On the salt balance of Tampa Bay

A three-dimensional, numerical circulation model, with resolution as high as 20 m at important mass conveyances (inlets, channels, bridge causeways, and rivers), is used to diagnose the point by point salt balances for Tampa Bay, FL. While the details of the salt flux divergences and the salt fluxes vary throughout the bay, each is fully three dimensional. On experimental duration (three month) average, the total (horizontal plus vertical) advective salt flux divergence is mainly balanced by the vertical diffusive salt flux divergence, except near the bottom of the deep shipping channel, where horizontal diffusive salt flux divergence is also important. Instantaneously, the local rate of change of salinity is primarily controlled by the advective salt flux divergence, with a secondary contribution by the vertical diffusive salt flux divergence everywhere and the horizontal diffusive salt flux divergence near the channel bottom. To examine the role of tidal pumping, the advective salt fluxes and divergences are further decomposed into the products of the mean salinity and velocity, and the correlation between the salinity and velocity fluctuations. The horizontal and vertical advective salt flux divergences by the mean quantities are equally large and counterbalancing (by continuity), with their sum being a small, but significant residual. The horizontal and vertical advective salt flux divergences due to tidal pumping are relatively small (when compared with the mean quantities) and counterbalancing; but, when summed their residual is comparable in magnitude to that by the mean quantities. So whereas the salt fluxes by tidal pumping are of secondary importance to the salt fluxes by the mean quantities, their total flux divergences are of comparable importance. The salt flux components in all three dimensions (axial, transverse and vertical) themselves vary along the Tampa Bay axis, and these findings may be typical of coastal plain estuaries given their geometrical complexities. Being that the distribution of salt flux bears upon the flux distributions of other scalars (e.g., nutrients, fish larvae, etc.) our findings for salt flux also have broader ecological implications.