Reed stands during different water level periods: physico-chemical properties of the sediment and growth of Phragmites australis of Lake Balaton

Abstract

Water level fluctuations play a vital role in regulating macrophytes of shallow lakes. Morphology and growth dynamics of Phragmites australis, together with physico-chemical parameters of the sediment, were studied at stable (not degrading) 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 parameters 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 management practice to counter reed die-back.