Assessment of the impacts of dredging and drainage on the mangrove soils from selected rivers in the niger delta, nigeria

Abstract

This study assessed the impact of dredging and drainage on mangrove soils of the Niger Delta, Nigeria. Samples from intact/un-drained mangroves and dredged/drained soils were collected from selected rivers in the Niger Delta and analysed. The rivers included Benin, Escravos, Warri, and Gbaraun and Sego Creeks. The field pH of the dredged soil was in the range of 3.7 – 3.9. On the other hand, the intact soil under mangrove vegetation and tidal cover had field pH in the neutral range (7.0 – 7.2). Upon peroxide oxidation, the pHs of the drained and un-drained soils were in the ranges of 1.5 -1.6 and 1.3 – 2.9 respectively. The results therefore indicated that the un-drained soils are potential acid sulphate soils (PASS), while the drained soil, which are already undergoing acidification are actual acid sulphate soils (AASS). Indications of acidification include field pH, peroxide oxidation pH, dried sample pH, and the presence of sulphur oxidizing bacteria and sulphate reducing bacteria. The study concludes that mangrove soil disturbance through dredging, drainage and exposure to air cause acidification. Keywords : Acidification, dredging, pH, mangrove, Niger Delta, oil exploration