Abstract

The abundance of polyphenolic compounds in four temporary ponds in Donana National Park (south-western Spain) was examined during three years of varying hydrology (1989-92). During flooding in 1989-90, the ponds received large amounts of allochthonous organic matter, as indicated by the relative increases in dissolved organic carbon (70-120 mg C L^-1), dissolved polyphenolic compounds (7.6-12.2 mg L^-1) and water colour (17-33 m^-1, A₄₄₀). As the ponds dried out, the concentration of dissolved polyphenols decreased rapidly in ponds with abundant submerged macrophytes, whereas the concentrations increased in unvegetated ponds. Very low concentrations of dissolved polyphenols (1.0-2.8 mg L^-1) were measured in all ponds when they refilled again after drought in October 1991. A large percentage of the initial amount of polyphenols (80%) and of soil organic matter (71%) disappeared from surface sediments after four months of drought. The temporary nature of these ponds enhanced the disappearance of allochthonous organic matter. It is suggested that sunlight and aerobic conditions promote the decrease of organic matter in pond sediments during drought.