ASSESSING MICROBIAL NITROGEN CYCLING CAPACITIES IN MATS OF INVASIVE D. GEMINATA IN NORTH SHORE STREAMS AND NEARSHORE LAKE SUPERIOR

Didymosphenia geminata (didymo) is an invasive and ecologically destructive nuisance alga whose spread has commonly been associated with the recreational fishing industry. Didymo was first identified in Lake Superior in the 1960s and is likely native to the lake. It has since been found in the Poplar River (in 2018) and eight other rivers along Minnesota’s North Shore. The spread of didymo into streams has two probable causes: aggressive colonization by invasive populations or changing environmental conditions allowing native Lake Superior populations to expand. This study examines shifts in microbial community composition and functioning in the presence of didymo mats, with a particular focus on nutrient cycling. Periphyton samples were collected from twenty-seven didymo-infected stream and nearshore lake sites; microbial communities were characterized using shotgun metagenomic sequencing approaches. Genes associated with nitrogen cycling and urea utilization were identified to describe nitrogen cycling pathways within didymo mats. Despite fully oxic river waters, genes associated with oxidative nitrogen pathways (including nitrogen fixation and nitrification) were either scarce or not present in mats across the samples. However, genes associated with reductive pathways and urea utilization were more abundant and nearly ubiquitous. This suggests that didymo mats create anoxic microenvironments that could serve as sources of nitrous oxide, a potent greenhouse gas. Finally, urea, either from fertilizers or other organisms, may serve as an important source of nitrogen.

Primary Presenter: Sarah Clauss, University of Minnesota-Duluth (sarahkclauss@gmail.com)

Authors:

Sarah Clauss, University of Minnesota-Duluth  (claus503@d.umn.edu)

Andrew Wood, University of Minnesota-Duluth  (wood0795@d.umn.edu)

David Burge, Science Museum of Minnesota, St. Croix Watershed Research Station  (burge236@d.umn.edu)

Mark Edlund, Science Museum of Minnesota, St. Croix Watershed Research Station  (medlund@smm.org)

Adam Heathcote, Science Museum of Minnesota, St. Croix Watershed Research Station  (aheathcote@smm.org)

Heidi Rantala, Minnesota Department of Natural Resources  (heidi.rantala@state.mn.us)

Cody Sheik, University of Minnesota-Duluth  (cssheik@d.umn.edu)