Impact of humic substances on Sphagnum denticulatum habitats

Abstract

In 10 softwater lakes of NW Poland (5 very acid and 5 slightly acid) three kinds of Sphagnum denticulatum Bridel [=S. auriculatum Schimper] habitats have been studied: oligohumic (<2.0 mg C_DHS dm^-3) and α-mesohumic (2.0-4.0 mg C_DHS dm^-3) and β-mesohumic (4.1-8.0 mg C_DHS dm^-3). During habitats humification in very acid lakes some water and sediment characteristics, such as pH, conductivity, TDS, and calcium concentration are low and almost invariable, whereas variable are the colour and clearness of the water. In low-acidity lakes the values of habitat characteristics are higher and also nearly invariable. The optimum habitats for S. denticulatum are oligohumic (<1.8 mg C_DHS dm ^-3), very acid (pH 4.0-4.4) sites found at depths from 4 to 8 m, where the species forms large and close carpets. In slightly acid lakes it is rare, grows at depths below 5 m and forms populations of very low density. In mesohumic habitats in both kinds of lakes S. denticulatum is a frequent species, but its populations are very thin there.