Research Journal of Chemical Sciences ______ ______________________________ ______ ____ ISSN 2231 - 606X Vol. 2 ( 3 ), 7 - 11 , March (201 2 ) Res.J.Chem.Sci. International Science Congress Association 7 Changes in Surface Water Physico - Chemical Parameters f ollowing the Dredging of Otamiri and Nworie Rivers, Imo State of Nigeria Iwuoha G.N. and Osuji L.C. Department of pure and Industrial Chemistry, University of Port Harcourt, Rivers State, NIGERIA Available online at: www.isca.in (Received 1 9 th September 201 1 , revised 6 th January 2012 , accepted 10 th Februry 2012 ) Abstract In an attempt to study the environmental impact of dredging on water quality, surface water quality parameters were monitored from June 2008 to October 2010. Samples were collected before and after dredging. Collected samples were analysed from five statio ns within the study area. The water physico - chemistry prior to dredging was consistent with that of researches done previously in that area. As a result of dredging however, the pH of the dredged canal was decreased from a mean value of 6.5 to 6.04, simila rly dissolved oxygen(DO) decreased from 13.88mg/l to 8.66mg/l, while TSS, BOD 5 and COD 5 decreased slightly after dredging. Acidity and alkalinity values did not show significant changes. Results of the ten - months post dredging monitoring of the Rivers water revealed that the water quality improved slightly during this period. The pH, DO, and TSS appreciated, while BOD 5, COD 5 turbidity, Total hardness, Acidity, Alkalinity, and Electrical conductivity depreciated to values close to pre - dredging concentration levels. We therefore concluded that the impact of dredging on the water quality is loca lised and short term. Keywords: Dredging, water quality, physico - chemical, otamiri and nworie rivers. Introduction Surface water typically transports three types of sediment namely: Dissolved load, suspended load and bed load. Chemical weathering in rocks produces ions in solution (e.g. Ca 2+ , Mg 2+ and HCO 3 - ), hence a dissolved load. Suspended sediments make surface water look cloudy or opaque; the greater the suspended load, the muddier the water. Bed load (silt, sand and gravel) settle on the bottom of the channel 1 . Surface water quality (SWQ) assessment/measurement falls into the following three categories: Physical characteristic: Temperature, colour, suspended solids and turbidity. Chemical characteristics: Nutrients, Minerals, Metals, Total Solids, DO, BOD 5 , C OD 5 , pH, Electrical conductivity, organic compounds, etc. Biological Characteristics: types and quantities of aquatic plants, animals, algae, bacteria and protozoa parasites 1, 2 . Dredging of several locations of Otamiri Rivers and Nworie Rivers (a tr ibutary of Otamiri River) were done in Owerri municipal and Owerri West l ocal g overnment of Imo State of Nigeria. Environmentalists have expressed fears over the impact of the dredging activities on the surface water quality of the affected Rivers, which h arbour aquatic life and serve as the sole source of treated water and recreation in the area 1 . In addition, turbidity plumes created as a result of dredging have been reported to cause a reduction in the population of phytoplankton and zooplankton 3 . During Dredging, waterway sediment, soil, creek banks and vegetation along the way of are typically removed and deposited as dredge spoils at the bank of the newly dredged canal. Since the dredged materials are uncapped and unconfined leachates with high turbidi ty often return to the body. This practiced have caused a number of environmental impacts including altered topography and hydrology, acidification and water contamination, which has resulted in vegetation damage and fish kill 4 - 8 . Bed sediment is a rese rvoir for heavy metals and is regarded as serious pollutants of aquatic ecosystems due to their environmental persistence, toxicity and ability to be incorporated into food chains 9 . Material and Methods Sampling and Sample Storage: For the purpose of this study, five (5) sample stations 1, 2, 3, 4 and 5 were established on the Rivers, (7 o 2E, 5 o 27N). Station 1 at r eservoir base area and it serves as control. Station 4 at Aba Road, about 2km downstream of Station 1, was there is massi ve solid waste dump. Station 2 at Nekede, about 3km downstream of station 4, where massive sand excavation is going on. Station 3 at FUTO, about 3km downstream of station 2, where dredging went on and station 5 at Nworie, a tributary of Otamiri River abou t 4 - 5km close to the point of confluence, where there was massive dredging. Surface water was collected periodically. On each occasion samples were taken from triplicate spots at each station to form one composite sample and the mean values noted for that season. Water samples were collected at 30cm below surface using 1 litre pol ythene bottle with screw caps. Research Journal of Chemical Sciences ______ _ _ _______________________________ ______________ _ ____ ISSN 2231 - 606X Vol. 2 ( 3 ), 7 - 11 , March (201 2 ) Res.J.Chem.Sci International Science Congress Association 8 During sampling, temperature, pH, turbidity, electrical conductivity, and total suspended solid were determined in - situ using thermometer, digital pH meter (Hach EC 20), turbidimeter (Hach 2100) and electrical conductivity/T SS meter (Hach CO 150) respectively. Separate samples were collected for d issolved oxygen (DO), c hemical oxygen demand (COD 5 ) and Biochemical oxygen demand (BOD 5 ) (using 125 ml reagent bottle with ground stopper). Standard methods were used for the laborat ory analysis. Titrimetric method was used for the determination of a cidity and a lkalinity, gravimetric method was used for s uspended solids, Winkler’s’ method was used for BOD 5 , and DO, open reflux dichromate oxidation method was used for COD 5 . Results an d Discussion The pH values at all the stations before the dredging were quite close, ranging from 6.4 to 6.8. The pH reduced slightly following dredging. Acidity and alkalinity values improved gradually throughout the remaining sampling period. The effect of temperature on the acidity is minimal, since temperature remained relatively stable during the study period. However, previous studies indicated that Niger delta waters are well buffered with pH ranging from neutrality to slightly alkaline. Therefore, i t is the presence of the unconfined dredged materials deposited adjacent to the canal that is helping to sustain the acidity of the canal via pyrite oxidation 10 . Turbidity of all the stations remained stable and similar before and after dredging. During t he dredging process, turbidity plumes were observed with turbidity and TSS increasing drastically at the dredging stations. Turbidity plumes have been reported to negatively impact estuarine organisms during dredging and disposal of dredged spoils, causin g dredging of primary productivity 10 . The study carried out during the dredging of the Cross River estuary, South East of Nigeria shows that water transparency decreased by over 25 - 50% for over a distance of 12km and that this effect was still persistent 1 8 months after dredging. The reason for the prolonged effect was attributed to the washing of leachates into the river from unconfined spoil dumps. Other studies have reported similar impacts following dredging. Electrical conductivity and BOD 5 showed s imilar pattern from station 1 down to station 5 i.e., gradual decrease downstream, before and after dredging 10 . Dissolved oxygen values showed gradual reduction downstream across the five stations and further reduction after dredging process, i.e., from a maximum of 16.1mg/l in the pre - dredging stage to (5.6 and 6.0) mg/l after dredging. Thus dispersion of organic matter, TSS downstream and oxidation of resuspended organic matter and pyrite after dredging are directly linked to DO depletion downstream and after dredging respectively. Resuspended organic matter and other oxygen - demanding substances are released as a result of dredging. BOD 5 and COD 5 showed a general increase and correlated negatively with DO. Total hardness varied at the respective site irr espective of the dredging operations. The same pattern was noted before and after the dredging operation. However, there was a slight decrease in total hardness after dredging. Conclusion The study shows that the dredging of Otamiri and Nworie (a tributary of Otamiri River) rivers near Owerri, triggered some physico - chemical changes of the water body particularly pH, TSS, DO, BOD 5 , COD 5 , turbidity, conductivity, acidity and alkalinity. Most of these physico - chemical changes were localized and s hort time (i.e. returning close to pre - dredging levels in less than ten months). Acknowledgement The authors are grateful to the management of Roefnel energy services for permission to use their laboratory for the analyses during the research. References 1. Iwuoha G.N., The impact of post dredging on surface water quality and sediment of Otamiri and Nworie rivers in Imo State of Nigeria . PhD thesis, university of Port Harcourt, Rivers State Nigeria (2011) 2. Todd D.K., Ground water Hydrogeology 2 nd edition. (1959) 3. Toumazis A.D., environmental impact dumping of dredged material at sea; a case study of the Limasol Port extension works , Wat. Sci. Technol ., 32 , 9 - 10 (1995) 4. Ohimain E.I., Environmental Impacts of oil mining activities in the Niger Delta m angrove ecosystem , In the proceedings of the International Mine Water Association (IMWA) conference held in Johannesburg, South Africa , Mine Water and the Environment , 503 - 517 ( 2003) 5. Ohimain E.I., Preservation of Niger Delta Wetland Resources Through prope r handling and Rehabilitation of Abandoned Waste Sulfidic Dredge Spoils , In: Environmental Science and Technology , 3 - 12 (2003) 6. Ohimain E.I., Available options for the bioremediation and restoration of abandoned pyritic dredge spoils causing the death of fr inging mangroves in the Niger delta , In: Biohydrometallurgy; a sustainable technology in evolution , 475 - 481 (2004) 7. Ohimain E.I., Environmental impacts of dredging in the Niger Delta , options for sediment relocation that will Research Journal of Chemical Sciences ______ _ _ _______________________________ ______________ _ ____ ISSN 2231 - 606X Vol. 2 ( 3 ), 7 - 11 , March (201 2 ) Res.J.Chem.Sci International Science Congress Association 9 mitigate acidification and enha nce natural mangrove restoration , 97 , 9 - 19 (2004) 8. Ohimain E.I., Bioremediation of heavy metal contaminated dredged spoil from a mangrove ecosystem in the Niger Delta , Ph.D . thesis, University of Benin, Benin City, Nigeria , (2001) 9. Mohsen M.Y., Mahmoud T.H., Amale, and Talaat A.S., Investigating the impact of flow conditions on metal content in the bed sediment , Thirteenth international water technology conference, IWTC , 13 , 983 - 997 (2009) 10. Elijah I.O., Tunde O., and Dorcas D.S., Changes in Water Physico - Chemical Properties following the Dredging of an Oil Well Access Canal in the Niger Delta , World Journal of Agricultural Sciences , 4(6) , 752 - 758 (2008) Table - 1 Recorded Values of Some Physico - Chemicals Parameters of Surface Water at va rious sites Acidity Alkalinity pH E/CNDTVY BOD - 5 COD - 5 DO TSS T - Hardness Turbidity SS1 4.1 2.4 6.4 22 18.45 43.83 16.1 42.1 10.12 0.04 SS2 3.8 3.1 6.5 26 15.63 45.4 14.6 60.2 10.27 0.04 SS3 4.5 4 6.4 24 16.23 40.41 15 43.1 17.5 0.04 SS4 2 3.1 6.8 24 13.8 53 11.3 81.7 5.05 0.04 SS5 2 4 6.4 20 17.37 47.6 12.4 23.4 1 0.04 MAX 4.5 4 6.8 26 18.45 47.6 16.1 81.7 17.5 0.04 MEAN 3.28 3.32 6.5 23.5 16.296 46.05 13.88 50.1 8.788 0.04 MIN 2 2.4 6.4 20 13.8 40.41 11.3 23.4 1 0.04 Table - 2 Recorded values of some Physico - Chemical Parameters of surface water at arious sites at Posttdredging Stage 13/02/2010 Acidity Alkalinity pH E/CNDTVY BOD - 5 COD - 5 DO TSS T - Hardness Turbidity SS1 4 2 6.22 20 12.8 39.6 9.6 40 8 0.03 SS2 4 3.2 6.15 26 11.52 32 8 60 8 0.04 SS3 4.8 4 6.4 25 11.52 32 8.8 40 16 0.03 SS4 2 3.3 6.1 24 9.6 40 5.6 80 4 0.03 SS5 2.4 4 6.37 19 12 38.6 8 20 0.8 0.02 MAX 4.8 4 6.4 26 12.8 40 9.6 80 16 0.04 MEAN 3.44 3.28 6.248 22.8 11.49 36.44 8 48 7.36 0.03 MIN 2 2 6.1 19 9.6 32 5.6 20 0.8 0.02 Table - 3 Recorded values of soil Physico - Chemical Parameters of surface water at various sites at Post - Dredging Stage 10/10/2010 Acidity Alkalinity pH E/CNDTVY BOD - 5 COD - 5 DO TSS T - Hardness Turbidity SS1 3.8 2.5 6.1 22 13.8 40.5 9.8 32.05 8.1 0.03 SS2 4 3 5.9 27 12.12 34 9.5 51.05 8 0.02 SS3 4.5 4 6.1 26 12.2 32.05 9.5 40 16.5 0.04 SS4 2 3.2 6 24 11.04 41.5 6 71 4 0.04 SS5 2 4 6.1 20 14.54 39.6 8.5 21 1 0.02 MAX 4.5 4 6.1 27 14.54 41.5 9.8 71 16.5 0.04 MEAN 3.26 3.34 6.04 23.8 12.74 37.53 8.66 43.02 7.52 0.03 MIN 2 2.5 5.9 20 11.04 32.05 6 21 1 0.02 Research Journal of Chemical Sciences ______ _ _ _______________________________ ______________ _ ____ ISSN 2231 - 606X Vol. 2 ( 3 ), 7 - 11 , March (201 2 ) Res.J.Chem.Sci International Science Congress Association 10 SS5 SS3 SS1 Figure - 1 Pictures of sample stations 5 and 3 during dredging. Station 1 at far right Figure - 2 Map of Owerri showing sampling points and Land usage Research Journal of Chemical Sciences ______ _ _ _______________________________ ______________ _ ____ ISSN 2231 - 606X Vol. 2 ( 3 ), 7 - 11 , March (201 2 ) Res.J.Chem.Sci International Science Congress Association 11 Figure - 3 Graphs showing changes in physico - chemical parameters just before dredging (10/06/2008) Figure - 4 Gra phs showing changes in Physico - Chemical parameters just after dredging (13/02/2010) Figure - 5 Graphs showing changes in physico - chemical parameters much after dredging (10/10/2010)