Wind effects on the spring phytoplankton dynamics in the middle reach of the Chesapeake Bay

•Phytoplankton tended to accumulate on the western flank of the middle bay.•The average mid-bay phytoplankton biomass was negatively related to stratification.•The up-estuary (southerly) winds were effective in enhancing the spring bloom.

The spring phytoplankton bloom, bridging nutrient loading and summer hypoxia in the Chesapeake Bay especially in its middle reach, is highly sensitive to physical forcing. In addition to riverine input, winds could be a noticeable driver of estuarine phytoplankton variability, affecting its water quality and ecosystem health. In this study, wind impacts on the spring bloom were investigated utilizing the 29-year (1985-2013) monitoring data and an existing FVCOM-ICM estuarine water quality model. The retrospective analysis revealed that winds exerted a significant control on the spring algal biomass in the middle bay, which could be as important as the effects of riverine inputs. According to the model simulation, the mid-bay spring algal bloom was mainly fueled by the riverine nutrients, and its biomass was higher on the western than that on the eastern flank. Numerical experiments indicated a negative relationship between stratification and the overall algal biomass. It was found that up-estuary (southerly) winds could induce upwelling, thus enhance primary production along the western shore, and increase phytoplankton transport to deeper waters, making up-estuary winds most effective in the mid-bay transverse phytoplankton enrichment. Given that the regional wind pattern is tightly coupled with the large-scale climatic variability, it is recommended to fully consider climatic effects on the lower food web in ecosystem management in the future.