Restoration impact of an uncontrolled phosphogypsum dump site on the seasonal distribution of abiotic variables, phytoplankton and zooplankton along the near shore of the south-western Mediterranean coast

Abstract

'In connection with the Taparura Project, we studied the distribution of phytoplankton and zooplankton communities in relation to environmental variables at 18 stations sampled during four coastal cruises conducted between October 2009 and July 2010 on the north coast of Sfax (Tunisia, western Mediterranean Sea). The inshore location was largely dominated by diatoms (66 %) represented essentially by members of the genera Navicula, Grammatophora, and Licmophora. Dinophyceae were numerically the second largest group and showed an enhanced species richness. Cyanobacteriae developed in association with an important proliferation of colonial Trichodesmium erythraeum, contributing 39.4 % of total phytoplankton abundances. The results suggest that phytoplankters are generally adapted to specific environmental conditions. Copepods were the most abundant zooplankton group (82 %) of total zooplankton. A total of 21 copepod species were identified in all stations, with an overwhelming abundance of Oithona similis in autumn and summer, Euterpina acutifrons in winter, and Oncaea conifera in spring. The phosphogypsum restoration had been acutely necessary allowing dominant zooplankton species to exploit a wide range of food resources including phytoplankton and thus improving water quality.

Spatial and seasonal variability of pico-, nano- and microphytoplankton at the bottom seawater in the north coast of Sfax, Eastern Mediterranean Sea

“…These results are in agreement with previous studies conducted in this area (Rekik et al 2012(Rekik et al , 2013(Rekik et al , 2014a. The seasonal temperature cycle showed ) ratio at the bottom was lower than the Redfield ratio (16:1) during three surveys (autumn, winter and spring) (see Table 1).…”

“…The resulting disturbance to the environment made it vital to evaluate the impact of restoration on the microbial assemblage that is the basis of the living resources in the Gulf of Gabès, a key economic and social issue. Initial conditions were determined through an investigation addressing microphytoplankton and zooplankton at the surface (Rekik et al 2012).…”

The characterisation and seasonal distribution of diatoms along Sfax northern and southern coasts (Gulf of Gabes, Eastern Mediterranean Sea) in relation to environmental conditions

“…The low pH values are likely the most important predictor among the physical factors and its negative influence on diatoms abundance (r = -0.64, p<0.05, n = 15) in southern part of the coast. The low pH values can reasonably be attributed to the industrial activity still in function in the south coast while it has been finished in the north Sfax coast (Rekik et al, 2013b). The seasonal variability shows that the littoral of Sfax is subjected to a clear seasonal cycle deference north coast species to south coast species.…”

“…Significant differences were observed in water temperature (r = 3.24 × 10 -19 , p<0.001, n = 15) and salinity (r = 2.58 × 10 -8 , p<0.001, n = 15) between northern and southern stations. Results revealed a striking difference between the two coasts about pH, with high acidification of seawater in the south, probably generated by industrial activity (Rekik et al, 2013b). Suspended matter was more important in the north (48.20 -201.56 mg l -1 ) than in the south (23.87 -61.44 mg l -1 ).…”

“…Suspended matter was more important in the north (48.20 -201.56 mg l -1 ) than in the south (23.87 -61.44 mg l -1 ). The high suspended matter values may be attributed to the shallowness of the sampled north stations, the spatial distribution of tiny particles and tidal action and to the recently added soil, not yet fully stabilised (Rekik et al, 2013b). The low concentrations of orthophosphate as well as their low magnitude relative to total phosphate show that restoration of the northern part of Sfax coast had positive effects on dissolved inorganic phosphate concentrations.…”