ABSTRACT
Conventional laboratory-derived methods including measurement of dry weight or carbon to estimate biomass or cell enumeration by direct microscopy are generally unreliable for estimating microbial biomass in natural aquatic environments. The heterogeneous distribution of cell sizes and morphologies and variable cell number-to-biovolume-to-biomass extrapolation factors complicate methods involving direct microscopy to determine total microbial biomass. Adenosine Triphosphate (ATP) has several unique characteristics which make it a reliable indicator of microbial biomass in aquatic environments. Data on the particulate ATP (P-ATP) content of a water or sediment sample can be extrapolated to total microbial biomass using C:ATP relationships derived from either laboratory or field studies. Many aquatic sediments are well stratified and characterized by steep depth gradients in microbial biomass. Consequently, it is imperative that the sampling and subsampling methods used to collect sediment for microbial ATP analysis preserve the unique depth distribution. This results in a disruption of the microbial biomass gradients that are of greatest interest to the microbial ecologist.
