Nutrient distribution and fluxes from three Mediterranean coastal rivers (NE Algeria) under large damming

Abstract

Nutrient distribution and fluxes into and from dams and into coastal waters from three rivers (NE Algeria) were assessed during a one-year period in three stations for each river: at the entrance and the exit of dam and at the outlet. The main characteristics of the rivers were the high levels of NH4 and PO4, even in dam entrances, contrarily to SiO4 levels that are still low upstream the dams. From the inorganic nutrient incoming fluxes, the dams trapped annually 42 to 93%, depending on the nutrient, but released in great levels dissolved organic forms at their exits. At catchment scale, dissolved nitrogen loadings reach 338 kg/km2/yr, in which the organic fraction forms up to 34%; while those of dissolved phosphorus reach 172 kg/km2/yr, with a great organic fraction. The Si:N ratios decreased while N:P ratios increased at river outlets, indicating large inputs of N over P in the lower catchments.