4.7 S EDIMENTS
4.7.1 Physicochemical Parameters
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±S
D
NNPC/R PI (1985)
Sediment Quality Guidelines (SQG)
Calcium 252 319 292±27 233 323 278±45 0.896
Magnesium 792 1026 910±107 931 2452 1691±76
1
0.536
Anions Chloride, mg/kg
1544 2268 1981±306 710 2197 1453±74
4
0.446
Sulphate, mg/kg
14.23 148.2 105.6±54.7 126.8 149.2 138.01±
11.19
0.3
Nitrate, mg/kg 1.89 2.65 2.32±0.27 4.92 5.17 5.05±0.1 3
0.023
Carbonate, % 0.02 1.55 0.62±0.64 0.36 1.27 0.82±0.4 6
0.984
Organics, (mg/kg) Aliphatic hydrocarbon
18.52 36.22 26.14±7.81 4.44 9.58 7.01±2.5 7
0.325
EIA REVALIDATION FOR FORCADOS-YOKRI INTEGRATED PROJECT (NAG WELLS)
Parameters Proposed Project Area
Control P
Values
Limits
Min Max Mean±SD Min Max Mean±S
D
NNPC/R PI (1985)
Sediment Quality Guidelines (SQG) Oil and Grease 19.58 45.28 33.44±11.63 4.09 16.24 10.17±6.
08
0.082
TPH, 20.2 44.03 32.33±10.74 5.03 12.14 8.59±3.5
6
0.029 50***
THC, 18.52 39.54 30.4±8.5 4.78 14.62 9.7±4.92 0.058
BTEX <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 - Phenol <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 -
PAH <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 - 1610*
Heavy Metals (mg/kg)
Iron 2214 2844 2559.75±27
0.04
2709 3405 3057±34
8
0.583 2%**
Zinc 36.72 91.05 63.44±19.42 30.96 186.11 108.53±
77.58
0.531 1/8/1976 121*
Cadmium 0.99 1.31 1.17±0.12 0.97 1.85 1.41±0.4
4
0.784 BDL-8.0 0.99*
EIA REVALIDATION FOR FORCADOS-YOKRI INTEGRATED PROJECT (NAG WELLS)
Parameters Proposed Project Area
Control P
Values
Limits
Min Max Mean±SD Min Max Mean±S
D
NNPC/R PI (1985)
Sediment Quality Guidelines (SQG)
Copper 4.87 10.63 8.76±2.29 8.61 9.22 8.91±0.3
1
0.649 31.6*
Chromium 8.95 12.81 10.78±1.38 11.33 12.1 11.72±0.
38
0.087 BDL-8 43.4*
Nickel <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 - BDL-28.6
27.7*
Lead <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 - BDL-37 35.8*
Vanadium 12.35 15.87 14.13±1.37 12.9 15.62 14.26±1.
36
0.969 BDL-40.8
Arsenic 54.91 80.82 69.55±9.43 70.6 134.17 102.39±
31.78
0.599 9.79*
Mercury <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 - 0.18*
Barium <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 - Manganese 16.24 22.71 19.36±2.31 28.38 34.93 31.65±3.
272
0.274 460**
Silver (Ag) <0.010 0 ± 0 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±S
D
NNPC/R PI (1985)
Sediment Quality Guidelines (SQG) Cobalt (Co) 12.49 19.76 15.5±2.71 15.88 17.76 16.82±0.
94
0.904
Microbiology
THB x104cfu/g 1 3.5 1.89±1.01 4.5 4.7 4.6±0.1 0.118
HUB, x104cfu/g
0 1.07 1.04±0.03 1.2 1.2 1.2±0 0.5
TF x104cfu/g 1 2.1 1.31±0.46 3 3.2 3.1±0.1 0.055
HUF, x104cfu/g
0 1 1±0 0 0 0 -
SRB, x103cfu/g
0 0 0 0 0 0 -
* McDonald, et al., 2000;** Persaud et al. (1993);*** Massoud, et al., (1996); SQG:
Sediment Quality Guideline
EIA REVALIDATION FOR FORCADOS-YOKRI INTEGRATED PROJECT (NAG WELLS)
Sediment pH, Total Organic Carbon (TOC) and redox potential
The sediments ranged from sandy to sandy-clay texture. The pH of the sediments ranged from 6.0 to 6.7 with no significant difference between project location and control. Zobel (1946) reports that pH values in recent sediments generally ranged from 6.4 to 9.5. The observed pH values are generally acidic which is related to that of the overlying water (section 4.1.1). Sediment pH is a master variable controlling the speciation and bioavailability of metals.
Total Organic Carbon (TOC) ranged from 0.04 to 0.09 % with no significant difference between project location and control. USEPA (2002) recommended the following assessment categories for TOC in sediments:
• Low: ≤ 1%,
• Intermediate: 1 to 3%,
• High: >3%.
The 3% level is usually taken as the threshold between pristine and contaminated sediments. All levels were within normal values for unpolluted sediments.
Redox Potential ranged from 102.2 to 155.3 mV. According to DeLaune et al. (1999) the redox conditions of estuarine sediment varies widely from approximately +500 mV (surface sediments) to approximately -300 mV (strongly reducing sediments). All measurement of redox were oxidizing as expected in oxygenated surface sediments. According to Zobel (1946) positive EH values are generally characteristic of bottom deposits which are well oxygenated, or those which consist of coarse sediments. This is in line with the sediment textures of the study area characterized by coarse (sandy) materials and low organic matter (<1% TOC) content.
Exchangeable Cations and Anions
Chloride ranged from 710 to 2268 mg/kg with no significant difference between project location and control. Sulphate ranged from 14.23 to 149.2 mg/kg, Sodium ranged from 2134 to 4630 mg/kg, Calcium ranged from 233 to 323 mg/kg while magnesium ranged from 792 to 2452 mg/kg with no significant differences between project location and control. There are no environmental limits for major ions in sediments. Their levels are related to those of the overlying water. The observed levels are normal for brackish environments. The major cations are important with regards to buffering processes involving neutralization of acidic conditions.
Nutrients
Nitrate ranged from 1.89 to 2.65 mg/kg in the project area and from 4.92 to 5.17 mg/kg at the control with significantly higher (P<0.05) concentrations in the control locations compared to the project area (Figure 4.16). There are no limits for nutrients in sediments, but their levels are important for biochemical processes within the sediment particularly as it relates to microbial degradation. Lower nitrate levels in project area may suggest greater microbial assimilation/activity. Total fungi were higher in project area and hydrocarbon utilizing fungi was only observed in the project area (see 4.2.4).
EIA REVALIDATION FOR FORCADOS-YOKRI INTEGRATED PROJECT (NAG WELLS)
Fig. 4.16: Spatial distribut ion of nitrate in t he FYIP N AG field (2018) Heavy metals
Nickel, lead, mercury, barium and silver were not detected in the sediment samples. The absence of nickel is a pointer to absence of petroleum pollution in the sediments since nickel is closely associated with crude oil and Ni:V ratios have been used to infer crude oil pollution. Iron ranged from 2214 to 3405 mg/kg with no significant difference between project area and control. Iron concentrations in sediment were within geochemical background of 2% (i.e. 20,000 mg/kg) (Persaud et al.,1993). Manganese ranged from 16.24 to 34.93 mg/kg with no significant difference between project location and control. All values were within those expected in natural unpolluted sediments of 460 mg/kg. Zinc ranged from 30.96 to 186.11 mg/kg with no significant difference between project area and control. Although some concentrations were higher than the maximum reported for the Niger Delta (76.0 mg/kg-NNPC/RPI, 1985) all values were within levels in unpolluted sediments (121 mg/kg-McDonald et al., 2000). Cadmium ranged from 0.97 to 1.85 mg/kg with no significant difference between project area and control. Values were within those of previous report for the Niger Delta (BDL-8.0 mg/kg) but some concentrations were above the recommended levels in unpolluted sediment of 0.99 mg/kg. The highest cadmium level of 1.85 mg/kg was obtained in the offshore control station SWC2 indicating that activities around the proposed project area are not responsible for the observed levels. Copper ranged from 4.87 to 10.63 mg/kg with no significant difference between project area and control. Copper concentrations were generally within the recommended limits in unpolluted sediments of 31.6 mg/kg. Chromium ranged from 8.95 to 12.81 mg/kg with no significant difference between project location and control. Values were relatively higher than historical report for the Niger Delta of BDL-8.0 mg/kg but within recommended limits for unpolluted sediment of 43.4 mg/kg. Vanadium ranged from 12.35 to 15.87 mg/kg with no significant difference between project area and control.
0 1 2 3 4 5 6
SD1 SD2 SD3 SD4 SDC1 SDC2
Nitrate (mg/kg)
Sediment Sampling Locations
EIA REVALIDATION FOR FORCADOS-YOKRI INTEGRATED PROJECT (NAG WELLS)
Levels of vanadium were within those of previous report for the Niger Delta of BDL-40.8. Cobalt ranged from 12.49 to 19.76 mg/kg with no significant difference between project area and control.
Organics
Benzene, toluene, ethylbenzene and xylenes (BTEX) and Polycyclic Aromatic Hydrocarbons (PAH) were not detected in the sediments indicating absence of recent and residual petroleum pollution. Figure 4.17 shows the spatial trend of hydrocarbon levels in the study area. Total Petroleum hydrocarbons (TPH) ranged from 5.03 to 44.03 mg/kg. Total Hydrocarbons (THC) ranged from 4.78 to 39.54 mg/kg while oil and grease (O&G) ranged from 4.09 to 45.28 mg/kg.
Concentrations of TPH was significantly higher at the project area (P<0.05) (particularly SW2 and SW3) than at the control indicating low level contamination around the proposed project area.
However, the concentration of TPH was well below the stipulated limit for unpolluted sediments of 50 mg/kg indicating absence of petroleum pollution in the sediment.
Figure 4.17: Spatial distrib ut ion of hydrocarbo ns in t he st udy area (2018) Microbiology
Total Heterotrophic Bacteria (THB) ranged from 1 to 4.7 x 104 cfu/g, HUB ranged from 0 to 1.2 x 102 cfu/g, TF ranged from 1 to 3.2 x 104 cfu/g and HUF ranged from 0 to 1.0 x 104 cfu/g. There were no significant differences between project and control in bacterial counts but fungal counts of TF was marginally higher (P=0.055) at control location than project area while HUF was only detected at the project area. According to Omiema and Ideriah (2012) viable bacteria in shallow surface sediments usually range in number between 109 and 1010 cells per cm3 For sea water, bacteria counts up to 109 per gram are recorded for sediments (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
0 10 20 30 40 50
SD1 SD2 SD3 SD4 SDC1 SDC2
Concentration (mg/kg)
Sediment Sampling Locations
TPH THC O&G
EIA REVALIDATION FOR FORCADOS-YOKRI INTEGRATED PROJECT (NAG WELLS)
to low levels of organic carbon in the sediments. The distribution of hydrocarbon-utilizing microorganisms is known to reflect the historical exposure of the environment to hydrocarbons (Atlas and Barth a, 1972). The ratios of HUB to THB were very low (<<10%) suggesting absence of petroleum pollution in the sediments.