Statistical Analysis of Spatial and Temporal Dynamics of a Bacterial Layer in an Aquatic Ecosystem

Abstract

Do active vertical mass movements occur within a population of phototropic bacteria in the meromictic Lake Cadagno? An experiment was conducted in vivo to record vertical profiles of the parameters turbidity and temperature in a spatial resolution of 30cm repeatedly over time. After eliminating the temporal dependencies within both the space-time data of turbidity measurements and temperatures, the respective spatial correlation structure can be estimated. Spatial prediction (Kriging) then offers a tool to enhance the observed spatial resolution of both processes. By means of the (temporally repeated) turbidity profiles the vertical position of the bacterial layer can be estimated at each time point. Obviously its vertical displacements in course of the observational time occur not only due to active bacterial swimming; additionally the bacteria are dragged along passively by internal waves in the lake. Eliminating this latter disturbing effect the estimated temperature (instead of depth) at the bounds of the layer in course of time allows to draw conclusions on the active component of bacterial movements. Such phenomena can be found especially at the lower bound of the bacterial layer with amplitudes up to more than 30cm.