Contribution for a Bio-surveillance Network Along the Medjerda Valley

In the context of climate change, Tunisia is particularly concerned by the global warming. Rising temperatures, varied precipitation and increasing occurrence of extreme events are some of the main’s indicators. Moreover, Tunisia has a high reliance on agriculture and mass tourism which are two very water-intensive sectors. By consequence, the understanding and evaluation of the only permanent river in Tunisia, Medjerda River, is crucial. The average contribution of this single river is about 1 billion cubic meters annually in total. The diagnosis of the health status of Medjerda wadi needs a multi-disciplinary approach to contribute for a bio-surveillance network along the Medjerda valley. To execute it, we focused on the meiofauna along the upstream and downstream continuum of Medjerda River between Ghardimaou heights and Kaleet El Andalous delta area which represents 217 km of distance from the first to the last station. We aim to determine some bio-indicators species to establish a bio-surveillance network based on meiofauna taxa and especially free nematodes. Various techniques were used. Among them, the use of a core barrel. From the very entry point of the river in Tunisian territory to the mouth of the river, five stations were chosen, three in the upper valley and two in the downstream part. In them, we applied the core sampling method using a 50 cm core barrel that we introduced almost entirely then transferred to a jar and fixed with formol and introduced almost entirely then transferred to a jar and fixed with formol. Screening levitation was used later. Abiotic parameters were measured by using a WTW 1.9.7i ®2 multiparameter system. Moreover, two reports were conducted to evaluate the hydrocarbons index by gas chromatography and the measure of the level of organochlorine pesticides (OCPs) by liquid/liquid extraction and CPG analysis. Those reports were conducted in association with the Centre International des Technologies de environnement de Tunis (CITET). The preliminary results show a relatively oxygenated water with organochlorines pesticides (OCPs) below the threshold of 1 µg/l and hydrocarbons under 0.1 mg/l. The conductivity is higher in downstream than in upstream, the same for the total dissolved solids (TDS) and the salinity. However, the degree of oxygenation is higher in the upper valley than in the down valley. Additionally, preliminary results of the meiofaunistic composition show a large predominance of Nematofauna among other taxa. Extensive identification is going to be done. Then, the structure of the Medjerda meiofauna will be correlated to abiotic parameters and chemical analysis.