2023 Early Hearing Detection & Intervention Conference

March 5-7, 2023 • Cincinnati, OH

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6/06/2017 | 11:15 AM - 11:30 AM | UNRAVELING THE MULTIFACETED EFFECTS OF CHANGING FLOW REGIMES ON CYANOBACTERIAL BLOOM POTENTIALS ON THE CAPE FEAR RIVER, NC | 306B

UNRAVELING THE MULTIFACETED EFFECTS OF CHANGING FLOW REGIMES ON CYANOBACTERIAL BLOOM POTENTIALS ON THE CAPE FEAR RIVER, NC

Since 2009, the 6th order Cape Fear River has experienced summertime blooms of the toxigenic cyanobacteria, Microcystis. Nutrient concentrations and bioassays indicate that nutrients are replete and phytoplankton growth rates are light limited. River flow trends indicate an increasing frequency of summertime low flow events during which thermal stratification can develop upstream of run-of-river dams. At the population level, low flow provides longer transit times for biomass to accumulate. At the cellular level, low flow enhances light availability due to increased water transparency and shallower depths. Reduced vertical mixing and development of thermal stratification can increase or decrease light availability depending on cell buoyancy. A 1-D Lagrangian competition model of positively buoyant Microcystis and a negatively buoyant diatom was developed and reproduced observed blooms based solely on river flow, temperature, and incident irradiance. Sensitivity analyses were used to determine the relative importance of the multifaceted effects of flow regime on Microcystis bloom development. Total phytoplankton biomass was most sensitive to changes in transit time. Microcystis or diatom dominance was most sensitive to changes in vertical mixing imposed by varying bed roughness and inclusion or elimination of a shallow thermocline.

C24 Eutrophication
C01 Algae
S20 Understanding physical controls on cyanobacteria dominance: toward prediction and prevention

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Presenters/Authors

Nathan Hall (), UNC Chapel Hill Institute of Marine Sciences, nshall@email.unc.edu;