The Development and Proliferation of Summer Algal Blooms in the Oligo/Polyhaline Portion of the Chesapeake Bay - Observational and Numerical Modeling Studie

Algal blooms occur annually in many parts of the Chesapeake Bay. The causes of algal blooms are complex and can be different in different regions. In this study, we will conduct data analysis for the observed data and adopt various methods to investigate algal bloom phenomenon in three separate regions in the oligo/poly-haline portion of the Bay. Chapter 1 provides a general introduction of the algal bloom research in the Chesapeake Bay.;In Chapter 2, an observational analysis and a numerical study on the algal blooms in Back River were conducted. A hypothesis was made that high pH can trigger sediment phosphorus release, which in turn can enhance chlorophyll-a and further increase pH to form a positive feedback loop. To test this theory, water quality model ICM coupled onto SCHISM was applied in Back River to study the phenomenon. Moreover, a pH model was developed to describe the aquatic chemistry. The model results with and without pH model were compared with Bay Program observations for verifying our hypothesis. It proves the importance of sediment phosphorus release on the algal blooms in Back River.;In Chapter 3, a theoretical study combined with data analysis on cyanobacteria blooms dynamics was conducted in the upper tidal James River. The theory integrates the physical transport and biological effects, which leads to a simple governing equation composed of an advection term and a phytoplankton net growth term, in both linear and nonlinear forms. In this study, we derived a general analytic solution to the equation. Then, we applied the theory in the tidal freshwater portion of the James River. The theoretical predictions of chlorophyll concentrations were compared with observational data and verified the validity of the solution. In addition, the factors related to the local chlorophyll maximum in tidal freshwater rivers were discussed.;In Chapter 4, an observational analysis and numerical experiments were performed to investigate the algal bloom in the polyhaline of the Chesapeake Bay. This exploratory study is aimed to explain the broad distribution of C. polykrikoides blooms in the lower Bay and the sudden disappearance of the bloom in 2014. A hypothesis is made regarding the origin of C. polykrikoides cysts. In this hypothesis, the cysts are considered to be originated from coastal ocean and their transport is under the influence of wind patterns and gravitational circulation. In this study, the hydrodynamics in the lower Chesapeake Bay was first analyzed. Then, a series of particle tracking experiments were conducted for investigating the physical transport of C. polykrikoides cysts under different environmental conditions. Finally, water quality model ICM was used to simulate the algal blooms caused by C. polykrikoides in the lower Bay by incorporating the biological features of C. polykrikoides. The model can generate reasonable magnitude of the algal blooms in 2012, 2013 and simulate no algal bloom condition in 2014.The result indicates that C. polykrikoides cysts could be originated from the coastal ocean, while temperature and wind patterns play important roles in further controlling the subsequent development of the blooms.