●

F-22

Lipót – Zsejkei channel

●

F-35

Mosonmagyaróvár – Mosoni Danube

●

F-17

Arak – Nagy Kerek

●

F-19

Danube, rkm 1824

●

F-N3

Arak, Nováki channel

●

Gázfűi Danube, Galambos

Mosoni Danube, Szilos

● – data provided x – no data provided, only mentioned in connection with WFD

F - Dragonflies (Odonata – aquatic larvae on the Slovak side + flying imagines as supplement, larvae and exuviae on the Hungarian side)

G - Mayflies and Caddisflies (Ephemeroptera and Trichoptera - aquatic larvae on the Slovak side + flying imagines as supplement, larvae and exuviae on the Hungarian side)

For E, F, G, H groups (macrozoobenthos) marked with “x” methodology according to WFD is used on the Hungarian side.

A short description of climatic and hydrological conditions in the year 2010, which influenced the development of observed groups of fauna and flora on both sides of the Danube, is given above in Part 6 – Forest Monitoring.

7.1. Phytocoenology

In the evaluated year two factors were important from the vegetation development point of view:

Phytocoenoses on monitoring areas No. 2600, 2604, 2612, and partially also on area No. 2603 can be regarded as stabilised. On the area No. 2600 a community of the driest level of floodplain forest occur, in which favourable changes were registered during the evaluated year: partial regeneration of trees and the absence of invasive plant species. The absence or negligible presence of invasive plant specie was proved in the wettest type of the floodplain forest on the area No. 2604. The species composition and the coverage values of the community on area No. 2612 are similar in recent years. Lower coverage of herb layer and their reduction to several nitrophilic species were caused by spring flood. This area is also characterised by successful rejuvenation of woods. The treetops of the 13-year old stand on the area No. 2603 have been basically already closed and high similarity values of herb layer prove the stabilisation of lower layers. The amount of invasive species decreased, but it is still rather abundant. On areas No. 2608 and 2609 changes evoked by clearing and subsequent reforestation with cultivated poplars are going on. At present poplars only create the shrub layer, which gradually increases its coverage. In herb layer on area No. 2608 the original nitrophilic species are dominant, while on the area No. 2609 the neophytic aster and indigenous snowflake dominate. Flooding hampers the spreading of glade and invasive species in both stands.

Before proceeding the phytocoenological record a large part of the inundation area was flooded (sites No. 28a, 28b, 30), similarly as in the previous year. The herb layer on the less flooded places was closed, however its height was lower. At sites were signs of flooding were observed on trees in the height of 40-110 cm, bare spots covered by mud and sediments occurred, the coverage of herb layer was significantly decreased temporarily. The oak-hornbeam stand on the area No. 31 was not flooded (similarly to the previous year), further strengthening of the shrub layer continues, in the shadow of which the plants reached lower coverage.

7.2. Terrestrial molluscs

The terrestrial mollusc’s community is stabilized on areas No. 2600, 2604 and 2612. The malakocoenose of the area No. 2600 is typical for the driest type of lowland forest, while the community on the area No. 2604 for the wettest variation of lowland forest. On this area, however, unfavourable increase of abundance of meso-hygrophilous species can be observed in recent years. The malakocoenoses on the area No. 2612 is not typical for lowland forest; it is a mix of species with different ecological demands, which are transported to the area from wider heterogeneous surroundings during strong floods. The development of malakocoenoses in young stands on areas No. 2603, 2608 and 2609 is affected by silviculture. Species-rich community on the area No. 2603 is not yet outlined; it is created by species of different types of lowland forest with regular occurrence of alien species. The malakocoenoses on the area No. 2608 is significantly degraded two years after the clearing, the abundance of hygrophilous species decreases. Signs of regeneration can be seen in the malakocoenoses on the area No. 2609, the abundance of hygrophilous and polyhygrophilous species increases. The return of native species is mostly registered with the closure of treetops.

Although the terrestrial mollusc’s community in the inundation shows certain fluctuation, no worsening tendency can be observed. The fauna remains quite diverse. The malakofauna of this region is endangered by silviculture (clearing). The malakofauna of the flood-protected area is, depending on local conditions, rather variable, but vulnerable. The strip of young forest on the bank of the Danube (at rkm 1824) is inhabited by very diverse malakocoenoses, which may play an important role (refuges) in regeneration of other species-poor sites, where the species can be spread during floods.

7.3. Aquatic macrophytes

In the Danube old riverbed two Hungarian monitoring sites are situated (No. 2 and 7). The monitoring site No. 2 is located in a bay behind a guiding structure in the main riverbed downstream of the bottom weir, where the water slowly flows. After damming the Danube macrophytes occurred here, but the riverbed bottom is already muddy and the presence of macrophytes was not proved since the year 2003. The banks and the guiding structure are overgrown by almond-leaved willow shrubs (Salicetum triandrae), which further extends. Rich in species macrophyte vegetation is observed on monitoring site No. 7, which is separated from the Danube old riverbed by the riparian vegetation of willow shrubs (Salicetum triandrae) and reed stand (Scirpo-Phragmitetum). The abundance of the invasive species Elodea Canadensis, as well as the unpretentious cosmopolitan species Ceratophyllum demersum was rare in the evaluated year; the occurrence of other species was very rare.

The observed river branches were characterised by increased water level in the evaluated year; the hydrologic situation in the branches is rather favourable in recent years. In the deep through flowing river branch on the area No. 2603 twice the number of macrophytes was recorded in comparison with the previous year, some of them could be drifted here by high flow rates. High water levels suppressed the marshy species in the dead arm on area No. 2604. The hydrological situation was more favourable for development of true aquatic vegetation, including several rare species. High water levels prevailed in last three years in the river arm on area No. 2608 as well. As a consequence the vegetation of most of ruderal and marshy species was eliminated, and even the invasive Solidago gigantea was not registered in the evaluated year. All yearlong water supply to the river branch on the area No. 2612 was reflected in massive development of aquatic vegetation. The macrophyte community was similar to the previous two years. The unfavourable fact is the continuous overgrowing of the open water area by invasive species Elodea nuttallii, in other, shallower parts, marshy species dominate.

The discharges supplied into the active floodplain were similar to discharges in previous years. Large part of the floodplain river branches is characterised by greater water depth, to which the stabilised species composition of macrophytes adapted. The water level in the Schisler arm (site No. 4) was so low in the previous year that the observation could not be performed. Water levels of the evaluated year were similar to levels measured two years ago, and the macrophyte species composition was similar as well. However, due to high flow velocities the macrophytes covered smaller part of the dead arm during summer months. Larger patches of submersible macrophyte species again covered the open water area of the Csákányi Danube (site No. 9), but they were degraded. The occurrence of the invasive species Elodea canadensis and the unpretentious cosmopolitan species Ceratophyllum demersum was very rare.

As a result of the continuous water supply growing conditions in the flood-protected area (monitoring sites No. 6 and 8), remained unchanged in last few years, therefore the species composition and the abundance of species of both sites are stable. The species number in the river branches is high; the presence of several rare or protected species is proved every year. The absence of the invasive species Elodea canadensis remains.

7.4. Aquatic molluscs

The evaluation of aquatic molluscs’ community in the Danube is based on data provided by the Slovak Party (Slovak observation areas No. 2600, 2608 and 2612). Based on these data the entire stretch of the Danube has been characterized by poor malakofauna in the last few years. In the evaluated year at all sites in the Danube only two species were registered: the non-native invasive Theodoxus fluviatilis and the ubiquistic species Dreissena polymorpha. Theodoxus fluviatilis had year-round presence and high levels of abundance in all samples. Dreissena polymorpha was recorded at low water levels. The reason for decline of native species from the Danube is not yet clear. This is probably an interaction of several factors – hydrological, trophical, physical and chemical.

The aquatic molluscs’ community in the river branch system on the Slovak side is monitored at areas No. 2603 and 2604. In both areas in recent years destruction of malakocoenoses can be registered, decline of populations of large species and significant decrease in abundance of smaller species. On the area No. 2604 it is probably caused by frequent decrease of water level in summer or autumn period. However, the destruction of community on area No. 2603 is registered despite the heterogeneous nature of the river arm, sufficient size of biotope and good conditions for its development. On this area several species had regular presence in the evaluated year, but in the dead arm on the area No. 2604 only one type of ubiquistic species was recorded.

Relatively rich communities of aquatic malakofauna did not show significant differences in comparison to previous years; they are stable and depend on actual site-specific conditions. The variety of malakofauna in wetlands of the flood-protected area does not reach the diversity registered in the inundation area.

7.5. Dragonflies (Odonata)

The focus of the monitoring of dragonfly communities on areas No. 2600 and 2608 was shifted from river arms to the coastal zone of the Danube, because samples taken in arms were have been poor in recent years. The Danube meanders are overgrown with macrophytes, to which the occasional occurrence of rheophilic and semirheophilic dragonflies is bound. Even richer odonatocoenoses occur on areas No. 2603, 2604 and 2612. The flow of water in the river arm on the area No. 2603 is convenient for rheophilic and semirheophilic species, while the overgrown meanders are populated by stagnicolous species. The various conditions of the river arm get closer to the situation before damming. The species-rich odonatocoenoses of the river arm on area No. 2064 is created by species of over-warmed waters, and permanent occurrence during the evaluated year had again one eurytopic species. Stagnicolous and eurytopic dragonflies occupy the divers habitats of the area No. 2612.

In the evaluated year 19 dragonfly species in the larval stage or as exuvia was confirmed. The odonatocoenoses of different types of water bodies developed differently due various interventions, but significant – trend changes were not registered in the inundation area. While the increased amount of water into the Mosoni Danube has had no effect on the dragonfly fauna composition, the water supply into the river branches on the flood-protected area (Gázfűi Danube, Nováki channel, Zsejkei channel, Lipóti channel) has had significant effect on the dragonfly fauna composition characteristic for slow flowing, sluggish waters with dense vegetation.

7.6. Crustaceans (Cladocera, Copepoda)

Evaluation of the development of Cladoceras and Copepods communities is based on results of the Slovak Party at monitoring areas No. 2600 and 2608, which are situated on the diverted stretch of the Danube. The Cladoceras and Copepods communities have become unstable and poorer in the last few years. Retreat of pelagic and increase of littoral species, and increase of invasive Cladoceras and Copepods is registered. These changes are partially influenced by the actual hydrologic situation in the river, but partially this could be attributed to the absence of side branches, that are richer in zooplankton, and could flow into this stretch of the Danube. Only in spring rather rich Cladoceras communities were registered on the area No. 2600 due to high water levels in the actual year, other samplings were very poor in both communities. The Cladoceras on the area No. 2608 were more abundant in autumn; the highest species number of Copepods (3) was recorded in the summer.

The development in Cladoceras and Copepods communities in the river arm on the area No. 2603 in the evaluated year was similar to the year 2009. Communities were poor in the medial and the dominance of littoral species persists there. This non-typical composition of zooplankton is a results of the low content of nutrients in the water and associated weak development of phytoplankton. Communities of overgrown littoral are stable, richer in species and littoral, phytophilous species dominate there as well.

The living conditions in the dead arm on area No. 2604 were more for Cladoceras and Copepods occurrence favourable in previous years, but the actual results indicate negative changes. Decrease in species number and abundance was registered in both communities, as well as decrease of euplanktonic species, indicating worsening of trophical conditions (due to intensive development of macrophytes). The ecological value of habitat decreases in term of the occurrence of Cladoceras and Copepods species.

The Cladoceras and Copepods communities on the area No. 2608 in the evaluated year were rather rich, with the dominance of euplanktonic species in both, the medial and littoral part of the river arm. The retreat of phytophilous representatives is evoked by the decline of macrophyte vegetation caused by water level fluctuation during the year. Several rare species were registered in the river arm.

The community of planktonic crustaceans on the area No. 2612 are rated as balanced in long-term, the river arm can be considered as original biotope, worthy of protection. Rich spring communities, mainly comprised by phytophilous species, were decimated by the summer flood. Since the macrophyte vegetation was flushed out, massive development of euplanktonic species followed.

Sampling of planktonic crustaceans in last two years was carried out only once a year; the number of recorded species is therefore rather low (33). Several rare species were registered in the evaluated year as well. The highest species diversity was repeatedly registered in the Lipóti marsh, and this site was also characteristic by the highest abundance in the evaluated year. The most abundant are the species of stagnant waters, bound to macrophyte vegetation. The communities confirm balanced ecological conditions of the dead arm.

In the Schisler dead arm low species diversity of the Cladoceras and Copepods communities was repeatedly recorded in the evaluated year. After last year’s high abundance values of present species, low abundance of representatives was registered in the evaluated year. One phytophilous Cladocera and euplanktonic Copepods reached the highest abundance. Generally, the typical species bound to macrophytes occur only with low abundance.

The weak population of the Csákányi Danube may be related to stronger water flow, since the river arm is a part of the water supply system into the inundation area. After the last year’s absence of representatives of Cladoceras and Copepods, only one Copepod was present in the sample taken in the evaluated year.

At monitoring site in the Zátonyi Danube situated in the flood-protected area, only 2 Copepod species with low abundance were registered in the evaluated year. This weak population of the river arm in the evaluated year may be attributed to retreat of macrophyte vegetation in last two years and following absence of several common phytophilous species. The monitoring results from the long-term point of view presented a high diversity and stability of this biotope.

7.7. Caddisflies and Mayflies (Trichoptera, Ephemeroptera)

Regarding the monitoring of mayflies, caddisflies, dragonflies and aquatic molluscs the Hungarian Party has gradually introduced the methodology according to the Water Framework Directive since 2007. These results are not fully comparable with the previous Hungarian results or the results of the Slovak Party, which continues to carry out the monitoring in accordance with the methodology set out in the Agreement 1995. The Slovak Party uses the methodology under WFD in surface water monitoring (Part 2 – Surface water quality). The Hungarian Party in the frame of Joint monitoring provided a table with a list of species registered during the observation according to WFD methodology for the whole region, and there are separately reported lists of species recorded on two sites: Gázfűi Danube – Galambos and Mosoni Danube – Szilos. Further evaluations of these data are not given in the Hungarian National report.

The Danube, according to results of the Slovak Party (monitoring areas No. 2600, 2603, 2608 and 2612), is inhabited by caddisflies and mayflies sporadically, with irregular occurrence of representatives in individual samples and in particular years. The recorded species are mostly rheophilic. Surviving of more abundant communities, however, can be supposed in hard-to-get medial sections of the flow.

Every observed river branches in the left side inundation area (monitoring areas No. 2603, 2604, 2608 and 2612) are very poor in terms of mayfly and caddisfly communities. Mayfly communities consisted of 2-3 species with low abundance and frequently irregular presence during the year. Present mayflies are mostly stagnicolous, eutrophic. Caddisfly communities were even poorer; in the evaluated year at most of sites no representative was recorded.

The Hungarian Party provided data obtained by observation under WFD. Mayfly communities consisted of 2-4 species by sampling site, with high abundance of Ephemera vulgata at monitoring site Gázfűi Danube – Galambos. Diversity of caddisfly communities were higher, 3-7 species by monitoring site.

7.8. Fish (Osteichtyes)

The ichtyofauna monitoring on both sides is carried out by electro-fishing. Difference exists in the power-output of the device, which decreases the comparability of results obtained by both Parties, difference exists in the frequency of monitoring as well.

The evaluation is based on Slovak observation results at monitoring areas No. 2600 and 2608, and Hungarian observation results at monitoring sites No. 10 and 11. From these results follow that the ichtyocoenoses of the diverted stretch of the Danube is stabilised in recent years, with relatively low species diversity and abundance, and with the dominance of eurytopic and non-native representatives. Their expansion is hindered by indigenous rheophilic species, which probably find their refuge in the not sampled medial part of the river.

Richer and more stabilised ichtyocoenoses occur in the river arm on monitoring area No. 2603 and upstream of the Foki weir on the area No. 2608, as they interact with the other arm or the main flow of the Danube. 2604 stable ichtyocoenoses occur. Eurytopic and indifferent representatives have dominant position on the area No. 2603, on the area No. 2608 upstream of the Foki weir several rheophilic species were recorded in the evaluated year. Expansive behaviour of invasive species (Neogobius sp.) is not observed on these areas.

Habitats of monitoring areas No. 2604, 2608 downstream of the Foki weir, and No.2612 are in contact with the other parts of the river branch system or with the Danube rarely, for a short time during floods, therefore their ichtyocoenoses are impoverished in terms of number of species and abundance. On the area No. 2604 species able to survive at high water temperature and lack of oxygen occurred, but the one expansive species reached the highest abundance. The fish abundance in the evaluated water rich year on the area No. 2608 downstream of the Foki weir was rather high, but return of rheophilic species was not registered. In the muddy and overgrown river arm on the area No. 2612 one species that requires higher oxygen content was recorded after the flood.

The ichtyofauna on the Hungarian side is monitored at two monitoring sites in the inundation area (No. 4 and 9) and at two monitoring sites in the flood protected area (No. 5 and 12). On these sites a stabilised ichtyofauna is registered in recent years; significant changes in species diversity or abundance were not recorded.

The ichtyofauna of the Schisler river arm (monitoring site No. 4) was restored and enriched after its artificial reconnection with the Csákányi Danube in the year 1997. The ichtyofauna is currently stabilised and rich in species. In parts overgrown by macrophytes phytophilous and limnophilic species occur, but in the last few years also the invasive Ameiurus melas has increased abundance. In the channel interconnecting the dead arm and the Csákányi Danube irregular occurrence of rheophilic fish species is observed as well.

The species diversity of ichtyofauna in the Csákányi Danube river arm (monitoring site No. 9) is high since introduction the water supply in 1995. The interconnection with the Danube is proved by the occurrence of rheophilic fish species, however, in terms of abundance of representatives, significant dominance of undemanding species Alburnus alburnus persists.

After introducing the water supply (in 1995), regeneration of ichtyofauna is observed at monitoring site No. 5 – Lipóti marsh. In recent years the species richness of this site is significant and balanced, with the dominance of eurytopic and lithophilic species. Permanent occurrence of the invasive Ameiurus melas was confirmed on this site.

Since introducing the water supply to the flood-protected area the ichtyocoenoses of the Gázfűi Danube (monitoring site No. 12) is stabilized as well. Moderately rich species diversity is composed mainly by marshy and limnophilic species, although the highest values of abundance reach the eurytopic fish species. Also on this site the occurrence of invasive Ameiurus melas was confirmed.

PART 7

Biological Monitoring