Evolution of Dissolved and Particulate Matter during the Ice-Covered Period in a Deep, High-Mountain Lake

Abstract

Changes in inorganic and organic matter beneath the ice in a deep oligotrophic lake are used to establish temporal and spatial scales of physical and biological processes involved in the dynamics of the system during low energy flow. Four phases were distinguished: (1) Ice-forming phase; light still penetrated the relatively thin snowpack, production was high, and a chlorophyll maximum developed close to the ice. (2) Transition towards a dark environment; light was reduced to very low levels by rapid snow accumulation, phytoplankton showed symptoms of shade adaptation, and nutrients and dissolved organic compounds changed markedly (e.g. soluble reactive phosphorus increased). (3) Central phase; for several months, loss processes (respiration, sedimentation) maintained constant rates, three zones of differing variability patterns were distinguished in the water column: an upper zone where biomass was higher and which was affected by exchange of substances with the cover during flooding processes, a middle zone with little change throughout the phase, and a deep layer, identified by catabolic activity, where diffusion of compounds from the sediment took place. (4) Thaw; sequential changes occurred near the surface owing to snowpack melting, chlorophyll reached the lowest winter values of the period in spite of light and nutrients, and nitrogen compounds changed significantly.