Chapter 7

In the year 2011 the biological monitoring continued without changes. The 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 2011 (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.

Table 7-1: The list of complex monitoring areas and monitoring sites in 2011

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 – oak forest

●

28b

B-02

Dunasziget – meadow

●

B-03

Halászi – oak forest Derék

●

B-04

Lipót – poplar forest, Gombócos closure

●

H-04

Dunasziget – Schisler dead 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

Gázfűi Danube, rkm 28.5

●

F-26

Dunaremete-Pálfi island, forest, river arm

●

F-27

Rajka – forest Felső

●

F-28

Novákpuszta –alder forest

●

F-31

Lipót – Zsejkei channel

●

F-35

Mosonmagyaróvár – Mosoni Danube

●

F-17

Arak – Nagy Kerek, alder forest

●

F-19

Danube, rkm 1824

●

F-N3

Arak, Nováki channel

●

GAZ

Gázfűi Danube, Galambos

MOS

Mosoni Danube, Szilos

● – data provided according to the Agreement x – evaluation according to WFD methodology

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.

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.

A short description of climatic and hydrologic conditions in the year 2011, which influenced the development of observed groups of fauna and flora on both sides of the Danube, is given in Part 6 – Forest Monitoring.

7.1. Phytocoenology

Phytocoenoses on monitoring areas No. 2600, 2604, 2612 can be regarded as stabilised. On the area No. 2600 community of the driest type of floodplain forest occur. Degradation of the tree layer continued in last year, and the decline of summer ecovalue for phytocoenosis was negative as well. The absence of invasive plant species persists. On the area No. 2604 several positive changes can be stated from the softwood lowland forest development point of view. Together with nitrophilous species one hygrophilous species also dominate, several water demanding species were registered again after their absence for several years, and the presence of invasive plant species remains negligible or they absent. The species composition and the coverage values of the individual layers of soft-wood forest on area No. 2612 are similar in last years. Differences in particular years can be identified in the herb layer only, depending on the occurrence of floods. The natural rejuvenation of woods also proves the favourable conditions on this area. On areas No. 2603, 2608 and 2609 changes evoked by clearing and subsequent reforestation with cultivated poplars are going on. The young poplar stand on the area No. 2603 is already aged 14, however signs of stabilisation were not registered in the evaluated year. The closure of tree tops was lower in comparison with the previous year, the shrub layer was significantly developed. A negative change in the herb layer was the absence of indicative species and the dominance of invasive Himalayan balsam (Impatiens glandulifera). Poplar stands on areas No. 2608 and 2609 create only shrub layer at present, which gradually increases its coverage. Several years after reforestation the ruderal and synantropic species in the herb layer on area No. 2608 disappeared, and the position of characteristic nitrophilous and hygrophilous species has strengthen. On the area No. 2609 the neophytic aster (Aster lanceolatus) and indigenous marshy (Leucojum aestivum) and nitrophilous species dominate. Spreading of invasive species was not noticeable on these two areas.

On the plot No. 28b (Dunasziget - meadow) decline of plant species is registered in last years, due to sprawl of high herbs. The Giant goldenrod (Solidago gigantea) dominated in the evaluated year. On the plot No. 28a (Dunasziget - forest) no signs of flooding have been noticed. In terms of tree layer no changes were registered in comparison with the previous year. Significant changes were not observed even in terms of the herb layer coverage, however, the species number was lower. The poplar stand on the plot No. 30 was cleared during the evaluated year and the area was subsequently reforested with oak seedlings (Quercus robur). The surviving herbal undergrowth had four times higher number of species compared to the previous year, with the dominance of weed and ruderal species. In the oak-hornbeam stand on the area No. 31 further strengthening of the shrub layer continues, which is becoming higher. In their shadow the herb species reach lower coverage, but in terms of species number no significant change can be noticed.

7.2. Terrestrial molluscs

The terrestrial mollusc’s communities are stabilized on areas No. 2600, 2604 and 2612. The malacocoenosis of the area No. 2600 is typical for the driest type of lowland forest, with the dominance of meso-hygrophilous and euryoecious species. The community on the area No. 2604 has a significant wetland character and represents the wettest variant of lowland forest. The unfavourable increasing tendency of the abundance of meso-hygrophilous species discontinued in the evaluated year. On the area No. 2612 malacocoenosis typical for flooded transient wetland forest was registered, with the dominance of forest hygrophilous species and one pioneer polyhygrophilous representative. The malacocoenoses on areas No. 2603, 2608 and 2609 were significantly degraded by clearing of the forest stand in previous years. At present they are in different stages of regeneration. On the area No. 2603 the shadow under the young stand increases, which provides wetter microclimate in the undergrowth. Therefore increases the abundance of forest hygrophilous species and the anthropogenic species retreats. Signs of degradation in the malacocoenosis on the area No. 2608 are still significant in the third year after the clearing, several hygrophilous species disappeared from the samples. In spite of this, regeneration of the community is expected within following 5-10 years. Preconditions for regeneration of the malacocoenosis are favourable also on the area No. 2609, where slight increase of the abundance of hygrophilous and polyhygrophilous species is registered in the fifth year since the clearing.

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

7.3. Aquatic macrophytes

The development of macrophytes in the Danube old riverbed is monitored on two Hungarian monitoring sites, No. 2 at rkm 1839 and No. 7 at rkm 1828. Monitoring in the year 2011 was not realized.

The hydrologic situation in the observed river branches was substantially less favourable than in the previous years. In the previous year the through-flowing river branch on the area No. 2603 was inhabited by macrophytes rich in species. The high number of species remained preserved also in the evaluated year, but in terms of dominance the invasive species Elodea nuttallii reached the dominant presence. In the dead arm on the area No. 2604 the true aquatic vegetation dominated also in the actual year. However, uncovering of the bottom of several sections in autumn caused they retreat. This site is still rich in rare species. After three years of favourable water levels on monitoring areas No. 2608 and 2612 long-term uncovering of the river branch bottom occurred in the evaluated year. Most of the observed river branch sections was richly populated with marshy species and annual plants. Positive fact is that even under these conditions there was no significant expansion of the invasive Giant goldenrod (Solidago gigantea) on the area No. 2608. However, an unfavourable fact is the constant overgrowing of the open water area by invasive species Elodea nuttallii on the monitoring area No. 2612.

Discharges supplied into the active floodplain were similar to discharges in previous years. Large part of the floodplain river branches is characteristic by greater water depth, to which adapted the stabilised species composition of macrophytes. The water level in Schisler arm (site No. 4) was high during sampling, water area was covered with submersed species, especially with the invasive species Canadian waterweed (Elodea canadensis) and shining pondweed (Potamogeton lucens). These species dominated also in Csákányi Danube (site No. 9), while the water area on both sites was covered with green algae (Cladophora).

Growing conditions in the flood-protected area (monitoring sites No. 6 and 8) were similar to that in previous years, what is associated with controllable water regime. The average species number of macrophytes have not changed. The water level in Lipóti marsh (site No. 6) was high. In comparison with the previous year the absence of cosmopolitan hornwort (Ceratophyllum demersum) was surprising. Several rare species were also missing and the invasive Canadian waterweed (Elodea canadensis) has appeared again. However, the species composition in terms of other unrooted macrophytes remained similar. Macrophytes in Zátonyi Danube (site No. 8) were highly similar to that in the previous year. The water area was covered with large patches of protected species (European white water-lily (Nymphaea alba), Yellow water-lily (Nuphar lutea), Floating fem (Salvinia natans)), from among submersed species the pondweeds (Potamogeton) and hornwort (Ceratophyllum demersum) were again plentiful. The absence of invasive Canadian waterweed (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 malacofauna, while the breaking decline in species number and abundance was registered in 2005. This decline was probably caused by interaction of several factors – hydrologic, trophic, physical and chemical. At present only the non-native invasive species Theodoxus fluviatilis and the ubiquistic species Dreissena polymorpha has regular occurrence in the Danube.

The aquatic molluscs’ community in the river branch system on the Slovak side is monitored at areas No. 2603 and 2604. In both areas destruction of malacocoenosis, decline of populations of large species and significant decrease in abundance of smaller species can be registered in recent years. On the area No. 2604 it is probably caused by frequent decrease of water level in the summer or autumn period, which results in conditions with lack of oxygen in the water. However, the destruction of community on the area No. 2603 is registered despite the heterogeneous nature of the river arm, sufficient size of biotope and good conditions for its development. At present the malacocoenosis is stabilized at 9-11 species, that achieve abundance of several dozens of individuals. The malacocoenosis on the area No. 2604 is significantly poorer, only one ubiquistic species has regular presence with low abundance.

Aquatic malacofauna in the Szigetköz region has great species diversity, with ability for regeneration. Relatively rich communities of aquatic malacofauna in inundation area did not show significant differences in comparison to previous years; they are stable. The variety of malacofauna of wetlands in the flood-protected area does not reach the diversity registered in the inundation area. Ensuring nature-close conditions would enable the improvement of the status of malacofauna community.

7.5. Dragonflies (Odonata)

The monitoring of dragonfly communities on areas No. 2600 and 2608 was shifted from river arms to the coastal zone of the Danube old riverbed, because samples taken in arms were had been very poor in recent years. The bays in the Danube old riverbed are overgrown with macrophytes, to which the occasional occurrence of rheophilic and semirheophilic dragonflies is bound. Their communities, however, are relatively poor, especially on the area No. 2608. More rich 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 or semirheophilic dragonflies, while the overgrown bays are populated by stagnicolous species. The various conditions of the river arm get closer to the situation before damming. The species-rich odonatocoenosis of the dead arm on area No. 2064 is created by species of over-warmed waters, which usually achieve only low abundance. Actual results likely indicate deteriorating conditions for the development of dragonflies in the river arm due to regular low water stages in autumn. It would be necessary to provide artificial rinsing of this river arm. Diverse habitats on the area No. 2612 are inhabited by stagnicolous, eurytopic and semirheophilic dragonflies species.

As a result of various interventions the odonatocoenoses of different types of water bodies developed differently in the course of monitoring. Increased discharges into the Mosoni Danube did not have significant influence on the composition of present odonatocoenosis typical for flowing water. However, the increased amounts of water supplied with the supply system have changed the communities of densely overgrown branches with stagnant water (Nováki channel, Lipót - Zsejkei channel). The number of rare species in their rich communities decreased, or they were replaced by species with wide tolerance. In parallel with this decrease of species diversity have been registered also on other sites. The results of recent years, however, in case of Nováki channel indicate the possibility to get back to the state before damming.

7.6. Crustaceans (Cladocera, Copepoda)

Evaluation of the development of cladocerans 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 cladocerans and copepods communities are unstable and have become poorer in last years. Gradual retreat of pelagic and increase of littoral species, and increase of invasive cladocerans and copepods is registered. Low water stages in the evaluated year could enable the development of crustaceans communities, but significant enrichment was observed only in case of cladocerans on the area No. 2608. Unlike the previous tendency, an increase of the portion of euplanktonic species has been recorded in both communities.

In terms of the development in cladocerans and copepods communities in river arm on the area No. 2603 the tendency of previous years continues. Zooplankton communities in medial are not typical due to the weak development of phytoplankton, what is associated with low content of nutrients in water. Communities are poor in species and the tychoplanktonic species dominate, which are rinsed out of the richly inhabited littoral. The emergence of cladocerans typical for temporary waters in the littoral indicates a decrease in connectivity of the river arm with the main flow.

The tendency in development of cladocerans and copepods communities in the dead arm on the area No. 2604 indicates deterioration of trophic conditions in recent years. Due to siltation and intensive development of macrophytes, what hampers the development of phytoplankton, depletion of zooplankton (filter-feeders) occurred. Decrease in species number is registered in both communities, along with mass occurrence of one species. The ecological value of habitat decreases in term of the occurrence of cladocerans and copepods species. Rinsing of the river arm would be beneficial.

The cladocerans 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. Several rare species were registered in the river arm as well. The copepods community was moderately rich in species, the species abundance was low. At the dominance of euplanktonic species this community can be classified as typical for parapotamon.

Planktonic crustacean communities on the area No. 2612 are assessed as balanced in long-term, typical for river arms of plesiopotamon type.. Due to low water levels in the actual year, decline of cladocerans species number was observed. In both communities the phytophilous species dominated.

The number of recorded species of planktonic crustaceans in the evaluated year was the lowest in the observation period (in comparison with the previous year only a half). The highest species number and also the highest abundance was recorded in Schisler dead arm, however these values are very low in terms of the whole period of observation. Typical species bound to macrophytes occurred only sporadically, more abundant were two species of euplanktonic copepods. More than 85 % of crustaceans were formed by different development stages of copepods (copepodits and nauplius).

The stable ecological conditions in the Lipóti marsh are manifested by balanced species number of crustaceans in long-term, with exception of some years, including 2011. The most abundant are mainly typical species of stagnant waters bound to macrophytes. However, their actual species number and abundance were very low.

At monitoring site in the Zátonyi Danube, that is situated in the flood-protected area, only three Cladocerans and two Copepod species with low abundance were registered in the evaluated year (similarly as in the previous year). Also typical phytophilous species in the evaluated year were absent again, or occurred sporadically. However, long-term observation results show high species diversity and stability of this habitat, with occurrence of several rare species.

The weak population of the Csákányi Danube may be associated with stronger water flow, since the river arm is a part of the water supply system into the inundation area. After the absence of representatives of Cladocerans and Copepods in the year 2009, only one euplanktonic Copepod species was present in the previous and in the actually evaluated year.

7.7. Caddisflies and Mayflies (Trichoptera, Ephemeroptera) and other groups of Macrozoobenthos

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 2006. 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 Danube, according to results of the Slovak Party (monitoring areas No. 2600, 2603, 2608 and 2612), is inhabited by caddisflies and mayflies sporadically. Recorded species are mostly rheophilic, however, their occurrence is irregular in individual samples and in particular years. Permanent absence of communities in samples can also occur for several years.

In terms of mayfly and caddisfly communities, all observed river branches in the left side inundation area (monitoring areas No. 2603, 2604, 2608 and 2612) are very poor in long-term. Mayfly communities at present consist of 1-2 stagnicolous or semirheophilic species, achieving low abundance and mostly irregular presence during the year. The occurrence of caddisflies was not registered in most of observed river branches, even contrary to increased number of samplings performed at several monitoring areas. Only in the river arm on the monitoring area No. 2603 three caddisfly species were recorded.

The result of macroinvertebrate groups observation, according to the methodology of WFD, is the assessment of ecological status of the monitored water bodies. Sampling of macroinvertebrates according to the WFD methodology the Hungarian Party carries out since 2006 on two sites: in the Gázfűi Danube at Dunasziget - Galambos, and in the Mosoni Danube at Dunaszeg - Szilos (water body type: Danube, side arms). After evaluation of the development of type-specific characteristic species and their density, and subsequent calculation of the Q_BAP index for the period 2006-2011 it can be concluded that:

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 and in the frequency of sampling, which decreases the comparability of results obtained by both Parties.

The evaluation of ichtyofauna in the Danube is based on Slovak observation results at monitoring areas No. 2600 and 2608, and Hungarian observation results at monitoring sites No. 10 and 11. Generally it can be stated that the ichtyocoenosis 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 invasive representatives. Their expansion is hindered by indigenous rheophilic species, which probably find their refuge in the not sampled medial part of the river. However, the results of both Parties indicate that the registered ichtyocoenosis is probably underestimated due to the low extent of observed area.

Richer and stabilised ichtyocoenoses occur in the river arms on monitoring area No. 2603 and upstream of the Foki weir on the area No. 2608, as these river arms interact with the other river arm or the main flow of the Danube. The dominant species of the ichtyocoenoses are eurytopic and indifferent fishes. On the area No. 2608, upstream of the Foki weir, after restoration of connection with the main flow of the Danube also rheophilic species use to be abundant. In the year 2011 this connection occurred in limited extent only. Expansive behaviour of invasive goby species (Neogobius sp.) is not observed on these areas. Decrease of species abundance is registered on both monitoring plots.

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. Slight enrichment of ichtyocoenoses after the flood in the previous year has not been noticed in the evaluated year. On the area No. 2604 species able to survive at high water temperature and lack of oxygen occurred with low abundance. Limiting factors for the ichtyocoenosis are high summer water temperatures and winter freezing. Dominant position achieves one expansive species. The ichtyocoenosis registered on the area No. 2608 downstream of the Foki weir was poor in species number with low abundance, without occurrence of rheophilic species. The ichtyocoenosis in the muddy and overgrown river arm on the area No. 2612 consist of 3-4 species, not demanding on oxygen content in the water and achieving low abundance, in long-term.

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; substantial changes in species diversity or abundance were not recorded.

In terms of ichtyofauna in the Schisler river arm (monitoring site No. 4) it can be stated, that the abundance of invasive black bullhead (Ameiurus melas) negligible in the evaluated year, and the increase of its abundance has been interrupted. This species in the Gázfűi Danube (monitoring site No. 12) has not occurred in the year 2011. In the Csákányi Danube exchange in dominance have been registered, the undemanding bleak (Alburnus alburnus) have been replaced with other indifferent species, common roach (Rutilus rutilus).

After introducing the water supply (in 1995), regeneration of ichtyofauna is observed at monitoring site No. 5 – Lipóti marsh. Significant species richness of the fish community persists. The abundance of invasive black bullhead (Ameiurus melas) remains low.

PART 7

Biological Monitoring