Original paper

Bacterial and phytoplankton responses to nutrient and pH changes during short term in situ experiments in two acidified lakes

Znachor, Petr; Vrba, Jaroslav; Nedoma, Jiří; Kopáček, Jiří

Abstract

In June and August 1999 bottle experiments examining the effects of phosphorus (P), dissolved inorganic carbon (DIC) enrichment, and pH manipulation (base addition) were conducted in two strongly acidified lakes (Čertovo and Plešné) located in the Bohemian Forest (Central Europe). Dinoflagellates and Chrysophytes (only in August) were present in each of the lakes. Chlorophytes and filamentous cyanobacteria were particularly dominant in Plešné Lake. A low concentration of dissolved reactive P (∼1 μg l-1) combined with high acid phosphatase activity (2-8 μmol l-1 h-1) and short P turnover time (∼2 min) indicated severe P limitation of phytoplankton growth in both of the lakes. After P addition, phytoplankton remained P limited as a consequence of low P availability due to its rapid incorporation into bacterial biomass. With pH treatment primary production was significantly reduced (by ∼70%) as a consequence of the hydrogen ion shock effect. Phytoplankton biomass was reduced (by ∼20%) as well, as the likely result of P precipitation with aluminium. The experimental DIC addition had no apparent effect on any of the parameters investigated. The experimental treatment did not favor photosynthetic activity of any examined phytoplankton species since there was a simultaneous decrease or increase in photosynthetic activity of all the species studied.

Keywords

phytoplanktonbacteriaresponseacidificationphotosynthetic activitylimitation