Case Studies - Coastal Lagoons: Ecosystem Processes and Modeling for Sustainable Use and Development - page 370

9.1 INTRODUCTION

I. Ethem Gönenç

This chapter presents selected case studies from different areas of the world. These
studies provide detailed information on how to apply the methodologies and practical
approaches discussed in the other chapters of this topic. These case studies are
examples of how to integrate modeling into the decision-making process for sus-
tainable management of lagoons. The brief summaries that follow outline the aim
and scope of these case studies.

9.1.1 G RANDE -E NTRÉE L AGOON

The first case study area is the Grande-Entrée Lagoon in the Gulf of St. Lawrence,
Québec, Canada. The aquaculture industries are focused on determining the carrying
capacity of the lagoon for shellfish to maximize production. As defined in previous
chapters, lagoons are shallow marine systems where tides and local and nonlocal
winds play a major role in the dynamics of water motion. The management of
shoreline ponds and/or caged/fenced areas for aquaculture depend on an understand-
ing of water movement. Normally, when local winds blow along a lagoon axis,
downwind drift currents ( see Chapter 3 for details) develop in the shallow areas near
both shores. Water pile-up at the lagoon end causes horizontal pressure gradients,
which in turn force upwind gradient currents somewhere in the lagoon between the
drift currents. The hypothesis put forth here is that gradient currents occur near the
bottom in the deeper parts, away from the surface wind stress.
This hypothesis was tested in Grande-Entrée Lagoon, using current observations
recorded at 1 m above the bottom. A three-dimensional (3D) numerical model and
empirical orthogonal function (EOF) analysis of currents and winds show that bottom
currents are negatively correlated with the wind directions. The numerical model is
first used to simulate the horizontally induced two-dimensional (2D) wind-induced
current fields. Results show that currents are quickly set up near both shores, and
that a weak and sluggish return flow occurs in between those shores. The model is
then used to simulate the 3D current structure under the same wind conditions. The
hypothesis is verified: gradient upwind currents occur in the deep layers of the lagoon
basin, while currents near the surface are oriented downwind. Such a 3D current
structure can have significant effects on water renewal in the bottom layers and on
the general lagoon ecosystem dynamics. It suggests that a 3D model should be
considered when developing lagoon ecosystem numerical models and when selecting
optimal sites for aquaculture development.

9.1.2 M AR M ENOR L AGOON

The second case study area is the Mar Menor, a coastal lagoon in the Mediterranean
Sea, Spain. As do many lagoons throughout the world, this area supports a wide
range of beneficial uses and socio-economic interests. It is recognized as an emblem-
atic environment of the Región de Murcia, on the southwestern Mediterranean coast