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 2008 (Fig. 7-1). Two new sites monitored in the frame of Water Framework Directive were added. 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 there exist differences in some monitoring methods on both sides, which should be eliminated after introducing classifications according to the Water Framework Directive during next years. Since 2006 the Hungarian side started to introduce an evaluation according to the Water Framework Directive in case of several groups, however the methodology and results are mentioned in the National and Joint Report marginally.

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-33

Danube, rkm 1849

F-34

Lipót - river arm

F-35

Mosonmagyaróvár - Mosoni Danube

●

F-17

Arak - Nagy Kerek

●

F-19

Danube, rkm 1824

●

F-N3

Arak, Nováki channel

●

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

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

H - Caddisflies (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 2008, which influenced the development of observed groups of fauna and flora on both sides of the Danube, is given above in Part 6.

7.1. Phytocoenology

Thanks to sufficient precipitation in the summer time (from middle of May to the end of July) the phytocoenoses, in spite of the absence of natural floods, were not influenced by moisture shortage even on areas, where the groundwater level fluctuated in the subsoil gravel layers (area No. 2600). The monitored phytocoenoses in the inundation area are stabilised (areas No. 2604, 2612), observed changes were mostly assigned to closure of treetops of the young tree layer (areas No. 2603, 2608, 2609). To ensure the creation of favourable moisture conditions of this region more effective usage of the existing objects of the water supply system would be necessary (regular artificial flooding). These measures probably would contribute to the retreat of invasive plant and animal species, which spread in this region (some species in compliance with the law have to be eliminated).

The average species diversity of phytocoenoses of observed monitoring sites have not changed significantly in comparison with previous years. On some sites considerable presence of invasive species was recorded. Damages caused by forest games on the shrub layer were frequently observed as well.

When evaluating the average leaf area values no significant changes were recorded in the evaluated year. Differences in the leaf area size in case of white willow in comparison with previous years remained in the existing range as for the influenced area so for the reference sites. The average leaf area values in case of pedunculate oak (Quercus robur) at Dunasziget practically reached same values as in the previous year.

7.2. Terrestrial molluscs

The terrestrial mollusc's community on a large part of inundation area is stabilized (on areas No. 2600 and 2612 on the level typical for dryer variants of floodplain forest; on area No. 2604 on the level typical for the most wet variants of the floodplain forest). Occasional observed changes could be mostly assigned to the impact of silviculture or actual hydro-meteorological conditions. During first years after clearing a tree layer retreat of polyhygrophilous and hygrophilous species is observed. When the treetops start to close continuous return of these species is detected. In some cases penetration of foreign species occur as well.

The terrestrial malakocoenoses in the inundation and in the flood-protected area is stabilised. Although in individual years fluctuation in biomass of communities can be registered, no worsening tendency can be observed. In last three years many species (including hygrophilous species) occur in amount of several hundreds or thousands of individuals. 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). More interesting macrophyte vegetation is observed on the 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). In the isolated part with stagnant water area macrophyte community rich in species occur. In the evaluated year it was less rich probably due to higher flow rates occurring approximately two weeks before date of observation.

The hydrological conditions in most of observed river arms were more favourable for development of macrophyte vegetation than in the previous year. The water levels and amount of precipitation were rather high; occurrence of terrestrial species spreading after shallowing and drying out of river arms was more rare. Some areas are still rich in protected species; spreading of invasive species Elodea nuttallii was registered only in single river arm. Macrophytes in the river arm used to supply water on the monitoring area No. 2603 develop more intensively during decreased discharges, when the flow velocity is low. The macrophyte community in the dead arm on monitoring area No. 2604 does not change. Following the destruction of the true water vegetation on the monitoring area No. 2608 in the previous summer the river arm was fulfilled by water during this summer and the marshy and terrestrial species, including ruderal species spreading from the adjacent cleared forest areas, overgrowing the river arm were eliminated. Only the Phalaris arundinacea and Urtica dioica survives. The macrophyte communities in the river arms on monitoring area No. 2612 had favourable conditions in he evaluated year. The open water area was overgrown by invasive species Elodea nuttallii. The other shallow parts similarly to the previous year had higher species diversity.

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 water flow on monitoring site No. 4 is very slight and the whole water level is covered by submersible macrophyte species. One vulnerable species occur as well. The flow velocity on monitoring site No. 9 is higher. Two very abundant macrophyte species were registered, but one of them is the invasive species Elodea canadensis.

The hydrological conditions of the flood-protected area (monitoring sites No. 6 and 8), thanks to the continuous water supply, remained unchanged in last few years. The species composition on monitoring site No. 6 was less rich in the evaluated year, but the protected species, except one, remained preserved. Occurrence of the invasive species Elodea canadensis was only occasional, on the site No. 8 it was not registered. The macrophyte species composition is stable, some species, including the rare ones, occurred abundantly.

7.4. Aquatic molluscs

The evaluation of the aquatic molluscs- community in the Danube is based on the data provided by the Slovak Party only for the second time (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. The results of the Slovak Party in last years demonstrate significant decrease of malakocoenoses on the diverted stretch of the Danube, as well as in the stretch below the confluence of the tailrace canal and the Danube old riverbed. Stable occurrence at present is detected for the foreign species Theodoxus fluviatilis only, which invasively spreads along the Danube. Irregularly with lower abundance the ubiquistic and indifferent species occur as well. 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 aquatic molluscs- community in the river branch system on the Slovak side is monitored at sites No. 2603 and 2604. The aquatic malakocoenoses on the area No. 2603 seemed to be stabilised till now, but the results in previous year intimated the beginning of its destruction. The results of the actual year, especially the presence of two species only in autumn, proved this tendency. Contrary to heterogeneous character of the river arm, sufficient size of the biotope and good conditions for their spreading, mainly the big species decline. Present species are mostly stagnicolous or ubiquistic. Unfavourable situation persist also in the dead arm on monitoring area No. 2604. The regular decrease of water level in summer or autumn period, accompanied by oxygen shortage due decay processes has destructive impact. Retreat of species number and significant decrease in their abundance at this site is provable. The most surprising in the evaluated year was the irregular occurrence of one ubiquistic species, which reached abundance of 1000 individuals and was the last abundant species of the dead arm one or two years ago.

The malakofauna variedness of the water bodies in the flood-protected area exceeds the variability of drier forest communities, but it does not reach the variety registered in the inundation area. The communities are not stable and depend on actual site-specific conditions. The fauna of these biotopes is probably vulnerable.

7.5. Dragonflies (Odonata)

The development of odonatocoenoses is considerably influenced by actual hydrological and climatic conditions. Poor communities, which occurrence is based on flying imagines registration only, with irregular occurrence and low abundance, occur on areas No. 2600 and 2608. More rich odonatocoenoses occur on areas No. 2603, 2604 and 2612. On the area No. 2603 rheophile, semirheophile and eurytopic species occur because the living conditions in the river arm are very various. The community on the area No. 2064 is rich in species, but only one eurytopic dragonfly had permanent occurrence. Thanks to the wet summer no overwarming of water in the dead arm and oxygen shortage occurred in the evaluated year. High species richness on the monitoring area No. 2612 most likely represents three different types of neighbouring biotopes - the Danube, sporadically through-flowing river arm and periodic depressions.

The dragonflies-community monitoring in 2008 did not proved significant, tendentious changes. As the most rich in species site in the Szigetköz region the Nováki channel at Arak village was considered again, with slowly flowing water and abundant aquatic vegetation.

7.6. Crustaceans (Cladocera, Copepoda)

Evaluation of the development of Cladoceras and Copepods communities is based on the results of the Slovak Party at monitoring site No. 2600 and 2608, which are situated on the diverted stretch of the Danube. This Danube stretch does not represent an optimal environment for planktonic crustaceans communities, however the results could be influenced by actual hydrological situation in the time of sampling or in a period before sampling (high differences in water level during summer and autumn). Communities in most of samples were poor in species number and in abundance again, especially during autumn, when the water level was very low. Unusual dominance of tychoplanktonic species remained preserved only on area No. 2600.

The Cladoceras and Copepods communities react on the actual water level in the river branches rather quickly. In comparison to the previous year the changes of water regime in the river branches were more significant. The water levels during the spring reached average values, but at the end of spring and beginning of summer (May-June) the water level reached highest values and the flow velocities were rather high (artificial flooding). During autumn the water level reached the lowest values. The flow velocity in the river arm on the area No. 2603 is high and the water is poor in nutrients content, so it does not represent favourable biotope for development of Cladocera and Copepod communities. Fluctuating number of Cladocera species and the high dominance of littoral species in medial of the river arm demonstrate rather unstable environment for this community. Euplanktonic species missing in the Copepod community as well, which is moreover less rich in species. The living conditions in the dead arm on area No. 2604 are more stable. However, a long-term decrease of Copepod species number is registered under these conditions as well, while in connection with the development of macrovegetation the Cladocera species number increases. The Cladocera and copepod communities on the area No. 2608 were rather poor, even the Copepods were missing during the summer period. Although the euplanktonic species dominated in these communities, penetration of littoral species into medial can be observed. The Cladocera community in the river arm on area no. 2612 was rich in species. Phytophilous littoral specie dominated throughout the year. During the last two years slight increase of species number was registered in the Copepod community as well, which is probably connected with increase of phytophilous species in the shallowing river arm.

In the observed river arms 36 Cladocera species and 11 Copepoda species were recorded in the evaluated year. In comparison with the previous year significant increase of Cladocera species occurred, mainly in the Lipóti marsh, where the highest abundance was registered as well. Repeated presence of several species was proved, which were missing in samples for several years.

In the evaluated year no further decrease of species diversity of Cladocera and Copepod communities was registered in the Schisler dead arm, but the abundance of the present species was lower. Euplanktonic Copepod dominated this year again, while the species bounded to macrophytes again occurred with low abundance only.

The composition of planktonic crustaceans in the Csákányi Danube changes every year, but low species diversity and low abundance of individuals remain. In last years little eurythermic species dominate. The weak inhabitancy of the river arm and unstable species composition can be connected to stronger flow of water because the river arm form a part of the water supply system in the inundation area.

At monitoring site in the Zátonyi Danube, situated in the flood-protected area, 18 species of Cladocera and Copepoda were registered in the evaluated year, which is more than in the previous two years. Repeated occurrence of several species, which were missing in the previous years, was registered, and one new species was recorded. The abundance of species in samples was low.

7.7. Caddisflies and Mayflies (Trichoptera, Ephemeroptera)

In the evaluated year, similarly as in the previous year, no caddisflies and mayflies observation results from the Hungarian side were available, obtained according to methodology set up in the frame of the Agreement 1995. The summarizing list of species of benthic invertebrates recorded with the methodology according to the Water Framework Directive, which is a part of the Hungarian National Report on environmental monitoring in 2008, contains every species of macrozoobenthos (including caddisflies and mayflies) recorded on 5 sampling profiles without their abundance. Based on this table was not possible to conduct detailed conclusions on development of these taxocoenoses in the evaluated year, although the data proved high species richness of caddisflies and mayflies communities in Szigetköz. But the results of the Slovak Party given below show very poor or even absence of these communities in the Danube and in the Slovak river branch system.

The Danube, according to the results of the Slovak Party (monitoring areas No. 2600, 2603, 2608 and 2612), is inhabited by caddisflies and mayflies sporadically. The absence of mayflies in the individual years occurs more often, but caddisfly communities (mostly Danube species) have irregular presence in samples. However, surviving of some caddisfly and mayfly species was proved by results obtained after sampling the hard-to-get medial sections of the diverted stretch of the Danube during last year.

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, however only one limnophilous mayfly species had stable occurrence in samples. Caddisfly communities were poor and were represented by irregular occurrence of limnophilous or semi-rheophilous species.

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 sides No. 10 and 11. 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 and slight decrease of species diversity can be observed. However, experts at present are on that opinion, that the magnitude of decrease is not so big as it was assumed in previous years. In last few years unambiguous spreading of foreign invasive species is observed, but their expansion is hindered by autochthonous rheophile species.

On the monitoring areas No. 2603 and 2604 stable, rich in species ichtyocoenoses occur. Increased abundance in the evaluated year was recorded at area No. 2603 only, due to high number of juvenile individuals and a presence of one expansive species. The community in the dead arm at area No. 2604 was less rich in this year, which proves the isolation of this river arm. Abundantly occurred the expansive black bullhead (Ameiurus melas) and limnophilous pumpkinseed fish (Lepomis gibosus) only.

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 why rich in species, stabilised ichtyocoenoses with high abundance of individuals and dominance of eurytopic fish species is registered in this part of the river arm. During the floods in 2002, 2005 and 2006, or during the high flow rates in 2007 the communication was restored in the river arm below the Foki weir as well, which lead to enrichment of ichtyocoenoses. However, in the evaluated year decrease of species diversity occurred again, while the abundance of species remain preserved yet. 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 abundance. Stable presence was registered only for three species, which are tolerant to oxygen shortage in the water, although such a situation, thanks to favourable hydrological and climatic conditions, did not occurred.

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).

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 Csákányi Danube river arm (monitoring site No. 9) is high since introduction the water supply in 1995, and rheophile fish species occur here as well. There were 17 species recorded again in the evaluated year, and the significant dominance one tolerant species (Rutilus rutilus) remains preserved.

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 occasional occurrence of rheophile species. In the evaluated year eurytopic and litophilous species dominated.

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 by marshy and limnophilous species, although eurytopic fish species remained dominant

PART 7

Biological Monitoring