Transport of nutrients from the Seybouse River to Annaba Bay (Algeria, SW Mediterranean).

Freshwater and dissolved nutrient inputs that entered the lower Seybouse River estuary were assessed in 2012 through a fortnightly surface water sampling both at a lower river station and at the estuary outlet. The Seybouse estuary delivered annually 950 × 106 m3 of freshwater yielding 83 kg N km-2 yr-1 of N-NH4 and 12 kg P km-2 yr-1 of P-PO4. More than 2/3 of the annual inputs of freshwater, Si(OH)4 and NO3 entered the sea during the flooding event of late February 2012. Si-Si(OH)4 and N-NO3 yields in the Seybouse estuary represented <1/3 those of the Mediterranean rivers. Annaba Bay is subjected to highly polluted waters from the Seybouse estuary, with significant NH4 (72 ± 37 µmol L-1) and PO4 (7 ± 4 µmol L-1) amounts. However it is characterized by low Si(OH)4 (104 ± 43 µmol L-1) amounts. Alteration of Si:N:P ratios at this bay suggest potential risk of eutrophication, except during and weeks after flood episodes.

Variability of the dissolved nutrient (N, P, Si) concentrations in the Bay of Annaba in relation to the inputs of the Seybouse and Mafragh estuaries.

Dissolved inorganic nitrogen (DIN), phosphate (PO4) and silicic acid (Si(OH)4) loads from the Seybouse and the Mafragh estuaries into the Bay of Annaba, Algeria, were assessed at three stations of the Bay over three years. The Seybouse inputs had high levels of DIN and PO4, in contrast to the Mafragh estuary's near-pristine inputs; Si(OH)4 levels were low in both estuaries. The DIN:PO4 molar ratios were over 30 in most samples and the Si(OH)4:DIN ratio was less than 0.5 in the Seybouse waters, but nearly balanced in the Mafragh. The specific fluxes of Si-Si(OH)4 (400-540 kg Si km⁻² yr⁻¹) were comparable in the two catchments, but those of DIN were several-fold higher in the Seybouse (373 kg N km⁻² yr⁻¹). The inner Bay affected by the Seybouse inputs had high levels of all nutrients, while the Mafragh plume and the outer marine station were less enriched.