ACTIVE NITROGEN CYCLING IS LINKED TO THE FORMATION AND PERSISTENCE OF HABS IN SANDUSKY BAY, LAKE ERIE (E)
Recent cyanobacterial-related water crises in Lake Erie point to an urgent need for greater understanding of harmful algal blooms (HABs) and their drivers. While much of the focus on HABs in Lake Erie is on the primary limiting nutrient, phosphorus (P), nearshore areas such as Sandusky Bay become limited by nitrogen (N) in the summer and are characterized by a distinct HAB composition (i.e., Planktothrix over Microcystis). Thus, N deserves more attention as a regulator of HABs in Lake Erie. Our study investigates (1) the drivers of N limitation and (2) the relationship of N cycling with the formation, persistence, and toxicity of HABs in Sandusky Bay. Stable isotope tracer approaches were employed to quantify rates of denitrification, anammox, and N fixation. Metagenomics and toxin analysis were examined as indicators of HAB presence and toxicity. Major decreases in nitrate concentrations in Sandusky Bay from early to mid-summer coincided with the greatest rates (µmol N m-2 h-1) of denitrification (64.8), nitrous oxide production (2.3), and anammox (8.1). N limitation in mid- and late summer was associated with Planktothrix blooms and the greatest rates of N fixation (1.1 µmol N L-1 h-1). Together, these results suggest that microbial N loss processes drive N limitation in Sandusky Bay, and that Planktothrix is bolstered by a superior ability to compete for scarce N and a potentially commensal relationship with N fixers. This work contributes to the emerging narrative of N as an important driver of HABs in the Great Lakes and beyond.
Salk, K. R., Michigan State University, USA, firstname.lastname@example.org
Bullerjahn, G. S., Bowling Green State University, USA, email@example.com
McKay, R. M., Bowling Green State University, USA, firstname.lastname@example.org
Ostrom, N. E., Michigan State University, USA, email@example.com
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