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Key-words:aquatic macrophyte, IBMR, river, Slovakia, Water Framework Directive Altogether, 62 taxa of macrophytes including 18 bryophytes and 16 macro-algal growths were determined at 87 survey sites (73 rivers) representing the both ecoregions in Slovakia (Pannonian and Carpathian) during the years 2010-2013. Bryophytes represented the dominant community in the Carpathians, while the occurrence of macro-algal growths was relatively balanced in both ecoregions. Ordination analyses (DCA) showed an obvious shift within studied survey sites from vascular plants to bryophytes, while macro-algal growths were more or less uniform distributed in the whole ordination space. Based on stepwise (forward) selection in CCA, altitude and water surfaces as a land use type were the main environmental factors responsible for this pattern and explained 13.7% of the variability. Variation partitioning showed that the shares of environmental variables on the total variation decreased in the following order: both groups together 8.3% (landscape and geographical variables, physicochemical variables), followed by landscape and geographical variables (5.8%) and purely physicochemical variables which had an insignificant effect on macrophyte composition. The importance of both groups (bryophytes and macro-algal growths) in ecological assessment was also confirmed by their contribution to the mean IBMR value determined for each water body type. Anyway, our study showed that their contribution to ecological assessment is not focused only on small mountain streams where they are dominant. They may obviously affect ecological assessment also in many water body types in lowland rivers and large upland rivers as well. Directive Cadre sur l'Eau montré un changement évident dans les sites de l'étude des plantes vasculaires vers les bryophytes, tandis que le développement des macro-algues était plus ou moins uniformément distribué. Basé sur une sélection progressive pas à pas en CCA, altitude et surfaces en eau comme le mode d'utilisation des terres ont été les principaux facteurs environnementaux responsables de cette tendance, expliquant 13,7 % de la variabilité. Le partitionnement de la variabilité a montré que la part des variables environnementales sur la variation totale a diminué dans l'ordre suivant : les deux groupes ensemble (8,3 %) (variables du paysage et géo-graphiques, variables physico-chimiques), suivis par le paysage et les variables géographiques (5,8 %) et les variables purement physico-chimiques qui avaient un effet négligeable sur la composition des macrophytes. L'importance de ces deux groupes (bryophytes et macro-algues) dans l'évaluation écologique a éga-lement été confirmée par leur contribution à la valeur IBMR moyenne déterminée pour chaque type de masse d'eau. Quoi qu'il en soit, notre étude a montré que leur contribution à l'évaluation écologique ne se concentre pas uniquement sur les petits ruisseaux de montagne où ils sont dominants. Ils peuvent évidemment avoir aussi une incidence sur l'évaluation...

Alien aquatic plants rank amongst the major threats to aquatic biodiversity and, since ongoing climate change is expected to facilitate their further spread, there is an urgent need for sound knowledge of their distribution and ecology. We collected published and unpublished data spanning the last ~130 years and performed the first comprehensive assessment of alien aquatic vascular plants in Slovakia with the following aims: (i) to prepare a national inventory, (ii) to assess the effects of climate and landscape on species diversity and (iii) to evaluate the habitat preferences of the species. The historical overview showed a strongly increasing trend in the number of alien species related to an increased amount of intensive research of aquatic vegetation over the last 30 years. Altogether, 20 neophyte alien aquatic plant taxa were recorded from 479 sampling sites. However, the species inventory seems to be far from complete and approximately 14 species are expected to remain undetected. Elodeacanadensis and E.nuttallii are the most frequently occurring alien aquatic plants, while eight other species have been found at a single site only. The majority of alien plants were deliberately introduced as aquarium ornamentals or released through pond waste. The fragmented information on local habitat conditions did not allow us to draw firm conclusions about the habitat preferences of alien aquatic plants. However, artificial water bodies are more frequently colonised by alien species than natural habitats (95% of aliens were found in artificial water bodies and 60% of them were recorded exclusively in these habitats) and many species have broad environmental tolerances (ability to colonise both standing and running waters, tolerances to a wide range of temperatures and water chemistry). Our results reaffirm the major role of increased temperatures and landscape modification in the distribution of alien aquatic plants and we can expect enhanced invasiveness and spreading of alien species into new habitats driven by climate change and land use intensification. Filling a main gap in the recognition of alien aquatic plant environmental preferences is a challenge for future research with the ultimate goal of maintaining natural aquatic plant diversity and ecosystem functioning.

Our study provides new knowledge about macrophyte assemblages and environmental variables of Slovak drainage and irrigation canals. The canal system, comprising ca. 15% of all flows in Slovakia, is one of the oldest in Central Europe. This information represents a first step toward exploitation of macrophytes as an obligatory biological quality element for the assessment of ecological potential according to the requirements of the Water Framework Directive. Among 61 canals studied, a total of 85 aquatic plant species (35 hydrophytes, 16 amphiphytes and 34 helophytes) were recorded during the years 2012-2014, including three neophytes and 18 threatened species. Physico-chemical variables explained the highest proportion of species variability, whilst hydromorphological variables and landscape variables were much less significant. Chemical oxygen demand, ammonium nitrogen, electrical conductivity, water pH, flow velocity and water depth were identified as most important drivers of species composition of aquatic macrophytes and explained 21.1% of the variability. The CCA results revealed differences in species composition of canals reflecting the geographical origin and environmental conditions as well, relating to South-Eastern and South-Western Slovakia. In conclusion, macrophytes in drainage and irrigation canals are able to reflect several environmental variables and might provide valuable information for bioindication in assessing the ecological potential.

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