CARBON AND NITROGEN SOURCES AND CYCLING IN PLANKTONIC MARINE ECOSYSTEMS
CARBON AND NITROGEN SOURCES AND CYCLING IN PLANKTONIC MARINE ECOSYSTEMS
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Date
2010
Authors
Keller, David Peter
Advisor
Hood, Raleigh R
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DRUM DOI
Abstract
Carbon and nitrogen are involved in many important biological and
environmental processes and can even influence the global climate (i.e. CO2 as a
greenhouse gas). In this dissertation the role of dissolved organic matter (DOM) in
marine C and N cycling is studied. Research is also presented that looks at
phytoplankton as potential sources of C and N in the upper Chesapeake Bay estuary
food web.
To better understand DOM cycling a model was constructed to simulate
dissolved organic carbon (DOC) and nitrogen (DON) cycling in marine surface
waters. Using the model DOM cycling was simulated in the context of: (1) a steady-
state comparison of idealized oceanic, coastal, and estuarine ecosystems, (2) the
seasonal cycle in eutrophic waters, and (3) a focus on the roles of viruses and
microzooplankton. The results suggest that DOM cycling is intricately tied to the
biomass concentration, ratio, and productivity of phytoplankton, zooplankton,
viruses, and bacteria. The first set of simulations highlights the importance of certain
processes in each ecosystem. The second set of simulations shows how DOM
cycling, particularly the sources of DOM, changes seasonally. The third set of
simulations highlights differences in the top-down and bottom-up roles of viruses and
microzooplankton and their subsequent effect on DOM cycling and trophic
interactions.
To better understand C and N cycling in the upper Chesapeake Bay the
biomass distribution and floral composition of the phytoplankton community was
studied during the winter and spring to determine if phytoplankton could play an
important role in the estuarine turbidity maximum (ETM) food web. This research
suggests that the general distribution of phytoplankton in the upper Bay is somewhat
like a classic estuarine "salt wedge" diagram with two distinct phytoplankton
communities separated by a zone of increased mortality due to salinity stress and
ETM entrapment. High concentrations of phytoplankton pigment degradation
products were often observed in the ETM suggesting that this is an area of high
phytoplankton mortality and/or an area where phytoplankton derived particulate
organic matter was being concentrated. These results suggest that phytoplankton
have the potential to play an important role in C and N cycling and the ETM food
web.