Environmental determinants of diatom assemblages along a North African wadi, the Kebir-East, North-East Algeria

A total of 322 benthic diatoms with the majority being cosmopolitan species was recorded during a survey of the catchment area of the Kebir-East wadi, northeast Algeria. The spatial distribution patterns of diatom communities in relation to environmental gradients were examined using Co-Inertia Analysis (CIA) for ascertaining the interdependence between physico-chemical descriptors and diatom assemblages in 182 samples, collected over a period of 3 years, across 23 sampling stations. There was a significant covariance between the environmental data set and the benthic diatom data set with the CIA highlighting correlations between environmental factors and diatom species. A clear longitudinal gradient was a main driver of diatom communities with upstream sites characterized by high dissolved oxygen concentrations and downstream sites characterized by high organic load and nutrient enrichment of the water. A further factor influencing the shape of diatom assemblages was related to the conductivity, and the high values possibly reflected the close proximity of the sea to the downstream sites. An anthropogenic impact was also most evident in structuring diatom assemblages at sites close to Lake Oubeïra where agriculture was concentrated.