World Journal of Agricultural Sciences 4 (6): 752-758, 2008 ISSN 1817-3047 © IDOSI Publications, 2008 Corresponding Author: Elijah I. Ohimain, Department Biological Sciences, Niger Delta University, Wilberforce Island, Amassoma, Bayelsa State, Nigeria 752 Changes in Water Physico-Chemical Properties Following the Dredging of an Oil Well Access Canal in the Niger Delta Elijah I. Ohimain, Tunde O. Imoobe and Dorcas D.S. Bawo 1 2 1 Department Biological Sciences, 1 Niger Delta University, Wilberforce Island, Amassoma, Bayelsa State, Nigeria Department of Animal and Environmental Biology, University of Benin, Benin City, Nigeria 2 Abstract: In an attempt to study the environmental impacts of dredging on water quality, surface water was monitored for over one year, from December 1997 to December 1998. Samples were collected twice before dredging, in December 1997 and in June 1998, corresponding to dry and raining seasons, respectively. Samples were also collected immediately after dredging in July 1998 and were monitored in August, September and December 1998. Collected samples were analyzed from five stations within the study area, station 1 - 5. Station 1 was in the dredged canal, which was originally a side branch of the Warri River tributary. In the Warri River tributary, Station 2 was 500m upstream and Station 3 was 1000m upstream of the mouth of the dredged canal, whilst Stations 4 and 5 were respectively 500m and 1000m downstream of it. Stations 3 and 5 represented the reference situation to which possible dredging effects could be compared. The water physico-chemistry prior to dredging was consistent with that of other locations within the Niger Delta. As a result of dredging however, the pH of the dredged canal was decreased from 7.2 to 4.0, dissolved oxygen (DO) decreased considerably from 6.0mg/l to 0.4 mg/L, while BOD was increased from 1.0 mg/l to 18.0 mg/L. COD, oil and grease, conductivity, 5 TDS and sulphate values similarly increased, while nitrate and alkalinity values decreased after dredging. At the dredged canal, turbidity and TSS increased rapidly after dredging, attaining a value of 11,398 NTU and 8200 mg/l respectively. Results of the six-month post dredging monitoring of the river water revealed that the water quality improved significantly during this period. The pH and DO appreciated while COD, BOD , oil and 5 grease, depreciated to values close to pre-dredging concentrations. We therefore conclude that the impact of dredging on water quality is localized and short term. Key words: Dredging Mangrove Niger Delta Oil exploration Warri River Water quality INTRODUCTION to the water body. This practiced have caused a number The Niger Delta is one of the most prolific oil and gas and hydrology [1-4], acidification and water provinces along the Atlantic Coast of West Africa. Oil contamination [5], which has resulted in vegetation and gas exploration activities in the Niger Delta are often damage and fish kills [1]. In addition, turbidity plumes constrained by access difficulties. Due to anatomising created as a result of dredging have been reported to network of creeks and river systems dominating the cause a reduction in the population of phytoplankton and landscape of the Niger Delta, oil and gas development zooplankton [6]. In the study carried out by Lewis et al. companies often times found it difficult to gain access to [7] in the Gulf of Mexico, environmental impacts of prolific hydrocarbon bearing zones. They often carry out dredging included reduction in numbers of benthic dredging in order to overcome this constraint. During species, increased turbidity, reduction of primary dredging, waterway sediment, soil, creek banks and productivity and mobilization and increased vegetation along the way of are typically removed and bioavailability of sediment trace metals. But the deposited as dredge spoils at the bank of the newly study concluded that the effects of dredging on dredged canal. Since the dredged materials are uncapped surface water pH, dissolved oxygen and temperature and unconfined leachates with high turbidity often return were negligible. of environmental impacts including altered topography