Browsing by Subject "Algae"
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Item Open Access Algae and Coal: Turning Pollution Into Prosperity(2010-04-30T20:31:58Z) McNamara, PatrickAlgae have long been researched as a potential source of biodiesel and biofuel because of their quick growth rate, simple inputs and ability to grow under environments unsuitable for many other plants. Using a Monte Carlo simulation, this analysis examines the circumstances under which an algae farm might become profitable now and in the future. The use of CO2 from fossil fuels, specifically coal-fired power plants, is potentially valuable for both the utility and the algae farm because algae require large amounts of CO2 for their high growth rates. My results show that the success of algae farms in the United States is currently unprofitable in the short and mid-term (five to ten years). Moreover their long term profitability is heavily dependent on the system design, fuel prices, location, the existence and increase of prices being placed on air pollutants such as CO2 and NOX, as well as successive scientific breakthroughs under reasonable assumptions.Item Open Access Evaluation of a Benchmark Model of Microalgae productivity towards Global Implementation(2020-04-24) Fils-aime, GuerbineAs climate change is better understood, numerous studies have identified technologies to help mitigate the negative effects of excess atmospheric carbon dioxide. Among these net negative carbon footprint technologies is marine microalgae, which has zero freshwater and arable land requirements and utilizes resources efficiently. This study assessed the fidelity of a benchmark algae production model in an effort to provide tools to optimize and expand this new source of sustainable fuels, feed and food. When comparing model estimations to real values, we found that this model consistently overestimated the algae biomass values even when accounting for key abiotic factors such as temperature, pH, and sunlight. The main assumptions of the model that were violated were maximum growth indicator, algae efficiency, and carbon to nitrogen ratio. Further studies are needed to find ways to make the model more accurate to predict biomass.Item Open Access Seasons in the Stream: River Ecosystem Phenology in a Changing Climate(2023) Thellman, Audrey NicolePatterns of primary productivity are primarily dictated by seasonal factors like light availability and temperature. In small rivers, primary productivity often peaks opposite that of terrestrial ecosystems, where overhanging canopies shade the river channel impeding light reaching the water surface. The degree to which river primary productivity is affected by the surrounding terrestrial environment depends on the river size. As rivers widen, river primary productivity increases, with more light reaching the stream channel. While light availability may set up the “window of metabolic opportunity” for river primary producers, factors like flow disturbance and grazing pressure from invertebrates can constrain the overall magnitude of gross primary productivity, or GPP. My dissertation seeks to evaluate what processes control the pattern and magnitude of primary productivity in rivers. I evaluate this driving question by analyzing the efficiency by which river ecosystems convert light energy into autotrophic biomass across 64 rivers (Chapter 2), through a series of in-depth experiments and careful monitoring of algae in a small forested river (Chapter 3), and in evaluating whether ice cover determines patterns of primary productivity along a river continuum (Chapter 4). Finally, I provide a framework for evaluating how climate change may be impacting the patterns of primary productivity in rivers (Chapter 5). In Chapter 2, we found that rivers are extremely efficient at converting light energy to biomass (i.e. have a high ecosystem light use efficiency, LUE). The range of LUEs reported in our study encompasses the entire range for any ecosystem LUE measured in forests, crops, lakes, and previous river studies. While river ecosystems have the potential to have high LUE on their “best days,” variability of flow constrains LUE throughout the year. In Chapter 3, we found that algae in the oligotrophic and steep headwaters of Hubbard Brook Experimental Forest were both more abundant than past studies and preferentially grew within substrates that simulate the physical structure of bryophytes. Throughout four separate nutrient diffusing substrate deployments, we found that nutrients rarely limited algal biomass. This chapter explores the previously unsuspected role of bryophytes in providing refugia for algae in this high-gradient and nutrient-poor stream. In Chapter 4, we combined three metrics of ice cover (satellite-, field camera-, and temperature-based) with a proxy for primary productivity across a river continuum. We found that satellite and field camera-based ice cover records reveal two important aspects of ice dynamics in a 3rd to 6th Strahler order river. First, river ice in narrow channels is dynamic, with more complete ice cover days and mid-winter breakups happening on the narrowest section of the reach. Second, ice cover is habitat-specific, with riffle sequences along the river never reaching complete ice cover. In comparing ice dynamics to a proxy of GPP, diel dissolved oxygen amplitude, we found that ice on rivers not only affects the overall pattern of primary productivity, but also affects our ability to measure primary productivity by affecting river gas exchange. Finally, in Chapter 5, I provide examples of relevant drivers of change for river ecosystem GPP in a warming climate. More studies that attempt to disentangle how climate change is affecting light availability, nutrients, temperature, ice cover, etc., or how climate change is shifting the “windows of metabolic opportunity” for rivers, will be imperative in the Anthropocene.
Item Open Access Top-Down Effects of Keystone Grazers on Benthic Macroalgae in Eastern Salt Marshes(2017-05-08) Loftus, KathrynBoth bottom-up and top-down forces can shape plant communities. In southern salt marshes, macroalgal growth is thought to be primarily controlled by bottom-up forces such as nutrients and physical factors. However, I noticed that Ulva lactuca, the green sea lettuce, showed heavy damage from grazing when it grew in the lower intertidal in salt marshes. In this study, I used experiments and observation work to test if two commonly occurring snails, Littoraria irrorata and Ilyanassa obsoleta, could control U. lactuca biomass in salt marshes. To test for top-down control, I employed field surveys, conducted feeding experiments, and analyzed data from a previously conducted field experiment. Lab experiments showed that both snails commonly graze on U. lactuca. Field experiments that excluded snails showed snails exert top-down control of marcoalagal growth. When snails were removed, biomass and percent cover increased throughout the summer, reaching a high of 91.33% and 64.16 g/m2 in August, respectively. In cages where snails were multiplied, biomass and percent cover of algae decreased throughout the summer, falling to 1.67% and 5.8 g/m2 in August, respectively. These results show that macroalgae in salt marshes are under strong top-down control, and suggest grazers, rather than physical stress, could account for the lower abundance of U. lactuca in salt marshes.