Connecting the blooms: tracking and establishing the origin of the record-breaking Lake Erie Microcystis bloom of 2011 using DGGE

Summer blooms of Microcystis now occur every year in Lake Erie with varying concentration, duration, and spatial extent. The recording-breaking bloom of 2011 began in the western corner of the lake during early summer, and reached its peak in late summer covering 2968 km(2). Start and peak blooms were offset by 3 mo and separated by 120 km, raising the question: Is Microcystis transported across the lake or do separate blooms arise from separate source populations? This study addressed this question by measuring the genetic diversity of Microcystis across the lake and throughout the summer. Seven sites separated by about 100 km were sampled monthly during the summer of 2011 for genetic analysis of the Microcystis population. Furthermore, 2 major rivers (Maumee and Sandusky) and lake sediments were sampled and collected prior to bloom formation to investigate source populations. Denaturing gradient gel electrophoresis was used to generate Microcystis-specific molecular fingerprints of the 16S-23S rRNA internal transcribed spacer region. Dendrograms and principal component analysis were used to investigate similarity among samples. Fingerprints of lake water samples were more similar to the sediments than tributaries, indicating the sediments were a more likely bloom source. All lakes samples collected were >50% similar with several universal bands, indicating Microcystis was transported west to east by water currents and that the beginning and peak blooms were not isolated. This information characterizes the origin and movement of this massive and problematic bloom, and can be used to inform management practices aimed at preventing blooms in Lake Erie.