A modeling study of the initiation of harmful algal blooms (HABs) in an estuary-subestuary system
Abstract:
The developed mathematical model describes the spatial distribution of the algal density during HAB initiation, as a result of physical-biological interactions, in a system with multiple inter-connected waterbodies. The theoretical analysis indicates that the model exists stable fixed points for spatial density gradients, and the associated equilibrium values of density ratios of two connected waterbodies are largely controlled by the flushing effect of physical transport processes. Flushing is revealed to be one key factor determining the locations of HAB initiation, and a HAB tends to appear early in locations with relatively large ratios of residence time to volume. The model explains well commonly observed distribution of HAB originating locations in the Bay.
To fully study critical environmental factors controlling the HAB initiation and interactions between physical and biological processes, a numerical HAB module is developed for C. polykrikoides, which considers those strategies including mixotrophy, vertical migration, grazing suppression, and resting cyst germination. The module is built into a physical-biogeochemical 3D model and applied to study C. polykrikoides blooms in the lower James River estuary. Results highlight that the mixotrophic growth is important to maintain a high growth rate of C. polykrikoides in this region, and confirm that the Lafayette River, a tributary of the James, is a primary originating location. Results also suggest that temperature and flushing are the two dominant factors controlling the interannual variability in the timing of bloom initiation (> 1 month) in the Lafayette River for the study period (2005-2013).