MEPS 389:17-29 (2009)  -  DOI: https://doi.org/10.3354/meps08175

ABSTRACT: 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 l (mg of cell)^–1 h^–1) more than doubled that observed in winter (0.51 l (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.

KEY WORDS: Carbon monoxide · Microbial uptake · Seasonal variation · Temperature dependence · Bacteria · Suspended particles · Estuarine waters · Gulf of St. Lawrence