Influence of Wind Strength and Duration on Relative Hypoxia Reductions by Opposite Wind Directions in an Estuary with an Asymmetric Channel

Abstract

Computer model experiments are applied to analyze hypoxia reductions for opposing wind directions under various speeds and durations in the north-south oriented, two-layer-circulated Chesapeake estuary. Wind's role in destratification is the main mechanism in short-term reduction of hypoxia. Hypoxia can also be reduced by wind-enhanced estuarine circulation associated with winds that have down-estuary straining components that promote bottom-returned oxygen-rich seawater intrusion. The up-bay-ward along-channel component of straining by the southerly or easterly wind induces greater destratification than the down-bay-ward straining by the opposite wind direction, i.e., northerly or westerly winds. While under the modulation of the west-skewed asymmetric cross-channel bathymetry in the Bay's hypoxic zone, the westward cross-channel straining by easterly or northerly winds causes greater destratification than its opposite wind direction. The wind-induced cross-channel circulation can be completed much more rapidly than the wind-induced along-channel circulation, and the former is usually more effective than the latter in destratification and hypoxia reduction in an early wind period. The relative importance of cross-channel versus along-channel circulation for a particular wind direction can change with wind speed and duration. The existence of month-long prevailing unidirectional winds in the Chesapeake is explored, and the relative hypoxia reductions among different prevailing directions are analyzed. Scenarios of wind with intermittent calm or reversing directions on an hourly scale are also simulated and compared.

Simulating climate change in a coastal watershed with an integrated suite of airshed, watershed, and estuary models

“…The influence of wind direction and velocity is an important episodic control on Chesapeake hypoxia. The 2017 Chesapeake Bay WQSTM provides a good representation of wind effects on estuarine circulation and water quality including the high wind velocity that is effective in mixing the water column and reducing hypoxia (Scully, 2010; Wang et al., 2015; Wang, Wang, Linker, & Hinson, 2016; Wang, Wang, Linker, & Tian, 2016). Changes in wind velocity predicted by the GCM ensemble were assessed for potential inclusion in climate change simulations.…”

Environmental Parameters Related to Hypoxia Development and Persistence in Jinhae Bay from 2011 to 2016 and Their Potential for Hypoxia Prediction

“…Rabalais et al [36] reported that four consecutive hurricanes reduced the hypoxic area of the Gulf of Mexico, which was contrary to forecasts. In the Chesapeake estuary, the wind-induced cross-channel circulation was more effective at de-stratification and hypoxia reduction than the along-channel circulation, by the wind strength and duration [37]. The following section assesses the possibility of hypoxia prediction from the air temperature and rainfall, which were strongly correlated with hypoxia among the climate parameters tested.…”

A data‐driven approach to detecting change points in linear regression models

“…The frequency and severity of low oxygen volumes (hypoxia and anoxia) have been highly variable in past decades and have persisted as a significant environmental problem in Chesapeake Bay. Hypoxia is the dissolved oxygen concentration, often defined as <2 mg/L, at which many aquatic organisms are physically stressed, whereas anoxia corresponds to complete depletion of oxygen, operationally defined as <0.2 mg/L (Diaz & Rosenberg, ; Testa & Kemp, ; Wang, Wang, Linker, & Hinson, ). Reduced oxygen in the bottom water of the Chesapeake occurs naturally due to biological processes, but the extent and severity of hypoxia and anoxia have increased in the past as a result of elevated nitrogen loading into the bay resulting from anthropogenic activities in the watershed (for example, see Hagy, Boynton, Keefe, & Wood, ; Kemp et al, ; Kemp, Sampou, Garber, Tuttle, & Boynton, ; M. Li et al, ; Scully, ; Testa & Kemp, , and the references therein).…”