Microbial carbon monoxide uptake in the St. Lawrence estuarine system

摘要

Microbial uptake of carbon monoxide (CO) in the Gulf of St. Lawrence and the estuary of the St. Lawrence River, Canada, typically followed first-order kinetics at ambient CO concentrations, [CO], but saturation kinetics occasionally occurred in spring. The first-order uptake rate constant, K_(co), decreased from the upper estuary (8.48 d~(-1)) to the lower estuary (3.94 d~(-1)) and the gulf (1.32 d~(-1)). K_(co) inversely varied with tide and decreased from its highest value in summer (7.52 d~(-1)) to intermediate values in spring (5.15 d~(-1)) and autumn (4.12 d~(-1)), and to its lowest value in winter (1.09 d~(-1)). Maximum K_(co) values always occurred in a turbidity maximum zone near the head of the estuary. An empirical model was proposed to account for the effect of particle-associated bacteria on K_(co). Temperature dependence of K_(co) obeyed Arrhenius behavior with the activation energy being lower in the upper estuary (21.5 kJ mol~(-1)) than in the lower estuary and gulf (32.7 kJ mol~(-1)). The combination of bacterial abundance and temperature can serve as an all-season predictive tool for K_(co). CO uptake rate versus [CO] plots show typical Michaelis-Menten kinetics or inhibition behavior at elevated [CO]. K_m was low and relatively invariable: 3.2 nmol l~(-1) [CO] in autumn and 4.9 nmol l~(-1) [CO] in winter. CO specific affinity in autumn (1.25 1 (mg of cell)~(-1) h~(-1)) more than doubled that observed in winter (0.51 1 (mg of cell)~(-1) h~(-1)). This study demonstrated strong seasonal variations in microbial CO uptake and complex influences of various biotic and abiotic variables on this process.