PART 7
Biological MonitoringThe 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, in 2006 were monitored at 20 monitoring sites on the Hungarian side (Fig. 7-1). From the methodological point of view there are still differences in some monitoring methods on both sides, which should be eliminated after introducing methods according to the Water Framework Directive and other EU directives during next years. In the evaluated year the Hungarian side have already applied methods 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. A short description of hydrological and climatic conditions in the year 2006, 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. PhytocoenologyThe left side river branch system Stabilized development of phytocoenoses can be observed in a greater part of the left side inundation area, which was several times influenced by flooding in the evaluated year. Typical phytocoenoses of lowland forest was registered at area No. 2604. Vegetation at area No. 2609 was similar, but the forest on this area was cleared during the spring and the undergrowth vegetation was devastated. This layer regenerated soon and it was lush already in the summer. At the area No. 2612 a typical phytocoenoses of the transient lowland forest can be found. Although the selective impact of floods caused some decrease in species composition nitrophilous species (Urtica dioica, Rubus Caesius) further determined the character of the herb layer. At the same time the species of fresh stands were replaced with more hygrophilous species. At area No. 2600 stabilised phytocoenoses can be found at present, which had been characterized by slow continuous drying out (starting in 1970-1980). The gradual drying out of the area stopped and the vegetation has stabilised on a dryer level. The coverage of tree layer is low, poplar trees have dry branches. The well developed shrub layer is rich in species, so the undergrowth vegetation occur mosaically, containing hydrophytes as well. The phytocoenoses of young poplar forest at area No. 2603 gradually stabilises. Closing of treetops slowed down in the last year, the coverage values did not increase. The shrub layer have not changed as well. The high species diversity of the herb layer, as well as the number of invasive plant species decreases. The moisture conditions of the area No. 2608 become gradually worse, although the worsening was not so evident thanks to several flood events occurring during last two years. Drying out of willows, and spreading of nitrophilous and invasive plant species indicate ruderalisation of the community. The forest stand on this area was cleared at the end of autumn 2006. Water supply of the river branch system in this region have to be solved. The right side river branch system The moisture conditions in 2006 were favourable thanks to ample precipitation, big flood in March/April and high discharges during the spring and early summer. As a consequence of this the species number and the coverage of the vegetation changed negligibly in comparison with the previous year. The height of herb layer was slightly lower compared to the previous year, when maximal values of the whole monitoring period were recorded. The species number was insignificantly higher. At some of monitoring areas retreat of Urtica dioica and invasive species was registered in a consequence of floods. The average leaf area values for pedunculate oak (Quercus robur) at Dunasziget was significantly higher in comparison to the previous years, when extensive damages caused by leaf-eating caterpillars were registered. The average leaf area on white willow (Salix alba) and alder (Alnus glutinosa) stands remained unchanged. The structure of phytocoenoses along the Mosoni Danube remained unchanged. Since introducing the water supply in 1995 the water level in the Mosoni Danube became stable. 7.2. Terrestrial molluscsThe left side river branch system The terrestrial mollusc’s community on a large part of inundation area are stabilized, observed changes in the most cases could be assigned to the impact of the silviculture. The most favourable moisture conditions occur at area No. 2604 and 2609, where typical marshy lowland forest communities occur, with the dominance of polyhygrophilous species and the absence of antropotolerant species. Clearing of the forest at area No. 2609 could influence the malakocoenosis on this area, although no significant changes were registered in the evaluated year. Malakocoenoses at monitoring areas No. 2600 and 2612 are stabilized, but on a dryer level.. The community at the area No. 2600 was influenced by gradual drying of this region in previous decades, but the situation has stabilised in last years. Mezohygrophilous species dominate in the present malakocoenoses, along with the presence of euryek species. The composition of community at area No. 2612 used to be similar, however in the evaluated year more hygrophilous species prevailed. This phenomenon is typical for a climax under conditions of cyclical flooding. Worsening of the hydrological regime in the region of Istragov island (plot No. 2608) invoked a medium degradation of the malakocoenoses. In the mollusc’s community euryek species are already abundant, their disappearance supposed after floods in the last two years was not confirmed. Surviving polyhygrophilous species could regenerate if the water supply to this region would be solved. The malakocoenoses at monitoring area No. 2603 has a mezohygrophilous character. Insignificant occurrence of polyhygrophilous species were registered in the young forest stand as well. Development of more hygrophilous mollusc's community is hindered by low ground water level and by rare occurrence of longer lasting floods. The right side river branch system In 2006 both, outside the flood protection dykes and in the floodplain mostly those mollusc species were registered as they had been collected in previous years. No new species was recorded at sampled sites in 2006. Natural and artificial floods in previous two years had favourable impact to the malakofauna in this region. The tendency of gradual decrease of species diversity and abundance of individual species registered in previous years has changed. In 2006 increase of species number and significant increase of abundance was recorded, at some of hygrophilous species several hundreds of individuals were registered. The mollusc communities at some sampling sites might be influenced by clearing the surrounding forest stands. An interesting phenomenon was noticed in connection with reforestation of several sites with different tree species. Some of alien tree species, as common horse chestnut and black walnut are clearly avoided by molluscs, while other tree species as hornbeam and maple are clearly preferred. 7.3. Aquatic macrophytesThe Danube In the Danube old riverbed two Hungarian monitoring sites are situated (No. 2 and 7). The old riverbed has not provided favourable conditions for development of macrophyte communities before damming the Danube. In the evaluated year decrease of species number stopped, however the mud coverage along the riparian habitats was still observed. The monitoring area No. 2 is situated in the main riverbed downstream of the bottom weir, where the decreased flow rate after damming the river enabled development of macrophyte communities. Since 1995, when higher flow rate was discharged to the Danube old river bed the macrophytes gradually retreated. At present no macrophyte stands are registered. Since 2003 only development of Salicetum triandrae can be observed. More interesting macrophyte growth is observed on the monitoring site No. 7, which is separated from the Danube old riverbed by shoreline vegetation of Salicetum triandrae and Scirpo-Phragmitetum. The water area is covered by macrophyte community rich in species. The left side river branch system High water levels and floods in last two years influenced the macrophyte communities at monitoring areas No. 2603, 2608 and 2612. Macrophyte growth at plot No. 2603 was flushed out, the subsequent regeneration proceeded slowly, slight spreading of an invasive species was registered. Longer occurrence of permanent hydro ecophasis in 2005 and 2006 resulted in an increase of macrophyte vegetation on monitoring plots No. 2608 and 2612. Retreat of invasive species and species intolerant to the wet biotopes was registered. In the last two years the macrophyte communities were very similar. As a consequence of equable hydrologic conditions the macrophyte community found in the marshy lake at plot No. 2604 is stable. Occurrence of several rare species remain preserved. The right side river branch system 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 stabilized species composition of aquatic plant communities, typical for moderately flowing branches, correspond to this (Plot No. 9). The development of rich aquatic vegetation in the dead arm on monitoring site No. 4 was similar to previous years. Spreading of invasive species Elodea canadensis was not observed, its retreat in the whole monitored region was registered. 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 compositions have not changed significantly as well, presence of protected species remain preserved. The density of reed and macereed stands slightly decreased, water area was covered by submersed and floating macrophyte species. 7.4. Aquatic molluscsThe Danube The evaluation of the aquatic molluscs’ community in the Danube is based on the data provided by both the Slovak and Hungarian Party (Slovak observation sites No. 2600, 2608 and 2612 are situated at rkm 1841, 1817 and 1804, Hungarian observation sites are situated at rkm 1831 and 1824). Observation results of the Slovak and Hungarian Party differs in 2006. While in 2005 decrease of species number and number of individuals was declared by both Parties, this tendency in 2006 was stated by the Slovak Party only. Samples of the Slovak Party contained weak occurrence of low number of species. On the contrary, comparing the results from the Hungarian side in 2006 with results in 2004 and 2005 significant increase of species diversity and abundance can be noticed. Populations of several species were very high, counting several hundreds of individuals. The left side river branch system The aquatic molluscs’ community in the river branch system on the Slovak side is monitored at sites No. 2603 and 2604. The different development of malakocoenoses at these two sites is conditioned by the connection of the river branch at monitoring site No. 2603 with the neighbouring river arms, while on the monitoring area No. 2604 a dead arm is observed. At site No. 2603 a stable mollusc’s community occurs, rich in species, which consist mainly of stagnicolous and indifferent species. Regarding the previous years the malakocoenoses at site No. 2604 is stable as well, however regarding the long term development it is poor due to dead arm isolation. In the evaluated year one ubiquitous species (Physa acuta) behaved expansively. Realization of artificial flooding could prevent repeated destruction of the community due to low water level in the summer. The right side river branch system The malakofauna in the inundation showed signs of disturbance already in the previous year. In 2006 further decrease of number of species and abundance was registered, at some monitoring sites dominance of communities changed as well (e.g. at Novákpuszta, rkm 1824 and 1831). Results along the Danube riverside showed malakofauna rich in species and abundant, similar to the state before damming the river. Although the strip is rather narrow, compared to the inundation area, it creates a reservoir of hygrophilous species of this region. 7.5. Dragonflies (Odonata)The left side river branch system The dragonflies community is rather poor in the whole observed area. In the last years besides larva's the flying imagines of dragonflies were registered as well, but neither this complementary method proved more rich odonatocoenoses. The poorest community was registered at area No. 2608, where only two imagines of one rheophile species were recorded. The gravel pit on the monitoring area No. 2600 was settled by dragonflies less abundantly in 2006, probably due to drying out during the autumn of previous year. The community was mainly composed by eurytopic species. In the river branch at monitoring area No. 2603 decrease of rheophilous species was registered and increase of species number typical for stagnant and over-warmed water. This change represents a shift towards a community present before the damming. Rich dragonflies community was registered at monitoring area No. 2604 only. This community consist of eurytopic species and species typical for over-warmed water, including vulnerable species. Negative influence has the oxygen deficiency, which repeatedly occurs in autumn. Artificial flooding could eliminate this problem. The odonatocoenoses at monitoring area No. 2612 is rather rich as well, however it includes three neighbouring biotopes – the Danube, sporadically through-flowing river branch and periodical depressions. In this wide range of biotopes rheophilous, eurytopic species and species tolerant to water shortage were registered. The right side river branch system The most significant change in the inundation area is the continuous water supply into the river branch system. In consequence of the applied water management communities of different water types reacted differently. There was no significant change in species composition of deep and shallow gravel pit lakes in the floodplain and outside the dykes. The fauna of previously slowly flowing side arms and mainly inland channels (Gázfűi river arm, Nováki channel, Zsejkei channel, Lipóti channel), which were overgrown by macrophytes, was replaced by species typical for flowing water (rheophilous) or eurytopic species. At the same time decrease of species diversity came up. The dragonflies species composition of regularly monitored sites in the inundation and in the flood protected area has stabilised at this level during last years. The increased amount of water in the Mosoni Danube did not affect the dragonfly communities. 7.6. Crustaceans (Cladocera, Copepoda)The Danube The development of Cladoceras and Copepods communities is evaluated based on the results of the Slovak side at monitoring site No. 2600 and 2608. Both communities were poor in the Danube till autumn, because of their flush out during floods, similarly as in previous year. From the long-term point of view decrease of species number can be observed. In both communities dominance of euplanktonic species prevailed. Their share in the Cladoceras community increased in last years, however they dominated before damming the river as well. The Copepods community reacted to the hydrological changes more mildly. The dominance of euplanktonic species remained preserved during the whole period of observation. The left side river branch system Generally, in river branches in the left side inundation gradual decrease of euplanktonic Cladoceras and Copepods species is ongoing, which dominated here before damming the Danube and before introducing the water supply. The most significant factor evoking this change at monitoring area No. 2603 is cutting down the riparian forest stand and subsequent development of macrophytes in the river branch. In river branches at monitoring area No. 2604, 2608 and 2612 progressive shallowing and overgrowing going on, so phytophilous species occurs as well. The overgrowing process slowed down at areas No. 2608 and 2612 in the evaluated year, because the monitoring sites were flooded several times. Increase of Cladocera species diversity was registered after floods. Artificial flooding could evoke similar effect in case of the dead arm at monitoring area No. 2604. Copepods respond slower to the above mentioned changes because they have lower ecological demands, especially regarding the water oxygen content and pH value. In this community euplanktonic species dominate constantly, except the monitoring area No. 2603, where the strong flow probably flushed out these species from the medial. The right side river branch system The Cladoceras and Copepods communities were rather rich in species in the observed region. Several new species for the area of Szigetköz were registered, return of species, which were not registered for several years, were observed as well. In 2006 the most rich in species community (21 species) was registered at Schisler dead arm, three new species were recorded. During the whole observation period (1991-2006) 69 species of Cladocera and Copepoda were registered, the yearly taxa number varied between 12 and 29. Few species, which were frequent earlier disappeared, while other species appeared and became frequent. The main reason of these variations was the artificial reconnection of the dead arm with the Csákányi Danube river branch in 1998. In the Csákányi Danube 6 species were recorded in 2006. During the whole monitoring period (1991-2006) 55 Cladoceras and Copepods species were registered. and the yearly taxa number varied between 4 and 30. Since introducing the water supply stronger flow and higher water levels slowed down the spreading of macrophytes, what resulted in a decrease of crustaceans species diversity. At monitoring site in the Zátonyi Danube, situated in the flood protected area, 15 species of Cladocera and Copepoda were registered in 2006. During the whole observation period (1993-2006) 69 species were recorded, including a lot of rare species. The taxa number varied between 5 and 41. In 2006 few species turned up, which were not detected from the Zátonyi-Danube for several years. The composition of Cladocera and Copepoda communities indicate the diversity and stability of habitats in the Zátonyi Danube. In the Lipóti march 9 Cladoceras species were registered in 2006. In the last two years no Copepods species were recorded. During the whole monitoring period (1993-2006) 83 Cladocera and Copepoda species were registered, the number of taxa varied from 11 to 43. Since 2004 the species diversity and the abundance decreases. The most abundant became phytophilous species, which dominate in the most of observed river branches. The increase of phytophilous species is connected with spreading of macrophytes in last few years. 7.7. Caddisflies and Mayflies (Trichoptera, Ephemeroptera)There are differences in the monitoring methods used by the Slovak and Hungarian Party for mayfly (Ephemeroptera) and caddisfly (Trichoptera) taxocoenoses. On the Slovak side the larvae of Caddisflies and Mayflies living in the water are observed and since 2004 flying around imagines as well. On the Hungarian side the flying imagines of both communities caught in a light trap were observed. Since 2006 observation methods according to the Water Framework Directive were used on the Hungarian side. These are based on observation of communities living at the river bottom and were performed as a part of surface water quality monitoring. The differences between results of the Slovak and Hungarian Parties still persist. The Danube The mayfly and caddis fly communities in the Danube according to the Slovak monitoring results, observed at monitoring sites No. 2600, 2603 and 2608, are very poor. No mayfly larva's or imagos were recorded in the evaluated year. Caddis fly representatives were recorded irregularly at individual samplings and their abundance was very low, but presence of three rheophile Danube species was proved. Extremely low flow rates in autumn enabled the sampling in deeper part of the medial and around the guiding structures. No additional species were found in these deeper parts of the river. Although the Hungarian results are based on one sampling they prove rich in species and abundant mayfly and caddis fly communities in the Danube. The results show a retreat of typical species for the Danube and their replacement by potamophilous and limnophilous species, which occur in the river branch system. The left side river branch system 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 caddis fly communities. The recorded species mainly had irregular occurrence in individual years and at individual samplings. More abundant mayfly communities occur at monitoring area No. 2604 only, where stagnicolous and phytophilous species are permanently present. The caddis fly community are more poor, macrophyte dependent species was found as well. At the other two sampling sites only one semirheophilous caddis fly species and one semirheophilous mayfly species were recorded. The right side river branch system In the evaluated year one sample was taken from the Gázfűi Danube river branch. From among the mayflies community the stagnicolous species Caenis horaria was very abundant, but the semirheophilous species Ephemera vulgata occurred abundantly too (over 1600 individuals). Semirheophilous species were abundant in the rich in species caddis flies community as well. 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 have changed several times. This can decrease the comparability of obtained results. The Slovak side uses an apparatus with 550 W power output, while the Hungarian side since 2004 uses an apparatus with 5000 W power output. The Danube 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 the results of both Parties follows that the ichtyocoenoses in the Danube river is stabilized in last years. Slight decrease in species diversity can be registered, but the results of particular samplings are highly dependent on the actual flow rate in the Danube and other circumstances of sampling. Simultaneously with the dominance of eurytopic species an increase of foreign expansionary rheophilous species of Neogobius family can be registered. However, spreading of foreign species is not intensive and is independent on hydropower structures. The left side river branch system On the monitoring areas No. 2603 and 2604 stable ichtyocoenoses occur. In river branches at monitoring site No. 2603 euryek species are the most abundant. In the evaluated year retreat of the expansive rheophilous species was registered in comparison with the previous year, but the abundances of the species were lower as well. The ichtyocoenoses in the dead river arm at monitoring site No. 2604 is stable, but due its isolation the species diversity and abundance of particular species is lower than at monitoring site No. 2603. In 2006 significant increase in abundance of the expansive species Ameiurus melas, for the first time registered in 2005, was recorded. Ichtyocoenosis at both partial monitoring sites at area No. 2608 consist of fish species having different ecological demands (eurytopic, rheophilous, limnophilous). The fish community below the Foki weir is not so rich in species due to less frequent connection with the Danube (during floods in 2002, 2005 and 2006). In both communities the euryekous species dominate, the abundance of expansive species remains low. The poorest ichtyocoenoses is found in the river branch at monitoring site No. 2612, which dried out in 2004. In 2006 four not oxygen demanding species was recorded. Restoration of the fish community was enabled by flooding of the monitoring area in 2006. The right side river branch system 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. In individual parts of the river arm limnophilous and rheophilous fish species were present. Eurytopic fish species dominate. The species richness of the fish community is significant and stable. In 2006 15 fish species was recorded. The state of ichtyofauna in Csákányi Danube (monitoring site No. 9) since introduction the water supply in 1995 is rather stable. There were 12 fish species recorded in 2006. Along with the dominance of eurytopic species several rheophilous fish species were recorded, proving the connection with the main riverbed. The slight decrease of species diversity in the period 2000-2003, explained with silting of the river bottom, have not been registered in last three years. The species richness of the fish community is significant. After introducing the water supply (in 1995), regeneration of ichtyofauna is observed at monitoring site No. 5 – Lipóti marsh. The species richness of this site is significant and balanced at present. In 2006 13 species were recorded, eurytopic fish species dominated. The hydrological conditions of the Gazfűi Danube (monitoring site No. 12) since introducing the water supply to the flood-protected area are equal to pre-dam conditions. Regarding the whole observation period the ichtyofauna was the most rich in 2005 (16 species). In 2006 11 fish species were registered. Eurytopic fish species remained dominant, with continuous presence of limnophilous and marsh fish species.
|
||||||
