Abstract
This study investigated the environmental quality of the Bizerte Lagoon (Tunisia) through an integrated approach that combined environmental, biogeochemical, and living benthic foraminiferal analyses. Specifically, we analyzed the physicochemical parameters of the water and sediment. The textural, mineralogical, and geochemical characteristics of the sediment, including total organic carbon, total nitrogen, simultaneously extracted metals (SEM), acid volatile sulfides (AVS), chlorophyll a, CaCO3, and changes in bacterial populations and carbon isotopes were measured. The SEM/AVS values indicated the presence of relatively high concentrations of toxic metals in only some areas. Foraminiferal assemblages were dominated by species such as A. parkinsoniana (20–91%), Bolivina striatula (<40%), Hopkinsina atlantica (<17%), and Bolivina ordinaria (<15%) that cannot be considered typical of impacted coastal lagoons both in Mediterranean and northeast Atlantic regions. The results of this work suggest that Bizerte Lagoon is a unique setting. This lagoon is populated by typical marine species that invaded this ecosystem, attracted not only by the prevailing favorable environmental conditions but also by the abundance and quality of food. The results indicate that the metal pollution found in some areas have a negative impact on the assemblages of foraminifera. At present, however, this negative impact is not highly alarming.
Highlights
The European Water Framework Directive (WFD, Directive 2000/60/EC) establishes that the ecological status of water bodies is assessed in terms of the quality of their biological, physicochemical, and hydro-morphological elements
The first factor is related to favourable/ less favourable environmental conditions whereas the second one to the production of acid volatile sulfides (AVS) and urban organic discharge. According to these two first factors, total organic carbon (TOC) content, C/N and total mesophilic counts (TMC) are secondary and less important variables. Numbers of taxa such as miliolids, including Q. seminula and Quinqueloculina bosciana, agglutinans, B. marginata and other buliminids, F. squamosa, B. compacta and H. atlantica, as well as Foraminiferal density (FD) and diversity indexes are positively related to δ13C, magnetic susceptibility and kaolinite content
Otherwise these variables are negatively related to simultaneously extracted metals (SEM)/AVS, total coliform (TC) and chlorophyll a (Chl a), which are instead grouped with A. parkinsoniana, B. striatula and B. pseudoplicata
Summary
The European Water Framework Directive (WFD, Directive 2000/60/EC) establishes that the ecological status of water bodies is assessed in terms of the quality of their biological, physicochemical, and hydro-morphological elements. Lagoons are subjected to significant environmental changes due to both natural and anthropogenic influences These influences include engineering constructions that alter their natural circulation patterns, the extraction or deposition of mineralogical materials, the exploitation of biological products, and water and sediment pollution that are the main causes of environmental degradation [2], [3], [4]. Different proxies, such as biogeochemical indicators [2], [5], [6], [7], [8], have been used to assess the water and sediment quality of coastal lagoons and to evaluate their environmental vulnerability
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