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Item Long-term and over winter phytoplankton community dynamics in Lake Bonney, Antarctica(Montana State University - Bozeman, College of Agriculture, 2017) Patriarche, Jeffrey Dennis; Chairperson, Graduate Committee: John C. PriscuLake Bonney is a hypersaline permanently ice-covered lake in the Taylor Valley, Antarctica that hosts simplified microbial food-webs. Studied since the 1960s, there are many aspects which are poorly understood. Logistical constraints have prevented sampling during the austral winter, a 4-month period of 24-hour darkness. Our knowledge of how the resident photosynthetic microorganisms respond during this period is limited. With inputs from ephemeral glacial-melt streams the lake level (stage) of Bonney has risen more than 3 m since 2004. With no outflow streams, the only known water loss is via ablation of the permanent ice-cover. A study of the spatial and temporal changes in the phytoplankton community structure during this period of rapid lake level rise is lacking. During the summers (November-January) from 2004-05 to 2014-15 an in situ submersible spectrofluorometer was deployed in Lake Bonney to quantify the chlorophyll-a concentrations (microgram L -1) of four functional groups of microalgae (green algae, brown/mixed algae, cryptophytes, cyanobacteria) using known excitation/emission spectra. During the 2013-14 field season this same instrument was mounted on autonomous cable-crawling profilers deployed in both east and west lobes of Lake Bonney, obtaining the first ever daily profiles of chlorophyll-a concentration at an annual scale. Following a summer of rapid lake level rise (2010-11), an increasing trend in depth integrated chlorophyll-a concentration was observed in Lake Bonney. During the same period, the nutrient poor surface water has become increasingly dominated by green algae. Dramatic shifts were also observed in the phytoplankton communities during the polar night. The highest concentrations of mean chlorophyll-a were measured during the 24-hour darkness. Algal spectral groups containing species capable of a mixotrophic metabolism (brown/mixed and cryptophytes) increased in concentration and relative abundance when photosynthetically active radiation was unavailable. This work provides valuable contributions to our knowledge of long-term and year-round phytoplankton community dynamics in Lake Bonney, and improves our understanding of the metabolic strategies employed by organisms in this high latitude permanently ice-covered lake.Item Spatial and temporal variations of phytoplankton populations in Lake Bonney, Antarctica(Montana State University - Bozeman, College of Agriculture, 2003) Tursich, Nicole LeaItem Diversity, productivity, and physiology of microorganisms in the stream-moat-lake transition of Lake Bonney, Antarctica(Montana State University - Bozeman, College of Agriculture, 2007) Moore, Joel Grant; Chairperson, Graduate Committee: John C. Priscu.Air temperatures exceeding 0°C in Taylor Valley, Antarctica 17-25 degree days each summer and constant solar irradiance melt glacial and lake ice to from liquid water moats at the edges of permanently ice-covered lakes. Moats are fed by glacial streams and interact with comparatively large volumes of ice-covered lake water. This study investigated stream influence on moat chemistry and microbial biomass, productivity and diversity in the moat of East Lake Bonney (ELB) and compared the moat to the ice-covered portion of ELB. Stream inflow was a source of dissolved ions, inorganic carbon (DIC) inorganic nitrogen (DIN), and soluble reactive phosphorus (SRP) to the moat. SRP was rapidly removed in the moat near the stream inflow. Melted ELB ice and biological uptake reduced concentrations of DIN and DIC, resulting in a negative relationship to the inflow. Stream nutrients were correlated with high chlorophyll a and bacterial biomass near the inflow, were positively correlated with bacterial diversity, and negatively correlated with phytoplankton diversity. Correlations between nutrient availability and microbial biomass suggest resource limitation with respect to DIN and SRP, and infer dependence of heterotrophic bacterioplankton on primary productivity.