Biology Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2749
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Item An evaluation of methods for measuring phytoplankton and ecosystem status in the Chukchi Sea(2020) Neeley, Aimee Renee; Harris, Lora A; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation represents a three-pronged approach for evaluating ecosystem-level changes in the Chukchi Sea: 1) evaluation of uncertainties in field measurements of absorption 2) direct measurements of phytoplankton taxonomy and the community’s interaction with the environment and 3) apply existing and new remote sensing tools to measure ecosystem-level changes over large spatio-temporal scales. The first and final chapters provide context for the dissertation and conclusions. The second chapter quantifies the magnitude of uncertainty within multiple methods for measuring particle absorption. The light field exiting the surface ocean is measured by satellite instruments as ocean color and is impacted by water column absorption. Biogeochemically-relevant products, such as phytoplankton and particle absorption are derived from the light field using algorithms. Therefore, accurate measurements of absorption are critical to algorithm development and validation. I employed a multi-method approach to estimate the precision of measuring optical density of particles on a filter pad using two common spectrophotometric methods, and assessed the uncertainty of the computational techniques for estimating ap. The uncertainty ranged from 7.48%-119%. Values of ap at 555 nm and 670 nm exhibited the highest values of uncertainty. Poor performance of modeled ap compared to measured ap suggests the uncertainties are propagated into bio-optical algorithms. The third chapter investigates the consequences of earlier seasonal sea ice retreat and a longer sea-ice-free season on phytoplankton community composition. The timing of sea ice retreat, light availability and sea surface stratification largely control the phytoplankton community composition in the Chukchi Sea. This region is experiencing a significant warming trend, decrease in sea ice cover, and a documented decline in annual sea ice persistence and thickness over the past several decades. I applied multivariate statistical techniques to elucidate the mechanisms that relate environmental variables to phytoplankton community composition in the Chukchi Sea using data collected during a single field campaign in the summer of 2011. Three phytoplankton groups emerged that were correlated with sea ice, sea surface temperature, nutrients, salinity and light. The fourth chapter evaluates a new remote sensing tool for its utility to trace trends in ocean color over the summer months, 2003-2018, in the Chukchi Sea. The apparent visible wavelength reduces an ocean color spectrum to one number that represents the apparent color of the water. Median trend analysis of apparent visible wavelength and Chlorophyll a indicated that an ecosystem-level change in phytoplankton and nonalgal particles has occurred, correlated with the loss of sea ice.Item RESPONSE OF PLANKTON COMMUNITIES IN COASTAL LAGOONS TO CHANGES IN NUTRIENT QUALITY AND QUANTITY: CASE STUDY OF FLORIDA BAY(2016) Shangguan, Yini; Glibert, Patricia M; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The Comprehensive Everglades Restoration Plan was initiated to return Florida Bay to a more natural ecological state. The C-111 project, one phase of this plan and initiated in 2012, was designed to increase freshwater flow into northern Florida Bay. However, it also alters the nutrient regime and, potentially, phytoplankton biomass and assemblage. This dissertation investigated the combined effects of changes in discharge and nutrient on phytoplankton biomass and assemblage in several interconnected, mesohaline coastal lagoon systems (lakes) of Florida Bay using field observations, mesocosm experiments, and a statistical box model. Field measurements on nutrients and phytoplankton were performed before and after C-111 implementation. After C-111, increased freshwater flow and phosphorus (P) input, but decreased salinity and nitrogen (N) input were observed. One set of the lagoon lakes, previously highly eutrophic (average chlorophyll a >20 ug L-1), had a nearly 50% decline in overall phytoplankton biomass. The other set of lakes, originally oligotrophic (average chlorophyll a <2 ug L-1), had a doubling of phytoplankton biomass. Phytoplankton assemblage in both sets of lakes shifted to picocyanobacteria. Mesocosm experiments (5 independent experiments, 5-10 day duration, 1000 L tanks) were conducted to test the effects of nutrient additions. Phytoplankton biomass increased 3 to 10-fold in the +P treatments (alone or +N), but did not increase substantially in the +N alone treatments. The +N+P treatments, particularly the +NO3-+P at a +N:P molar ratio of 32 led to a 20-fold increase in diatoms, whereas N in the form of +NH4+ yielded a > 2-fold increase in picocyanobacteria. A statistical box model based on relationships measured in the field under different salinity regimes was developed to simulate flow, nutrients, and phytoplankton changes in the eutrophic lake chain. Model output showed that higher freshwater discharge decreased phytoplankton biomass in the upper of the connected lakes, but the lower lake had a high potential to generate algal blooms, which is consistent with the field data. Also, picocyanobacteria tripled following an increase in dissolved organic nitrogen (DON). This study recommends co-management of both P and N, particularly NH4+ and DON in Florida Bay if picocyanobacteria blooms are to be controlled.Item PHYTOPLANKTON AND NUTRIENT DYNAMICS WITH A FOCUS ON NITROGEN FORM IN THE ANACOSTIA RIVER, IN WASHINGTON, D.C. AND WEST LAKE, IN HANGZHOU, CHINA(2016) Jackson, Melanie Leigh; Glibert, Patricia M.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Nutrient loading has been linked with severe water quality impairment, ranging from hypoxia to increased frequency of harmful algal blooms (HABs), loss of fisheries, and changes in biodiversity. Waters around the globe are experiencing deleterious effects of eutrophication; however, the relative amount of nitrogen (N) and phosphorus (P) reaching these waters is not changing proportionately, with high N loads increasingly enriched in chemically-reduced N forms. Research involving two urban freshwater and nutrient enriched systems, the Anacostia River, USA, a tributary of the Potomac River feeding into the Chesapeake Bay, and West Lake, Hangzhou, Zhejiang Province, China, was conducted to assess the response of phytoplankton communities to changing N-form and N/P-ratios. Field observations involving the characterization of ambient phytoplankton communities and N-forms, as well as experimental (nutrient enrichment) manipulations were used to understand shifts in phytoplankton community composition with increasing NH4+ loads. In both locations, a >2-fold increase in ambient NH4+:NO3- ratios was followed by a shift in the phytoplankton community, with diatoms giving way to chlorophytes and cyanobacteria. Enrichment experiments mirrored this, in that samples enriched with NH4+ lead to increased abundance of chlorophytes and cyanobacteria. This work shows that in both of these systems experiencing nutrient enrichment that NH4+ supports communities dominated by more chlorophytes and cyanobacteria than other phytoplankton groups.Item Regulation of estuarine phytoplankton and bacterial urea uptake and urease activity by environmental factors(2006-11-13) Solomon, Caroline Miller; Glibert, Patricia M; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The regulation by environmental factors of two enzymes involved with urea utilization - urea transport and urease - in estuarine phytoplankton and bacteria was studied in cultures of five phytoplankton species, in Chesapeake Bay and Choptank River assemblages, and in bioassay and mesocosm experiments. In these experiments, temperature and nitrogen availability (NO sub 3 minus, NH sub 4 plus, and urea) were found to regulate urea uptake and urease activity. However, regulation by these environmental factors was dependent on the composition of the plankton community. Dinoflagellates were found to have the highest urease activity in culture among five phytoplankton species (Prorocentrum minimum, Karlodinium veneficum, Heterocapsa triquetra, Storeatula major, and Isochrysis sp.) in culture on a per cell and per cell volume basis with an optimized method to measure urease activity. Urease activity was also lower when the dinoflagellates were grown on NH sub 4 plus than when grown on NO sub 3 minus or urea, suggesting repression by NH sub 4 plus. Higher rates of urea uptake and urease activity in Chesapeake Bay and the Choptank River were often associated with the presence of dinoflagellates and cyanobacteria during the warmer months. Rates were also higher under N-limitation when these phytoplankton were present than under P-limitation when diatoms were present. Rates of urea uptake and urease activity in natural assemblages were repressed when NO sub 3 minus and NH sub 4 plus concentrations exceeded 40 and 5 ug at N l to the negative 1, respectively. Rates of urea uptake and urease activity decreased in response to additions of NH sub 4 plus in bioassay and mesocosm experiments. In these experiments, dinoflagellates had the highest urea uptake and urease activity on a per cell basis while cyanobacteria had the highest urea uptake and urease activity on a per cell volume or per chlorophyll a basis. The difference in regulation of urea uptake and urease activity among the diatoms, dinoflagellates and cyanobacteria provide some biochemical explanantions about how they utilize urea under contrasting environmental conditions.Item Climate forcing of phytoplankton dynamics in Chesapeake Bay(2006-05-23) Miller, William David; Harding, Jr., Lawrence W; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Climate has long been recognized as an important driver of phytoplankton dynamics. In Chesapeake Bay, climate variability is manifest as differences in timing and magnitude of freshwater flow. Interannual differences of freshwater flow influence phytoplankton through effects on light and nutrient distributions. Understanding how climate forces temporal and spatial patterns of phytoplankton biomass (Chla) and primary productivity (PP) is an important area of research as we attempt to predict effects of climate change and nutrient enrichment on estuarine ecosystems. This Dissertation describes climate forcing of Chla and PP using a synoptic climatology to quantify climate variability and ocean color remote sensing to assess phytoplankton variability. I developed a synoptic climatology using surface sea-level pressure data for the eastern United States to characterize regional climate because large-scale climate indices are not strongly expressed in this region. The long time series (1989-2004) of remotely sensed ocean color measurements provided high spatial and temporal resolution that allowed me to resolve interannual differences of Chla and PP. I show that the frequency-of-occurrence of synoptic-scale weather patterns during winter explained 54% of the variance in spring freshwater flow to Chesapeake Bay through interannual differences in precipitation and water storage in the basin as snow and ice. Winter weather patterns were also linked to interannual variability of several characteristics of the spring phytoplankton bloom (timing, position, magnitude) through their effects on precipitation and freshwater flow. Multiple linear regression models of winter weather pattern frequencies on regional Chla explained between 23-89% of the variance of the time series. Climate variability in winter-spring also influenced summer and annual integral production through nutrient loading associated with the spring freshet, explaining between 43-62% of the variance of integral production. Finally, I quantified the effects of Hurricane Isabel on Chesapeake Bay phytoplankton dynamics and showed that event-scale climate perturbations can have significant impacts on ecosystem dynamics as well as seasonal and regional carbon cycling. Together these analyses highlight the importance of climate forcing of Chla and PP in Chesapeake Bay and support predictive models that explain significant amounts of the variance of these important ecosystem properties.