Theses and Dissertations from UMD
Permanent URI for this communityhttp://hdl.handle.net/1903/2
New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item Investigating the Microbial Diversity and Ecophysiology of Filamentous Cyanobacteria on the Susquehanna Flats, Chesapeake Bay(2024) Keller, Shayna Aryn; O'Neil, Judith M; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The Susquehanna Flats is a biodiverse and resilient submerged aquatic vegetation (SAV) bed just below the mouth of the Susquehanna River in the Chesapeake Bay. The Susquehanna River, the largest tributary of the Chesapeake Bay, discharges more water than all other tributaries in the Bay combined. This makes the SAV bed at the Susquehanna Flats important for nutrient removal of the water discharged into the headwaters of the Bay. The Susquehanna Flats is also a unique part of the oligohaline portion of the Chesapeake Bay as it is one of the most prolific and diverse SAV beds that make up ~8% of SAV in the Chesapeake Bay. The SAV bed was devastated by Hurricane Agnes in 1972 and did not reappear until the early 2000s when an extended dry period and long-term reductions in nutrient loading facilitated its resurgence. Since then, it has recovered to be the most abundant and biodiverse SAV bed within the upper Chesapeake Bay. However, a nitrogen fixing filamentous Cyanobacteria, morphologically identified as Microseira (Lyngbya) wollei, has seasonally bloomed at the Susquehanna Flats since the early 2000s. Over the ensuing decade, anecdotal evidence suggested an overall increase of Cyanobacteria on the SAV beds on the Susquehanna Flats, which raised concerns about the impact of this growth on the resilience of the recovering SAV bed. Despite the consistent summer blooms, the filamentous Cyanobacterial mats and its microbiome at the Susquehanna Flats has not been molecularly identified and its characteristics have not been investigated to date. Additionally, new DNA sequencing technology has become more readily available, and the identification and taxonomy of the Cyanobacteria family Oscillatoriaceae, of which Microseira (Lyngbya) wollei is a part of, has become more refined and organized. Due to this, molecularly identifying the filamentous Cyanobacterial mats and investigating its microbiome has become much easier with current methods that can provide detailed taxonomic information that can help implement management strategies. Using PacBio long-read amplicon sequencing on the 16S rRNA genes and Illumina short-read amplicon sequencing on the nifH genes of the filamentous Cyanobacteria mats and a newly observed mucilaginous Cyanobacteria mat collected at the Susquehanna Flats, the host organisms and microbial compositions were revealed. The results indicate that the dominant filamentous Cyanobacterial mat host is Microseira (Lyngbya) wollei and these mats contain a complex microbial community. The host of a newly observed mucilaginous mats was revealed to be a novel strain of Phormidium sp. To understand the basic nutrient requirements and preferences of the Microseira (Lyngbya) wollei at the Susquehanna Flats, nutrient bioassay growth and nitrogen fixation experiments were initiated to assess its growth and nitrogen fixation qualities. Samples received nutrient treatments of nitrate, phosphate, nitrate + phosphate, and ammonium compared to the growth of control samples that did not receive nutrient treatments in the summers of 2022 and 2023. The results demonstrated that Microseira (Lyngbya) wollei has variable growth rates, with higher rates in the mid to late part of the summer season, with significant growth stimulations from added nitrogen and phosphorus. In terms of nitrogen fixation, rates were higher in the beginning of the season, with significant stimulation with phosphorus additions. It is likely that lower rates measured at the end of the season, were due to the increased availability of regenerated nitrogen within the system. More detailed investigation of the seasonal nutrient dynamics are warranted to fully understand the dynamics between these Cyanobacterial mats and the SAV beds.