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 21 monitoring sites on the Hungarian side in 2009 (Fig. 7-1). The list of the complex monitoring areas on the Slovak side and monitoring sites on the Hungarian side is given in Tab. 7-1. From the methodological point of view differences in some monitoring methods existed during the monitoring on both sides. At present some differences result from gradual introduction of evaluation according to the Water Framework Directive, which is not in the same state on the Hungarian and Slovak sides.

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

●

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

●

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

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

G - Mayflies and Caddisflies (Ephemeroptera and Trichoptera - aquatic larvae on the Slovak side + flying imagines as supplement, flying imagines 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 2009, 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

Moisture conditions were favourable in the evaluated year, what resulted from rather high precipitation amounts and high water levels, that occurred several times during the year, and at one occasion it resulted in flooding a large part of the inundation area. Phytocoenoses on monitoring areas No. 2600, 2604 and 2612 can be regarded as stabilised. On the area No. 2600 a community at the driest level of floodplain forest occur, and further degradation of its status is not expected. Favourable moisture conditions were suitable also for 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 last years. On areas No. 2603, 2608 and 2609 changes evoked by clearing and subsequent reforestation going on. The young tree layer on area No. 2603 is already stabilised and the treetops are closed; the composition of underlying layers gradually stabilises as well. Poplars on areas No. 2608 and 2609 were planted in 2008 and 2009 respectively, so at present they create the shrub layer only. The plant layer consists of plant typical for cleared areas, with the dominance of original nitrophilous species, native wetland species appear as well. In case of every observed area it can be stated that due to intensive flooding the spreading of invasive species (Impatiens glandulifera, Solidago gigantea) significantly retreated, potentially these species disappeared.

The phytocoenological records in the evaluated year were taken after the flood, which affected the large part of inundation area (from among the observed areas only the area No. 31 at Halászi with oak-hornbeam stand was not affected). The areas in the inundation were covered by mud and sediments, which overlaid the plant vegetation. As a result the actual species number and the coverage values were temporarily low in comparison with previous years. In the oak-hornbeam stand on area No. 31 strengthening of the shrub layer was registered, similarly to previous years.

When evaluating the average leaf area values significant changes in the evaluated year were recorded on single area only. Differences in the leaf area size in case of white willow in comparison with previous years remained in the range of previous years.

7.2. Terrestrial molluscs

The terrestrial mollusc’s community on a large part of inundation area is stabilized (on area No. 2600 on the level typical for drier variants of floodplain forest; on area No. 2612 on more wet level, and on the area No. 2604 on the level typical for the wettest variants of the floodplain forest). Changes observed on areas No. 2603, 2608 and 2609 are assigned to the impact of silviculture. In young forest stands during first years after the clearing low representation of polyhygrophilous and hygrophilous, increase of species diversity, and penetration of foreign species is observed. The return of native species is mostly registered with the closure of treetops.

Although the terrestrial mollusc’s community in the inundation and the flood-protected area shows certain fluctuation, no worsening tendency can be observed; the fauna is variable. Since 2006 many species (including hygrophilous species) occur in amount of several hundreds or thousands of individuals. In drier forest stands on the flood-protected area stable malakocoenoses was observed. The young forest in the strip on the bank of the Danube (at rkm 1824) is occupied by very varied malakocoenoses, which can play an important role in regeneration of other low-in-species places, where 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 situated in a bay behind a guiding structure in the main riverbed downstream of the bottom weir. Macrophytes occurred here after damming the Danube, but since 2003 they are not registered and the banks and the guiding structure are overgrown by almond-leaved willow shrubs (Salicetum triandrae). Rich in species macrophyte vegetation is observed on monitoring site No. 7, which is separated from the Danube old riverbed by a shoreline vegetation of willow shrubs (Salicetum triandrae) and reed stand (Scirpo-Phragmitetum). Significant representation of the invasive species Elodea Canadensis, as well as the unpretentious cosmopolitan species Ceratophyllum demersum was registered in the evaluated year.

There was enough water in the river branches in Slovak inundation area till the autumn. In the deep through flowing river branch on the area No. 2603 almost the same number of macrophytes and similar species composition was recorded as in the previous year. During higher flow rates in the spring and in the summer only one macrophyte species occurred along the weir, the other species (including rare species) started to develop in the second half of summer when the water level decreased. Changes in the stabilised macrophyte community of the dead arm on area No. 2604 can be assigned to higher water levels during the spring and in the summer, which suppressed the development of marshy species in the actual year. The hydrological situation was more favourable for development of the true aquatic vegetation, including several rare species. High water levels during the spring and in the summer eliminated or suppressed the development of ruderal species (penetrating from the cleared neighbouring area) and marshy species in the river arm on area No. 2608 as well. Unfavourable is a fact that several individuals of the invasive species Solidago gigantea settled in the bottom of the river arm. Continuous water coverage of the river arm on area No. 2612 and relatively high air temperatures were reflected in the massive development of aquatic plants. The macrophyte community was similar as in the previous year; the species diversity in some parts of the river branch was even higher. The unfavourable fact is the continuous overgrowing of the open water area by invasive species Elodea nuttallii.

The discharges supplied into the active floodplain were similar to discharges in previous years. Large parts of the floodplain river branches are characteristic by higher water depth. The open water area of the Csákanyi Danube (site No. 9) was covered by larger patches of submersible macrophyte species, and the portion of the invasive species Elodea canadensis was significantly lower in comparison with the previous year. The water level in the Schisler arm (site No. 4) during the year 2009 was so low, that it was not possible to carry out the sampling from a boat.

The growing conditions in the flood-protected area (monitoring sites No. 6 and 8) thanks to the continuous water supply, remained unchanged in last few years, therefore the species composition of particular sites is stabilised. The species number in the river branches is high, the presence of several rare protected species is proved every year. The invasive species Elodea canadensis was not registered in the evaluated year.

7.4. Aquatic molluscs

The evaluation of the aquatic molluscs’ community in the Danube is based mostly on the data provided by the Slovak Party (Slovak observation areas No. 2600, 2608 and 2612); the Hungarian Party did not provided data for the Danube in the frame of the Joint monitoring for the evaluated year (only data for alluvial forest at rkm 1924). The whole Danube stretch according to results of the Slovak Party is characterized with poor malakofauna in last years. Stable occurrence during the evaluated year on most of observed areas had the foreign invasive species Theodoxus fluviatilis only. Irregularly with lower abundance the ubiquistic, indifferent, and possibly rheophile species occurred. The reason of retreat of the original species is not clear so far. Probably it is an interaction of several factors – hydrological, trophical, physical and chemical. The spreading of Ancylus fluviatilis in the Danube stretch around Dunaremete proves the good recolonisation ability of aquatic molluscs.

The aquatic molluscs’ community in the river branch system on the Slovak side is monitored at sites No. 2603 and 2604. On both areas slow destruction of malakocoenoses can be registered in last years. On the area No. 2604 it is probably caused by frequent decrease of water level in summer or autumn period, accompanied by oxygen shortage. However, the retreat of big species and decrease of abundance of dominant species on the area No. 2603 is registered contrary to the heterogeneous character of the river arm, sufficient size of the biotope and good conditions for their spreading. Only two unpretentious species occurred regularly in the evaluated year.

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

7.5. Dragonflies (Odonata)

The development of odonatocoenoses is considerably influenced by actual hydrological and climatic conditions. Poor communities with irregular occurrence and low abundance of mostly eurytopic species occur on areas No. 2600 and 2608. More rich odonatocoenoses occur on areas No. 2603, 2604 and 2612. Conditions in the river arm on area No. 2603 are more and more similar to conditions of Danube’s river arms in the past. Suitable conditions for odonatocoenoses were created in meanders overgrown by macrophytes, where stagnicolous species settle and replace the rheophile and semirheophile species registered in previous years. The community on the area No. 2064 is rich in species, but only one eurytopic dragonfly had permanent occurrence during the evaluated year. The dragonfly species present are typical for over warmed water overgrown with macrophytes. Conditions in the river arm on area No. 2612 are favourable for dragonfly community. The odonatocoenoses does not change significantly; regular occurrence of several stagnophilous species was registered in the evaluated year.

Twenty dragonfly species in the larval stage or as exuvia was proved in the evaluated year. The odonatocoenoses of different types of water bodies developed differently due various interventions, but significant – trend changes were not registered.

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 are unstable in last years and getting poor. This is partially influenced by the actual hydrologic situation in the river, but partially this could be attributed to the absence of side branches, which are richer in zooplankton, flowing into this stretch of the Danube. Both communities in the evaluated year, mainly in the littoral part of the flow, were exceptionally poor in species number, as well as in abundance, most likely also thanks to unfavourable hydrologic regime during sampling.

The Cladoceras and Copepods communities react on the actual water level in the river branches rather quickly. Similarly as in the last year the spring average water levels were followed by high water levels during the summer, and in the autumn the water level reached the lowest values.

Although the river arm on the area No. 2603 with high flow velocity and with water poor in nutrients content does not represent the most suitable habitat for development of Cladocera and Copepod communities, these communities are stabilized and typical for through flowing river arms. Regarding the species number the Cladoceras community is richer, but the abundance is higher in Copepods community. In both communities littoral a phytophilous species dominate in long-term, euplanktonic species almost missing.

The living conditions in the dead arm on area No. 2604 are more stable and favourable for Cladoceras and Copepods occurrence, especially for the phytophilous species living in the developed macrophyte community. The number of euplanktonic species is lower in both communities, but their abundance is higher. Since the diversion of the Danube increase of species diversity in Cladoceras community in littoral and medial can be observed. Considering the high species diversity of Cladoceras and Copepods, and the presence of rare species in Slovakia, the area is worth to protect.

The Cladoceras and Copepods communities on the area No. 2608 were rather poor, especially during the summer, when they was flushed out by high discharges. In the autumn, during low water levels certain species of Cladoceras and Copepods bred excessively. Although the euplanktonic species still dominate in both communities, the number of phytophilous Cladocera species increases.

The community of planktonic crustaceans on the area No. 2612 developed under favourable conditions in the evaluated year; the river arm was connected with other water bodies during the summer. This hampers the process of fulfilling of the river arm, which is proved by high species diversity and abundance of Cladoceras. Rather high is the species number of Copepods in the river arm as well. The phytophilous species bound to rich macrovegetation dominate in both communities.

In the observed river arms 31 planktonic crustaceans species were recorded in the evaluated year, which is the lowest value registered since the monitoring started. This is probably connected with the fact, that only one sampling was realized during the year. Species abundantly occurring every year were found in samples, except one species that is new for this region. The highest species diversity was repeatedly registered in the Lipóti marsh; the highest abundance was recorded in the Schisler river arm, while in the Csákanyi Danube no representatives were recorded.

In the evaluated year low species diversity of Cladocera and Copepod communities was registered repeatedly in the Schisler dead river arm, but the abundance of the species present was high. Euplanktonic Copepod dominated again, while the species bounded to macrophytes occurred with low abundance only.

Contrary to this the communities in the Lipóti marsh in long-term are composed mainly by species living on macrophytes in stagnant water bodies. Rather stable species composition proves balanced ecological conditions in the river arm; some changes in last years were recorded in abundance of particular species only.

The absence of planktonic crustaceans in the Csákányi Danube during the only sampling in the summer can be attributed to very high flow velocity in the river arm, which is a part of the water supply system into the inundation area. In the previous years also poor Cladocera and Copepod communities were registered only.

At monitoring site in the Zátonyi Danube, which situated in the flood-protected area, only 3 species of planktonic crustaceans with low abundance were registered in the evaluated year. The reason of this weak population of the river arm in the evaluated year can be low spreading of macrophytes and the related retreat of phytophilous species, which dominated in previous years. Several rare species were registered at this site during the monitoring.

7.7. Caddisflies and Mayflies (Trichoptera, Ephemeroptera)

Regarding the monitoring of mayflies, caddisflies, dragonflies and aquatic molluscs the Hungarian Party since 2007 gradually introduces the methodology according to the Water Framework Directive. These results are not fully comparable with the previous Hungarian results or the results of 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 summarizing the species at three monitoring sites during one sampling, which was carried out according to WFD methodology, and a table of occurrence of particular groups, families, possibly species of macrozoobenthos at individual sampling sites in the evaluated year. These data were not evaluated according to WFD metrics, but concerning the right side river branch system following statements were derived.

The Danube, according to results of the Slovak Party (monitoring areas No. 2600, 2603, 2608 and 2612), is inhabited by caddisflies and mayflies sporadically; the absence of communities (mainly mayflies) is frequent as well. The absence of mayflies and caddisflies in the year 2009 was registered only below the confluence of the tailrace canal and the Danube old riverbed. On the other sampling areas – situated along the diverted stretch of the Danube – mostly rheophilous mayflies and caddisflies were registered. However, surviving of more abundant communities can be supposed in the hard-to-get medial sections, what was proved by results of sampling at a groyne during low water levels in 2007.

Every observed river branches in the left side inundation area (monitoring sites No. 2603, 2604 and 2612) are very poor from the point of mayfly and caddisfly communities. Mayfly communities in last years consist of 3-4 species (limnophilous, eutrophic), however their occurrence is not stable during the year. Caddisfly communities were even poorer and at these sites irregular presence of one or two species, with different ecological demands, was registered.

The macrozoobenthos sampling in the Hungarian inundation area was carried out in the Schisler arm and in the Csákanyi Danube. 34 taxons of 15 taxonomic groups were recorded. Higher number of species and groups was registered in the Schisler dead arm. The most abundant and the most stable occurrence had the chironomids (Chironomidae), mosquitoes (Culicidae), horse flies (Tabanidae), Limnomysis benedeni and Physa acuta.

Sample on the flood-protected area was taken from the Zátonyi Danube from stones in the flowing water. The most abundant were chironomids (Chironomidae), mayflies species of the genus Baetis and Bithynia tentaculata.

Regarding the whole area of interest on the Hungarian side it can be stated that two-winged insects (Diptera), aquatic molluscs (mainly conches), mayflies (Ephemeroptera), bugs (Heteroptera) and caddisflies (Trichoptera) had abundant occurrence. Again it is possible to confirm the incongruence with the Slovak results, according to which only sporadic occurrence of mayflies (Ephemeroptera) and caddisflies (Trichoptera) was registered in the left side inundation area of the Danube.

7.8. Fish (Osteichtyes)

The ichtyofauna monitoring on both sides is carried out by electro-fishing. Difference exists in the power-output of the apparatus, 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 site No. 10. Sampling at monitoring site No. 11 was not carried out in the evaluated year. From these results follow that the ichtyocoenoses of the diverted stretch of the Danube is stabilised in last years, but from the long-term point of view retreat of rheophilous species can be observed, which are replaced mainly by eurytopic species. Slight decrease of species diversity and abundance of representatives can be observed as well. In last several years unambiguous spreading of foreign invasive species is observed. Their expansion is hindered by autochthonous rheophile species, which occur in the medial part of the river, what was confirmed by results of monitoring in previous years and international surveys.

On monitoring areas No. 2603 and 2604 stable ichtyocoenoses occur. Eurytopic and indifferent representatives have dominant position in rich in species and abundant community on area No. 2603. Further expansion of the alien species Neogobius melanostomus was not registered. The ichtyocoenoses in the dead arm at area No. 2604 was less rich in species and less abundant, and it was not enriched even during flooding in the summer. The species present are able to survive at high water temperatures and oxygen shortage.

The ichtyocoenoses at area no. 2608 were observed on two sub-areas, which differ in connection with the Danube main riverbed. Regular communication with the Danube main riverbed occurs in the river arm upstream from the Foki weir. So, this is the reason why this part of the river arm has stabilised ichtyocoenoses with high abundance of individuals and dominance of eurytopic fish species. During the floods in 2002, 2005, 2006 and 2009, or during the high flow rates in 2007 the communication was restored in the river arm below the Foki weir as well, what lead to enrichment of ichtyocoenoses. However, after the decrease of species diversity in 2008 decrease of abundance was registered in 2009. Expansive behaviour of foreign species of Neogobius genus was not registered on any of the sub-areas.

The ichtyocoenoses on the monitoring area No. 2612 in last years (especially since 2004, when it dried out) is very poor in species and with low abundance. Enrichment of ichtyocoenoses was not registered even after reconnection with other water bodies during the flood wave in June. Only three species, which are tolerant to oxygen shortage in the water, were recorded, however their abundance was higher in comparison with the previous year.

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). Stabilised ichtyofauna is registered in last years at every site; 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 Csákányi Danube in 1997. At present there is rich in species and stabilised ichtyofauna. In parts overgrown by macrophytes phytophilous and limnophilous species occur, but in the channel interconnecting the dead arm and Csákányi Danube seasonal occurrence of rheophilous fish species is observed.

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 rheophile fish species. Significant dominance of undemanding species (Alburnus alburnus) was observed in the evaluated year.

After introducing the water supply (in 1995), regeneration of ichtyofauna is observed at monitoring site No. 5 – Lipóti marsh. In last years the species richness of this site is significant and balanced, with the dominance of eurytopic and lithophilous species.

Since introducing the water supply to the flood-protected area the ichtyocoenoses of the Gazfűi Danube (monitoring site No. 12) is stabilized as well. Moderately rich species diversity is composed mainly by marshy and limnophilous species, although the highest values in abundance reach the eurytopic fish species.

PART 7

Biological Monitoring