Seasonal variation of nutrient salts and heavy metals in mangrove (Avicennia marina) environment, Red Sea, Egypt

摘要

In the Egyptian Red Sea coast, nutrient salts, major ions, and heavy metals ion concentrations were examined in mangroves and the results were compared to respective concentrations in a reference area. Water samples were collected during the four seasons of 2012 from three different mangrove regions, Safaga, Abo Gheson, and El Quseer, besides, a mangrove free region, Marsa Alam. A temporal variation in the chemical composition of seawater of the mangrove and reference regions was recorded. Phosphorous and nitrogen forms were measured and calculated. Fe, Mn, Cu, Zn, Ni, Cr, Cd, and Pb ions were measured in water samples. Redfield nitrogen to phosphorous ratio explained the oligotrophic nature of the Red Sea. Ca and Mg ions besides total alkalinity showed negligible variations. The relatively greater concentration values of ammonium, 242.11 g/l, dissolved inorganic nitrogen, 315.55 g/l, and oxidizable organic matter, 0.4 mg-O-2/l, may be caused by the impact of mangroves. Seawater contamination by heavy metals was assessed, using the metal index, in the mangrove regions which, compared to the reference region, were highly contaminated. Analysis of variance showed no significant variation among mangrove stations. Principal component analysis suggested that El Quseer and Safaga, mangrove regions, were contaminated by metal ions. Safaga possessed the highest concentration of Cd and Zn ions, while the highest concentrations of Mn, Cu, Ni, and Pb ions were observed at El Quseer. This may be attributed to industrial and shipping activities. It is concluded that the mangrove ecosystem along the Red Sea highly affects marine environment.