Date of Award

Winter 2008

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Ocean & Earth Sciences

Committee Director

Margaret R. Mulholland

Committee Member

Richard C. Zimmerman

Committee Member

Larry P. Atkinson

Committee Member

Antonio Mannino

Committee Member

Gary Schafran

Abstract

Seasonally resolved nutrient and carbon fluxes from estuaries to the coastal ocean are poorly constrained. Nutrient and carbon cycling in highly productive regions like the Chesapeake Bay outflow plume and surrounding coastal environments greatly affect our global understanding of carbon cycling. The overall questions for the research described in this dissertation stem from the need to close global carbon budgets, and obtain a fundamental understanding of nutrient dynamics in a coastal region heavily influenced by seasonality and human impacts.

Within the framework of physical characteristics of the outflow plume and through the characterization of nutrient concentrations, primary productivity rates, and the uptake of nitrogen using stable isotopes, I identified three different plume types that differentially provided nutrients and created conditions either suitable or unsuitable for primary productivity in the coastal zone. A jet-like plume, where there were winds consistently from the north accompanied by high freshwater flow from the Bay, delivered high amounts of chlorophyll from the Bay. In contrast, two types of diffusive plumes occurred when winds came from the south accompanied with low freshwater discharge and were either influenced by estuarine or oceanic processes. The diffusive-estuarine plume delivered dissolved nutrients creating conditions suitable for high primary productivity rates in the coastal zone while the diffusive-oceanic plume generally had low primary productivity and nitrogen uptake rates.

A secondary study compared and contrasted hydrography, nutrient availability, primary productivity rates and nitrogen uptake rates in three distinct regions of the Mid-Atlantic Bight: the plume regions influenced by the Delaware and Chesapeake Bays, the mid-shelf region between the Delaware and Chesapeake Bays influenced by both coastal and oceanic processes, and the southern shelf region below the Chesapeake Bay influenced by the Gulf Stream. Areal rates of carbon uptake were not significantly different among regions, and were higher than most published values of annual areal rates for the Mid-Atlantic bight. Annual areal nitrogen uptake rates were also calculated, providing carbon to nitrogen uptake ratios which were lower than the canonical Redfield ratio. These findings have implications regarding modeled estimates of carbon uptake based on nitrogen uptake and vice versa.

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DOI

10.25777/fq40-ym57

ISBN

9780549928560

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