Alkaline phosphatase activities and the relationship to inorganic phosphate in the Pomeranian Bight (southern Baltic Sea)

Abstract

Alkaline phosphatase activities (APA) were estimated along salimty gradients between the mouth of the Szwina and the open Pomeranian Bight (Baltic Sea) and compared to the distribution of phytoplankton biomass (chlorophyll a, chl a), bacterial counts, and inorganic phosphate. APA and chl a showed a linear decrease along the gradents and correlated with each other. For the interaction between APA and phosphate, a threshold concentration of 1 pM phosphate was found. Below this threshold, 2 mechanisms characterize the relationship between APA and phosphate: (1) an increase in specific APA of algal cells at phosphate concentrations of <0.2 pM and (2) a linear correlation between APA and the phytoplankton biomass at phosphate concentrations of between 0.2 and 1 pM. The inverse relation between APA and phosphate was also shown in mesocosm experiments.