Vertical distributions of blooming cyanobacteria populations in a freshwater lake from LIDAR observations

Abstract

Abstract The vertical distributions of freshwater cyanobacteria populations are important to plankton community structure, ecology and for influencing water column optical properties relevant to remote sensing. In August of 2014, we examined the vertical structure of a cyanobacteria bloom across the western basin of Lake Erie with new technologies, including LIDAR and a digital holographic system. In addition, vertical profiles of environmental and optical properties were made. The active LIDAR penetrated the water column, and provided a detailed picture of the particle distribution for the whole water column. The holographic system provided digital images processed for particle size, count and identification of Microcystis and Planktothrix - the two main cyanobacteria genera that were present. The correlations between the LIDAR backscatter intensity and the cyanobacteria cell counts from holography averaged to 0.53 and ranged from −0.13 to 0.96 based on nearest matchups. The vertical structure of the overall cyanobacteria population was influenced by wind speed, and to a lesser degree the solar heating of surface waters. On a more detailed level, Microcystis populations were consistently nearer to the surface relative to Planktothrix. Pigments from surface samples revealed a higher degree of photoprotection for Planktothrix-dominated communities. The vertical distributions of the cyanobacteria genera were related to light intensity in the water column and known tolerances and/or preferences for each genus. Vertical profiles of optical properties supported the patterns seen in the LIDAR and holographic data, and had direct implications on the exiting light field. These combined data provide a unique view into the natural variations in spatial (vertical and horizontal) distribution patterns of cyanobacteria and resulting impacts on remote sensing detection and associated interpretations, and demonstrate the potential for these technologies to observe cyanobacteria in lake environments.