Shallow Water Estuary Research Articles

Implicit solution for estuarine hydrodynamic modelling

This is a two-dimensional, finite difference, vertically averaged hydrodynamic model for shallow water estuaries. It utilizes three time levels and solves for current components in alternating direction exclusively by an implicit scheme. The purpose of using the implicit approach is to minimize the instability problem by which the usual implicit-explicit alternating scheme is inherently plagued when grid size is small or when water depths are deep. This is due to the explicit scheme limitation, whose time step is governed by the Courant-Friedrich-Lewy criterion. By the implicit-implicit scheme, a large time step would greatly reduce the CPU time. An effort was also made to model the effects of canals in the estuarine system. A different grid system than Leendertse's was used to lessen the lateral smoothing in Chezy coefficients caused by the large gradient of water bottom features. This grid system has both water elevation and depth measured at the center of the grid and is especially applicable for uneven grid-size models. The computer program is written to ensure easy-to-use features so that this model can be readily applied to different estuaries.

Feeding Ecology of Eelgrass Fish Communities

The principal components in the diets of fishes utilizing eelgrass (Zostera marina) beds in the shallow water estuaries near Beaufort, North Carolina, were detritus, planktonic copepods, and epifaunal crustaceans. Food produced within the eelgrass beds such as eelgrass, crustaceans, gastropods, and detritus, could have accounted for approximately 56% by weight of the diet of the eelgrass fish community. Pinfish (Lagodon rhombiodes) under 35 mm feed primarily on planktonic copepods, thereafter detritus gradually replaced copepods. When pinfish reached a length of about 70 mm they became more omnivorous consuming a greater proportion of plant material and polychaetes. Changes in feeding habits may have been responsible for significant differences in the weight-specific caloric contents observed between three size groups of both pigfish and pinfish. All species except one did not feed in the beds at night even though biomass of all fish was twice as high at night than during the day. The eelgrass fish community does not appear to be food-limited because the total annual food production in the beds is greater than the total annual food consumption by the eelgrass macrofauna.