Heavy Metal Levels and Distribution in Water, Sediments and Benthic Macroinvertebrate of Woji Creek and Bonny Estuary, Rivers State, Nigeria
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The occurrence and distribution of heavy metals in excess of natural loads has become a problem of increasing concern. The study on macro faunal distribution and heavy metal contamination of Woji creek and upper reaches of the Bonny Estuary was necessary to determine the impact of anthropogenic perturbations and heavy metal contamination on macrofaunal abundance, composition and physicochemical characteristics of the water body. Physicochemical characteristics, distribution of macrobenthic invertebrates and heavy metals in surface water, sediment and macrobenthic fauna of Woji creek and upper reaches of the Bonny Estuary, Niger Delta- Nigeria were investigated over a two year period (October, 2012 to September, 2014). A total of ten stations were established along the main creek course and water, sediment and macro faunal samples were collected at the different locations monthly using standard ecological and chemical methods. Population-level (density, size distribution), community-level (species richness matrices) and multivariate analysis of community composition were used to evaluate responses of macro fauna to ecological imbalance induced by anthropogenic pollution in the Woji Creek and upper reaches of the Bonny Estuary. Heavy metals (Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Cd and Pb) levels in water, sediment and crab (Uca tangeri) were determined using Inductively Coupled Plasma Mass Spectrometry (ICP-MS) Agilent 7500c. The surface water temperature (28.23 ± 2.120C), showed seasonal changes typical of the Niger Delta region while the pH with a mean value of 6.66 ± 0.39 did not significantly vary throughout the study period irrespective of season. Total Organic Carbon (TOC) was generally low (0.23 ± 0.06) and there were no seasonal variation in Biochemical oxygen demand (BOD). Higher nutrients levels were observed at sampling locations closer to areas receiving the abattoir effluents than the upstream and DO levels (4.14 ± 2.87 mg/l) within the sampling stations were generally higher in the rainy season. The correlation coefficient of the physicochemical parameters of water showed significant differences between most of the parameters. There was positive correlation with salinity, pH and conductivity at (p>0.05), and negative correlation with salinity and temperature at (p > 0.01). Physicochemical properties of the water body were mostly within set limits (FMEnv). The results of the macrobenthic invertebrate analysis revealed that macrobenthic invertebrates were represented by 26 species belonging to 3 phyla and 5 classes (Oligochaeta, Polychaeta, Gastropoda, Crustacea and Bivalvia). Polychaeta dominated the faunal composition with 12 species, Gastropoda and Bivalvia had 6 species. Capitella capitata, Nereis diversicolor, Lumbriconereis japonica and Ophidonais serpentine were well distributed and abundant. Uca tangeri accounted for the highest in density while Nereis diversicolor and Uca tangeri were the most widely distributed. However, the abundance in species diversity of macrobenthic invertebrate encountered was lower compared to earlier studies. Most heavy metals were below detection limit in water but recorded significant increases in sediment and biota (p ˂ 0.05). The levels of heavy metals in sediments were in the decreasing order; Fe ˃Mn ˃ Cu ˃Ni˃ Co ˃ Zn ˃ As ˃ Cr ˃ Pb ˃ Cd. The observed mean concentrations of heavy metals in surface water varied from -0.0002mg/L for Cadmium (Cd) - 2.8272 mg/L for Iron (Fe) in the dry season and 0.0002mg/L (Cd) – 7.8677mg/L (Fe) in the wet season while the results of the spatiotemporal variation in sediment heavy metals revealed a mean concentration that varied from 0.03mg/kg (Cd) – 30058.9mg/kg (Fe) in the dry season and 0.02mg/kg (Cd) - 33873.94mg/kg (Fe) in the wet season. The observed levels of heavy metals accumulated in Uca tangeri were; Fe ˃ Cu ˃ Fe ˃ Mn ˃ Zn ˃ Ni ˃ As ˃ Cr ˃ Pb ˃ Cd. Although the trend of the heavy metals in the crab (Uca tangeri) was lower than those observed in sediment with the exception of Cu, evaluated Biosediment accumulation factor (BSAF) was relatively higher for Cd, Cu and Ni. The results of the computed pollution load indices; Enrichment factor (EF), Pollution Load Index (PLI) and Degree of Contamination (Cd) indicated low levels of enrichment and moderately contaminated ecosystem while Geoaccumulation index (< 0) also revealed an unpolluted ecosystem. Compared sediment quality guidelines (SQG) revealed that the levels of heavy metals in sediment were less than the probable effect level. However, Target Hazard Quotient (THQ) revealed that consumers of the crab, Uca tangeri might be at risk of non-carcinogenic health hazard after a prolonged period. The implication of this present finding calls for vigilance, continous monitoring and risk assessment.
A Thesis Submitted to the School of Postgraduate Studies, University of Lagos
Marine Sciences , anthropogenic perturbations , Heavy Metal Contaminations , Water Body , Research Subject Categories::NATURAL SCIENCES::Earth sciences
Ibanga, L.B (2016). Heavy Metal Levels and Distribution in Water, Sediments and Benthic Macroinvertebrate of Woji Creek and Bonny Estuary, Rivers State, Nigeria. A Thesis Submitted to University of Lagos School of Postgraduate Studies Phd Thesis and Dissertation, 59pp.