Over the past decades, the problems posed by Hydrocarbon contamination have become a source of concern. Environmental pollution have adversely affected all forms of biodiversity, infringing on the ambient quality of the abiotic environment such as; soil water and air ¹. As established in literature, consistent exploration of hydrocarbon have incured rapid decline of biodiversity ². Statistically, it was reported that Nigeria have recorded over 4000 hydrocarbon spill between 1976 and 1996. In Akwa Ibom, incident of oil spill was quantified to be over 1000000 barrel, posing grave consequences to the coastal environment ³.

Hydrocarbon or crude oil is a homogenous fluid substance with carbon as its massive substantial component. Notwithstanding, the origin of hydrocarbon dwells on two school of thought, being the abiotic theory and the biotic or biogenic theory. The formal believes crude oil originated from inorganic substances, while the latter adduce its origin to anaerobic decomposition of organic matter. As established by Obuasi ⁴, the biogenic theory was able to prove the presence of porphyrins as a biomarkers of chlorophyll, in samples isolated from hydrocarbon.

As a result of anthropogenic activities associated with the emission of hydrocarbons, including but not limited to; pipeline sabotage, accidental discharge and rupture of pipeline, large volumes of hydrocarbons contaminants are released into the environment. Such releases often pose immediate, or long term ecotoxicological and environmental degradation. The toxicity of hydrocarbon pollutants pose grave consequences to both terrestrial and aquatic environments, thereby affecting keystone biota of the ecosystem ¹.

Hydrocarbons are common residual pollutant found in most organic waste around oil and gas exploration facilities ⁵. These pollutant are usually transported through runoff, accidental vessels discharge, ruptured pipelines, and even by the act of sabotage ⁶. The flow station is in Bayelsa state, which is a wetland with several river, creek and endangered species ¹. The impacts of hydrocarbon exploration and exploitation on biodiversity in the area needs to be quantified. As such, this research have become necessary in order to unravel the potential impact of possible hydrocarbon pollutant in the study area.

Results of the physicochemical properties of the recipient surface water in the study area is presented in Table 1. Results showed that the pH values ranges from 6.58 ± 0.04 - 6.76 ± 0.01, with a slightly higher value of 6.77 ± 0.02 in the control station. The highest pH value was indicated midstream, while the lowest value was downstream. In water quality assessment, lower pH values indicates acidity, compared to higher pH value which reflects alkalinic water. Notwithstanding, the WHO threshold values stipulates pH value 6.50 - 8.50 for safe and potable water. Notwithstanding, the pH values of the water from the study area was almost neutral. Thereby falling within the safe range (6.50 – 8.50), stipulated by World Health Organisation. Result on the conductivity of the water ranges from 168. 30 ± 13.98 - 194.57 ± 3.78 µS/cm (Table 1). The highest conductivity value was indicated downstream compared to upstream which had the lowest conductivity value (Table 1). There is no stated regulatory limit for conductivity. However result of the control had value (180.67 ± 0.33 µS/cm) that was in similar trend with the study area (Table 1).

Result on turbidity of the water sample was in the range of 8.29 ± 0.04 - 10.66 ± 0.02 NTU (Table 1). Comparatively, the control station had higher turbidity value (18.68 ± 0.07 NTU). Meanwhile the highest and lowest turbidity values were indicated downstream and upstream respectively. The World Health Organisation stipulates that the turbidity of potable water should not exceed 5 NTU, as such result indicates that the water is not suitable for drinking purpose. Since water is a universal resource, tolerable limits varies depending on the affected species, therefore the intended use of the water must be put into consideration.

As presented in Table 1, the level of salinity of the water ranges from 0.07 ± 0.00 - 0.09 ± 0.00 mg/l, with control value of 0.08 ± 0.00 mg/l. Furthermore, the highest and lowest values downstream and upstream respectively. The salinity level of the study area was relatively low and within stipulated threshold limit of 600 mg/l (Table 1). The results of Total Suspended Solid (TSS) ranges from 11.29 ± 0.04 - 13.66 ± 0.02 mg/l, with a higher control value of 17.53 ± 0.02 mg/l (Table 1). Results also indicated that highest TSS value was recorded downstream, which lowest TSS value was upstream (Table 1).

The results of Total Dissolved Solids (TDS) ranges from 72.67 ± 1.45 - 90.00 ± 0.58 mg/l, with a higher value of 104.00 ± 2.08 mg/l in the control station (Table 1). Based on spatial distribution, the highest TDS value was recorded downstream. On the other hand, he lower TDS value was recorded upstream (Table 1). Results of Total Solid (TS) ranges from 83.96 ± 1.4 9 - 103.66 ± 0.60mg/l, with a higher value of 221.66± 2.08mg/l in the control station. Also the highest level of total solid was recorded downstream as opposed to a lower value upstream (Table 1). The tolerable limit of total solid in water is 1600mg/l, therefore total solid in the water is in conformance with regulatory limit.

Result of the ionic assessment of the water samples is presented in Table 2. The level of sulphate ranges from 2.43 ± 0.01 - 4.28 ± 0.02 mg/l. Meanwhile the value of sulphate in the control station was 4.66 ± 0.02 mg/l. The reported level of sulphate in this study complied with the regulatory limit (100 mg/l). The highest level of sulphate was recorded downstream, compared to result upstream that recorded the lowest value of sulphate (Table 2). Compared to values of the control station (0.33 ± 0.01 mg/l), the level of nitrate in the study area ranged from 0.19 ± 0.01 - 0.28 ± 0.01 mg/l (Table 2). Also, the highest and lowest values of nitrates were recorded downstream and upstream respectively (Table 2). There is no stated regulatory limit for nitrate, but comparison of spatial values to values of the control station indicate similar trending.

Carbonate ion level ranges from 1.14 ± 0.07 - 2.06 ± 0.07 mg/l with higher value (2.56 ± 0.03 mg/l) in the control station. Notwithstanding, the highest and lowest level of carbonate ion were recorded downstream and upstream respectively. In addition, the regulatory limit of carbonate was not specified, but the higher level of carbonate reported in the control station indicates lesser impact of carbonate in the study area (Table 2). The level of calcium (Ca) ranges from 8.45 ± 0.10 - 11.70 ± 0.25 mg/l. In addition, the control station recorded higher value of 12.03 ± 0.37. Notwithstanding, calcium level complied with the allowable limit of WHO (Table 2). The values of calcium was extremely low and conform to the threshold value of WHO (Table 2). Similarly, highest level of calcium was recorded downstream, while the lowest value was reported upstream (Table 2).

The level of magnesium ranges from 1.14 ± 0.07 - 2.56 ± 0.03 mg/l. Meanwhile a higher value (2.66 ± 0.07mg/l) was recorded in the control station. While all values of magnesium complied with regulatory limit of WHO, the highest and lowest levels of magnesium were similarly recorded downstream and upstream respectively. Furthermore the levels of sodium ranged from 4.37 ± 0.15 - 5.62 ± 0.03 mg/l, while the control station had higher value of 5.66 ± 0.03 mg/l. Meanwhile the highest and lowest levels of sodium were recorded downstream and upstream respectively. The levels of potassium was highest downstream and lowest upstream. Notwithstanding, spatial potassium level ranges from 1.76 ± 0.01 - 2.21 ± 0.01 mg/l. No regulatory limit, but potassium level was higher in the control station 2.45 ± 0.03 (Table 2).

Generally the measured concentration of TPH in the study area were low, compared to THC. Notwithstanding, the values of THC ranges from 0.92± 0.08 - 1.51±0.03 mg/l, with a lower value in the control station 0.10 ± 0.00 mg/l (Figure 2). In addition, the levels of Total Hydrocarbon content (THC) was highest downstream and lowest upstream (Figure 2). The levels of Total Petroleum Hydrocarbon ranged from 0.37± 0.13 - 0.76±0.07 mg/l, while the reported value of the control was lower (0.04± 0.00 mg/l). Furthermore, the highest level of TPH was indicated downstream, while the lowest level was upstream (Figure 2). As established, the Nigerian regulatory limit states that the residual concentration of THC in the environment should not exceed 50 mg/l, therefore values reported in this study were quite low and complied with regulatory limit.

Figure 2. Levels of Total Hydrocarbon and Petroleum Content

As established in literature, Hydrocarbon pollutant in surface water can adversely affect aquatic biota ^{3, 8, 9}, by disrupting their productivity and metabolic rate ¹⁰. Although the extent of adverse effect is largely dependent on the affected specie ^{11, 12}. The adverse effect can be either directly or indirectly. For instance, when the physicochemical properties of surface water is beyond tolerable limit, biota that depends on such water body are adversely affected. Biota have the ability to directly accumulate hydrocarbon toxicant into their tissues. Fortunately, results of this study generally indicated low degree of contamination, in terms of physicochemical properties of the recipient water body around the flow station.

Result of TPH in our study is very low and in tandem with to values of 0.045 to 0.307 mg/l in the water samples from Algoa Bay showing as reported by Adeniji et al. ¹³. On the other hand, higher levels of TPH have been reported by several authors in Africa and other countries around the world. They include Ceuta harbour in North Africa ¹⁴, and Musa Bay ¹⁵, as well as the Barnegat-Bay-Little Egg Harbor Estuary, located in the United States ¹⁶. Hydrocarbon contaminant sink down to affect sediment as abyssal sink ¹².

This study investigated the impact of Etelebou Flow Station on surface water on the Gbarain, axis of Bayelsa State, Nigeria. Fortunately, results indicated very low level of contamination on recipient water bodies around the flow station. The assessed physicochemical parameters were within regulatory limit. The assessed ionic content of the water was low as well. Similarly, the levels of TPH and THC were very low and tolerable. In most cases, physicochemical properties of samples from the control station were even higher. Generally, the order of contamination were reported as; Downstream > Midstream > Upstream. This study concludes that emissions from the flow station should be monitored regularly, in order to avert potential adverse Impacts.