SHALLOW LAKES Reed stands during different water level periods: physico-chemical properties of the sediment and growth of Phragmites australis of Lake Balaton Viktor R. Tóth Received: 24 March 2015 / Revised: 19 January 2016 / Accepted: 6 February 2016 © Springer International Publishing Switzerland 2016 Abstract Water level fluctuations play a vital role in regulating macrophytes of shallow lakes. Mor- phology and growth dynamics of Phragmites australis, together with physico-chemical parameters of the sediment, were studied at stable (not degrad- ing) and die-back (degrading) sites of Lake Balaton over an 8-year period that included low and average water levels. Lower water level increased plant density and green leaf number, positively affecting photosynthetically available leaf area. Nevertheless, rhizome carbohydrate content was not influenced by water level decrease. The physico-chemical parame- ters of the sediment did not vary greatly, although the nitrogen and phosphorus content and the midsummer redox potential of the sediment were higher at the low-water period. During the transition from average to low water levels, the sediment shifted from severely anoxic to poorly oxidised levels, with more favourable nutrient content, while the amount of ammonia and sulphides decreased, too. It was shown that lowering water levels could act on plants via increased redox potential of the sediment and could counteract the die-back of Phragmites, suggesting the effectiveness of water level decrease as a manage- ment practice to counter reed die-back. Keywords Redox potential · Morphology · Growth dynamics · Carbohydrates · Water level changes Introduction Water depth is one of the crucial factors that controls zonation, distribution and progression of Phragmites australis within lakes (Coops et al., 1996; Vretare et al., 2001; Engloner & Papp, 2006; To ´th & Szabo ´, 2012). Numerous studies have shown that, due to specific cytological and biophysical features, com- mon reed is able to tolerate high and prolonged inundation (Armstrong et al., 1994; Crawford & Braendle, 1996; Vartapetian & Jackson, 1997). A continuous gas space within the plant tissue called aerenchyma runs down from the aerial to the underground parts of the plant, channelling air from leaves to rhizomes and roots. This flux of atmo- spheric gases is driven by humidity-induced partial pressure differences between the air and the sub- stomatal space (Armstrong & Armstrong, 1991). Without it, the reed could suffer complete or partial oxygen deprivation due to high microbial oxygen consumption within the sediment (Brinson et al., 1981; Crawford & Braendle, 1996). To survive Guest editors: M. Bekliog ˘lu, M. Meerhoff, T. A. Davidson, K. A. Ger, K. E. Havens & B. Moss / Shallow Lakes in a Fast Changing World V. R. Tóth (&) Hungarian Academy of Sciences, Centre for Ecological Research Balaton Limnological Institute, Klebelsberg Kuno u ´t 3, Tihany 8237, Hungary e-mail: toth.viktor@okologia.mta.hu 123 Hydrobiologia DOI 10.1007/s10750-016-2684-z