Date Awarded


Document Type


Degree Name

Doctor of Philosophy (Ph.D.)


Virginia Institute of Marine Science


Harry V. Wang

Committee Member

Jian Shen


The shallow water region is an important portion of the estuarine and coastal waters, since it encompasses the entire land-water margin as the buffer zone and supports one of the most productive ecosystems. When light can penetrate to the sediment, it triggers the benthic microalgae community to perform photosynthesis, resulting in a benthic-pelagic exchange flux different from that of the deeper water. This study utilized the laboratory-measured benthic flux, and a suite of well-calibrated numerical models to examine the eutrophication process in the Lynnhaven River Inlet system with special emphasis on: the role played by benthic microalgae, and nutrient budgets (sources, sinks, and pathways) of the system. An unstructured grid hydrodynamic model UnTRIM developed for the shallow water environment was applied to the Lynnhaven to quantify the transport time scale and as the input for the water quality model. Based on the skill assessment result, it was clear that the presence of benthic microalgae is indispensable for an accurate and realistic calibration of the water quality model. Analysis of field samples in the laboratory experiments demonstrated that benthic microalgae performed photosynthesis under light conditions in surficial sediments, resulting in the net uptake of nutrients and the release of oxygen both to the overlying water column and down to the sediment. Based on the results of annual nutrient budgets, it was shown that the major external source for nitrogen and phosphorus was from nonpoint source loadings. There were three comparable sinks: export to the Bay, burial in the deep sediment, and ditrification in the case of nitrogen. One of the major pathways for nitrogen and phosphorus was the internal recycling. The regenerated dissolved nutrients that were recycled in the water column were more than two times larger than the current total nutrient external loadings. Sensitivity tests showed that, due to their retention capacity, benthic microalgae's presence could decrease the overall export to the Bay, enhance the internal recycling, and increase the denitrification rate in the sediment.



© The Author