Impact of Climate Variation and Human Adaptation on the Physical Transport Processes and Water Exchange in Chesapeake Bay

• Main Author: Du, Jiabi
• Format: Text
• Language: English
• Published: W&M ScholarWorks 2017
• Subjects: Oceanography; North Atlantic; North Atlantic oscillation
• Online Access: https://scholarworks.wm.edu/etd/1516639465; https://doi.org/10.21220/V5DN0N; https://scholarworks.wm.edu/context/etd/article/1191/viewcontent/Du_vims_0261D_10017.pdf

The efficiencies of water exchanges in both vertical and horizontal directions reflect the overall impact of various physical processes and serve as important indicators of physical control over a variety of ecological and biogeochemical processes. The vertical exchange between surface layers and bottom layers of a waterbody has proved to exert great control over the hypoxic condition, while the horizontal exchange between an estuary and coastal ocean determines the flushing capacity of the estuary and the retention rate of riverine materials. Various processes, such as tidal flushing, tidal mixing, gravitational circulation, and lateral circulation, can affect water exchange. Therefore, water exchange processes are complex and varying in time and space in estuaries. Besides the impact of numerous forcing variables, large-scale climate oscillation, sea-level rise, and human activities can result in a change of estuarine dynamics. Two biologically relevant timescales, residence time (RT) and vertical exchange time (VET), are used in this study to quantify the overall horizontal and vertical exchange, aiming to understand the physical transport control over the ecosystem functioning in a simpler way. A long-term simulation of VET in the Chesapeake Bay over the period of 1980-2012 revealed a high spatial and seasonal similarity between VET and the dissolved oxygen (DO) level in the mainstem of the Chesapeake Bay, suggesting a major control over the DO condition from the physical transport. Over the past three decades, a VET of about 20 days in the summer usually indicates a hypoxic condition in the mainstem. Strong correlation among southerly wind strength, North Atlantic Oscillation index, and VET demonstrates that the physical condition in the Chesapeake Bay is highly controlled by the large-scale climate variation. The relationship is most significant during the summer, during which time the southerly wind dominates throughout the Chesapeake Bay. By combining the observed DO data with modeled VET, decoupling the ...