Biology Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2749
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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 Plant-sediment Interactions and Biogeochemical Cycling for Seagrass Communities in Chesapeake and Florida Bays(2007-12-17) Nagel, Jessica; Kemp, William M; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Seagrasses are prominent, productive components of shallow coastal ecosystems worldwide. The role of seagrasses in biogeochemical cycling varies widely across ecosystems, and this is due in large part to the complex interactions and feedbacks among processes controlling dynamics of carbon, oxygen, nutrients, and dissolved organic matter (DOM). This dissertation examines the importance of the keystone seagrass species, Thalassia testudinum, to biogeochemical cycling at the community and ecosystem levels in Florida Bay. The research presented here also describes the consequence of disturbances, such as shifts in species composition and seagrass dieback, on biogeochemical processes in both Florida and Chesapeake Bays. In Florida Bay, T. testudinum was shown to stimulate sediment microbial activities and benthic production of oxygen, inorganic nitrogen, and DOM relative to adjacent benthic communities without seagrass but containing benthic microalgae. Strong diel patterns in net fluxes of these solutes in both communities underscore the importance of photosynthesis. Ecosystem-level production (P) and respiration (R) rates were also enhanced in T. testudinum communities. Clear seasonal and regional variations in P and R were evident across Florida Bay, with lowest rates reported in the northern regions. Seagrass dieback had a negative effect on sediment nitrification rates and net ecosystem production (P-R) at one site in Florida Bay, and loss of seagrass habitat may result in significant changes to biogeochemical budgets within this system. In mesohaline Chesapeake Bay, the ephemeral submersed plant species, Ruppia maritima was also shown to stimulate organic production, nutrient cycling, and sediment biogeochemical processes compared to benthic communities without seagrass; however, the more persistent native species, Potamogeton perfoliatus, had an even greater impact on these processes. Collectively, the results of this research reveal the potential significance of seagrass to biogeochemical cycling in Chesapeake and Florida Bays and suggest that disturbances, such as seagrass dieback or shifts in species composition, may substantially alter biogeochemical budgets within these systems.