Effects of Groundwater Inputs to the Hydraulic Circulation, Water Residence Time, and Salinity in a Moroccan Atlantic Lagoon

Soukaina Elyaagoubi,Karim Hilmi,Jovita Mėžinė,Georg Umgiesser,Francesco Maicu,Mehdi Maanan,Artūras Razinkovas-Baziukas

doi:10.3390/jmse10010069

Abstract

The finite element model SHYFEM was used to study the hydrodynamics and variability of water level, salinity, temperature, and water residence time (WRT) in the Oualidia lagoon located on the Moroccan Atlantic coast. The lagoon hosts a RAMSAR convention-protected area and also offers a set of valuable ecosystem services providing the source of income for the local population. To assess the effects of submarine groundwater discharge (SGD) inputs in the study area, four simulations were set up using different SGD inputs estimates in addition to tidal forcing, bathymetry, meteorological data including solar radiation, rain, and wind, in addition to boundary conditions in the Atlantic such as salinity, water level, and water temperature. The model was calibrated and validated using hydrodynamic measurements of previous studies in 2012 and 2013. The final results from the model are in good agreement with measured data. The simulation with SGD input ~0.05 m3 s−1 produced salinity values closest to the observed ones. Calculated spatial distribution of WRT, temperature, and salinity reduced to coordinates in two PCA axes is consistent with lagoon zones developed earlier using the benthic macroinvertebrate distribution. The calculated spatial distribution of WRT allowed us to evaluate the placement of oyster aquaculture farms and small-scale fisheries in relation to water quality issues existing in the lagoon.

Highlights

Coastal lagoons are considered as the most important life and human wellbeing provider areas in both terrestrial and water body parts
Modeled Water Temperature oceanic water from the Atlantic Ocean and submarine groundwater discharge (SGD) flows from a karstic aquifer system
There are two main sources of water input to the Oualidia lagoon-exchange of the oceanic water from the Atlantic Ocean and SGD flows from a karstic aquifer system

Summary

Introduction

Coastal lagoons are considered as the most important life and human wellbeing provider areas in both terrestrial and water body parts. They are the most highly productive coastal features as their ecosystem offers a decently valuable natural benefit, ecologically, culturally, and socioeconomically [1]. The lagoon of Oualidia is a shallow saltwater estuary, maintained by fresh SGD inflow [2,3,4]. It can be described as an important system that offers a trove of natural wealth despite its relatively small size of 7 km long and 1 km wide. The lagoon has been one of the most important oyster farming areas since 1950, and for this reason, it has been called the “traditional oyster capital” in Morocco [5,6,7]

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Results

Conclusion