2023 Early Hearing Detection & Intervention Conference

March 5-7, 2023 • Cincinnati, OH

5/21/2018 | 10:00 AM - 10:15 AM | AMMONIUM REGENERATION DRIVES SUMMER BLOOMS OF PLANKTOTHRIX IN SANDUSKY BAY | 420 B

AMMONIUM REGENERATION DRIVES SUMMER BLOOMS OF PLANKTOTHRIX IN SANDUSKY BAY

Sandusky Bay (SB; Lake Erie) receives high nutrient loads (N and P) from an agricultural watershed. Eutrophication and cyanobacterial blooms (cyanoHABs) persist throughout summer in SB, dominated by Planktothrix agardhii, also the main producer of microcystin in SB. Non-N2 fixing cyanobacteria (e.g., Microcystis and Planktothrix), thrive on chemically reduced N forms (e.g., NH4+ and urea). Monitoring NH4+ turnover rates improves our understanding of cyanoHABs and NH4+ contributions to sustaining blooms. We quantified NH4+ regeneration and potential uptake using 15N isotopes in SB throughout the summer bloom and compared NH4+ uptake kinetics during a Planktothrix bloom in SB and a Microcystis bloom in Maumee Bay. NH4+ uptake rates in SB increased with bloom progression from June to August, with dark rates achieving parity with light rates in August. Regeneration rates were also significantly higher in August than June. Half-saturation constants (Km) in SB decreased throughout the bloom but increased in Maumee Bay, suggesting differing competitive dynamics. In late summer, N concentrations are low, and cyanoHABs rely on regenerated NH4+ for biomass and toxin production. We also hypothesize a community shift and increasing heterotrophic contribution to NH4+ uptake in the phycosphere.

Nitrogen
Phytoplankton
Nutrient Recycling

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Presenters/Authors

Justyna J. Hampel (), Wright State University, hampel.4@wright.edu;