PART 7Biological MonitoringThe biological monitoring of agreed groups of aquatic or terrestrial fauna on the Slovak side was performed on six complex monitoring areas. On these are phytocoenological observations were realised as well. Moreover in 1999 the aquatic macrophyton observation was started again. The same groups of fauna and flora, agreed in the frame of the joint monitoring, are monitored at 31 monitoring sites on the Hungarian side (Fig. 7-1). There are differences in some monitoring methods (observation of Trichoptera and Ephemeroptera groups, evaluation of aquatic macrophytes). 7.1. PhytocoenologySignificant signs of drying out on the monitoring area No. 2600, which were already present before damming the Danube, became more intensive after the damming due to the significant decrease of ground water level. Under the gradual rearrangement of phytocoenoses hygrophilous species are replaced by mezohygrophilous ones. In 1999 signs of drying out were not observed in every layer of phytocoenoses (as in 1998). But thinning of crowns, dry branches and decrease of leaf area of the Populus alba was observed. The monitoring area No. 2603 is situated downstream of the intake structure and the moisture conditions remained unchanged. Plant communities are stabilised, the herb layer is dense and vital, coverage of the shrub layer was similar to the previous years. The cutting off the neighbouring forest stand influenced the tree layer in 1999. Mechanical damage was also observed. The monitoring area No. 2604 from the biological point of view can be characterised as area with very weak signs of damage. In the tree and shrub layers there were not observed any changes. However the soil layer is fully saturated by water there were changes in the species composition of the herb layer observed due to the not realised artificial floods. The vegetation of monitoring areas No. 2608, 2609 and 2612 is stabilised. Natural floods flooded the areas in the spring 1999 and herb layer coverage was very low. The shrub and tree layers did not show any significant changes. The Hungarian Party in the frame of the monitoring of Gabčíkovo project impacts performs the monitoring of plant communities and reeds in summer period. The vegetation period in 1999 was rich in precipitation and the high discharges on the Danube caused flooding of inundation area in the lower Szigetköz. Composition of dominant species on the respective monitoring sites is relatively stabile, but on some of them higher occurrence of species belonging to drier biotopes were observed in the last years. The coverage of the herb layer on every monitoring site was higher in comparison to the previous year and some of hygrophilous species, which was not observed in the previous year, occurred again. The results of the leaf area measurement show that on monitoring areas with low ground level the leaf area is smaller. But due to the favourable climatic conditions in 1999 this adaptation of trees was not so significant. Regarding the reed stands at the oxbow lake at Lipót, Kisbajcs and Malomszer can be stated that the homogenous character of the reed stands and low number of species remained preserved. The occurrence of the terrestrial species is low too due to high water level often covering the depressions. The reed stand at Dunakiliti show mixed character and reeds in a shallow lake at Cvek near Cikolasziget dried up. In the species composition terrestrial species were dominant. 7.2. Terrestrial molluscs (Terrestrial mollusca)The most significant changes in the terrestrial molluscs community were observed on the monitoring area No. 2600, which is not supplied by the water from the water supply system. This area was not flooded from 1991 and is situated in the region under strong drainage effect of the Danube. From 1996 stabilisation of the molluscs community is observed corresponding to mezohygrophilous community characteristic for the transient wetland. Cutting off the neighbouring forests stand influenced the mollusc’s community on area No. 2603 in 1999. The eurytopic species dominate. On the area No. 2604 due to improving of the hydrological conditions the hygrophilous species dominate. The mollusc’s community has stabilised. The species composition of mollusc’s communities on monitoring areas No. 2608, 2609 and 2612 confirm the typical communities for wetland. However, on the monitoring area No. 2608 there is a high number of eurytopic species. The terrestrial molluscs fauna on these areas have not changed since damming the Danube. Floods during high discharges on the Danube influence these monitoring sites. The Hungarian Party in the frame of joint monitoring provided data only from one monitoring site. The species composition along the Mosoni Danube remained unchanged. Based on data from one monitoring site it is not possible to evaluate regional changes. 7.3. MacrophytesSimilarly to the previous years the growth rate, the composition and the amount of macrophytes were determined by the site-specific hydrological conditions, water supply, temperature and light conditions. Evaluation of macrophytes monitoring in 1999 is based on observations on both Slovak and Hungarian side. On the monitoring area No. 2603 there were no macrophytes observed in the Danube main riverbed. Their occurrence was confirmed in depressions in the former river bed only. Comparing to the years 1990-1991 the amount of macrophytes in the river branches were reduced due to the continuous water supply. Their occurrence is limited only along the structures and banks. The macrophyte communities in the dead arm on the monitoring area No. 2604 are similar to that in 1990-1991. Borders of the dead arm are covered by stand belonging to the association Phragmitetum communis, the open water area is almost fully covered by Ceratophyllum demersum, including some rare species. On the monitoring area No. 2608 the macrophyte observation was performed in the shallow parts of the river arms, which were covered by water in 1990-1991. In 1999 they were without water and the development of the vegetation is typical for dry arm bed occasionally flooded by water. The marshy parts of the monitoring area are still covered by the association Phragmitetum communis. Very rich macrophyte communities were observed on the monitoring area No. 2612 where a very large scale of different conditions in the river arms exists. Comparing to the years 1990-1991 the macrophyte communities remained unchanged. Conditions created by high discharges during the vegetation period on the monitoring site No. 2 in Danube river bed on the Hungarian side – higher depth, higher flow velocity – were not favour to the macrophyte development in 1999. On the monitoring site No. 7, separated from the main river bed, the aquatic macrophyte stands were more abundant, rich in species and with high number of individuals. The living conditions in the inundation area were determined by the ongoing water supply. The amount of water, discharges and the flow velocity were similar to the previous year, but due to the high discharges in the Danube the suspended solids content was higher, which negatively influenced the development of macrophytes on the monitoring site No. 9. The extension and the amount of macrophytes on the monitoring site No. 4, similarly to the results from 1998, were reduced (permanent connection was created between the Schissler arm and the Csákányi Danube in 1997). Although the vegetation cycle on the flood protected monitoring site started later, due to the climatic conditions, the species diversity and the number of individuals in July and August were similar to the previous year. The original species with flowing leaves dominated (Nymphaea alba at site No. 4, on the Zátonyi Danube, Nuphar lutea at site No. 6 at Lipót). On the monitoring site on Zátonyi Danube widely spread rare Hydrocharis morsus-ranae was observed again. 7.4. Aquatic molluscs (Aquatic mollusca)The Danube The evaluation of the aquatic molluscs community in the Danube is based on the data provided by the Slovak Party (monitoring areas No. 2600, 2608 and 2612). The taxocoenoses of aquatic molluscs in the Danube are from the point of view of species composition relatively stabile The species Ancylus fluviatilis, Lymnaea ovata and Bithynia tentaculata remain dominant. In the last years increase of their abundance can be observed (especially on the monitoring area No. 2612). The left side river arm system The aquatic molluscs community in the Slovak river arm system is monitored on sites No. 2603 and 2604. The parapotamal of monitoring site No. 2603 has heterogeneous character and is characteristic by high biodiversity of the aquatic molluscs community. The plesiopotamal of the monitoring area No. 2604 is isolated from the other part of the inundation area and the area is characterised by low species richness. The right side river arm system According to the monitoring results on selected monitoring areas it can be stated that there were 24 different species detected. 7.5. Dragonflies (Odonata)The Odonata communities on the Slovak side are rather poor in species composition on every monitoring area during the whole observed period ( 1992-1999). The rheophile and semirheophile Odonata species confirms the through flowing character of the parapotamal at monitoring site No. 2603. In the plesiopotamal of the area No. 2604 mainly stagnicolous species were observed, which can indicate the change from plesiopotamal to paleopotamal. The other monitoring areas were very poor concerning the diversity and abundance of the dragonflies. There were no significant changes observed in dragonflies’ species composition on the Hungarian monitoring sites. The species diversity in 1999 remained poor and fluctuated between 3 and 6. 7.6. Crustaceans (Cladocera, Copepoda)The Danube According to the long term observation of the Cladocera community It can be stated that littoral and benthic species gradually increased. The ratio between the pelagic and tychoplanctonic species is comparable to the ratio before damming the Danube. In the Copepoda community no significant changes were observed in 1999. In general the euplanktonic species prevailed slightly (locality No. 2608). According to the Hungarian results the species composition and the number of individuals differed on different monitoring sites in the Danube. The left side river arm system In general, the water supply introduced in 1993 caused decrease of pelagic and increases of tychoplanctonic species of Cladocera. On monitoring site No. 2603 the increase of species diversity continued in 1999. The Copepoda species composition in comparison to the previous years remained unchanged, but differs a lot from the species composition before introducing the water supply in 1993, when consisted of euplanktonic species only. On the monitoring site No. 2604 (plesiopotamal) the increase of tychoplanctonic species of Cladocera continued in 1999. During the observation period only changes in species dominance occurs in very rich in species and abundant taxocoenose of Copepoda. On the monitoring site No. 2608, not influenced by the water supply, the euplanktonic species prevail, and no significant changes were recorded. The monitoring site No. 2612 (plesiopotamal), situated downstream of the influenced river stretch, is continuously overgrown by macrophytes. This is reflected in the Cladocera and Copepoda communities where number of tychoplanctonic phytophile species increases. The right side river arm system and the flood protected area in the Szigetköz In 1999 low number of species and individuals in crustaceans communities were recorded. Similar results were obtained in the period 1995-1997 after introducing the water supply from the Danube, when the macro vegetation due to raised water level and higher flow velocities diminished. In the Schissler dead arm, monitoring site No. 4, after the interconnection with the supplied river branch system, the amount of macrophytes decreased, which leaded to decrease of phytophile crustaceans communities too. They were replaced by euplanctonic species, among which the Bosmina longirostris and Eucyclops serrulatus dominate. The increase of species number and individuals detected in 1998 on the monitoring site No. 5 (Zátonyi Danube) in the flood protected area was not confirmed in 1999. The low number of species diversity and number of individuals can be explained by different sampling method used in 1999. The most rich species diversity and abundance was observed on the monitoring site No. 6 (Lipót marsh), which is overgrown by very diverse macrophyte communities. 7.7. Caddisflies and Mayflies (Trichoptera, Ephemeroptera)There are differences in the monitoring methods of caddisflies (Trichoptera) and mayflies (Ephemeroptera) taxocoenoses used by the Slovak and Hungarian Parties. On the Slovak side the larvae of caddisflies and mayflies living in the water are observed, while on the Hungarian side the imagines are monitored. The Danube There were gradual changes observed in the caddisflies and mayflies communities. The changed living conditions after damming the Danube - decreased water depth and increased transparency of water - caused that scrapers are replacing filtrators. The results in 1998 indicated that this process has stopped, but results in 1999 it did not confirm. In general the caddisflies and mayflies communities are poor in species and number of individuals too, similarly to the period before damming the Danube. The left side river arm system The increase of number of rheophile and semirheophile species in mayflies and caddisflies communities, detected after introducing the water supply on the monitoring sites where increase of flow velocity occurred on the Slovak side (e.g. No. 2603), was confirmed also in 1999. The species composition of caddisflies and mayflies on the monitoring area No. 2604 confirm the ongoing continuous change of plesiopotamal to paleopotamal. The caddisflies (Trichoptera) and mayflies (Ephemeroptera) communities on the monitoring site not influenced by damming the Danube or by the water supply (e.g. No. 2612) remain relatively poor. The right side river arm system According to the results of the Hungarian side the mayflies’ community of the Mosoni Danube is relatively rich and in the period 1996-1999 remained unchanged. The caddisflies taxocoenose in the right side river arm system, comparing to the species composition observed on the Slovak side, is rich in species. This is probably caused by the differences in the monitoring methods. The structure of the caddisflies community is changing after introducing the water supply. Similarly to the results in 1998 increase of species diversity and number of individuals was also detected in 1999. 7.8. Fish (Osteichtyes)The monitoring method, the random point abundance sampling using electrofishing, used by both Slovak and Hungarian Parties, allows sampling to the depth of 1.5 m. This means that this monitoring method in deep water bodies (depth over 1.5 m) allows only the observation of littoral and water surface fish species. The fish species living at the bottom and in deeper pelagial cannot be sampled correctly by this method. This is the main reason why the monitored ichtyofauna is relatively poor in species according to the monitoring results, both before and after damming the Danube. The Danube Based on the observation on the monitoring areas No. 2600 and 2608 on the Slovak side and monitoring sites No. 10 and 11 on the Hungarian side the fish community in the Danube main river bed seems to be stabile. In 1999 all of the fish species detected in previous years were observed and the rheophile and eurytopic species dominate. In the period 1994-1999 25 species were detected on the monitoring site No. 10 (rkm 1833). On the monitoring site No. 11 there were 21 species detected in the period 1997-1999. The left side river arm system The ichtyofauna of the monitoring area No. 2603 is stabile. The negative tendency after damming the Danube were reverted after introducing the artificial floods in 1995. In the fish taxocoenoses on the monitoring site No. 2603 the limnophile and eurytopic species (Perca fluviatilis, Esox lucius) dominate. The part of the monitoring site No. 2608, upwards from the Foki weir, which is connected to the main riverbed, is characteristic by frequent occurrence of rheophile species. Due to the connection with the main river bed the species diversity remained high. However, dominant are the eurytopic fish species, like downwards from the Foki weir. Low number of species and low number of individuals are characteristic for the monitoring area No. 2604 (plesiopotamal). Stabilisation of the fish community typical for the stagnant water going on at this monitoring site. The species composition is characteristic for the ichtyofauna of dead arms. The water regime on the monitoring site No. 2612 is not influenced by the operation of the hydropower station and the ichtyocoenoses consist of limnophile and eurytopic species. The right side river arm system A dynamic regulation of the water supply and restoration of connection of river arms with the Danube main riverbed was enabled after putting the submerged weir into operation. The two openings in riverbank enable the fish to migrate between the river branch system and the river. On the monitoring site No. 9 – Csákányi Danube 12 fish species were detected in 1999 and after introducing the water supply in 1995 rheophile fish species occur in the river branch again. Species present in the river branch system before the water supply or even before the damming remained present also in the recent species composition. In 1999 14 fish species were detected in the Schissler arm – monitoring site No. 4. The number of species increased significantly after reconnection with the Csákányi Danube. In the river branches with stagnant water limnophile fish species were abundant. The monitoring sites in the flood protected area are situated at Gázfűi Danube and Lipót marsh. In 1999 11 fish species were detected at monitoring site No. 12 -Gázfűi Danube, where the species Rutilus rutilus was dominant. Very abundant were the species Carassius carassius and Tinca tinca characteristic for stagnant water bodies. On the monitoring site No. 5 at Lipót some of rheophile species were detected in 1998. Two new species were detected in 1999 (Misgurnus fossilis and Silurus glanis) and none of the rheophile fish species occurred.
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