influence of land-based sources on the nutrients level in Abu-Qir bay

ABSTRACT

Surface and bottom water samples were collected bimonthly during the year 1990 at 23 localities covering Abou-Qir Bay area. The concentrations of P, N and Si showed great temporal as well as spatial variations. Significant positive correlation coefficients were found between most of nutrient salts and chlorophyll a, explaining the dependence of phytoplankton growth on these ions. The calculated inverse correlations between the nutrient contents and salinity, on the other hand, demonstrated the allochthonous origin of most of these salts. Phosphorus appears as the most important limiting factor where the N P ratio average ranged between 24 1 and 36 1 at the off- and near-shore localities, respectively. Occasionally, nitrogen tends to be a controlling factor particularly during winter and autumn seasons, where the N P ratio was found below 4.5 1. The Si P ratio varied widely from >100 1, affected by different factors. The high ratios calculated for September samples collected at the near- shore localities may have resulted from autochthonous processes [regeneration from sediments for silicates] as well as from allochthonous contribution [drainage water]. The ratios were highly reduced during winter as a result of diatom uptake. Chlorophyll a biomass in Abou-Qir water was found in a considerable concentration [0 - 9.57 mg/m3] with an annual average of 1.15 mg/m3