Diel changes in the alkaline phosphatase activity of bacteria and phytoplankton in the hypereutrophic Villerest reservoir (Roanne, France)

Abstract

The diel changes of the size fractionated alkaline phosphatase activity (APA) were studied in relation to several abiotic and biotic factors in Villerest reservoir (located on the Loire river, near the city of Roanne, France), bihourly during two days in July 1992 . The APA measured in this work exceeded considerably those reported in the literature, suggesting that dissolved mineral phosphorus was not available to microorganisms . At 1 m, the APA was primarily due to bacteria which actively assimilated organic P compounds released by photosynthetic algal metabolism . At 5, 10 and 20 m, the APA was predominantly algal . The high concentrations in SRP (soluble reactive phosphorus) would indicate that orthophosphates were not bioavailable . The reverse (i.e. availability to phytoplankton) would have resulted in undetectable levels of P-PO4 -due to the massive proliferation of algae in Villerest reservoir . 49

Exchange potentials of phosphorus between sediments and water coupled to alkaline phosphatase activity and environmental factors in an oligo-mesotrophic reservoir

“…Similar trends have been reported from different aquatic ecosystems [27]. The decline in orthophosphate concentrations was accompanied by the aerobic bacterial activation together with that of the phosphatase alkaline synthesis, and both algal and zooplankton activities corroborating findings reported in the literature [18,19,28,29]. Moreover, both total APA and its specific activity were lower at station 1 than at station 2, in which we never reached anoxia-inducing release of particulate and thus unavailable orthophosphates.…”

“…However, the release of phosphorus by sediments may have been favoured by bacteria without involving the APA. Our suggestion went along with the study of several authors [12,18,35] who pointed out the role played by microorganisms in managing phosphorus concentrations in environmental anoxic conditions. At station 1, the bacterial development was sustained by intense loads of urban organic matter (from the Taounate city), resulting in a drastic oxygen depletion at the bottom of the reservoir.…”

“…Indeed hypolimnetic oxygen concentrations were low from May to August 1998 (< 4 mg l −1 ) due to bacterial degradation of sedimented phytoplankton [36]. These anoxic conditions made the release of phosphorus closely dependent on bacteria, which were shown to solubilize P-Fe complexes through excretion of low-weight molecules [36,37] and to catalyse iron hydroxide [38,39]. In addition, other works [14,40,41] indicated that the bacterial synthesis of organic acids from the degradation of organic matter yielded a decrease in pH, which induced, when anaerobic conditions prevailed, the dissociation of P-Ca complexes.…”

“…The released phosphate is taken up by microorganisms favoured by the location of phosphatases that may be membrane-bound or confined to the periplasmic space [13][14][15]. While several authors described seasonal and/or diel changes in the alkaline phosphatase activity from the water column of different ecosystems [8,[16][17][18][19], none to our knowledge investigated the distribution patterns of the alkaline phosphatase activity (APA) at the water-sediment interface by in situ benthic chamber measurements.…”

Seasonal changes in zooplanktonic alkaline phosphatase activity in Toulon Bay (France): the role of Cypris larvae

“…The above described filters (90, 5 and 0.25 lm) were placed into filtered (0.25 lm) seawater. Phosphatase activity was measured at 25°C with paranitrophenyl phosphate (p-NPP) as the substrate, by reading absorbance at 410 nm (Reichardt et al, 1967;Jamet et al, 1995). A range of substrate concentrations (0.01-15 mM) was prepared in filtered (0.25 lm) seawater.…”