Seasonal dynamics of Nitzschia palea in relation to environmental parameters in Sidi Chahed Reservoir and its tributaries (Oued Mikkes and Oued Mellah), Morocco

Abstract

This study investigates the spatio-temporal dynamics of the pollution-tolerant diatom Nitzschia palea and its environmental drivers in the Sidi Chahed Dam and its tributaries, Oued Mikkès and Oued Mellah (Morocco), a reservoir impacted by geogenic salinization and anthropogenic pressures. Monthly monitoring of water quality and diatom assemblages was conducted over the 2022–2023 hydrological year across six stations, encompassing the main tributaries and the reservoir’s water column. Results revealed pronounced environmental gradients, with Station S1 on Oued Mellah (draining Triassic evaporites) exhibiting extreme salinity (max 0.20%), conductivity (3.82 mS/cm), and chloride levels (1625.9 mg/L). While ANOVA indicated significant seasonal variation overriding spatial differences for most parameters, N. palea’s relative abundance (0–39.5%) showed significant positive correlations with salinity (ρ = 0.44), conductivity (ρ = 0.44), calcium (ρ = 0.42), and chlorides (ρ = 0.41). Its dominance was highest at the saline inflow (S1) and within the reservoir’s metalimnion (S5), peaking during autumn and summer under low-flow, high-evaporation conditions. Our findings suggest that N. palea serves as a robust bioindicator of combined geogenic and anthropogenic stressors in semi-arid reservoirs, and may play a role in structuring microbial communities under salinity pressure, though further functional studies are needed to confirm this. This work underscores the need to interpret diatom signals within the geological and climatic context of Northwest African freshwater ecosystems.