Aquatic macrophytes and water current velocity in the Danube River |
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| Authors: | Georg A. Janauer Udo Schmidt-Mumm Brigitte Schmidt |
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| Affiliation: | 1. Taihu Laboratory for Lake Ecosystem Research, State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing, 210008, China;2. University of Chinese Academy of Sciences, Beijing 100049, China;3. School for the Environment, University of Massachusetts Boston, Boston, MA 02125, USA;1. University of Antwerp, Department of Biology, Ecosystem Management Research Group, Universiteitsplein 1C, B-2610 Wilrijk, Belgium;2. Ghent University, Department of Civil Engineering, Hydraulics Laboratory, Sint-Pietersnieuwstraat 41, B-9000 Ghent, Belgium;3. Netherlands Institute of Ecology, Centre for Estuarine and Marine Ecology, P.O. Box 140, 4400 AC Yerseke, The Netherlands;4. University of Limpopo, Department of Biodiversity, PBag 1106, 0727 Sovenga, South Africa;1. University of Pannonia, Georgikon Faculty, P.O. Box 71, Keszthely H-8361, Hungary;2. P.O. Box 7, Miki-cho Post Office, Ikenobe 3011-2, Kagawa-ken 761-0799, Japan;1. Northern Rivers Institute, School of Geosciences, University of Aberdeen, Aberdeen, AB24 5BW Scotland, UK;2. Scottish Environment Protection Agency, 6 Parklands Avenue, Eurocentral, Holytown, North Lanarkshire, ML1 4WQ Scotland, UK;3. University of Glasgow, Glasgow, G12 8QQ Scotland, UK;4. Department of Geography and Environmental Studies, University of Zambia, Lusaka, Zambia;5. Freshwater Research Centre, Cape Town, South Africa and Faculty of Science, Nelson Mandela Metropolitan University, Port Elizabeth, South Africa;6. Department of Geography, University College London, London, England, UK |
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| Abstract: | Water currents are among the strongest environmental variables determining the occurrence and/or abundance of aquatic plants and the European Water Framework Directive (WFD) considers river morphology and current conditions important aspects of reference conditions. We used the database of the Joint Danube Survey JDS-2, organised by the International Commission for the Protection of the Danube River (ICPDR, Vienna), to assess the relationship between water flow velocity and the occurrence and abundance of aquatic macrophyte to be species along the navigable reach of the Danube River. Species abundance was assessed in accordance with European Standard EN 14184-2003. Flow velocities were assessed close to the plant stands and estimated in 4 classes, worked out in earlier studies in combination with flow meter measurements, which is appropriate for the conditions in this large river. Statistical analysis revealed that only survey units with either no visible flow or those with fast flow were characterised by indicator species with high significance. Still water conditions or barely visible flow (flow class 1) were indicated by Potamogeton friesii, Nitellopsis obtusa and Trapa natans, and by Potamogeton perfoliatus, Potamogeton nodosus and Stuckenia pectinata. Lemna minor, indicative for flow class 1 as well, was detected in all the other flow classes, too: in all these cases it established its stands closely intermingled with other aquatic species. For survey units with slow (flow class 2) or intermediate flow (flow class 3). No statistically significant indicator species could be determined. The highest flow velocities (flow class 4) were significantly indicated by Fissidens rufulus, Cinclidotus fontinaloides and Cinclidotus riparius. Occurrence of aquatic mosses was also highly related to the Berger–Parker dominance index in NMDS analysis. In the same analysis, but towards the smallest flow velocities, the majority of vascular species and the Simpson diversity index were closely related. The spectrum of life forms was considerably reduced under medium and high flow velocity conditions. With regard to Simpson species diversity, our analysis indicates an agglomeration of diversity in the Middle Danube reach that includes the Iron Gates impoundment. Our results offer a first look at the macrophyte/water flow relationship of a very large river in Europe, the Danube. |
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