Responses of ecotypes of Phragmites australis to increased seawater influence:: a field study in the Danube Delta, Romania

The effects of locally increased salinity in a complex of Fine and Giant reed (Phragmites australis) clones were investigated in the Tataru channel (Danube Delta, Romania). Following digging of the Tataru channel, the area closest to the sea became isolated from freshwater input, causing saline conditions to develop due to its proximity to the sea. The other side of the channel remained a freshwater area. The impact of increased salinity on the regression of reed was studied and related to a possible difference in susceptibility to high salt concentrations between different clones (Octoploid Giant reed versus Tetraploid Fine reed). Measurements were made in survey plots situated on both sides of the channel. In freshwater, Giant reed had higher and thicker shoots than Fine reed, but stem density was much smaller, resulting in a lower biomass per surface area of Giant reed. Growth of both Giant and Fine reed was severely reduced at the saline east side of the channel. A significant interaction was found between reed type and salinity. Giant reed density, height, stem diameter and biomass were more strongly affected by saline conditions than Fine reed. The salinization of the parts east of the channel might thus have affected Giant reed stands more strongly than Fine reed stands. The implications for reed succession under increased salinity in the delta are discussed. (C) 1999 Elsevier Science B.V. All rights reserved.