Phosphatase activity in salt-ponds of the Bay of Cádiz Actividad fosfatásica en salinas de la Bahía de Cádiz

Acid and alkaline phosphatase activities (E.C.3.1.3.2 and E.C.3.1.3.1, respectively) were measured in seawater and sediments from different sites of a salt-pond of the Bay of Cadiz. The profiles of enzymatic activity relative to depth were also analysed. Initially, the optimum conditions (pH, temperature, substrate concentration and amount of sample) for determining enzymatic activities were studied. The apparent activation energies for alkaline phosphatase activity in seawater and sediments were 53.8 and 48.6 kJ mol -1 , respectively. The Km and Vmax were 10.6 mM and 89 µg of 4-nitrophenol g -1 h -1 and 8.42 mM and 145 µg of 4-nitrophenol L -1 h -1 for sediments and seawater, respectively. Both types of enzymatic activity reached high values in seawater and sediments; in the confined areas of the salt-pond the values were around 100 µg of 4-nitrophenol L-1 h-1 for seawater and higher for sediments. In general, clear seasonal evolutions for both types of enzymatic activity were found in the seawater, with maxima at the end of summer and minima in winter. No seasonal pattern was evident in the sediment. Stratification of phosphorus regeneration was observed in the sediment column but there was no stratification at depths greater than 15 cm.