6/06/2017  |   11:00 - 11:15   |  306B

Predicting cyanobacteria dominance in a shallow eutrophic reservoir Cyanobacteria blooms are increasingly recognized as a threat to the integrity of freshwater reservoirs, diminishing their value as water supplies, wildlife habitats, and recreational areas. While cyanobacteria have been studied for decades, our ability to predict and mitigate the formation of these blooms remains limited. In this study, we explore factors driving cyanobacteria dominance in a shallow eutrophic reservoir in the southeastern United States (Jordan Lake). Our ongoing study focuses on linkages between blooms, artificial mixing, and climate variability; as understanding these relationships is critical to cyanobacteria management. Here, we present results from a multi-year monitoring effort of the reservoir’s thermal regime, mixing rates, phytoplankton, and other water quality characteristics. Based on the thermal regime data and meteorological inputs, we develop a mechanistic turbulent diffusion model that is applied to estimate temperature and vertical mixing rates throughout time. Furthermore, we develop a multi-level statistical model to explore relationships among cyanobacteria, mixing, and other biophyiscal factors. Current results indicate that vertical mixing may play an important role in modulating cyanobacteria dominance, though additional data and modeling are required to better isolate the different mechanisms affecting bloom formation.

Daniel Obenour (Primary Presenter/Author), NC State University, drobenour@ncsu.edu;


Yue Han ( Co-Presenter/Co-Author), NC State University, yhan10@ncsu.edu ;


Jeremy Smithheart ( Co-Presenter/Co-Author), NC State University, jwsmithh@ncsu.edu;


Robyn Smyth ( Co-Presenter/Co-Author), Bard College, rsmyth@bard.edu;


Tarek Aziz ( Co-Presenter/Co-Author), NC State University, tnaziz@ncsu.edu;


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6/06/2017  |   11:15 - 11:30   |  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.

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


Hans Paerl ( Co-Presenter/Co-Author), UNC Chapel Hill Institute of Marine Sciences, Hans_Paerl@unc.edu;


Scott Ensign ( Co-Presenter/Co-Author), Stroud Water Research Center, ensign@stroudcenter.org;


Daniel Wiltsie ( Co-Presenter/Co-Author), NC State University, dpwiltsi@ncsu.edu;


Astrid Schnetzer ( Co-Presenter/Co-Author), NC State University, aschnet@ncsu.edu;


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6/06/2017  |   11:45 - 12:00   |  306B

A Novel Water Column Reactor for Exploring the Effects of Mixing on Harmful Algal Blooms The formation of harmful algal blooms (HABs) in freshwater systems is an increasingly common occurrence. HABs produce a range of negative consequences from taste and odor issues in drinking water to the endangerment of human and ecosystem health. Artificial mixing has been utilized in several reservoirs as a means for source water control, however our understanding of the effects of mixing on phytoplankton community dynamics is limited due to the numerous factors effecting mixing and phytoplankton in natural systems. Our research group has built a novel, laboratory-based Water Column Reactor (WCR) to mimic shallow lake conditions in an aim to better understand the effects of mixing on phytoplankton community dynamics. The WCR is 2 m tall and has a diameter of approximately 30 cm. 14 ports are evenly spread to facilitate nutrient addition and sampling at variable depths. An artificial light source allows the growth of algal species through photosynthesis. A flexible mixing system will allow the exploration of variable mixing depths and intensities. In this presentation, we will discuss the development and configuration of this system as well as results from preliminary testing with cyanobacteria.

Tarek Aziz (Primary Presenter/Author), NC State University, tnaziz@ncsu.edu;


Alexandre Mangot ( Co-Presenter/Co-Author), NC State University, amangot@ncsu.edu;


Daniel Obenour ( Co-Presenter/Co-Author), NC State University, drobenour@ncsu.edu;


Astrid Schnetzer ( Co-Presenter/Co-Author), NC State University, aschnet@ncsu.edu;


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6/06/2017  |   12:00 - 12:15   |  306B

Periodic wind mixing enhances cyanobacterial dominance in large, shallow, eutrophic Lake Taihu, China Harmful blooms of cyanobacteria (CyanoHABs) have increased globally. Cyanobacterial dominance is controlled not only by nutrient supplies but also by physical processes induced by wind. Using field observations and mesocosm bioassay experiments, we investigated the impact of turbulence generated by wind on the phytoplankton community composition in large, shallow eutrophic Lake Taihu, China. During summer, when wind waves were strong in central lake, diatoms and green algae seemed to dominate while cyanobacteria dominated in more sheltered, highly eutrophic Meiliang Bay. Bioassays showed phytoplankton only grew well within the upper 1 meter of the water column in Lake due to high turbidity. Turbulence-induced bioassays showed that diatoms and green algae were favored by continuous turbulent mixing. However, short-term intermittent turbulence enhanced dominance by cyanobacteria. Increased water depth following the early summer monsoon reduced the influence of turbulence on phytoplankton biomass and composition. Climatice changes have led to warming and lower wind speeds in Taihu basin. Resultant enhanced stratification enhanced dominance by buoyant CyanoHAB species. This study suggests that the duration of wind events and their associated hydrodynamics are key factors for cyanobacterial dominance in Taihu.

HAI XU (Primary Presenter/Author), Nanjing Institute of Geography & Limnology, Chinese Academy of Sciences, hxu@niglas.ac.cn;


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6/06/2017  |   12:15 - 12:30   |  306B

RISE AND FALL OF TOXIC BENTHIC FRESHWATER ANABAENA: BUOYANCY AND DISPERSAL Freshwater benthic cyanobacteria in rivers produce cyanotoxins and affect aquatic food webs, but knowledge of their ecology lags behind planktonic cyanobacteria. The buoyancy of benthic cyanobacterial mats was studied to understand implications for dispersal and the spread of harmful algal blooms in the Eel River, California. Field experiments were used to investigate the effects of oxygen bubble production and dissolution on the buoyancy of benthic algal mats dominated by Anabaena in response to light and dark exposure. Floating and sinking occurred within minutes and were driven by photosynthesis, rather than intracellular changes in carbohydrates or gas vesicles. Light experiment results showed that in a natural light regime, mats remain floating for at least 4 days, while in the dark mats begin to sink in <24 hours. Floating Anabaena samples were collected from 5 sites in the watershed and found to contain the cyanotoxins anatoxin-a and microcystin, with higher concentrations of anatoxin-a than microcystins. Maintaining buoyancy for days, the presence of bubbles in Anabaena mats will markedly increase their downstream dispersal distances over negatively buoyant taxa, threatening human and animal public health in rivers where cyanotoxin producing Anabaena mats occur.

Keith Bouma-Gregson (Primary Presenter/Author), U.S. Geological Survey, kbouma-gregson@usgs.gov;


Mary Power ( Co-Presenter/Co-Author), University of California, Berkeley, mepower@berkeley.edu;
Dr. Mary E. Power is Professor in the Department of Integrative Biology at the University of California, Berkeley. She was awarded an honorary doctorate by Umea University, the Kempe Medal for distinguished ecologists, and the Hutchinson Award from the American Society of Limnologists and Oceanographers. She is a member of the California Academy of Science, the American Academy of Arts and Sciences, and National Academy of Sciences, USA. She has served on the Editorial Board of PNAS (2014 to present) and Science (2006-2009). Mary also served as President of the American Society of Naturalists, and of the Ecological Society of America. Since 1988, she has been the Faculty Director of the Angelo Coast Range Reserve, (one of the UC Natural Reserve System sites, a 3500 ha reserve protected for university teaching and research). She has studied food webs in temperate and tropical rivers, as well as linkages of rivers, watersheds and near-shore environments. Focal organisms include cyanobacteria, algae, invertebrates, fish, estuarine crustaceans and terrestrial grasshoppers, spiders, lizards, birds and bats. By studying how key ecological interactions depend on landscape and temporal contexts, her group hopes to learn how river-structured ecosystems will respond to changes over space and time in climate, land use, and biota. Her group also collaborates closely with Earth and atmospheric scientists in site-based research to investigate linkages among riverine, upland, and near-shore ocean ecosystems.

Myriam Bormans ( Co-Presenter/Co-Author), University of Rennes, myriam.bormans@univ-rennes1.fr;


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