Seasonal Variation of Physicochemical Parameters of Water and Sediments from Iko River, Nigeria

Abstract

The seasonal  and  locational  variation of physicochemical parameters viz, p H, dissolved oxygen , biochemical oxygen demand, conductivity , salinity, chloride, sulphate, nitrate , ammonium ion , total nitrogen , total organic carbon , total hydrocarbon and exchangeable cations , in water and sediments of Iko River, South Eastern Nigeria were investigated . The import of this investigation is that Iko River , is in Iko Petroleum Belt of the Niger Delta that has suffered from years of intense petroleum exploitation , recent cases of oil bunkering in the area and moreso, its closeness to the Atlantic Ocean. In both dry and wet seasons considered , the variation of p H was not significant, and  was within the WHO limit of 6.5 to 8.0 for an unpolluted streams and rivers, while the salinity , chloride and exchangeable cations , were above WHO limits , indicating a high degree of saline water intrusion and influence in the water chemistry of the river  from the Atlantic Ocean. The sediment of  the river had acidic characteristics  and were predominantly of medium to fine grained sand ( > 70 % )  and less of silt ( < 15 % ) and clay ( < 10 % ) , indicating that Iko River is not an important sink for heavy metal and organic pollutants , implying that in a case of accidental discharge of chemical pollutants , will stay in the water column a longer time, thus accessible to the biota. Interestingly, the total hydrocarbon content of the sediments were greater than 200 mg/kg , the levels set for an area that is heavily polluted with petroleum.  Based on the physicochemical parameters of the water, the pollution index determined for the wet season gave a value of 0.97, which is less than a value of 1 for an unpolluted surface water body, but gave a pollution index of 1.34 during the dry season, which could be attributed to dilution from the surface runoff. The variation of the dissolved oxygen was not significant in both seasons and were higher than 5.0 mg/l  WHO limit for surface waters , and indicated a highly  oxidized environment . The phosphate content of the sediment of the river was lower in both seasons than average for soils , whereas , total nitrogen, total organic carbon and sulphur contents were higher than average for soils.

Keywords: Iko River, Sediments, Water, Physicochemical Parameters, Seasonal Variation, Pollution Index