Original paper

Effects of sediment pore water qualities on the decline of Stratiotes aloides L. stands in Bremen, Germany

Zantout, Nada; Wilfert, Philipp; Smolders, Alfons J.P.; Weber, Gert; Zacharias, Dietmar


The aquatic macrophyte Stratiotes aloides L. is regarded as a key species for valuable ditch ecosystems characterized by high biodiversity and is an important indicator for the ecological condition of these systems. Recently, a decline of the species in northwestern Germany has been observed. This study focuses on the influence of sediment pore water qualities on the vitality of S. aloides. Investigations were carried out on three grassland areas with extensive ditch systems near the city of Bremen in winter 2009. For two of the sites, Hollerland and Werderland, S. aloides populations are dominant and largely vital whereas a strong decline has been observed in the third site, Niedervieland. Results of pore water analyses revealed significant site-specific differences in some critical parameters for the vitality of S. aloides. In Niedervieland the mean ammonium concentration (541 μmol L−1) was about four times higher, the orthophosphate concentrations (126 μmol L−1) about 14 times higher and the alkalinity (8.5 mequiv. L−1) was almost twice as high as in Hollerland and Werderland. Key parameters in the pore water can have indirect (high alkalinity of the sediment pore water, eutrophication of the water layer due to high phosphate concentrations) or direct (ammonium and sulphide toxicity) negative effects on S. aloides stands. Elevated concentrations of these key parameters were present in Niedervieland, corresponding with the observed decline of S. aloides at this site.


phosphatealkalinityammonium toxicitysulphide toxicityeutrophication