Angiosperms in acidic waters at pH 3 and below

Abstract

Colonisation of extremely acidic waters (pH ≤3) by aquatic angiosperms occurs widely, but is poorly documented. Unlike acid rain affected and other naturally acidic aquatic ecosystems, waters with pH ≤3 usually have a high conductivity, with high concentrations of SO42- and often high concentrations of Fe3+, other heavy metal ions and Al3+. Where Fe3+ concentration is high, as in many mine waters, it provides a strong buffering system. In such waters, the biogeochemical Fe cycle exerts over water chemistry and the availability of nutrients and carbon for organisms. Biological activity is limited by low concentrations of phosphorus and inorganic carbon (DIC), which in this pH range is essentially all in the form of dissolved CO2. A number of angiosperms grow in such waters including Phragmites australis, Typha spp. and Juncus bulbosus, though the last is the only one reported to grow totally submerged in waters with pH ≤3 . J. bulbosus occurs in many lignite mining lakes in Lusatia (north eastern Germany) with pH ≤3. The characteristics and possible survival strategies for this and other species are discussed.