Organic acids in the sediments of wetlands dominated by Phragmitesaustralis: evidence of phytotoxic concentrations

Abstract

Spatial and seasonal variations in concentrations of lower organic acids in the sediments of stands of Phragmites australis (Cav.) Trin. ex Steud. were studied in wetlands in the Czech Republic (Rožmberk fishpond), Hungary (Lake Fertö and Kis-Balaton), and Denmark (Vejlerne Nature Reserve). Pore water concentrations of lactic, formic, acetic, propionic, butyric, oxalic, citric, tartaric, malic and fumaric acid were analysed by HPLC and shown to vary both qualitatively and quantitatively between sites. Acetic acid was prevalent at all sites, and dominated together with citric, malic, and tartaric acid at Rožmberk fishpond, with lactic and oxalic acid at Lake Fertö and Kis-Balaton, and with lactic and propionic acid at Vejlerne Nature Reserve. The maximum total concentrations of organic acids recorded were 2984 and 2215 μmol l −1 at a land and a deep-water site of Rožmberk fishpond, 1673 and 2216 μmol l −1 at a healthy and damaged stand of Lake Fertö, 1006 and 1642 μmol l −1 at a healthy and damaged stand of Kis-Balaton, and 570 and 223 μmol l −1 at a healthy reed stand and a lagoon at Vejlerne Nature Reserve, respectively. At Rožmberk fishpond the concentrations of lower organic acids were considered sufficiently high to diminish the plants vigour and possibly to induce die-back. At Lake Fertö and Kis-Balaton the organic acids are unlikely to have had a toxic effect on the reeds at the sampling time because of the relatively high pH (∼7) in these wetlands. However, because of the great spatial and seasonal variability in organic acid speciation and concentration, organic acid phytotoxity may affect the reed also at these sites. At Vejlerne Nature Reserve, the toxic effect on the reeds is unlikely because of consistently low concentrations of organic acids.