PART 7
Biological MonitoringThe biological monitoring of agreed groups of aquatic and terrestrial fauna is carried out on six complex monitoring areas on the Slovak side. On these areas the phytocoenological observations were realised as well, which record the spring and the summer aspect of plant communities. Moreover in 1999 the aquatic macrophytes observation was restarted again. 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). There are differences in some monitoring methods on both sides (e.g. similarity index of plant communities is not evaluated on the Hungarian side; evaluation of ecological analysis of terrestrial plant communities and the evaluation method of aquatic macrophytes differs on both sides; reed communities on the Slovak side are not observed as detail as on the Hungarian side; the monitoring of Ephemeroptera, Trichoptera and Odonata on the Slovak side is based on aquatic larvae observation, while on the Hungarian side it reside in observation of imagines). 7.1. PhytocoenologyThe left side river branch system The changes of the biota on the monitoring area No. 2600 are caused by gradual long-term drying up of the locality, which was already observed since seventies of the twentieth century. The moisture conditions of the locality were relatively favourable in the year 2002 due to two strong floods in the inundation area. This was slightly presented in development of individual layers of plant communities. Though the community show stabilization signs in the last years, in the summer period of the year 2002 higher coverage values of all three layers were recorded – there was no premature defoliation in the tree layer recorded, not even mosaic loosening of coverage in the herb layer. However, the development of eco-index for moisture in comparison with the previous year shows further slight decrease, what indicate continuous retreat of species with higher demand on water. Monitoring areas No. 2603 and 2604 are situated downstream of the intake structure to left side river branch system, thanks to what the moisture conditions have not changed significantly after damming the Danube and high water level can be kept in the river branches too. Some change was recorded in the flood regime of the region and in case of the monitoring area No. 2603 attention should be aimed also to changes caused by the drainage effect of the Danube. Phytocoenological monitoring on the monitoring area No. 2603 (TMP 9A) was restarted in the five-year-old cultivated poplar stand after interruption in the period 1998-2001 due to cut out. The coverage values of the tree and shrub layers of young stand were still relatively low. Comparing to the results of the original stand till 1997 the highest changes were recorded in the species diversity of the herb layer. Its value was three-times higher due to the spreading of weeds, synantrophic, heliophilous and invasive species into the not well-developed stand. In the following years, after development of the stand and successive decrease of above mentioned tychocenous species, return of the community to the state before damming can be expected. In the composition and the coverage of the tree and shrub layer of the monitoring area No. 2604 no significant changes were recorded. Continuous presence of original plant communities in 2002 was proved by high value of Jaccard’s similarity index of the spring relevé of the herb layer (2001/2002) too. The strong natural flood in August, which is an important factor of the softwood development point of view, influenced the results of the summer relevé. Monitoring areas No. 2608 and 2609 are situated in a region where the backwater effect upstream the confluence of the tailrace canal and the Danube old riverbed eliminates the impact of Gabčíkovo waterworks. Although the situation in the lower of Istragov island (area No. 2609) is stable, the solution of the water regime should not be underestimated. The moisture regime of the area No. 2608 was very favourable in the year 2002. The development of the tree and shrub layer was similar to the previous years. Some changes were observed in development of the herb layer in the spring only, since the spring flood slowed it down. Decreasing tendency of species number of wet and very wet biotopes on monitoring area No. 2608 is warning. Further changes in eco-indexes for light, temperature and soil nitrogen (probably not directly connected with the operation of Gabčíkovo hydropower station) recorded during previous years were no noticed in 2002. On the monitoring area No. 2609 preserved willow stand is present, typical for softwoods. Due to favourable moisture regime changes of the phytocoenoses are not expected. The reference monitoring area No. 2612 is situated downstream the confluence of the tailrace canal and the Danube old riverbed, where the direct impact of the Gabčíkovo waterworks is insignificant. In spite of the presence of stable poplar stand, the similarity value of the stand in summer relevé (2001/2002) was reduced. The decrease of the value can be explained by realisation of selected cutting out of small trees and shrubs and by impact of the strong flood in August as well. The right side river branch system The Hungarian Party performs the monitoring of plant communities and reeds in the summer period only. The phytocoenological survey in 2002 was realised before the strong flood in August, therefore impacts of the two strong floods were not expressed in the relevé of this year. The medium and long-term impacts of floods will be noticed in following years. The results of phytocoenological survey were similar to the results of previous year. On the areas with the strongest decrease of ground water level (along the Danube old riverbed) increase of xerophylous plants was confirmed in the meadow communities. Plants of the herb layer in the forest communities of these localities were lower and their coverage was smaller too. On the flooded sampling sites in the active floodplain large quantity of floating material was left over, causing plant-less patches in some places. The reed stands (Kisbajcs – Szavai canal, Lipót – marsh lake, Arak - Malomszer) in the flood-protected area with good water supply are continuously stable. They differ significantly from the reed stands in the upper part of the Szigetköz region, which are becoming drier, thinner and weedier. Only the reed stand at the Cvek shallow near Cikolasziget (in flood-protected area) is observed since 2001. The monitoring site in the inundation area near Dunakiliti – Száraz erdő was tilled and destroyed. Drying up of reed stands occur in this area, the terrestrial plants became dominant. 7.2. Terrestrial molluscsThe left side river branch system The process of drying out in the area of monitoring site No. 2600, which was recorded in previous decades, speeded up after diverting the Danube. The terrestrial mollusc’s community had stabilized at medium degradation level of the original community of dryer softwoods type. Absence of polyhygrophilous species, decrease of hygrophilous and typical forest species continued in 2002 as well, eurytopic and mesohygrophilous species were dominant. In the year 2002 the monitoring of terrestrial malakocoenose in the original monitoring site “9A” of the monitoring area No. 2603 was restarted. The community in the young poplar stand of the monitoring area “9A” was very similar to malakocoenose of neighbouring willow stand “9B” in the last year, however other species were dominant. Comparison of the results before damming the Danube proves continuous presence of favourable biotope conditions for development of floodplain forest. At present the mollusc’s community consists of mesohygrophilous and mesophilous forest species with significant presence of polyhygrophilous species. Thanks to regulated water regime (realization of artificial floods) permanent presence of natural wetland community of terrestrial molluscs can be observed on the monitoring site No. 2604. Polyhygrophilous and indicative species remain dominant in the year 2002 as well. In spite of regular flooding of the monitoring site No. 2608, strong decrease of polyhygrophilous species and increase of species diversity, untypical for the floodplain forests, probably reflects the impacts of the changed flood regime. The changes of water regime in the area of monitoring site No. 2609 after diverting the Danube are minimal thanks to the backwater effect. Also in the year 2002 the species diversity of malakocoenose was naturally low and similar to previous years. The community continuously consists of almost polyhygrophilous species only. The hydrological regime of the area downstream the confluence of the Danube old riverbed and the tailrace canal was not changed. The area is regularly flooded and the present populations of malakocoenoses represent wide surroundings of the monitoring site No. 2612. The long list of recorded species consists of species with various ecological demands. The right side river branch system The terrestrial molluscs community in the inundation area as well in the flood-protected area is intact. According to the registered data there were no significant changes in the mollusc fauna, neither in the Danube and Danube branches, nor in the Mosoni Danube and gallery forest on the flood-protected side. Fresh shells of Paladolhia oshanovae can be found on the Danube bank, which refer to the steady occurrence of this species living under the ground. 7.3. Aquatic macrophytesThe growth rate, the composition and the amount of the macrophytes were determined by the site-specific hydrological conditions, regulated water supply as well as by the temperature and light conditions. Two strong floods were important factor in the year 2002. Monitoring of macrophytes is carried out on both Slovak and Hungarian side. The evaluation of recorded species on the Slovak side is done by the Braun-Blanquet method, while on the Hungarian side the Kohler index is used. Starting from the year 2003 the Slovak side will use the Kohler index too in order to get comparable results. The 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 in the main riverbed where the flow rate prevents creating of macrophyte communities. Due to the two strong floods in 2002 the Danube bank line was modified. There was recorded the spreading of littoral willow stands of shrub habitus and Phalaroides arundinacea community only. 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 the part of water area was isolated and it had a macrophyte community rich in species in the year 2002. The left side river branch system The state of macrophyte community on the monitoring area No. 2603 in the period after damming the Danube is stable, however comparing to the state before damming it is different. The species diversity and abundance decreased due to the deep and flowing water after introducing the water supply into the river branch system. Macrophytes mainly occur along the line structures and at the places protected before the strong flow. Mass spread of invasive neophyte Elodea nuttalii was characteristic for the whole monitored area in the year 2002. The results of macrophyte monitoring in the dead arm of monitoring area No. 2604, since restarting the macrophyte monitoring (1999-2002), are comparable with findings before damming the Danube. The communities’ development is directly influenced by hydroecophase development in the vegetation period and the year 2002 was very favourable from this point of view. The marshy lake is bordered by a reed stand of the association Phragmitetum communis, the open water area is almost fully covered by Ceratophyllum demersum, in the littoral endangered aquatic and marshy species occur. The development of macrophyte communities in numerous depressions and arms in the monitoring area No. 2608 depend on ecophases’ development in the actual year. The limose ecophase (when the ground water level directly influencing the root system of plants only) was present only in the northern part of the arm in the year 2002; comparing to the previous year the community species diversity was higher (except the autumn relevé, when the species were washing out by strong flood in August). Colonies of the Carex family was recorded in some places of the arm. Variable type of arms in the area of monitoring site no. 2612 are settled by wide scale of macrophyte communities. The water level in the year 2002 was relatively high and the presence of permanent hydroecophase was frequent too. The macrophyte communities of open water areas and littoral marshy biotopes were similar to communities of previous years with the permanent frequent presence of invasive neophyte Elodea nuttalii. The right side river branch system The discharges supplied into the active floodplain were similar to discharges in previous years, except the flood waves in March and August. After creation of permanent connection between the Schissler river arm (monitoring area No. 4) and the Csákányi Danube (in the year 1997) the water depth increased and a slight water flow formed in the river arm. In the river arm algae growth occurred and rhizophytic macrophyte species were present in small groups in the year 2002. The impact of the flood wave in August was minimal in this river arm. Strong washing out was recorded in the Csákányi Danube river arm – monitoring area No. 9. The community in July mainly consisted of rhizophytic species, similarly to previous years, which were creating larger groups on open water. Due to permanent water supply the hydrological conditions of the flood-protected area remained unchanged in 2002 again. Dredging of the riverbed influenced the macrophyte development on canal-like part of the monitoring area No. 6 – marsh lake Lipót. The macrophyte community of this monitoring site in 2002 consisted of rhizophytic species besides floating leaves species and pleustophytic species. The rhizophytic species spread mainly on the western part of the river arm, where process of muddying was recorded. The growing conditions on the monitoring area of Zátonyi Danube (site No. 8) were significantly influenced by the flood in August. The macrophytes were washed out from deeper parts of the river arm. In July relevé the species Nymphaea alba dominate in open water and the species Ceratophyllum demersum in submerged layer. The spreading of some thermophilous species decreased due to absence of extreme air temperatures. 7.4. Aquatic molluscsThe Danube The evaluation of the aquatic molluscs’ community in the Danube in 2002 is based on the data provided by both the Slovak and Hungarian Party (Slovak observation sites are situated at rkm 1841, 1817 and 1804, Hungarian observation sites are situated at rkm 1831 and 1824). Based on observations it can be stated that the molluscs’ community in the Danube is stable, a slight increase of abundance of species indifferent to the flow velocity was observed. The left side river branch system The aquatic molluscs’ community in the river branch system on the Slovak side is monitored on areas No. 2603 and 2604. Because of connection of the river branch at monitoring site No. 2603 with the neighbouring river arms and the Danube, high species diversity of community can be continuously observed. The aquatic malakocoenose consisted of stagnicolous and indifferent species for the whole year. Influence of the flood in August was minimal. In spite of wide food-offer of abundant macrophyte community the isolated aquatic molluscs’ community of the dead river arm on monitoring area No. 2604 was very low species richness and abundance during the last years (including 2002). Thanks to the temporary connection with neighbouring river branch system during the strong flood in August 2002 increase of species diversity can be expected in the following years. The right side river branch system No significant changes in malakofauna of the right side river arm system were recorded in 2002. 7.5. Dragonflies (Odonata)The left side river branch system The species composition of dragonflies’ community on the Slovak side during the whole observed period is rather poor. Monitoring of dragonflies in the monitoring area No. 2600 was in 2002 restored in a gravel pit, which is filled up with Danube water and had muddy-gravel bottom. Newly formed biotope was not overgrew by macrophytes for the time being and the dragonflies’ community was poor. Presence of one eurytopic dragonfly species was recorded only, but settling of biotope in the following years can be expected. The abiotic conditions of aquatic biotopes on the monitoring area No. 2603 was not changed since introducing the water supply to river branch system (in 1993). In the flowing water with higher depth mainly rheophilous and semirheophilous dragonflies occur. Only in the years 2000 and 2001 the dominance of eurytopic species was recorded. The state of odonatocoenose represents relatively stable community, which settles moderately flowing waters. Comparing to previous years the species diversity of dragonfly larvae on the monitoring area No. 2604 was slightly richer and occurrence of stagnicolous vulnerable species was recorded besides eurytopic species. Due to the flood in August the transformation of plesiopotamal to paleopotamal and the degradation of the dead river arm slowed down. The biotope conditions on the monitoring area No. 2608 are unfavourable for dragonflies’ communities. Due to muddy bottom and absence of macrophytes no representative of mentioned community have been recorded since 2000. Moving of the sampling site to a more favourable biotope near the original monitoring site will be necessary. Monitoring of odonatocoenose on the monitoring area No. 2612 was moved to neighbouring river arm with more favourable conditions for dragonflies’ occurrence in 2002. Only flying imagines after flood in August represented the community, which consist of eurytopic, semirheophilous and thermophilous species. The right side river branch system The species composition of odonatocoenoses of shallow and deeper gravel pits in the inundation and flood-protected area has not changed significantly. Higher amount of water released into the Mosoni Danube did not influenced the composition of dragonflies’ community. However, the increased amount of water in the previously slow flowing river arms with abundant macrophytes significantly altered the previous conditions. Instead of rich, typical stagnant water fauna, eurytopic and riverain species, and decrease of species diversity in some places were recorded in 2002 again. 7.6. Crustaceans (Cladocera, Copepoda)The Danube Evaluation of development of Cladoceras and Copepods communities is based on the results of the Slovak side. The stabilised conditions of the Danube old riverbed allow formation of the stable communities of Cladoceras and Copepods. Their species diversity is rather high as well as the proportion of euplanktonic and tychoplanktonic species in last years is comparable with results of pre-dam period. Their development in respective years is influenced by actual spreading of macrovegetation in the river. The left side river branch system The state of Cladoceras and Copepods communities in the river arm on monitoring area No. 2603 was stable during last years. The tendency of increase of tychoplanktonic species dominance in medial and littoral zone of the river arm, started after putting the intake structure at Dobrohošť into operation (in 1993), remained as well. The cut out of forest realized close to the river arm could evoke community changes in following years. The tendency of overgrowing of the dead river arm on the monitoring area No. 2604 causes gradual loss of dominance of euplanktonic Cladocera species, because their living conditions became worse. Although the species number in 2002 was similar to that in previous years, the tychoplanktonic species predominated the euplanktonic species for the first time. Their decrease was not observed not even after declining of macrovegetation after the flood in August. The increase of tychoplanktonic species is noticeable in rich Copepods community as well, but it is not so intensive. Interruption of the permanent dominance of euplanktonic species of Cladocera in the medial and littoral of the river arm occurred in 2001 for the first time. In 2002 the euplanktonic and tychoplanktonic species were equally present, however in some cases prevalence of tychoplanktonic species was recorded. The spreading of tychoplanktonic species can point to the muddying and overgrowing of the river arm. However, monitoring results of the Copepods community cannot prove this tendency. This community with high species richness is characterised by significant dominance (above 90%) of euplanktonic species. In mixed samples of medial and littoral in naturally overgrew river arm on the monitoring area No. 2612 the abundance of euplanktonic Cladocera species decreases practically during the whole observed period. In last years the tychoplanktonic species dominate. Significant prevalence of euplanktonic species was recorded only in autumn sample in 2002, when the abundant macrovegetation of river arm was removed by strong flood in August. Similar tendency in Copepods community was not observed till now. Although a moderate decrease of species diversity in Copepods community was observed in 2002, the dominance of euplanktonic species in yearly averages remained during the whole observed period (except 1999). The right side river branch system The number of species was the highest in the Lipóti marsh – 34 species. The highest abundance of respective species was observed in the Schissler river arm again, where the dominance of pelagic Cladoceras remained. Increase of the species number and abundance of individuals of planktonic crustaceans, which was recorded in Zátonyi Danube and Csákányi Danube in previous year, have not repeated in the year 2002. The species diversity of Cladoceras and Copepods communities decreased at almost every sampling site in comparison to the year 2001. The most frequent species were Bosmina longirostris, Chydorus sphaericus and Pleuroxus truncatus. The summer abundance was low, however in September, after the summer flood, the abundance of zooplankton remarkable increased. 7.7. Caddisflies and Mayflies (Trichoptera, Ephemeroptera)There are differences in the mayflies (Ephemeroptera) and caddisflies (Trichoptera) taxocoenoses monitoring methods used by the Slovak and Hungarian Party. On the Slovak side the larvae of mayflies and caddisflies living in the water are observed, while on the Hungarian side the flying imagines are monitored. The Danube Changes of ecological conditions in the Danube old riverbed resulted in changes in mayflies and caddisflies’ communities. The monitoring results on the Slovak side indicate presence of very poor mayflies community with irregular occurrence of semirheophilous and stagnicolous species. The Hungarian side describes a huge occurrence of mayflies of eutrophic water bodies in the main Danube at Rajka, based on flying imagines observations (mainly Caenis horaria, Caenis robusta). The middle section of the Danube is still characterized by rheophile fauna. According to the results of the Slovak Party the caddisflies’ community of the Danube consisted of only one natural species Brachycentrus subnubilus in 2002. The occurrence of this filtrator species indicate the continuous decrease of scrapers, spread in the Danube due to changes of food-offer after damming the river. The experts of the Hungarian party recorded significantly higher number of species and number of individuals in 2002 again, which indicate good state of water bodies. The left side river branch system The mayflies and caddisflies communities in the left side river branch system are generally characterised by decrease of species diversity and low number of individuals of present species. The mayflies and caddisflies communities in the river arm of monitoring area No. 2603 were very poor in species number and abundance in the last years. They are composed by irregularly present semirheophilous to stagnicolous species. The development of the community in the next years will be probably influenced by impacts of forest cut out in river arm surroundings. Due to the favourable hydrological (floods) and meteorological (without strong warming up of the water body) conditions the development of the mayflies and caddisflies communities in the plesiopotamal of area No. 2604 was favourable in 2002. Increase of species number, abundance and constant occurrence of mayflies and caddisflies was recorded after their absence in 2000 and sporadic presence of mayflies in 2001. The stagnicolous species and species dependent on macrophytes spreading were mainly present. The mayflies and caddisflies communities in the river arm on the monitoring site No. 2608 were very poor in last period. Presence of different species the in respective years was very irregular. No mayflies and caddisflies larvae were found in the year 2002. The mayflies’ community in the monitoring area No. 2612 is represented by single stagnicolous species during the last years. In 2002 it occurred during the whole year, but in low abundance. After two years long absence two caddisflies species were recorded in 2002, one of them had relatively high abundance. The right side river branch system Different results in monitoring of mayflies and caddisflies on the Slovak and Hungarian side have been reached in the river branch system too. The species diversity and the abundance of mayflies’ species on the Hungarian side are significantly higher. The highest numbers were recorded on monitoring site at Mosoni Danube near Feketeerdő. Huge occurrence of mayflies of eutrophic water bodies (Caenis horaria, Caenis robusta) was recorded in the Lipót marsh. On the other side in the Lipót marsh and at Mosoni Danube the semirheophilous species Ephemera vulgata was repeatedly observed. The caddisflies community in the Szigetköz region is very rich, which is proved by high species number and high number of individuals. The proportion of species, with mass occurrence in previous years, had stabilised. For all types of water bodies there exist species, which occurred with minimal abundance in the past and now belong to the dominant species of the community. Similarly further occurrence of some rare and valuable species was proved. Based on the caddisflies communities’ development and composition the water bodies of Szigetköz region are in a good state. 7.8. Fish (Osteichtyes)The ichtyofauna monitoring on the both sides is carried out by electro-fishing (with moderate high power-output apparatus – 600 W). In the year 2002 very high power-output electro-fishing boat was alternatively used on the Hungarian side as well (10000 W). The mentioned apparatus has higher range and therefore allows observation of deeper parts of water. Due to the different species-selectivity of the mentioned methods, the obtained results are not directly comparable with the data of previous years. The methods of electro-fishing have limited range and they are species-selective, therefore they cannot give complete results. The Danube The evaluation is based on Slovak observation results on monitoring areas No. 2600 and 2608 and Hungarian observation results on monitoring sides No. 10 and 11. In general it can be stated that the fish community in the Danube is stable; no changes were recorded during last years. After diversion of the Danube decrease of the number of rheophilous species was recorded. Eurytopic species replaced them. The species richness in the last few years is at this level stable. By using of high power-output apparatus on the Hungarian side there were recorded further species in 2002, which were not registered in previous years. The ichtyocoenoses of the Danube is rich in species. The results of respective years are fluctuating, depending on the actual flow rate during sampling. The left side river branch system The ecological conditions in the river branch system at Bodíky (monitoring area No. 2603) have changed after introducing the water supply in 1993. The ichtyocoenose of the area is characteristic by stability in last years, with the dominance of eurytopic species. During the floods in 2002 individuals of the surrounding sections were fetched by water, so the abundance of some of the present species was higher. Rather high species diversity of the ichtyocoenose in the dead arm on area No. 2604, which was probably formed due to the absence of high air temperatures and warming up of the water body in 2001, remained also in 2002. Continuous presence of this positive state can be explained by the connection of dead river arm with living river branch system during the flood in March and August. In the community the dominance of limnophilous species persists. The ichtyocoenose on the monitoring area No. 2608 is observed on two partial monitoring sites in the river branch system (upwards and downwards from the Foki weir), which differs in their connection with the Danube. The monitoring site upwards from Foki weir is during higher flow rates connected with the Danube. The fish community is stable, with quite high species diversity and abundance as well as with dominance of eurytopic species. The flood in August caused further enriching the fish of community in this locality. In the isolated part of the river arm, downwards from Foki weir, the flood caused moderate increase of the low species number and increase of species abundance approximate four times. Further positive impact of the flood was the return of the rheophilous species to the part of river arm downwards from the Foki weir, where eurytopic species also dominate. The reconnection of the river arm on monitoring area No. 2612 with the Danube during floods in 2002 caused some changes in ichtyofauna. Throughout the ten years long isolation of the river arm, it lost its spawning place function which was followed by significant decrease of number of present fish species and number of individuals (to 3-4 limnophilous species). The presence of 10 species was proved in 2002, with the abundance approximately four times higher. The eurytopic species became dominant, furthermore the occurrence the species of very warm water bodies Misgurnus fossilis diminished. The development of this ichtyocoenose in the area downstream of the confluence of the Danube old riverbed and the tailrace canal depends on the development of the Danube hydrological regime. The right side river branch system The ichtyocoenose of inundation area is monitored on two monitoring sites – No. 9 and No. 4. The monitoring sites in the flood-protected area are situated at Gazfűi Danube and Lipót marsh. The ichtyofauna on the monitoring site No. 9 – Csákányi Danube in 2002 consisted of 7 fish species, similarly to previous years. Occurrence of rheophilous species in 1992 indicated the connection between the Csákányi arm and the Danube. During years 1993-1994, when insufficient water amount was supplied to the river branch system, the rheophilous species diminished, while phytophilous species appeared. The connection between the river arm and the Danube was restored in 1995 by introducing of water supply by the underwater weir in rkm 1843. Consequently reduction of aquatic vegetation, decrease of phytophilous species occurred and rheophilous species reappeared. The species composition in last years is stable; the species richness of community is moderately rich. The ichtyofauna of the Schissler river arm restored after its artificial reconnection with Csákányi Danube in 1997. The species number radically increased, the species richness of the fish community is moderately rich at present. 12 species were recorded in 2002. During the last years the eurytopic fish species preserves their dominance. In the year 2002 10 fish species were detected at monitoring site No. 12 – Gazfűi Danube. Moderately rich species richness which consist of eurytopic and limnophilous species is characteristic for this monitoring site. The eurytopic species Rutilus rutilus remain dominant. Since 1998 the characteristics of fish community are stable and comparable to the results obtained before damming the Danube. After introduction of the water supply to the monitoring site No. 5 – Lipót marsh regeneration of ichtyofauna is observed. The species diversity increases since 1994, at present time the species richness of the locality is significant. 9 species were recorded in 2002. The monitoring results are balanced in last years with the dominance of eurytopic species. The limnophilous species occur in the community too.
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