Ábrahám Levente (szerk.): Válogatott tanulmányok VI. - Natura Somogyiensis 19. (Kaposvár, 2010)
BALÁZS A. & ERDŐS L.: Botanical survey of Southern Transdanubian oxbow lakes and the changes of the last 10 years
42 NATURA SOMOGYIENSIS tected species, the water-weeds and the invasive species and on the changes of their quantity during the last years. A detailed description about the dispersion of these invasive species at the shore of these oxbow lakes has not been given so far, so we would like to fill this gap with our survey. We would like to point to the aspects which endanger the oxbow lakes: the lack of forested buffer zones, the pollution from the angling activity, the introduction of the adventive herbivorous fish species and, in the case of the Új-tó, the problem caused by the high water-level. Material and methods All of the oxbow lakes under study are situated on the Drava plain, in Southern Transdanubia. Mean annual temperature of the study area is 10.2-10.8 °C (AMBRÓZY and KOZMA 1990). Mean annual precipitation is 680-750 mm ( AMBRÓZY and KOZMA 1990). The Drava plain belongs to the phytogeographic province Pannonicum, region Eupannonicum, district Titelicum (BORHIDI and SÁNTA 1999). Six oxbow lakes were chosen for our study, in which occurence of Nymphaea alba was recorded in earlier studies. Below we give a brief characterization of the oxbow lakes under study, based on the data of DÉNES and ORTMANN-NÉ AJKAI (1999, 2006) and PECZE (2001). Bresztik: This oxbow lake can be found on the flood-protected area, it is privately owned and its angling exploiter is the Angler Association of Sellye. Water supply originates from underground water. It is visited frequently by anglers and its vegetation along its shores is interrupted by stages. The oxbow lake is surrounded by cultivated fields from the north and by reed beds from the south. Vájási-tó: This oxbow lake is situated on the flood-plain. Its exploiter is the Angler Association of Drávasztára. It is surrounded by cultivated and uncultivated fields, secondary dry sand steppe and a dry oak forest patch. Zalátai Ó-Dráva: It can be found on the flood-protected area and it is owned by 342 private people. Its exploiter is the Angler Association of Zaláta and Surroundings. It has no connection with any water-supply systems, thus its water supply comes from the precipitation and the ground-water. This oxbow lake is surrounded by treelines and narrow forest stripes. Mailáthpusztai-tó: It is located on the flood-protected area, its owner and exploiter is the Angler Association of the Worker of Ormánság. It can be filled from the ditch in Kisszentmárton and its water can be drained off to the River Drava. Along its shore, several stages have been built. The oxbow is bordered by narrow forest stripes, behind which cultivated fields can be found. Hótedra: It is situated in the inundation area. Its owner is the Hungarian State and its exploiter is the Angler Association of Siklós and Surroundings. This oxbow lake has connection with the River Drava when the river has high water-level, but it also gets water supply from ground-water flow. A lot of stages can be found on its eastern shore. Also, angling is allowed from boats. It is surrounded almost entirely by cultivated fields. Új-tó (part of the Kovácshida lake-system): This oxbow lake originates from a former turf-pit and it is situated on the flood-protected area. It is owned by the Beremend Cement-works Angler Association. It is bordered from all sites by settlements, a highway and cultivated fields.
