Initial microbiological response in lakes to the Mt St Helens eruption

Abstract

No published reports exist on the early stages in the establishment and succession of microbial communities and associated chemical and geochemical transformations in aquatic environments shortly after a volcanic event. Much of our understanding of volcanic lakes has come from studies carried out years to centuries after the eruption, when the lakes were already stabilized. Here we document the chemical and microbiological responses of lakes and hydrothermal environments in the blast zone near Mt St Helens 3–4 months after the eruption of 18 May 1980. Within weeks of the eruption, the impacted lakes became anaerobic, ultraeutrophic and developed extensive populations of bacteria, some of which were not common to those environments. By August 1980 both assimilative and dissimilative nitrogen cycle reactions were regulating the extent of chemosynthetic, photosynthetic and heterotrophic activities occurring in the lakes. Recovery of the lakes to their normal oligotrophic state will result in part from oxygen production by photosynthesis and anaerobic oxidation of reduced metals, gases and organic compounds coupled with denitrification.