THE IMPACT OF POLLUTION ON MANGROVE PLANT (AVICENNIA MARINA) ON THE RED SEA COAST OF EGYPT

Abstract

This study was carried out on grey mangroves Avicennia marina populations inhabiting the Red Sea Coast in Egypt. The present investigation aimed to; study the ecological status of A. marina population, study the cycling of heavy metals (Zn, Cu, Fe, Mn, Ni, Pb, Cd and Co) within 9 locations of A. marina populations, study the translocation and accumulation of heavy metals in A. marina organs and the changes in total phenolic compounds concentration as a response of the plants to heavy metals accumulation. The studied sites were located in the inshore zone of the Red Sea varied between mangrove shrubs (Um Dehais), small forests (Km 17 S. Safaga, Sharm El bahari, Wadi El Gemal and N. Qula'an) to complete extended forests (Abu Minqar Island, Wadi Abu Hamra, Hamata and Wadi Lehmi). All of them are considered uni-species communities consist of A. marina mangrove trees. Studying the ecological status of A. marina population within four selected sites (Km 17 S. Safaga, Wadi Abu Hamra, Sharm El bahari and Wadi El Gemal), studying the grain size analysis and the heavy metals content in slack water, bulk sediments and sediment fine fractions (Ø3, Ø4 and Ø5) as well as studying the heavy metals content and the changes in the total phenolic compounds content of A. marina parts (pneumatophores, leaves and fruits) along nine sites showed the following results:  A. marina populations in the four sites showed two different size structures; one of them represented the lowest two small size classes and the other represented the mature and old trees. Al-Sharm El Bahari showed high percentage of A. marina young tress in comparison with Summary 93 mature and old trees, this indicates that recruitment in this site is frequent  Within the chosen sites El Sharm El Bahari showed the highest percentage of seedlings; however seedlings were absents from Wadi Al Gemal and Wadi Abu Hamra.  The average heights (m/ind) and crown diameter (m/ind) of A. marina trees in the studied sites are less than 5 m/ind, reflecting the harsh limiting environment (high salinity, low rainfall, unfavorable temperatures).  Wadi Al Gemal subjected to overgrazing, which impacts on A. marina population include considerable reduction in the green parts of the trees, dryness of the uppermost and outermost parts of the grazed branches and pneumatophores beside destruction of pneumatophores under the feet of camels.  Heavy metals concentration within the slack water follow the order of Fe>Zn>Cd>Cu>Pb>Ni>Co>Mn.  Abu Minqar recorded the highest concentrations Fe, Ni and Mn in the slack water. The highest concentrations of Zn, Cu, Mn, Pb and Cd were recorded in Um Dehais site while Abu Hamra and Um Dehais sites recorded the highest Co concentration.  According to concentration of heavy metals in slack water the 9 sites classified to 4 groups; Group I contains Um Dehais site, group II contains Abu Minqar and Sharm El Bahary sites, group III contains W. Al- Gemal, North Qula’an and Hamata and group IV contains W. Lahmi, K 17 S. Safaga, and Abu Hamra. Summary 94  Sediments underling A. marina plants are formed of high percentage of sand and low percentage of mud in the nine sites. The Fine fractions, Ø3, Ø4 and Ø5 represent the essential constituent of the fine sediments. These fractions have the ability to retain and transport heavy metals.  Analysis of sediment showed that the accumulation of heavy metals follows the order of; Fe>Mn>Zn>Ni>Cu>Pb in bulk sediment, Fe>Mn>Zn>Cu>Pb>Ni in Ø3 fraction and Fe>Mn>Zn>Cu>Ni >Pb in Ø4 and Ø5 fractions.  Most of metals recorded higher contents in sediments than water this may be due to the reducing nature of the mangrove sediments that capture the different metals in insoluble form as metal sulphides as well as the continuous water mixing that leach the dissolved metal forms from the water column.  The cluster analysis classified the nine sites based on heavy metals concentrations within the bulk sediments to three groups; group I contains the northern sites; Um Dehais, Abu Hamra, Abu Minqar and Km 17 S. Safaga. The southern sites separated in; group II that contains Hamata and Sharm El Bahary sites and group III that contains Wadi Al- Gemal, North Qula’an and Wadi Lahmi sites.  Metal interactions in the bulk sediments were more evident than the different fractions and were restricted between Fe, Mn, Zn, Ni and Cu depending on the bio-availability with Fe and Mn oxides and the essential plant needs.  Fe was the highest bio-accumulated metal in leaves, roots and fruits of A. marina plants followed by Zn and Pb. The bioaccumulation of the heavy Summary 95 metals follow the order of; Fe>Zn>Pb>Cu>Ni>Mn in fruits, Fe>Zn>Pb>Mn>Cu>Ni in roots and Fe>Zn>Mn>Pb>Cu>Ni in leaves. The highest accumulation part was; fruits for Zn and Cu, leaves for Mn and roots for Pb.