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

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 (Rozmberk fishpond), Hungary (Lake Ferto 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 Rozmberk fishpond, with lactic and oxalic acid at Lake Ferto 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 mu mol l(-1) at a land and a deep-water site of Rozmberk fishpond, 1673 and 2216 mu mol l(-1) at a healthy and damaged stand of Lake Ferto, 1006 and 1642 mu mol l(-1) at a healthy and damaged stand of Kis-Balaton, and 570 and 223 mu mol l(-1) at a healthy reed stand and a lagoon at Vejlerne Nature Reserve, respectively. At Rozmberk fishpond the concentrations of lower organic acids were considered sufficiently high to diminish the plants vigour and possibly to induce die-back. At Lake Ferto 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 (similar to 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. (C) 1999 Elsevier Science B.V. All rights reserved.