Tunisian reservoirs : diagnosis and biological potentialities

International audienc

Variabilité du phytoplancton en relation avec les facteurs environnementaux dans un lac salé temporaire

To establish a relationship between environmental variables and phytoplankton dynamics, physicochemical characteristics and phytoplankton sampling were performed in Sabkhet El Adhibet (Southeastern Tunisia) monthly from November 2005 to April 2006 and from November 2006 to April 2007 (the site dries annually between May and late October). All measured water quality variables showed considerable seasonal variation, and quantitative and qualitative differences in phytoplankton communities were recorded. The maximum phytoplankton density was recorded in January 2006, whereas lowest values occurred in November 2006. Sixteen species belonging to 6 orders were recorded, among which diatoms (52.1 %) and chlorophytes (39.8 %) were the most abundant. The correlation analysis between phytoplankton (density and composition) and abiotic variables revealed that orthophosphate is the major factor affecting the phytoplankton dynamics, and there were no correlation between phytoplankton and all the other environmental parameters. The PCA analysis of the phytoplankton composition and density revealed two main PCA axis explaining 82.99 % of the variance. The first axis was associated with diatoms, cryptophytes, euglenophytes, dinophytes and total phytoplankton, with a contribution of 21.8, 21.6, 21.3, 17.4 and 17.4 %, respectively. The second axis was correlated with chlorophytes (55.3 %) and cyanobacterias (26.3 %)Dans ce travail, afin de déterminer l'impact des différentes variables environnementales sur le phytoplancton dans un milieu hypersalé, un suivi des paramètres abiotiques et biotiques a été réalisé au niveau de Sabkhet El Adhibet (sud-est Tunisien), durant les périodes allant de novembre 2005 à avril 2006 et de novembre 2006 à avril 2007 (le site étant sec entre le début du mois de mai et la fin du mois d'octobre). Les résultats obtenus ont permis l'identification de 16 espèces de phytoplancton, appartenant aux groupes des diatomées, chlorophycées, dinophycées, euglénophycées, cryptophycées et cyanobactéries. La plus grande densité microalgale a été observée en décembre 2005 et janvier 2006 avec respectivement 8,6 et 14,6 106 cellules.L-1, alors que la plus petite densité a été enregistrée en novembre 2006 avec 0,19 106 cellules.L-1. L'analyse de la composition en phytoplancton révèle que ce sont les diatomées et les chlorophycées qui présentent la fraction la plus importante du phytoplancton, avec respectivement un maximum de 97,8 % (novembre 2006) et 95,7 % (janvier 2007). Le pourcentage moyen décroissant, relatif à chaque groupe de phytoplancton, de toute la période d'investigation est comme suit: diatomées (52,1 %), chlorophycées (39,8 %), dinophycées (3,2 %), euglénophycées (3 %), cryptophycées (1,1 %) et cyanobactéries (0,8 %). Toutefois, nous remarquons une grande variation mensuelle de la composition phytoplanctonique avec les diatomées et les chlorophycées présentes au niveau de tous les échantillons, tandis que les dinophycées, les euglenophycées et les cryptophycées sont absentes au niveau de nos échantillons durant certaines périodes de l'année. L'étude de la corrélation, entre la composition et la densité des phytoplanctons avec les différents paramètres abiotiques, montre que c'est l'orthophosphate qui affecte le plus la dynamique et la variation phytoplanctonique dans le milieu. Par ailleurs, aucune corrélation n'a été observée entre le phytoplancton et les autres paramètres environnementaux

Tunisian reservoirs: diagnosis and biological potentialities

Due to scarcity, irregular rainfall and increasing water demand, several reservoirs have been built in recent decades in Tunisia to meet water needs for essential uses, which is generally done without analysis of their capacity to maintain a high quality of aquatic life and equitable distribution of water resources. Currently, 90% of available water resources are already mobilized and climate change exacerbates the country's aridity which makes it difficult to monitor water needs. With a view to contributing to their effective management and setting future directions for controlling and improving inland fish productivity, a comparative limnological study was carried out on 8 artificial reservoirs that were stocked with mullet fry. This study, based on a review of existing data, provides information on the availability and quality of inland water resources in relation to international standards and the biological potential (plankton, fish and other organisms) of these reservoirs. The satisfactory water quality for aquatic life, as well as the significant growth and production of introduced species associated with the rearing of mullet fry, clearly show that, despite several problems, Tunisian reservoirs represent an important potential that still needs to be developed. To this end, we recommend to improve the fishing techniques and the stocking of mullet fry. In addition, the strengthening of fishermen's groups, the encouragement of private initiative and the quality control of water and fish meat are highly requested

Systematic review of a RAMSAR wetland and UNESCO biosphere reserve in a climate change hotspot (Ichkeul Lake, Tunisia)

Tunisia\u27s Ichkeul Lake is among the most productive ecosystems in the Mediterranean, with a great regional value thanks to its diversity of habitats. It is an important overwintering area for waterfowl species. It is a RAMSAR wetland, a National Park, a UNESCO World Heritage, and a Biosphere Reserve. This review paper provides a broad overview of the climatic, hydraulic, biogeochemical features, bio-resources, and bio-productivity of the Lake. The interconnectivity between the different environmental components of the lake is presented, highlighting the main characteristics of this vital ecosystem. Its ecosystem consists of a permanent lake bordered by temporary marshes. It is connected to the Mediterranean Sea via Bizerte Lagoon under a typical semi-arid to sub-humid bio-climate with wet and dry seasons. The winter rainfall fills up the rivers and lake with freshwater that overflows into the Tinja River. In summer, high evaporation reduces the water level and allows seawater to enter the wetland from Bizerte Lagoon. The ecosystem is threatened by pollution, the damming of its main rivers, and climate change. The unsustainable water management has resulted in fundamental environmental modifications, as evidenced by the large variation in the salinity, water level, productivity of water plants, and the decline in venue and stop-overs of waterbirds. The current situation is a warning that indicates a general perturbation of the resources of this particular site and of Tunisian wetlands in general, especially that the Mediterranean region has been designated as a climate change hotspot. Accurate hydrological management is needed to boost the physical functioning of the ecosystem, and to gain deeper knowledge of the different phases of the water cycle and its relationship to other long-term environmental cycles for sustainable water management strategies in the most water-scarce region in the world

Harmful epiphytic dinoflagellate assemblages on macrophytes in the Gulf of Tunis

International audienc

Phytoplankton variability with relationships to environmental factors in a temporary salt lake

To establish a relationship between environmental variables and phytoplankton dynamics, physicochemical characteristics and phytoplankton sampling were performed in Sabkhet El Adhibet (Southeastern Tunisia) monthly from November 2005 to April 2006 and from November 2006 to April 2007 (the site dries annually between May and late October). All measured water quality variables showed considerable seasonal variation, and quantitative and qualitative differences in phytoplankton communities were recorded. The maximum phytoplankton density was recorded in January 2006, whereas lowest values occurred in November 2006. Sixteen species belonging to 6 orders were recorded, among which diatoms (52.1 %) and chlorophytes (39.8 %) were the most abundant. The correlation analysis between phytoplankton (density and composition) and abiotic variables revealed that orthophosphate is the major factor affecting the phytoplankton dynamics, and there were no correlation between phytoplankton and all the other environmental parameters. The PCA analysis of the phytoplankton composition and density revealed two main PCA axis explaining 82.99 % of the variance. The first axis was associated with diatoms, cryptophytes, euglenophytes, dinophytes and total phytoplankton, with a contribution of 21.8, 21.6, 21.3, 17.4 and 17.4 %, respectively. The second axis was correlated with chlorophytes (55.3 %) and cyanobacterias (26.3 %).Dans ce travail, afin de déterminer l’impact des différentes variables environnementales sur le phytoplancton dans un milieu hypersalé, un suivi des paramètres abiotiques et biotiques a été réalisé au niveau de Sabkhet El Adhibet (sud-est Tunisien), durant les périodes allant de novembre 2005 à avril 2006 et de novembre 2006 à avril 2007 (le site étant sec entre le début du mois de mai et la fin du mois d’octobre). Les résultats obtenus ont permis l’identification de 16 espèces de phytoplancton, appartenant aux groupes des diatomées, chlorophycées, dinophycées, euglénophycées, cryptophycées et cyanobactéries. La plus grande densité microalgale a été observée en décembre 2005 et janvier 2006 avec respectivement 8,6 et 14,6 106 cellules. L-1, alors que la plus petite densité a été enregistrée en novembre 2006 avec 0,19 106 cellules. L-1. L’analyse de la composition en phytoplancton révèle que ce sont les diatomées et les chlorophycées qui présentent la fraction la plus importante du phytoplancton, avec respectivement un maximum de 97,8 % (novembre 2006) et 95,7 % (janvier 2007). Le pourcentage moyen décroissant, relatif à chaque groupe de phytoplancton, de toute la période d’investigation est comme suit : diatomées (52,1 %), chlorophycées (39,8 %), dinophycées (3,2 %), euglénophycées (3 %), cryptophycées (1,1 %) et cyanobactéries (0,8 %). Toutefois, nous remarquons une grande variation mensuelle de la composition phytoplanctonique avec les diatomées et les chlorophycées présentes au niveau de tous les échantillons, tandis que les dinophycées, les euglenophycées et les cryptophycées sont absentes au niveau de nos échantillons durant certaines périodes de l’année. L’étude de la corrélation, entre la composition et la densité des phytoplanctons avec les différents paramètres abiotiques, montre que c’est l’orthophosphate qui affecte le plus la dynamique et la variation phytoplanctonique dans le milieu. Par ailleurs, aucune corrélation n’a été observée entre le phytoplancton et les autres paramètres environnementaux.Ben Naceur Hachem, Fathalli Afef, Ben Rejeb Jenhani Amel, Romdhane Mohamed Salah. Phytoplankton variability with relationships to environmental factors in a temporary salt lake. In: Revue d'Écologie (La Terre et La Vie), tome 68, n°3-4, 2013. pp. 335-345