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- All Subjects: Sargasso Sea
- Creators: Neuer, Susanne
- Creators: Russell, Jazmine Barkley
- Status: Published
Description
Safe, readily available, and reliable sources of water are an essential component of any municipality’s infrastructure. Phoenix, Arizona, a southwestern city, has among the highest per capita water use in the United States, making it essential to carefully manage its reservoirs. Generally, municipal water bodies are monitored through field sampling. However, this approach is limited spatially and temporally in addition to being costly. In this study, the application of remotely sensed reflectance data from Landsat 7’s Enhanced Thematic Mapper Plus (ETM+) and Landsat 8’s Operational Land Imager (OLI) along with data generated through field-sampling is used to gain a better understanding of the seasonal development of algal communities and levels of suspended particulates in the three main terminal reservoirs supplying water to the Phoenix metro area: Bartlett Lake, Lake Pleasant, and Saguaro Lake. Algal abundances, particularly the abundance of filamentous cyanobacteria, increased with warmer temperatures in all three reservoirs and reached the highest comparative abundance in Bartlett Lake. Prymnesiophytes (the class of algae to which the toxin-producing golden algae belong) tended to peak between June and August, with one notable peak occurring in Saguaro Lake in August 2017 during which time a fish-kill was observed. In the cooler months algal abundance was comparatively lower in all three lakes, with a more even distribution of abundance across algae classes. In-situ data from March 2017 to March 2018 were compared with algal communities sampled approximately ten years ago in each reservoir to understand any possible long-term changes. The findings show that the algal communities in the reservoirs are relatively stable, particularly those of the filamentous cyanobacteria, chlorophytes, and prymnesiophytes with some notable exceptions, such as the abundance of diatoms, which increased in Bartlett Lake and Lake Pleasant. When in-situ data were compared with Landsat-derived reflectance data, two-band combinations were found to be the best-estimators of chlorophyll-a concentration (as a proxy for algal biomass) and total suspended sediment concentration. The ratio of the reflectance value of the red band and the blue band produced reasonable estimates for the in-situ parameters in Bartlett Lake. The ratio of the reflectance value of the green band and the blue band produced reasonable estimates for the in-situ parameters in Saguaro Lake. However, even the best performing two-band algorithm did not produce any significant correlation between reflectance and in-situ data in Lake Pleasant. Overall, remotely-sensed observations can significantly improve our understanding of the water quality as measured by algae abundance and particulate loading in Arizona Reservoirs, especially when applied over long timescales.
ContributorsRussell, Jazmine Barkley (Author) / Neuer, Susanne (Thesis advisor) / Fox, Peter (Committee member) / Myint, Soe (Committee member) / Arizona State University (Publisher)
Created2018
Description
Phytoplankton comprise the base of the marine food web, and, along with heterotrophic protists, they are key players in the biological pump that transports carbon from the surface to the deep ocean. In the world's subtropical oligotrophic gyres, plankton communities exhibit strong seasonality. Winter storms vent deep water into the euphotic zone, triggering a surge in primary productivity in the form of a spring phytoplankton bloom. Although the hydrographic trends of this "boom and bust" cycle have been well studied for decades, community composition and its seasonal and annual variability remains an integral subject of research. It is hypothesized here that proportions of different phytoplankton and protistan taxa vary dramatically between seasons and years, and that picoplankton represent an important component of this community and contributor to carbon in the surface ocean. Monthly samples from the Bermuda Atlantic Time-series Study (BATS) site were analyzed by epifluorescence microscopy, which permits classification by morphology, size, and trophic type. Epifluorescence counts were supplemented with flow cytometric quantification of Synechococcus, Prochlorococcus, and autotrophic pico- and nanoeukaryotes. Results from this study indicate Synechococcus and Prochlorococcus, prymnesiophytes, and hetero- and mixotrophic nano- and dinoflagellates were the major players in the BATS region plankton community. Ciliates, cryptophytes, diatoms, unidentified phototrophs, and other taxa represented rarer groups. Both flow cytometry and epifluorescence microscopy revealed Synechococcus to be most prevalent during the spring bloom. Prymnesiophytes likewise displayed distinct seasonality, with the highest concentrations again being noted during the bloom. Heterotrophic nano- and dinoflagellates, however, were most common in fall and winter. Mixotrophic dinoflagellates, while less abundant than their heterotrophic counterparts, displayed similar seasonality. A key finding of this study was the interannual variability revealed between the two years. While most taxa were more abundant in the first year, prymnesiophytes experienced much greater abundance in the second year bloom. Analyses of integrated carbon revealed further stark contrasts between the two years, both in terms of total carbon and the contributions of different groups. Total integrated carbon varied widely in the first study year but displayed less fluctuation after June 2009, and values were noticeably reduced in the second year.
ContributorsHansen, Amy (Author) / Neuer, Susanne (Thesis advisor) / Krajmalnik-Brown, Rosa (Committee member) / Sommerfeld, Milton (Committee member) / Arizona State University (Publisher)
Created2010
Description
The biological carbon pump acts as part of the global carbon cycle through the photosynthetic fixation of inorganic carbon into dissolved and particulate organic carbon by phytoplankton. Previously, the biological carbon pump was attributed to large aggregates and zooplankton fecal pellets since their size and density results in faster sinking rates, efficiently exporting organic carbon to deeper depths in the ocean. However, recent studies have indicated that small cells, known as picoplankton, contribute significantly to the formation of sinking particles. The presence of exopolymeric substances (EPS), among them sticky transparent exopolymeric particles (TEP) and proteinaceous coomassie stainable particles (CSP), serve as influential factors of export flux and aggregation. The presence of heterotrophic bacteria can also affect aggregation and sinking velocity, as seen in previous studies, and is likely attributed to their EPS and TEP production. The staining and visualization of TEP and CSP allow for the qualitative determination of these types of EPS from bacteria isolated from sinking particles collected with particle interceptor traps at various depths in the Sargasso Sea. I study the presence of TEP and CSP in particle-associated bacteria. Cultures of picocyanobacteria, consisting of xenic Synechococcus and axenic Prochlorococcus, were used to establish positive and negative controls for stained isolate analysis. Marinobacter adhaerens served as a tertiary control for an axenic culture that stains positive for TEP. I chose six isolates of bacteria isolated from sinking particles to be stained and visualized to test for the secretion of TEP and CSP. Four of the isolates stained positive for both TEP and CSP, including Pseudoalteromonas sp., Erythrobacter sp., and Marinobacter sp., while one isolate, Micrococcus sp., stained positive only for TEP, and the last isolate, another Marinobacter sp., stained positive for only CSP. These results are important in understanding the role of plankton organisms in the formation of sinking particles.
ContributorsLivar, Britni (Author) / Neuer, Susanne (Thesis director) / Cadillo-Quiroz, Hinsby (Committee member) / Cruz, Bianca (Committee member) / School of Life Sciences (Contributor, Contributor) / Barrett, The Honors College (Contributor)
Created2021-05
Description
The biological carbon pump in the ocean is initiated by the photosynthetic fixation of atmospheric carbon dioxide into particulate or dissolved organic carbon by phytoplankton. A fraction of this organic matter sinks to depth mainly in the form of microaggregates (5-60 μm) and visible macroaggregates. These aggregates are composed of cells, minerals, and other sources of organic carbon. Exopolymeric substances (EPS) are exudated by heterotrophic bacteria and phytoplankton and may form transparent exopolymeric particles (TEP) that act as a glue-like matrix for marine aggregates. Heterotrophic bacteria have been found to influence the aggregation of phytoplankton and in some cases result in an increase in TEP production, but it is unclear if marine heterotrophic bacteria can produce TEP and how they contribute to aggregation. Pseudoalteromonas carrageenovora, Vibrio thalassae, and Marinobacter adhaerens HP15 are heterotrophic marine bacteria that were found associated with sinking particles in an oligotrophic gyre station in the subtropical North Atlantic. These bacteria were grown in axenic cultures to determine growth, TEP production, and aggregation. They were also inoculated into roller tanks used to simulate open ocean conditions to determine their ability to form macroaggregates. Treatments with added kaolinite clay simulated aeolic dust input from the Sahara. M. adhaerens HP15 had the highest TEP concentration but the lowest cell-normalized TEP production at all growth stages compared to the other bacteria. Additionally, M. adhaerens HP15 also had the lowest microaggregate formation. The cell-normalized TEP production and microaggregate formation was not significantly different between P. carrageenovora and V. thalassae. All bacteria formed visible macroaggregates in roller tanks with clay addition and exhibited high sinking velocities (150-1200 m d-1) that are comparable to those of aggregates formed by large mineral ballasted phytoplankton. Microaggregates in the clay treatments declined during incubation, indicating that they aggregated to form the macroaggregates. The findings from this study show for the first time that heterotrophic bacteria can contribute to aggregation and the export of organic carbon to depth in the ocean.
ContributorsLivar, Britni (Author) / Neuer, Susanne (Thesis advisor) / Hartnett, Hilairy (Committee member) / Cadillo-Quiroz, Hinsby (Committee member) / Arizona State University (Publisher)
Created2022