Making the watershed connection: the influence of cyanobacteria, sediment, and nutrient loading and hydrology on cyanobacterial bloom initiation in the nearshore environment

Nearshore algal blooms appearing along the southern coastline of the western arm of Lake Superior ranging from Duluth Harbor to the Apostle Islands appear to coincide with large storm events that flush sediment and nutrients from the watershed into the nearshore.  The concept of “fluvial seeding” has been hypothesized, but the limited available data have not always agreed on the influence of riverine cyanobacteria on open lake algal bloom initiation.  Using cultivation and genomics, our work assessed fluvial flow of cyanobacteria with nutrient and sediment loading from the Siskiwit and Bois Brule tributaries to the Lake Superior nearshore.  Water and sediment samples were collected and added to selective cyanobacteria media.  Additionally, DNA from environmental samples and cultivations were sent for Bacteria 16S rRNA amplicon sequencing to characterize and compare the cyanobacteria community along the tributary to nearshore continuum.  Quantitative PCR targeting Cyanobacteria 16S rRNA was analyzed to determine cyanobacteria relative abundance in relation to sediment and nutrient loading.  Viable cyanobacteria cells were cultivated from tributary samples and genomically similar signatures of Cyanobium, Pseudanabaena, and Nostocaceae species were detected from tributary environmental samples and cultivations. Additional data are needed to understand whether cyanobacteria seeding originates in the tributaries themselves, whether fluvial flow is simply transporting these cells to the nearshore from upstream, or if there are multiple sources seeding the nearshore. 

Primary Presenter: Carrie Givens, U.S. Geological Survey (cgivens@usgs.gov)

Authors:

Carrie Givens, U.S. Geological Survey, Upper Midwest Water Science Center  (cgivens@usgs.gov)

Anna Baker, U.S. Geological Survey, Upper Midwest Water Science Center  (abaker@usgs.gov)

Rebecca Kreiling, U.S. Geological Survey, Upper Midwest Environmental Sciences Center  (rkreiling@usgs.gov)

Eric Dantoin, U.S. Geological Survey, Upper Midwest Water Science Center  (edantooin@usgs.gov)

Patrik Perner, U.S. Geological Survey, Upper Midwest Water Science Center  (pperner@usgs.gov)

Alexei Rose, U.S. Geological Survey, Upper Midwest Water Science Center  (arrose@usgs.gov)

Jeanette Cruz, U.S. Geological Survey, Upper Midwest Water Science Center  (jmcruz@usgs.gov)

Shelby Sterner, U.S. Geological Survey, Upper Midwest Water Science Center  (ssterner@usgs.gov)

Krimson Anderson, U.S. Geological Survey, Upper Midwest Water Science Center  (kanderson@usgs.gov)

Richard Kiesling, U.S. Geological Survey, Upper Midwest Water Science Center  (kiesling@usgs.gov)

Paul Reneau, U.S. Geological Survey, Upper Midwest Water Science Center  (pcreneau@usgs.gov)