Boughrara Lagoon Research Articles

Assessment of sediment quality in the Mediterranean Sea–Boughrara lagoon exchange areas (southeastern Tunisia): GIS approach-based chemometric methods

Concentrations of selected heavy metals (Cd, Pb, Zn, Cu, Mn, and Fe) in surface sediments from 66 sites in both northern and eastern Mediterranean Sea-Boughrara lagoon exchange areas (southeastern Tunisia) were studied in order to understand current metal contamination due to the urbanization and economic development of nearby several coastal regions of the Gulf of Gabès. Multiple approaches were applied for the sediment quality assessment. These approaches were based on GIS coupled with chemometric methods (enrichment factors, geoaccumulation index, principal component analysis, and cluster analysis). Enrichment factors and principal component analysis revealed two distinct groups of metals. The first group corresponded to Fe and Mn derived from natural sources, and the second group contained Cd, Pb, Zn, and Cu originated from man-made sources. For these latter metals, cluster analysis showed two distinct distributions in the selected areas. They were attributed to temporal and spatial variations of contaminant sources input. The geoaccumulation index (I (geo)) values explained that only Cd, Pb, and Cu can be considered as moderate to extreme pollutants in the studied sediments.

Quantitative Determination of Gymnodimine-A by High Performance Liquid Chromatography in Contaminated Clams from Tunisia Coastline

Quantitative determination by high performance liquid chromatography (HPLC) was performed for gymnodimine-A (GYM-A), a phycotoxin responsible for the contamination of Tunisian clams. This study demonstrates a rapid and reproducible HPLC-ultraviolet (UV) method for extraction, detection and quantification of GYM-A in toxic clams. The extraction of GYM-A from the digestive gland of clams in acetone, subsequent clean-up with diethyl ether and extraction with dichloromethane is the more valid protocol. Chromatography analyses were performed using a gradient of acetonitrile-water (10:90 to 90:10), containing trifluoroacetic acid (0.1%) for 20min at 1mL/min rate with a C18 column. Recovery rates exceeded 96%, and limits of detection and quantification were 5ng/mL and 8ng/g digestive gland, respectively. Repeatability and reproducibility were tested for various samples containing different levels of GYM-A. A significant correlation was observed between toxicity level of samples and the determined amount of GYM-A. Also, the persistence of GYM-A in contaminated clams from Boughrara lagoon was demonstrated. The kinetics discharge study of GYM-A in controlled medium, during 1month, showed that the process of depuration was biphasic with an exponential discharge of 75% of the total amount of sequestered GYM-A during the first 12days followed by a slow discharge (>10%) for the subsequent days up to the seventeenth day. This is the first time that a quantitative study of GYM-A in clams from Tunisian coasts is performed through the development of a new method for detection and quantify of this phycotoxin. We found HPLC-UV a reliable and suitable alternative to the mouse bioassay.

Population structure, distribution and relative abundance of Cerastoderma glaucum (Mollusca: Bivalvia) from the Bou Ghrara Lagoon (Gulf of Gabès, southern Tunisia)

In the first description of the population structure of the cockle Cerastoderma glaucum , a preliminary stock assessment and spatial distribution have been investigated in the Bou Ghrara Lagoon. The main results collected about this species in the coastal zone of the lagoon from 2003 through to 2004 have been recapitulated. A total of 671 cockles was collected, treated and the demographic structure of this species was studied. In terms of geographical occupation, maps of the population distributions were drawn. They showed that this population has a significant fluctuation in the colonized surface, which was roughly divided into five sites. The consequence was a remarkable biomass which represented 220 tons of fresh weight (average 15.53 g m −2 ) and high abundance levels reaching over 156 million individuals. The distribution of the species has also been investigated in consideration with the size which varies markedly according to location, while the shell length ranged between 6 and 29 mm. Additional factors influencing the population distribution are discussed and it is concluded that bottom characteristics, food potential (organic matter content of the sediment, phytoplankton rates and seagrass organic matter) and physicochemical factors were the fundamental factors controlling the spatial distribution of C. glaucum .

Sea level variability and tidal resonance in the Gulf of Gabes, Tunisia

Sea level variability in the Mediterranean Sea is dominated at meso- and synoptic scales by meteorologically induced motion except, in some regions where tidal resonance occurs. One such region is the Gulf of Gabes where tidal amplitudes can reach 1 m during spring tides. Sea level fluctuations were recorded at four stations around the Gulf of Gabes, during 86 days in 2003 and at three stations, within the Boughrara lagoon in the southern Gulf, during about 30 days in 1999. Spectral analysis reveals that tides are responsible for most of the variance found in sea level fluctuations. Harmonic analysis results are discussed and amplitude and phase estimates for the four major constituents (K1, O1, M2, and S2) are compared to estimates from previous studies. Based on simple dynamical arguments, it is shown that the Gulf of Gabes has the right dimensions to entertain tidal resonance for most semi-diurnal tidal harmonics. The low-frequency sea level fluctuations are finally described in relation to atmospheric forcing. They are spatially coherent and respond to both easterly winds at periods near 6.5 and 14 days and as an inverse barometer at periods close to 4–6 days.

Response of free-living Nematodes to the quality of water and sediment at Bou Chrara Lagoon (Tunisia) during winter 2000

The Bou Ghrara lagoon, a stretch of water in southeastern Tunisia, has shown an alarming reduction of its fishery resources since 1993. In order to study the response of free-living nematodes to the water and sediment quality of this area, thirteen stations have been sampled. According to this study, the heavy metal, organic carbon and hydrocarbon content of sediments are key factors negatively influencing the density, biomass and diversity of the nematofauna.