Abstract
Field observations were collected near the mouth of the Bagaduce River, Maine, in order to understand how complex features affect the intratidal and lateral variability of turbulence and vertical mixing. The Bagaduce River is a low-inflow, macrotidal estuary that features tidal islands, tidal flats and sharp channel bends. Profiles of salinity, temperature, and turbulent kinetic energy dissipation (ε) were collected for a tidal cycle across the estuary with a microstructure profiler. Lateral distributions of current velocities were obtained with an acoustic doppler current profiler. Results showed intratidal asymmetries in bottom-generated vertical eddy diffusivity and viscosity, with larger values occurring on ebb (Kz: 10−2 m2; Az: 10−2 m2/s) compared to flood (Kz: 10−5 m2/s; Az: 10−4 m2/s). Bottom-generated mixing was moderated by the intrusion of stratified water on flood, which suppressed mixing. Elevated mixing (Kz: 10−3 m2; Az: 10−2.5 m2/s) occurred in the upper water column in the lee of a small island and was decoupled from the bottom layer. The near-surface mixing was a product of an eddy formed downstream of a headland, which tended to reinforce vertical shear by laterally straining streamwise velocities. These results are the first to show near-surface mixing caused by vertical vorticity induced by an eddy, rather than previously reported streamwise vorticity associated with lateral circulation.
Highlights
Estuarine circulation is responsible for the transport and fate of sediments, pollutants, and organisms between marine and freshwater environments
Cross sections of currents are presented for two transects taken during maximum flood and ebb tidal phases; and time series of currents, buoyancy frequency, Richardson number, turbulent kinetic energy (TKE) dissipation rates, and vertical mixing were presented at stations 1 and 2, as those locations exhibited the most notable mixing patterns
The main messages were that elevated mixing can occur on ebb tide relative to flood from velocity shears destabilizing a more homogenous water column on ebb when salty water at depth and fresh water near surface is flushed from the estuary
Summary
Estuarine circulation is responsible for the transport and fate of sediments, pollutants, and organisms between marine and freshwater environments. The strength of the circulation dictates the productivity and overall health of an estuary [1], which are important variables in estuaries containing aquaculture operations, such as the study site in the present paper. This subtidal flow was traditionally thought to be a balance between the barotropic and baroclinic pressure gradients and friction [2,3]. More recent work identified that nonlinear advection and tidal asymmetries in vertical mixing (stress divergence) had the potential to modify tidally averaged flows [4,5,6]. Multiple other mechanisms could create asymmetries in stress divergence and influence subtidal currents
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
