The impact of acidic organic matter on the diversity of underwater vegetation in soft water lakes

This paper addresses underwater vegetation in soft water lakes which are influenced by the anthropogenic input of allochtonic dissolved organic matter (DOM) from drained bogs. The aim of this work is to test the hypothesis regarding the role of DOM in shaping the diversity of underwater vegetation. Large differences in underwater vegetation habitats, the limitation of their occurrence to increasingly shallower littoral (the depth of the lower limit of their occurrence decreased from 12 m up to 1 m) and the regression of underwater vegetation were observed in lake types ranging from oligohumic (median (Me) of DOC in water = 2.5 mg C dm-3) to polyhumic (Me of DOC = 35.6 mg C dm-3). The gradual simplification of internal plant patch structure occurred and the Shannon-Weaver diversity index decreased (Me 0.04 → 0.00). Fewer species were observed in the lakes (Me 9 → 2), and the underwater vegetation covered increasingly smaller areas. Species replacement did not occur and no invasive species appeared.