The effect of dissolved organic carbon on pelagial and near-sediment water traits in lakes

The effect of dissolved organic carbon (DOC) on the environmental conditions of macrophytes has been studied in 35 lakes divided into soft- and hardwater: oligohumic (<4.0 mg C dm-3), α-mesohumic (4.0-8.0 mg C dm-3), β-mesohumic (8.1-16.0 mg C dm-3) and polihumic (>16.0 mg C dm-3). The optimum environmental conditions for macrophytes have been found in oligohumic lakes, characterised by low water colour and its good transparency. In soft- and hardwater lakes increasing concentration of DOC is accompanied with an increase in the colour (r=0.95), while the visibility decreases. With increasing DOC in the near-sediment layer the pH values decrease while the concentration of nitrogen increases and the concentration of phosphorus slightly increases. In hardwater lakes with increasing DOC concentration, the redox potential, conductivity, total hardness and calcium concentration in the near-sediment water decrease, whereas the content of CO2 remains at a very low level.