4.6 A QUATIC S TUDIES
4.6.1 Physicochemical Parameters of Surface Water
EIA REVALIDATION FOR FORCADOS-YOKRI INTEGRATED PROJECT (NAG WELLS)
EIA REVALIDATION FOR FORCADOS-YOKRI INTEGRATED PROJECT (NAG WELLS)
Parameters
Proposed Project Area Control
P Values
Limits
MIN MAX Mean±SD MIN MAX Mean±SD NNPC/RPI
(1985) Chemical Oxygen Demand (COD),
mg/l 9.58 18.2 14.35±3.1 12.55 13.28 12.92±0.365 0.18 1.9-2460
Alkalinity, mg/l 400 460 430±22 220 420 320±100 0
Bicarbonate (CO32-) mg/l 488 561.2 524.6±27.28 268.4 512.4 390.4±122 0.05
Nitrate, mg/l 0.5 0.6 0.56±0.04 0.53 0.57 0.55±0.02 0.317
Nitrite (NO2-), mg/l 0.01 0.03 0.02±0.01 0.02 0.02 0.02±0 1
Phosphorus, mg/l 0.02 0.09 0.05±0.036 0.013 0.029 0.021±0.01 0.655 Phenol, mg/l <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 -
MAJOR ANIONS
Chloride (Cl-), mg/l 4.33 9235 3478.6±3561 4.254 53.18 28.72±24.46 0 Sulphate (SO42-), mg/l 25.08 49.71 34.94±9.93 15.97 24.63 20.3±4.33 0.043
MAJOT CATIONS
Na2+, mg/l 3546 8461 5929±2340 1953 4333 3143±1190 0
K+, mg/l 188.58 443.7 321.6±116.2 118.82 223.89 171.36±52.54 0
Ca2+, mg/l 70.74 109.37 90.95±17.96 64.78 87.43 76.11±11.33 0.213
Mg2+, mg/l 359.11 1280 822.5±431 287.34 355.39 321.37±34.02 0
EIA REVALIDATION FOR FORCADOS-YOKRI INTEGRATED PROJECT (NAG WELLS)
Parameters
Proposed Project Area Control
P Values
Limits
MIN MAX Mean±SD MIN MAX Mean±SD NNPC/RPI
(1985)
HEAVY METALS
Cadmium, (mg/l <0.005 <0.005 <0.005 <0.005 <0.005 <0.005 1
Zinc, (mg/l) 0.55 0.62 0.6±0.029 0.544 0.57 0.555±0.011 0.655 BDL-0.77
Iron, (mg/l) 0.45 3.68 1.431±1.32 0.5 0.64 0.57±0.07 0.655 BDL-4.75
Copper, (mg/l) 0.02 0.04 0.03±0.01 0.029 0.032 0.031±0.002 0.18
Chromium, (mg/l) <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 1
Nickel, (mg/l) <0.002 <0.002 <0.002 <0.002 <0.002 <0.002 1 BDL-0.52 Lead, (mg/l) <0.002 <0.002 <0.002 <0.002 <0.002 <0.002 1 BDL-0.66 Vanadium, (mg/l) <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 1 BDL-1.56 Arsenic, (mg/l) <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 1
Mercury, (mg/l) <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 - Barium, (mg/l) <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 - Magnesium, (mg/l) <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 - Silver, (mg/l) <0.002 <0.002 <0.002 <0.002 <0.002 <0.002 - Cobalt, (mg/l) <0.001 0.29 0.13±0.12 <0.001 0.25 0.25±0 0.317
ORGANICS
EIA REVALIDATION FOR FORCADOS-YOKRI INTEGRATED PROJECT (NAG WELLS)
Parameters
Proposed Project Area Control
P Values
Limits
MIN MAX Mean±SD MIN MAX Mean±SD NNPC/RPI
(1985) Total Petroleum Hydrocarbon (TPH),
(mg/l) 0.006 0.212 0.109±0.103 0.361 0.361 0.361±0 0.18
Total Hydrocarbon Content (THC),
(mg/l)l 0.118 0.241 0.193±0.053 0.29 0.61 0.45±0.16 0.18
Oil and grease (O&G), (mg/l) 0.112 0.24 0.187±0.055 0.261 0.27 0.266±0.005 0.18 70.7 BTEX, (mg/l) <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 - PAH, (mg/l) <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 - Aliphatic Hydrocarbon, (mg/l) <0.031 0.241 0.124±0.117 <0.031 0.305 0.305±0 0.18
MICROBIOLOGY
THB x 102cfu/ml 1 2 1.34±0.39 1 1 1±0 0.317
HUB x 102cfu/ml 0 0 0±0 0 0 0±0 -
Total Fungi x 102cfu/ml 1 1.05 1.02±0.02 0 0 0±0 0.94
HUF, x 102cfu/ml 0 0 0±0 0 0 0±0 -
Total Coliform, MPN/100ml 14 29 22.5±5.94 23 34 28.5±5.5 0.655
Faecal Coliform Count, MPN/100ml 0 0 0±0 0 14 14±0 0.317
EIA REVALIDATION FOR FORCADOS-YOKRI INTEGRATED PROJECT (NAG WELLS)
Temperature
Temperature ranged from 27.8 to 29.7oC with no significant difference between the project location and control. The measured temperatures are normal for tropical coastal waters.
pH, Conductivity, Salinity, Total Dissolved Solids (TDS)
Hydrogen ion concentration (pH) varied between 7.5 and 7.9 with no significant difference between proposed project location and control. The pH is normal for tropical marine waters.
According to CWT (2004), the pH of seawater is usually between 7.5 and 8.4. Wetzel (1983) reports that the pH of marine waters is similar to that of estuarine waters and is usually stable between 7.5 and 8.5 worldwide. NNPC/RPI (1985) reported a range of 3.1-8.6 for surface waters of the Niger Delta. Lethal effects of pH on aquatic life occur below pH 4.5 and above pH 9.5 (Researchgate, 2017).
Electrical conductivity, Salinity and Total Dissolved Solids are interrelated parameters of salt concentration. Electrical conductivity ranged from 12040 to 42150 µS/cm with significantly higher (P<0.05) values around the project location compared to control. The fact that conductivity was higher around the proposed project area than further offshore at SWC2 may indicate local influence of saline conditions due to tides or effluent discharges. NNPC/RPI (1985) reported a range of 10-42,100 µS/cm for surface waters of the Niger Delta. The observed conductivity values are typical of brackish waters. Estuaries usually have electrical conductivity typically from >1500 to 51,500 µS/cm with values increasing as salinity increases (NSW, 2010). The levels of salinity (8,2-32.1 ppt) and TDS (6301-22260 mg/l) are also characteristic of brackish waters (Fondriest Environmental Inc, 2014).
Dissolved oxygen (DO), Oxidation-Reduction Potential (EH), Chemical Oxygen Demand (COD) and Biochemical Oxygen Demand (BOD)
The levels of DO, EH, COD and BOD are all indicators of the redox conditions in the environment.
Dissolved oxygen concentrations ranged from 5.38-5.43 mg/l with no significant difference between study locations and control. According to Chapman (1996) DO concentrations in unpolluted freshwaters are usually close to, but less than, 10 mg/l. Concentrations below 5 mg/l may adversely affect the functioning and survival of biological Community while levels below 2 mg/l may lead to the death of most fish. The observed DO levels are normal in brackish tropical waters. The moderately lower values may be attributed to the effect of salinity because the amount of oxygen that can dissolve in water, decreases as salinity increases (NOAA, 2017). NNPC/RPI (1985) reported a range of 2 to 9 mg/l for the Niger Delta. The present concentrations are normal for the study area.
The redox potential (EH) ranged from 135.5 to 186.1 mV with no significant difference between project location and control. According to Chapman (1996) surface waters containing dissolved oxygen are usually characterized by a range of EH values between +100 mV and +500 mV. The observed EH values are in tandem with the levels of DO in the waters.
EIA REVALIDATION FOR FORCADOS-YOKRI INTEGRATED PROJECT (NAG WELLS)
Chemical Oxygen Demand varied between 9.58 and 18.2 mg/l while BOD ranged from 4.11-8.31 mg/l with no significant difference between facility location and control. According to Chapman (1996) the concentrations of COD observed in surface waters can reach up to 20 mg/l in unpolluted waters indicating that the waters were unpolluted by organic matter. Also, NNPC/RPI (1985) reported a range of 1.9 to 2460 mg/l in the Niger Delta waters indicating that the observed values are usual for the study area. The BOD values were also within levels that do not indicate organic pollution. Typical natural water has a BOD from 0.8 to 5 mg/l (Alken Muray, 2006).
Alkalinity
Surface water alkalinity ranged from 220-460 mg/l. Alkalinity is the measurement of the water's ability to neutralize acids. It represents the buffering capacity of water and its ability to resist a change in pH. According to USEPA (2006) alkalinity of seawater averages 116 mg/l with lower values in brackish water.
Turbidity and Total Suspended Solids (TSS)
Turbidity and TSS are related parameters indicating particulates load in water. Turbidity ranged from 13.4 to 81.7 NTU while TSS ranged from 24.2 to 34.6 mg/l. The USEPA guidelines on suspended solids for the protection of fisheries resources prescribes values below 25 mg/l as indication of no harmful effects. In Estuaries, turbidity less than 10 NTU is considered healthy while poor water quality is indicated by levels above 20 NTU (NSW (2010). For most surface waters, turbidity is usually between 1 NTU and 50 NTU with possibility of higher values after heavy rains when the water levels are high while lower values can be expected in still water where suspended particles have settled (Researchgate, 2017). The observed levels of turbidity and TSS are indicative of poor water quality but such levels are commonly encountered in natural tidal waters due to tide-induced resuspension of sediments.
Nutrients
Nitrate ranged from 0.5-0.6 mg/l with no significant difference between project location and control. Nitrate levels above 22 mg/l in natural waters normally indicates man made pollution (Chapman, 1996). In marine environments, levels of 0.44 to 0.89 mg/l are considered ideal (Alken Murray, 2006) indicating that the water was unpolluted with regards to nitrates. Nitrites ranged from 0.1-0.3 mg/l with no significant difference between project location compared to control.
Nitrites occur in water as an intermediate product in the biological breakdown of organic nitrogen, their presence may infer recent input of organic wastes. According to Alken Murray (2006) the level of nitrite considered ideal for marine fish is between 0.04 and 0.15 mg/l. The observed levels should be expected because of multiple sources of organic matter inputs including tidal export from associated mangrove swamps.
Phosphate ranged from 0.013 to 0.09 mg/l with no significant difference between project area and control. According to Chapman (1996), phosphorus ranges from 0.02 to 0.06 mg/l in most natural waters. NNPC/RPI (1985) gave a range of 0.049 to 0.584 mg/l for phosphate in rivers of southern Nigeria. Present values are therefore normal for the Niger Delta.
EIA REVALIDATION FOR FORCADOS-YOKRI INTEGRATED PROJECT (NAG WELLS)
Major Anions and Cations
Chloride ranged from 4.25 to 9235 mg/l while sulphate ranged from 15.97 to 49.71 mg/l with significantly higher levels at the project location compared to control. Chloride and sulphate are major anions which contribute to the salinity of marine waters. For typical ocean waters, average concentration of chloride is 19,345 mg/l and that of sulphate is 2,701 mg/l (Anderson, 2008). These typical ocean levels are usually diluted in estuaries and in the vicinity of large rivers discharging into the sea as is typical of the present study area (Mouth of Forcados River) (Garrison, 2005).
RPI/NNPC (1985) reported values of 3 to 18,648 mg/l for chloride and BDL to 2,796 mg/l for sulphate in waters of southern Nigeria. The values of chloride and sulphate obtained are normal for the study area. However, the observation of higher values of chloride and sulphate within the proposed project area compared to control (SWC2) which is further offshore may indicate local saline intrusion due to tides or saline discharges.
Sodium, potassium, calcium and magnesium are major cations that contribute to the salinity of marine waters. Sodium ranged from 1953 mg/l to 8461 mg/l, potassium ranged from 118.82 to 443.7 mg/l, calcium ranged from 64.78 to 109.37 mg/l and magnesium ranged from 2.72 to 2.83 mg/l with significantly higher values at project location compared to control. Levels of major cations in sea water (Hem, 1985) average 10500 mg/l for sodium, 380 mg/l for potassium, 410 mg/l for calcium and 1350 mg/l for magnesium. Concentrations of major cations were within normal levels for nearshore waters. Lower values compared to average sea water is associated with riverine dilution. Figure 4.7 shows the spatial distribution of major cations in the surface water.
Although SWC2 is the farthest offshore location and should naturally show the highest levels of major cations, concentrations at SW2 and SW3 within the proposed project area were the highest.
A similar trend was found in conductivity, chloride and sulphate levels. This may be attributed to variations in tidal conditions during sampling or saline effluents from variable marine operations in the area.
EIA REVALIDATION FOR FORCADOS-YOKRI INTEGRATED PROJECT (NAG WELLS)
Figure 4.7: Spat ial distribut ion of major cations in surface w ater of the FYIP NAG field (2018)
Heavy metals
The level of dissolved metals in seawater is normally quite low (Turekian 1977). Cadmium, chromium, nickel, lead, vanadium, arsenic, mercury, barium, manganese and silver were not detected in the water samples. Zinc ranged from 0.55 to 0.62 mg/l, iron ranged from 0.45 to 3.68 mg/l and coper ranged from 0.02 to 0.04 mg/l with no significant difference between project location and control. Cobalt ranged from undetectable concentrations to 0,29 mg/l with no significant difference between project location and control. NNPC/RPI (1985) reported iron and zinc levels of BDL to 4.75 and BDL to 0.77 mg/l respectively for Niger Delta area indicating that the measured levels were within normal values for the study area. The level of zinc is well below harmful concentrations to aquatic biota of 120 mg/l (Alken Muray, 2006).
Organics
Levels of organics including Oil and grease (0.11-0.27 mg/l), Total Hydrocarbons (0.006-0.361mg/l) and Total Petroleum Hydrocarbons (0.118-0.61 mg/l) at the project location were not significantly different from those of the control. Polycyclic Aromatic Hydrocarbons and BTEX were generally below detection limits. The recommended maximum concentrations of mineral oil for drinking water supplies and fisheries protection are generally between 0.01 and 0.1 mg/l.
Concentrations of 0.3 mg/l or more of crude oil can cause toxic effects in freshwater fish (Alken Muray, 2006). Variable levels of oil pollution are usual in the Niger Delta area. NNPC/RPI (1985) reported average value of 70.7 mg/l of oil and grease for water of the Niger Delta indicating that the observed concentrations are normal for the study area.
0 1000 2000 3000 4000 5000 6000 7000 8000 9000
SW 1 SW 2 SW3 SW4 SW C1 SW C2
Concentration (mg/l)
Surface water sampling stations Na2+, mg/l K+, mg/l Ca2+, mg/l Mg2+, mg/l
EIA REVALIDATION FOR FORCADOS-YOKRI INTEGRATED PROJECT (NAG WELLS)
Microbiology
Total Heterotrophic Bacteria (THB) counts ranged from 1.0 to 3.0 x 102 cfu/ml, Total Fungi (TF) ranged from 0 to 1.05 x 102 cfu/ml. THB and TF did not show any significant difference between project area and control. According to Omiema and Ideriah (2012) viable bacteria in overlying water are typically about 106 and 107 cells per ml. For sea water, bacteria numbers generally range from 103 to 106 per ml (Azam et al., 1983). Bacterial abundance is also related to the organic matter concentration and to hydrological phenomena (Azam et al., 1983). The counts of bacteria and fungi were generally low which may be attributed to low levels of organic carbon and nutrients in the water. Hydrocarbon Utilizing Bacteria (HUB) and Hydrocarbon Utilizing Fungi (HUF) were not observed in the project area and control. The distribution of hydrocarbon-utilizing microorganisms is known to reflect the historical exposure of the environment to hydrocarbons (Atlas and Barth a, 1972). Absence of HUB and HUF are indicators of unpolluted environment with respect the petroleum hydrocarbons.