POLLUTION STATUS OF GBALEGBE RIVER, DELTA STATE, NIGERIA

Abstract

Pollution of inland waters, limits their contributions to fish food supply. Regular monitoring of water quality in Nigeria is germane to aquatic pollution management. However, information on pollution dynamics, of highly anthropogenic impacted Gbalegbe River is limited. Therefore, the pollution status and its impact on physical, chemical, and biological parameters of Gbalegbe River, Nigeria were investigated.

Gbalegbe River (12.5 km)was spatially stratified into eight stations (S1 – low human activities; S2 – glass production factory; S3 – power plant; S4 – rubber processing mill; S5 – Oil farm tanks; S6 – Automechanic shops; S7 – Cassava processing mill and S8 – Sand mining) based on proximity to key anthropogenic activities. In each station, three sampling points were randomly selected. Temporal stratification covered wet (March - October) and dry (November – February) seasons. Water, sediments, Phytoplankton, Zooplankton and Benthic Invertebrates (BI) samples were collected from each station forth-nightly for 24, months following standard methods. Fish samples were collected from local fishers. Water samples were analysed for Dissolved Oxygen (DO, mg/L), Temperature (oC) and Biological Oxygen Demand (BOD, mg/L) using standard procedures. Phytoplankton, Zooplankton, BI and fish samples collected were counted and identified to species level. Diversity indices such as Shannon-Weiner (H) and Evenness (E) were calculated. Heavy Metals (HM) - Copper, Chromium and Lead in water (mg/L) and sediment (mg/Kg) were assessed using standard procedures. Pollution indices: Modified degree of Contamination in sediment (mCd): ˂ 1.5 (very low) to ≥ 32 (very high) and Geo-accumulation index (I-geo): 0 (unpolluted) to ≥ 5 (extremely polluted) were determined to assess HM contamination level. Data were analysed by using descriptive statistics and ANOVA at α0.05.

The highest (4.52±0.56) and least (3.13±0.67) DO were obtained in S1 and S2, respectively. Temperature and BOD ranged from 24.28±5.84, 28.45±2.06 (S3 and S2) to 0.65±0.03, 1.59±0.69 (S1 and S2), respectively. Temperature values were 27.55±1.60, 26.94±1.97; DO (5.75±0.73, 4.00±0.66) and BOD (1.10±0.67, 1.38±0.71) in dry and wet seasons, respectively. Individual number and species of phytoplankton recorded were 928, 25; Zooplankton (5,545; 23); BI (14,675; 22) and fish (14,308; 32), respectively. Highest and least dominant Phytoplankton were Pseudo – Nitzschia autralis (6.9%), Tchophyton ajelloi (0.1%); Zooplankton: Diaptomus species, (3.1%), Harpacticoid copepods (0.4%); BI: Hesperocorixa castanea (4.1%), Gyrinus species (0.3%) and fish: Clarias anguillaris (9.6%), Malapterurus electricus (0.3%), respectively. Diversity indices were: for phytoplankton H=3.61, 2.07; E=0.83, 0.17; zooplankton (H=3.81, 2.27; E=0.72, 0.41); BI (H=3.74, 1.99; E=0.73, 0.29) and fish (H=3.10, 1.99; E=0.71, 0.35) in wet and dry seasons, respectively. Highest and least significant levels of Copper (0.19±0.03, 0.11±0.02); Chromium (0.78±0.13, 0.03±0.01) and Lead (0.25±0.12, 0.10±0.01) in water were recorded in S2 and S1, respectively. Copper in sediment ranged from 0.07±0.02 to 0.19±0.04; Chromium (0.06±0.02 to 0.34±0.01) and Lead (0.03±0.01 to 0.08±0.02) in S2 and S1, respectively. The mCd was 0.15 while I-geo for Copper, Chromium and Lead were (0.02, 0.04); (0.03, 0.06) and (0.97; 0.02) in dry and wet seasons, respectively.

Gbalegbe River is fairly polluted with Lead, however, heavy metal contamination is generally low, thus its rich biodiversity could be threatened.