No abstract

Sediments in the southwestern Baltic Sea showed variable correlations between heat production rate, adenosine triphosphate (ATP) concentration, and activity of the electron transport system (ETS). There was excellent correlation between heat flux and ATP for beach sand but none for subtidal sand. Heat production/ATP, heat production/ETS, and ETS/ATP ratios are 3.5, 2.8, and 1.8 times higher, respectively, for sandy beach sediments than for sandy subtidal sediments. Heat production/ATP ratio in a batch culture of the obligate anaerobic fermenter, Bacteroides sp. was relatively stable during growth phase but decreased greatly from stationary through senescent phases, indicating that at least part of the variability in the correlation between heat production rate and ATP in sediments might be due to differences in the physiological state of bacteria. Long-term storage of sediments resulted in decreases in both ATP concentration and rate of heat production, possibly due to exhaustion of food substrate, of electron acceptors, or changes in microbial composition. Inferring differences in metabolic rates of very different sediment samples from differences in ATP or ETS activity alone could be misleading. Direct metabolic rate measurements are essential in addition to ATP or ETS activity measurements for accurate understanding of the differences and changes in sediment metabolism. When dealing with unknown mixtures of metabolic types in sediments, direct calorimetry has the advantage of measuring equally well the rate of production of a common end-product of all kinds of metabolic activities.