Contribution to a biosurveillance network along the lower and upper Medjerda Valley (southern Mediterranean, North Africa)

In the context of climate change, Tunisia is particularly concerned about global warming. Moreover, Tunisia has a high reliance on agriculture and mass tourism, which are two very water-intensive sectors. Consequently, understanding and evaluating the only permanent river in Tunisia, the Medjerda River, is crucial. An innovative and multidisciplinary approach to contribute to a biosurveillance network along the Medjerda Valley is needed to diagnose the health status of Medjerda wadi. This work aimed to contribute to the establishment of a biosurveillance network along the Tunisian section of the river. To execute this, we focused on the meiofauna along the upstream and downstream continuum of Medjerda River between the Ghardimaou Heights and the Kalaat El Andalus delta area, which represents a distance of 217 km from our first station to our last station. We aimed to determine some bioindicator species that could be used to establish a biosurveillance network based on meiofauna taxa and, especially, free nematodes. Various techniques were used, among them the use of a core barrel. Six stations were chosen: three in the upper valley and three in the downstream part. The preliminary results show relatively oxygenated water with organochlorine pesticide (OCP) levels below the threshold of 1 µg/l and hydrocarbon levels under 0.1 mg/l. The conductivity is higher downstream than upstream; the same is true of the total dissolved solids (TDS) and the salinity. However, the degree of oxygenation is higher in the upper valley than in the lower valley. Additionally, preliminary results for the meiofaunistic composition show a large predominance of nematofauna among other taxa.