Response of hornwort (Ceratophyllum Demersum L.) to water level drawdown in a turbid water reservoir

Abstract

The research focuses on the effects of seasonal water level drawdown on the submerged vegetation in a turbid water reservoir measured through the biomass, the maximum depth of colonization and the occurrence frequency of hornwort Ceratophyllum demersum L. Furthermore, the underwater light intensity, water turbidity and biovolume of planktonic algae were determined to evaluate the environmental factors affecting the development of macrophytes. Because of low global radiation in late summer, the irradiance in the period following the water level drawdown was lower compared to the preceding period, but still above the species tolerance level. Nonetheless, the water level regulation improved the underwater light conditions for submerged macrophytes through the water level reduction. Plant biomass, the incidence of C. demersum and the maximum depth of macrophyte colonization increased after the water level drawdown in deep phytolittoral, whereas no effects were observed in shallows. Our research showed that the water level changes could be a useful tool in treatments aimed at maintaining the aquatic vegetation and improving the water quality in regulated water bodies.