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Linking dynamics of transport timescale and variations of hypoxia in the Chesapeake Bay
Author(s) -
Hong Bo,
Shen Jian
Publication year - 2013
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
eISSN - 2169-9291
pISSN - 2169-9275
DOI - 10.1002/2013jc008859
Subject(s) - chesapeake bay , hypoxia (environmental) , oceanography , environmental science , dynamics (music) , estuary , geology , chemistry , physics , oxygen , organic chemistry , acoustics
Dissolved oxygen (DO) replenishment in the bottom waters of an estuary depends on physical processes that are significantly influenced by external forcings. The vertical exchange time (VET) is introduced in this study to quantify the physical processes that regulate the DO replenishment in the Chesapeake Bay. A 3‐D numerical model was applied to simulate the circulation, VET, and DO. Results indicate that VET is a suitable parameter for evaluating the bottom DO condition over both seasonal and interannual timescales. The VET is negatively correlated with the bottom DO. Hypoxia (DO <2 mg L −1 ) will develop in the Bay when VET is greater than 23 days in summer if mean total DO consumption rate is about 0.3 g O 2 m −3 d −1 . This critical VET value may vary around 23 days when the total DO consumption rate changes. The VET volume (volume of water mass with VET >23 days) can account for 77% of variations of hypoxic volume in the main Bay. The VET cannot explain all the DO variations as it can only account for the contribution of physical processes that regulate DO replenishment. It is found that the short‐term vertical exchange process is highly controlled by the wind forcing. The VET volume decreases when the high‐speed wind events are frequent. The summertime VET volume is less sensitive to short‐term variations (pulses) of river discharge. It is sensitive to the total amount of river discharge and the high VET volume can be expected in the wet year.