Interaction of alkaline phosphatase with minerals and sediments: Activities, kinetics and hydrolysis of organic phosphorus

Alkaline phosphatase (APase) plays an important role in phosphorus (P) cycling in water and sediments of lakes. Interaction of APase with minerals including goethite and montmorillonite, and sediments from Lake Tai (Ch: Taihu) and Lake Dianchi were investigated. Degradation and bioavailability of organic P (P_o) in sediments were further investigated by APase hydrolysis and solution ³¹P-nuclear magnetic resonance (NMR) spectroscopy. Little APase is adsorbed by sediments, but APase could be strongly adsorbed by goethite and montmorillonite. Some adsorptive sites could be occupied by organic matter or ions in sediments from lakes. Activities of APase immobilized by sediments could be reduced to 1.3% to 5.3% of that of free APase. However, APase immobilized by goethite and montmorillonite could retain 27.3% and 21.6% of the activity of free APase. Thus, the majority of APase is likely dissolved in overlying water or loosely adsorbed by sediments in lakes. Enzymatic hydrolysis and liberation of orthophosphate from suspensions of sediments were 0.26-4.25 mg kg^-1 that was readily bioavailable to algae or other organisms. After APase hydrolysis, ³¹P NMR analysis showed that no detectable changes in P_o or condensed P in sediments extracted by NaOH-EDTA. Thus, P_o immobilized in sediments couldn't be directly hydrolyzed by APase, but more P_o immobilized in the sediments could be hydrolyzed by APase when they were released into the overlying water under appropriate conditions. Treatments, such as additions of Al hydroxides dosing, would not adsorb or immobilized P, but also immobilized phosphatase, thus decreasing activity of phosphatase and bioavailability of P_o in a eutrophic lake.