Alkaline phosphatase activity in the Laholm Bay, south-eastern Kattegat

Abstract

Measurements of alkaline phosphatase activity (APA) and experimental investigations of limiting nutrients for phytoplankton biomass formation were performed using water from Laholm Bay, SE Kattegat. Alkaline phosphatase activity was insignificant during the autumn and spring phytoplankton blooms which indicates that phosphorus is not a limiting nutrient for phytoplankton growth in the area. Nitrogen additions greatly increased chlorophyll production in the enrichment experiments during the spring bloom, and to a lesser extent the rest of the year. Water from rivers entering the Laholm Bay greatly stimulated phytoplankton growth when mixed with Laholm Bay water. APA increased in flasks with river water additions indicating phosphorus limitation of phytoplankton growth. The results are explained by the high N/P ratio in river water and low ratio in Bay water.