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, are monitored at 31 monitoring sites on the Hungarian side (Fig. 7-1), however the evaluation in the Hungarian National report sometimes present monitoring results from different sites in individual years. There are still differences in some monitoring methods on both sides. Continuous application of European directives will probably support further harmonization in near future. A short description of hydrological and climatic conditions in the year 2005, influencing 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. This region is represented by monitoring areas no. 2604, 2609 and 2612. Slight changes in vegetation on the plot No. 2604 are attributed to changes in the flood regime after diversion of the Danube. Preservation of typical communities upstream and downstream the confluence of the tailrace canal and the Danube old riverbed (plots No. 2609 and 2612) might be endangered in case of long lasting low flow rates due to the riverbed erosion. Unfavourable moisture conditions for the lowland forest occur in the area upstream of the water supply canal in the upper part of the inundation area (plot No. 2600) and in the region of Istragov island (plot. No 2608). Drying up of the area around the monitoring plot No. 2600 have started in 1970-1980; at present this unfavourable tendency slows down and stabilizing. The vegetation is in fact dependent on precipitation. Higher amount of precipitation in 2005 postponed the defoliation and no mosaic loosening of coverage in the herb layer occurred. However, few dry trees appear every year, the plant layer is atypically rich and two invasive species spread intensively. Signs of disturbance in the herb layer can be seen after the extremely dry summer in 2003. Willows dried out, neophytes and ruderal species spread. Water supply is required in this region. Since observations on the monitoring plot No. 2603 are performed in a young poplar stand, closing of treetops determines the development of vegetation. This impact on the shrub layer is not so remarkable, but in the plant layer decrease of atypically high species number and number of invasive species is evident. The right side river branch system The vegetation period 2005 was richer in precipitation in comparison to the previous year. This was reflected in increase of biomass of the plant layer at the monitoring areas. Simultaneously several of the meadow plants were higher than ever before in the whole monitoring period. The species number was slightly lower in the evaluated year, but the decrease is not significant. The average leaf area values were higher on willow along the Danube and on oak stands in comparison to the previous year. The leaf area on willows and alder stands in the upper part of the Szigetköz region remained unchanged. Since introducing the water supply in 1995 the water level in the Mosoni Danube became stable. No impact on vegetation along the Mosoni Danube, which could be assigned to the diversion of the Danube, was registered. 7.2. Terrestrial molluscsThe left side river branch system The terrestrial mollusc’s community of large part of inundation area are stabilized. In the most moisturized regions (represented by areas No. 2604 and 2609) typical marshy wetland forest communities occur. These communities might be secondarily influenced by silviculture. At monitoring areas No. 2600 and 2612 typical communities of drier lowland forest occur. The community on the area No. 2600 has stabilised in last years. Its development reflected the continuous ground water level decrease in several decades. The gradually increasing treetop closure in the young poplar stand on monitoring area No. 2603 allowed the creation of mezohygrophilous mollusc’s community. Insignificant occurrence of polyhygrophilous species results from rare occurrence of floods and low ground water level. Worsening of the hydrological regime in the region of Istragov island (plot No. 2608) invoked a medium degradation of the malakocoenose. In the mollusc’s community euryek species are present. The right side river branch system Monitoring of the terrestrial molluscs community in 2005 have been again carried out by random sifting method in 15 minutes time (years 2004 and 2005). The decreasing tendency in species number recorded in the previous year was proved in 2005 again. This fact reflects the shortcomings of the random sifting method, which detects rare species with significantly less probability. On the other side, the decrease involves bigger species with longer life cycle, mainly in the central parts of drier areas. This could reflect the absence of regular natural flooding, however the inundation area was artificially flooded in last two years. 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. The monitoring area No. 2 is situated in the main riverbed downstream of the bottom weir, where the flow rate prevents developing of macrophyte communities. The monitoring site No. 7 is separated from the Danube old riverbed by shoreline vegetation of Salicetum triandrae and Scirpo-Phragmitetum. Due to its intensive spreading a part of water area was isolated and it had a macrophyte community rich in species in last years. The left side river branch system The most stabile macrophyte community is found in the marshy lake at plot No. 2604. The monitoring results are comparable with findings before damming the Danube. Deep arms with flowing water on the monitoring area No. 2603 are settled by macrophytes mainly along the line structures. In last few years they were washed out by floods and regenerated repeatedly. On monitoring plots No. 2608 and 2612 the macrophyte communities are conditioned by water level in river branches and alternation of ecophasis. On both monitoring areas species of wet and marshy biotopes could be found. Where hydroecophase permanently occurred rare and endangered species were present. An unfavourable fact was the presence of invasive species on the monitoring plot No. 2608 in last few years. 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, which corresponds to stabilized species composition of aquatic plant communities on both monitored area (plots No. 4 and 9). 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. However, spreading of Elodea canadensis, an invasive species is observed in the whole Szigetköz region. 7.4. Aquatic molluscsMonitoring of aquatic molluscs on the Hungarian side in 2005 was carried out according to changed methodology – the presence and the abundance of aquatic species was examined in a sample of riverbed sediments (app. 3 litres), which was introduced in the previous year. The 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, from among Hungarian observation sites only the observation site at Kisbodak, rkm 1831 is mentioned since 2004). These observations show significant decrease in species number as well as in number of individuals in 2005. Occurrence of several species became sporadic, the mass occurrence of other species have been reduced to several individuals. The Slovak Party supposes that the reason of this fact is a thick layer of mud on the shoreline rocks, which eliminated the development of algae and decreased the food offer. 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 malakocoenose of the 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 stabile mollusc’s community occurs, rich in species, which consist mainly of stagnicolous and indifferent species. The malakocoenose at site No. 2604 regarding the wide food offer is not adequate. It became poor due to the long-term isolation. At present expansion of one widely spread species is registered. The right side river branch system Based on the results in 2005 the occurrence of a stabile mollusc’s community in the right side river arm system, observed in last years, was disturbed. Most of the previously observed species were not recorded. Even the species proving the presence of suitable living conditions in river branches (Paladilhia oshanovae, Unio crassus) were missing. On the other side, it has to be taken into account, that the methodology introduced last year is less suitable for observation of species spectrum. Rare and randomly occurring species are hardly observable by this method. 7.5. Dragonflies (Odonata)The left side river branch system According to the monitoring results the dragonflies community is rather poor in the whole left side inundation area, the observed river branches became unsuitable for dragonfly occurrence, mainly due to missing macrophytes. This problem is most noticeable on monitoring site No. 2608, where the Odonata community is observed in the Danube since 2005. However, the community in the Danube is poor as well. In the area at site No. 2612 the dragonflies settled the depressions only, which were flooded at higher water levels. Species tolerant to water shortage were registered. As a consequence of the development in previous years the dragonflies community at monitoring site No. 2604 was rich in species and the number of individuals was high in the spring 2005. Decrease in species number and number of individuals was registered in autumn due to low water level and related low content of oxygen in the water. In the river branch at monitoring site No. 2603 a stable odonatocoenose, living in moderately flowing lowland water, is registered. In last years spreading of rheophilous species was detected, however in 2005 the number of rheophilous species decreased. The present species composition is more similar to the dragonfly species composition recorded before damming the Danube. The gravel pit observed on the monitoring area No. 2600 was abundantly overgrown by macrophytes in 2005. Corresponding to this favourable conditions several pioneer species of dragonfly community were present. The number of present dragonflies’ larvae as well as imagines continuously increases. The species composition was mainly composed by stagnicolous species and species tolerant to drying up, but semi rheophilous dragonfly species were registered as well. The right side river branch system The most significant change in the in the inundation area is the continuous water supply into the river branch system. The fauna of the previously slowly flowing side arms, which were overgrown by macrophytes, was replaced by species typical for flowing water (rheophilous) or eurytopic species. The species composition of odonatocoenoses of regularly monitored sites has stabilised during last years. The species composition of the Mosoni Danube river branch had not passed this kind of transformation. 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, where decrease of abundance and species number in both communities continued. The same tendency was registered in previous year. The decrease at monitoring site No. 2600 in the actual year was caused by flushing out the individuals of both communities. At the monitoring site No. 2608 more intensive decrease was registered at euplanktonic species of Cladocera, which dominated before diversion of the Danube. In general, the Copepods community show smaller fluctuations in the whole monitoring period. 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. Euplanktonic species dominated here before damming the Danube and before the water supply. Nowadays at several monitoring sites tychoplanktonic species dominate; this change is most significant in the Cladoceras community. Copepods have lower ecological demands, especially regarding the water oxygen content and pH value. At individual monitoring sites it is possible to identify the reasons of these changes. At the monitoring site No. 2603, along with the regulated hydrologic regime, the spreading of macrophytes, evoked by better light conditions after clearing the neighbouring forest, influences the present communities. On monitoring sites No. 2604 and 2612 natural fulfilling of dead river arms going on. Continuous isolation of the river branch at monitoring site No. 2608 and rare connection with the main riverbed led to an increase of euplanktonic species in the Cladocera community, which is rich in species. The right side river branch system High water levels have slowed down the spreading of macrophytes and related spreading of phytophilous Cladoceras and Copepods in 2005. Moreover increase in fish population was observed as well, which resulted in decrease of phytoplankton biomass. Under these circumstances decrease in crustaceans species diversity have been detected in comparison to the previous years. The number of individuals was low as well; the highest abundance was again recorded in the Schisler dead arm in autumn. 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 are observed. This can be one of the reasons that the monitoring results of both sides differ. In 2005 no data for caddis flies community from the Hungarian side were presented in the Joint monitoring. 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. Representatives of both communities are recorded irregularly at individual samplings. Gaining of additional data from deeper parts of the river, planned in 2005, was not carried out due to inadequate technical equipment. The mayflies and caddis flies species present in 2005 indicate mainly conditions typical for slowly flowing river branches. Similar statement follows from the Hungarian monitoring results as well. The results show a gradual nearing of the mayflies’ community composition in the Danube and in the river branch system, which are created with potamophilous and limnophilous species. Contrary to the Slovak results the Hungarian monitoring results repeatedly prove the presence of rich mayflies’ community in the Danube. 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. Their presence at monitoring site No. 2608 was not proved since 2002. The recorded species mainly had irregular occurrence in individual years and at individual samplings. The river branch on monitoring area No. 2603 in settled by semirheophilous species, in the dead arm at monitoring site No. 2604 stagnicolous and phytophilous species occurred. Weak communities in the river branch at monitoring site No. 2612 consisted of stagnicolous species mainly, while one mayfly species was always present, caddisflies were recorded sporadically. The right side river branch system Mayflies were represented by community living in the river arm at Lipót. This community consisted of four species, living mainly in stagnant and eutrophic water bodies. The species Caenis horaria was very abundant and presence Caenis lactea became stable. No caddis flies observation and evaluation was carried out in 2005 on the Hungarian side. 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 4500 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. In general, the fish community in the Danube old riverbed is stable under changed condition caused by the river diversion. Spreading of foreign expansionary species (Neogobius kessleri and Neogobius melanostomus) can be considered for a most significant change. Together with them several eurytopic species occurs. However, spreading of foreign species is independent on hydropower structures, they are abundant on the whole Slovak-Hungarian stretch of the Danube. The left side river branch system Under conditions stabilised by water supply, stable fish population occurs in the river branches at monitoring area No. 2603. The ichtyocoenose is rich in species and is created mainly by eurytopic species, with very high abundance in 2005. The ichtyocoenose in the dead river arm at monitoring site No. 2604 is stable as well. However due to long-term isolation is rather poor in species and abundance as well. No overheating of the water occurred in summer 2005, so higher abundance of one limnophilous and one expansive species was recorded. The ichtyofauna at monitoring area No. 2608 is observed at two partial monitoring sites in the river branch system – upwards and downwards from the Foki weir. The river branch upwards from Foki weir is during higher discharges connected with the Danube, so the ichtyofauna is rather rich. Although all of ecological fish groups are present to some extent (rheophilous, limnophilous), in last years eurytopic species dominate. The river branch under the Foki weir is isolated in long-term, and the fish population became poor gradually. Several fish species were registered, with dominance of one eurytopic species. The worst situation was found at monitoring area No. 2612. In small dead arm no fish population was detected in 2005, probably due to drying out of the river branch at the end of previous year. The monitoring area lies under the confluence of the tailrace canal and the Danube old riverbed, so it has a natural hydrologic regime. 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 after its artificial reconnection with Csákányi Danube in 1997. In individual parts of the river arm limnophilous and rheophilous fish species were present. The species richness of the fish community is significant and stable, eurytopic fish species dominate in last years. The state of ichtyofauna in Csákányi Danube (monitoring site No. 9) since introduction the water supply in 1995 is rather stable. Along with high abundance of eurytopic species, an expansive rheophilous fish species was recorded. The slight decrease of species diversity, explained with silting of the river bottom at the sampling site, was interrupted in the evaluated year. After introducing the water supply (in 1995), regeneration of ichtyofauna is observed at monitoring site No. 5 – Lipóti marsh. Eurytopic species are dominant. The species richness of this site is significant and balanced at present. 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. Eurytopic fish species remained dominant, with continuous presence of phytophilous species. Presence of invasive rheophilous species Neogobius kessleri was recorded again, but its abundance remains low.
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