Context: Dams construction appears to have multi-dimensional effects on the river environment, and it especially affects the thermal condition of rivers. Aims: The objective of this work was to assess downstream thermal responses to the Charef Dam in relation to the water flow and the water residence time. Methods: During the year 2012, the hydrological parameters upstream and downstream of the dam were monitored. Key results: Salinity, electrical conductivity, total dissolved solids (TDS) and water flow all responded similarly, with larger magnitudes in waters upstream of the dam than downstream, whatever the season. In terms of flux, the Charef Dam retains 59 and 56% of the incoming water and TDS fluxes respectively. Furthermore, the upstream water temperature is higher than that of the downstream in 83% of samples. During the dry season, the thermal response of the waters downstream of the Charef Dam can exceed 2°C (downstream cooling). Conclusions: Despite being a small dam, the water residence time (2.3 years) in the Charef Dam has a significant effect on the downstream water temperature. Implications: These temperature changes may cause significant physicochemical and biological issues. Restoration practices such as increasing discharges during dry seasons and riparian cover restoration could mitigate thermal impacts and minimise negative effects.

This study investigated water and nutrient fluxes along five coastal river–reservoir continuum in northeastern Algeria under contrasting hydrological conditions, with particular emphasis on the coupling effects of dams and high-flow events in a semi-arid Mediterranean environment. The objectives were to quantify dissolved nutrient concentrations and fluxes, evaluate reservoir retention and stoichiometric modifications, and assess their implications for downstream coastal ecosystems. Fortnightly sampling campaigns were conducted from January to December 2012 across 23 stations distributed along five rivers and eight reservoirs. Nutrient analyses included dissolved inorganic (DIN) and organic nitrogen (DON), phosphate (PO₄³⁻), and dissolved silica (DSi). The exceptionally wet conditions recorded during 2012 strongly altered hydrological and biogeochemical functioning across the river–reservoir–coastal continuum. High-flow period contributed nearly half of the annual freshwater discharge exported to the southwestern Mediterranean Sea and generated exceptionally large nutrient inputs to reservoirs and coastal waters. Reservoirs retained substantial fractions of inorganic nutrients (DIN: 56%, PO₄³⁻: 55%, DSi: 47%), with lower retention in small, rapidly flushed reservoirs, while acting as net DON sources. A distinctive feature of the studied watersheds was the unusually high contribution of ammonium (NH4+) relative to nitrate (NO3-), reflecting strong untreated domestic wastewater influence. Reservoirs also induced marked seasonal shifts in nutrient stoichiometry. Under low-flow conditions, longer residence times promoted decreasing DIN:PO₄³⁻ ratios, whereas flood conditions enhanced NO3- transport and increased DIN:PO₄³⁻ ratios. The interaction between high-flow period, dam regulation, and anthropogenic activities generated highly dynamic nutrient regimes that differ markedly from those reported for temperate Mediterranean regions.

Mediterranean coastal ecosystems are strongly influenced by land-derived nutrient inputs, yet information on nutrient transfers from North African watersheds remains scarce. This study quantified water and nutrient fluxes along five river–reservoir–coastal continuums in northeastern Algeria and assessed how dam regulation, high-flow events, and human activities modify nutrient delivery to coastal waters. Fortnightly sampling during the exceptionally wet year 2012 covered 23 stations across five coastal rivers and eight reservoirs. Dissolved inorganic nitrogen (DIN), dissolved organic nitrogen (DON), phosphate (PO₄³⁻), dissolved silica (DSi) were monitored to evaluate nutrient transport, retention, stoichiometric changes, and the Index of Coastal Eutrophication Potential (ICEP) along the land–sea continuum. The exceptionally wet conditions generated large freshwater and nutrient exports to the Mediterranean coast, with flood events contributing a substantial fraction of annual transfers. By retaining more than half of the incoming DIN and PO₄³⁻ loads, reservoirs substantially reduced nutrient delivery to coastal waters, thereby modifying the intensity and composition of land-derived nutrient reaching the sea. Reservoir nutrient retention and the exceptionally wet conditions resulted in predominantly negative ICEP values, indicating low coastal eutrophication potential. The studied watersheds were characterized by unusually high ammonium (NH₄⁺) contributions relative to nitrate (NO₃⁻), indicating a strong influence of untreated domestic wastewater. Dam regulation and hydrological variability significantly altered nutrient stoichiometry, with low-flow conditions favoring lower DIN:PO₄³⁻ ratios and flood periods enhancing NO₃⁻ transport and increasing DIN:PO₄³⁻ ratios. These findings highlight the need for a land–sea continuum perspective to assess nutrient enrichment in North African Mediterranean coastal waters.