Temperature dependence of aerobic respiration in a coastal sediment

The direct temperature dependence of aerobic respiration was determined in sediment from Aarhus Bay, Denmark, in incubations shorter than 12 h at temperature intervals of 1.7°C. Oxygen consumption showed a bimodal distribution between −2 and 80°C indicating the presence of distinct non-thermophilic and thermophilic populations. The thermophilic oxygen consumption had minimum, optimum, and maximum temperatures of 40, 55, and 65°C, respectively, and accelerated strongly after a lag phase of 2–3 h, which may be due to an activation of spores. The source of this dormant thermophilic population is unknown. Oxygen consumption by the non-thermophilic population had minimum and maximum temperatures of <−1 and 45°C, respectively. The optimum temperature increased from a broad plateau of 20–30°C in late winter to 30–35°C in late summer, and the apparent activation energy in the natural temperature range (0–15°C) increased from ∼50 to ∼70 kJ mol−1, corresponding to Q10 values of ∼2.0 and ∼3.0, respectively. These changes indicated an adaptation of the aerobic population to seasonal temperature conditions. Due to the seasonal adaptation and to diffusive limitations, a relatively weak temperature dependence of the area-specific aerobic mineralisation rate in the sediment was calculated, Q10=1.8. Model calculations further demonstrated significant shifts in the relative importance of aerobic and anaerobic mineralisation due to seasonal temperature variation, with less importance of aerobic respiration and a larger fraction of benthic oxygen consumption coupled to the reoxidation of reduced inorganic compounds during summer than during winter.