This study investigates the impact of sand dredging activities on coastal ecosystem and community survival around Ibeshe area of the Lagos Lagoon, Nigeria. Surface water and bottom sediment samples were collected from locations partitioned into Dredged Area (DA) and Undredged Area (UA) in the lagoon for laboratory analyses. Questionnaires were administered to community dwellers and sand miners to further analyze perception of locals. Significant differences in water quality parameters and sediments properties from Dredged and Undredged areas, and highly significant relationship between sand dredging and unsustainable ecological practices in Ibeshe were observed. One way ANOVA test indicates that all water quality parameters measured with exception of turbidity and nitrate concentration were not significantly different (P > 0.05) between Dredged and Undredged area. With exception of moisture content other sediment parameters measured were not significantly different (P > 0.05) between Dredged and Undredged areas. The project also determined the impact of dredging activities on the fisheries and fishing business in the environment. Turbidity values revealed that fishes will be negatively affected due to dredging activities; moreover dwellers pay little or no attention to conservation of the area due to unawareness. Sand dredging operations negatively influence ecological resources and water composition of the area. This project is designed to randomly sample the opinion of sand mining operators and residents; and questionnaires were administered to obtain data. Strict regulation and enforcement will assist to control ecological destruction and solve problems facing the lagoon environment.
Dredging entails the excavation of material from sea, river or lake beds and its relocation elsewhere; it is a necessary activity in infrastructural development. Amongst others, it improves navigable depths in ports, harbours and shipping channels, water and flood management, creation of new lands and habitats, and derivation of minerals from underwater deposits which is crucial for sustainable development of nature resources, economic values and quality of life [
Impacts of dredging on water column due to excavation and bottom sediments removal include, increase in turbidity which is consequent to the resuspension of sediments [
Emerging increase in anthropogenic pressures, including dredging of estuarine systems, warrants the development of physical, biological and chemical indicators of water quality and ecological change for effective policy implementations in aquatic systems [
Ecological impacts emanating from the dredging of vulnerable environments are damages to flora and fauna, topographic and hydrological alterations coupled with water quality impairments. Zooplankton, phytoplankton, benthic invertebrates and vegetation are other components of the aquatic environment affected by dredging activities [
Sediment characteristics are a determinant factor in contamination of dredged marine environments. This is due to the retention and adsorption of contaminants to sediments by contaminants that have settled on the bottom of marine water beds [
Mangrove zones bordering estuarine environments are characterized by sediments and soils rich in iron sulphides [
Although resuspension of sediments and subsequent increased turbidity brought about by dredging enhances the attenuation of light thus influencing phytoplankton abundance, this factor might not be critical to hinder phytoplankton productivity in dredged areas [
Nigeria is a developing country whose urban cities, particularly Lagos, are expanding at a high rate, thus sand dredging will continue to be a major source for land reclamation purpose and building materials for housing development. Consequently, sand dredging operations would still be very much relevant to the construction industry in Lagos state in actualizing its mega city pursuit and will remain so for several years.
Monitoring the dynamics of marine environments with respect to effects of dredging is necessary to evaluate as well as to predict its long-term physical and chemical stability. This could be accomplished by considering the results of parameters collected in pre-dredging and dredging phases. However, a more inclusive phase should be post-dredging phase, to establish the recuperative capability of marine environments and adjoining coastal areas to their natural state after dredging operations.
Ibeshe is one of the important coastal communities around Ikorodu waterfront characterized by several years of sand wining using manual or mechanical dredging operations; artisanal fisheries and transportation. However, over the years dredging of the lagoon has been a profit oriented activity with detrimental consequence on the environment. Apparently, impacts are destruction of wetlands and mangrove swamps, persistent water turbidity, disappearance of certain phytoplankton and zooplankton, including several species of macro-benthos which ultimately affect fishery production and distribution.
Limited studies exist on impacts of dredging activities on marine environments, particularly on the composition of water during the course of dredging operation. In addition, paucity of information on fisheries responses, distribution and abundance in the Lagos lagoon poses challenges which demands urgent observation. The present study seek to investigate the impacts of sand dredging on the ecology of Lagos lagoon in Ibeshe coastal community area, viz-a-viz its influence on water composition, fish and fisheries distribution as well as the perception of coastal community dwellers to environmental effects of sand dredging are discussed.
Ibeshe coastal community is located along Lagos Lagoon in Ikorodu, Lagos state on the Southwestern part of Nigeria coastline within longitude 3.47˚ to 3.29˚E and latitude 6.55˚ to 6.41˚ (
major source from River Owuru and flows into Lagos Lagoon at Ipakodo from where it receives tidal influence. The lagoon is utilized for multiple purposes including artisanal fishing, sand mining, transportation and domestic uses.
In other to establish biophysical status of the study area, collection of sediments and surface water samples were made at six sampling locations. Soil sample was collected at North East of Kudos Engineering Company (one of the existing dredging company operating in Ibeshe water front). Locally made boat was used as means of transport on the lagoon and the samples were collected at three different locations within the lagoon for both the Dredged area and Undredged area. Three Samples (sediments and waste water) for the Undredged area was first collected within the same location, the first sample for the Undredged area was taken at a depth of 1.95 m with major coordinate Latitude 6˚34'32.132" and Longitude 3˚28'16.59", second sample was taken at 2.13 m depth with major coordinate Latitude 6˚34'29.694" and Longitude 3˚28'11.899" at a distance 159 m apart. The third sample for the Undredged area was collected at a depth of 2.66 m with coordinate Latitude 6˚34'32.074" and Longitude 3˚28'8.645" at a distance of 128 m from the second point, the depth of sample collected was determined with the aid of a meter rule that was deep into the lagoon. Soil sample collected manually by divers, was immediately kept in polythene bags to prevent atmospheric and other environmental interactions. Waste water was also collected in this location with a white plastic keg to determine the physico-chemical quality of the water.
Samples for Dredged area were collected from a dredger that was in operation and discharging sand into a barge. The depths of the samples collected were determined from the dredger machine. The first sample collected for the Dredged area was taken at a depth of 11.3 m with coordinate Latitude 6˚34'37.292" and Longitude 3˚28'0.997", second samples was collected at a depth of 19.0m with coordinates Latitude 6˚34'26.36" and Longitude 3˚28'25.051" at a distance of 812 m apart. The third sample was taken at a depth of 15 m with coordinate Latitude 6˚34'30.627" and Longitude 3˚28'23.72" at a distance of 140 m from the second location. Water samples were also collected at these locations to determine the quality of the water. The samples collected for first sediments and waste water was taken to the laboratory to determine heavy metals in the sediments and hardness. Chemical Oxygen Demand (COD) and Biological Oxygen Demand (BOD) were also determined. Sample analyses were carried out for surface water and bottom sediment, using [
The results obtained from the analyses carried out above was compared to LASEPA standard to determine if the impact of dredging activities in the lagoon is of low, intensive or high impact on the environment.
Questionnaires were administered to Ibeshe coastal community dwellers to access the perception of dredging activities in their community. Fifty (50) questionnaires were administered and were all retrieved on the field to preclude loss of information from any of the respondents. Responses from the administered questionnaires collected were interpreted with the aid of statistical representation (pie charts), Figures 2(a)-(h).
Physico-chemical data were classified accordingly and were compared for variability using one-way Analysis of Variance (ANOVA). We assumed a normally distributed variables since observations were maintained at same geographical location throughout the sampling periods. Also, to better explain higher ordered interaction expected in this study, Pearson’s product moment correlation coefficient was used to evaluate relationships among the variables.
Water quality parameters of Dredged and Undredged area of the lagoon are
Parameters | N | Undredged Mean ± SD | Dredged Mean ± SD | LASEPA Standard |
---|---|---|---|---|
Colour | 3 | 180.7 ± 145.5 | 290.3 ± 107.8 | 250 Pt.Co.APHA |
Temperature | 3 | 25.7 ± 1.7 | 25.9 ± 1.2 | 40 |
pH | 3 | 6.7 ± 1.7 | 7.3 ± 1.3 | 5.5 - 9.0 |
Turbidity | 3 | 16.9 ± 2.2 | 23.1 ± 0.5 | FTU |
Conductivity | 3 | 70.2 ± 8.5 | 82.4 ± 19.0 | µS/cm |
Total suspended solid | 3 | 24.0 ± 15.1 | 2.7 ± 3.2 | 100 mg/l |
Total dissolved solid | 3 | 114.7 ± 99.3 | 155.3 ± 49.1 | 2100 mg/l |
Total solid | 3 | 138.7 ± 110.4 | 178.0 ± 49.5 | 2200 mg/l |
Total acidity (mg/l) | 3 | 36.0 ± 6.1 | 50.3 ± 7.5 | NS |
Total alkalinity (mg/l) | 3 | 86.7 ± 46.2 | 90.0 ± 39.1 | NS |
Chloride | 3 | 29.7 ± 4.7 | 29.3 ± 5.9 | 250 mg/l |
Nitrate | 3 | 1.3 ± 0.2 | 0.3 ± 0.3 | - |
Phosphate | 3 | 1.1 ± 0.1 | 1.5 ± 0.3 | - |
Sulphate | 3 | 4.0 ± 1.0 | 4.3 ± 2.3 | - |
Phenol | 3 | 0.0 ± 0.0 | 0.0 ± 0.0 | 1.0 mg/l |
Oil and Grease | 3 | 0.0 ± 0.0 | 0.0 ± 0.0 | 10.0 mg/l |
Dissolved oxygen | 3 | 5.5 ± 0.3 | 5.5 ± 0.5 | Not Less than 2 |
COD | 3 | 0.3 ± 0.6 | 0.0 ± 0.0 | 200 mg/l |
BOD | 3 | 0.1 ± 0.1 | 0.0 ± 0.0 | 50 mg/l |
Iron | 3 | 0.3 ± 0.3 | 0.5 ± 0.4 | 10.0 mg/l |
Sodium | 3 | 1.5 ± 0.4 | 2.4 ± 1.9 | - |
Potassium | 3 | 0.4 ± 0.1 | 0.3 ± .0.5 | 200.00 mg/l |
Total Plate Count | 3 | 73.3 ± 49.2 | 143.3 ± 77.7 | 0.5 mg/l |
One-way ANOVA test indicates that all sediment sample parameters measured with exception of moisture content were not significantly different (P > 0.05) between Dredged and Undredged areas.
presented in
Sediment samples showed similar trend as in water samples with values of temperature, nitrate and other parameters in Dredged and Undredged areas. One-way ANOVA test indicates that all sediment sample parameters measured with exception of moisture content were not significantly different (P > 0.05) between Dredged and Undredged areas.
Natural waters normally contain very small quantities of several essential metals including Fe, Cu, Ni, Mn, Zn, and Co. Aquatic organisms require these metals in trace amount, hence are referred to as trace elements or micronutrients. These metals become toxic when represent in relatively high concentrations and are non-biodegradable but are easily assimilated and bioaccumulates in aquatic organisms. However, the values of the metals in the water-body were in concentration below the LASEPA acceptable limit.
We evaluate the relations between variables in Dredged and Undredged areas using Pearson Product Moment Correlations coefficient (
Parameters | N | Undredged Mean ± SD | Dredged Mean ± SD | LASEPA Standard |
---|---|---|---|---|
Temperature | 3 | 28.83 ± 0.15 | 28.80 ± 0.30 | 35 - 40 |
pH | 3 | 7.21 ± 0.08 | 7.40 ± 0.14 | 6.0 - 9.0 |
Conductivity | 3 | 0.26 ± 0.13 | 0.14 ± 0.06 | 0.1 µS/cm |
Nitrate | 3 | 2.34 ± 2.00 | 1.60 ± 2.19 | 250 mg/kgN |
Phosphate | 3 | 0.48 ± 0.41 | 0.37 ± 2.12 | 150 mg/kgp |
Sulphate | 3 | 7.67 ± 4.72 | 7.00 ± 9.64 | 300 mg/kgS |
Zinc | 3 | 0.59 ± 0.95 | 0.29 ± 0.49 | <1 |
Copper | 3 | 0.04 ± 0.44 | 0.02 ± 0.00 | NS |
Iron | 3 | 0.00 ± 0.02 | 0.00 ± 0.00 | 5 mg/kg Fe |
Manganese | 3 | 0.13 ± 0.16 | 0.36 ± 0.52 | NS |
Lead | 3 | 9.73 ± 6.45 | 9.68 ± 13.24 | 5.0 mg/kg |
Potassium | 3 | 0.02 ± 0.03 | 0.11 ± 0.11 | 725 mg/kg k |
Nickel | 3 | 0.02 ± 0.03 | 0.02 ± 0.03 | NS |
Moisture | 3 | 1.07 ± 0.22 | 0.15 ± 0.05 | 0.250 |
% Organic Carbon | 3 | 58.05 ± 1.11 | 59.39 ± 0.61 | NS |
% Organic Matter | 3 | 407.38 ± 533.23 | 100.95 ± 1.05 | >6 |
Colour | Temp | pH | Turb | Cond | TSS | Acidity | Alkalinity | NO3 | PO4 | SO4 | DO | COD | BOD | Cu | Fe | Na | Pb | Cd | K | |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Colour | 1 | |||||||||||||||||||
Temp | 0.886* | 1 | ||||||||||||||||||
pH | 0.618 | 0.416 | 1 | |||||||||||||||||
Turb | 0.203 | −0.161 | −0.088 | 1 | ||||||||||||||||
Cond | −0.192 | −0.474 | −0.129 | 0.605 | 1 | |||||||||||||||
TSS | −0.749 | −0.705 | −0.691 | 0.276 | 0.221 | 1 | ||||||||||||||
Acidity | 0.320 | −0.038 | 0.353 | 0.714 | 0.057 | 0.114 | 1 | |||||||||||||
Alkalinity | −0.849* | −0.945** | −0.635 | 0.325 | 0.582 | 0.793 | 0.001 | 1 | ||||||||||||
NO3 | −0.312 | 0.130 | −0.196 | −0.845* | −0.559 | 0.122 | −0.687 | −0.189 | 1 | |||||||||||
PO4 | 0.655 | 0.484 | 0.270 | 0.514 | −0.337 | −0.154 | 0.794 | −0.434 | −0.460 | 1 | ||||||||||
SO4 | 0.349 | 0.479 | −0.100 | 0.107 | −0.667 | 0.148 | 0.399 | −0.398 | 0.158 | 0.768 | 1 | |||||||||
DO | −0.706 | −0.732 | −0.803 | 0.268 | 0.476 | 0.574 | −0.187 | 0.869* | −0.223 | −0.385 | −0.351 | 1 | ||||||||
COD | −0.839* | −0.700 | −0.499 | −0.113 | 0.126 | 0.882* | −0.156 | 0.682 | 0.452 | −0.465 | −0.051 | 0.371 | 1 | |||||||
BOD | −0.839* | −0.700 | −0.499 | −0.113 | 0.126 | 0.882* | −0.156 | 0.682 | 0.452 | −0.465 | −0.051 | 0.371 | 10.000** | 1 | ||||||
Cu | 0.137 | 0.197 | 0.158 | −0.478 | −0.214 | −0.695 | −0.433 | −0.280 | −0.003 | −0.239 | −0.386 | 0.071 | −0.601 | −0.601 | 1 | |||||
Fe | 0.153 | −0.013 | 0.026 | 0.114 | 0.221 | −0.507 | −0.069 | 0.030 | −0.546 | −0.032 | −0.441 | 0.379 | −0.654 | −0.654 | 0.809 | 1 | ||||
Na | −0.179 | −0.343 | −0.365 | 0.313 | 0.348 | −0.052 | 0.004 | 0.430 | −0.580 | −0.056 | −0.362 | 0.739 | −0.316 | −0.316 | 0.549 | 0.884* | 1 | |||
Pb | −0.336 | −0.541 | −0.279 | 0.272 | 0.357 | 0.039 | 0.087 | 0.548 | −0.575 | −0.127 | −0.452 | 0.744 | −0.166 | −0.166 | 0.502 | 0.821* | 0.956** | 1 | ||
Cd | −0.372 | −0.412 | −0.164 | 0.319 | 0.265 | 0.769 | 0.301 | 0.432 | 0.119 | −0.018 | 0.173 | 0.012 | 0.781 | 0.781 | −0.951** | −0.828* | −0.557 | −0.442 | 1 | |
K | 0.290 | 0.496 | 0.156 | −0.324 | −0.921** | −0.056 | 0.227 | −0.565 | 0.429 | 0.574 | 0.869* | −0.566 | −0.046 | −0.046 | −0.142 | −0.454 | −0.515 | −0.525 | 0.029 | 1 |
*Correlation is significant at the 0.05 level (2-tailed). **Correlation is significant at the 0.01 level (2-tailed). N = 6.
0.885, P = 0.05; n = 6), whereas, colour showed negative correlation with COD (r = 0.839; P = 0.01; n = 6), BOD (r = −0.839; P = 0.05; n = 6) and alkalinity (r = −0.526; P = 0.05; n = 6). Turbidity showed negative correlation with nitrate (r = −0.845, P = 0.05; n = 6). Since most nitrogen loading into aquatic systems has often been implicated with anthropogenic influence, stronger correlation between nitrate and turbidity may suggest some influence from mining activities.
Water quality parameters of Dredged and Undredged area of the lagoon is presented in
This study revealed significant differences in water quality parameters and sediments properties from Dredged and Undredged areas, and highly significant relationship between sand dredging and unsustainable ecological utilization of the water system.
One way ANOVA test indicate that all water quality parameters measured with exception of Turbidity and Nitrate concentration, were insignificantly different (P > 0.05) between Dredged and Undredged areas. With exception of moisture content other sediment parameters measured were insignificantly different (P > 0.05) between Dredged and Undredged areas. Also, the project assessed the impact of dredging activities on the fisheries and fishing activities in the environment, although water parameters are insignificantly affected this is well corroborated by the responses from the respondents (50 per cent) stating no effects on fishing activities
In comparison to LASEPA standard, physico-chemical parameter except for turbidity and nitrate contents were within acceptable standards as illustrated in
This work shows distribution pattern of metals in surface sediments is generally within permissible limits, however except for Lead which is higher in both Dredged and Undreged areas of the lagoon, following trends in Ria De Aveiro Lagoon in Portugal [
As COD and BOD results varied strongly with TSS (
Ibeshe area is rural wherein most of the dwellers are not informed on the need to conserve the environment and lack access to information on the importance of conservation,
The result of laboratory analysis conducted coupled with the information deduced from the questionnaires administered on the water samples collected and respondents’ responses indicate negative impact on fishery distribution. As a result of high turbid situation generated by dredging activity, [
It was discovered that the physico-chemical parameter results recorded during the dredging phase of the study location appeared to be lower in concentration and closer to a quality water condition when compared to pre-dredging average values from a 5 km radius from the study area. Prior to year 2009, a great deal of indiscriminate activities such as effluent discharge from industries and abuse of the water body by riparian community is evident, this perhaps explains the low water quality observed in the pre-dredging phase.
Consequent upon the aforementioned development, Lagos State Government banned all forms of dredging activities in the state and ultimately called for joint monitoring exercise by the Ministry of Waterfront Infrastructure and Development, LASEPA and Ministry of Environment against illegal dredging operations. However, this period of focused routine monitoring, regulation, enforcement and prosecution exercise carried out by the Lagos State Government is believed to be responsible for the relatively stable status of the physico-chemical parameters in the water body.
Aquaculture has a promising future in Lagos State [
The research focuses on peoples’ perception on the effects of dredging activities on water quality and fishery distribution in Ibeshe waterfront of Ikorodu area of Lagos lagoon. As revealed by the study and previous studies, Ibeshe coastal community is one of the important areas of Ikorodu waterfront. It is a coastal region characterized with long years of sand mining by either manual or mechanical dredging, artisanal fisheries and transportation. However, over the years, these dredging activities have been found to be profit oriented, only on the part of the operators and oftentimes to the detriment of the riparian communities and the environment at large. Consequently, some impacts resulting from this sand mining operation include destruction of wetlands and mangrove swamps, continual turbid appearance of water-body, disappearance of certain phytoplankton and zooplankton including several species of macro-benthos which ultimately affect fishery distribution.
In addition to sand dredging, uncontrolled discharge of domestic and industrial wastes also has pollution implications as they alter concentrations of the water composition and its quality. However, in order to achieve sustainable and environmentally suitable condition of sand dredging activities in Lagos State, it is opined that the policy and regulation governing this operation should be enforced more effectively.
However, this project reveals that dredging activities have altered the lithology of the study area and also dredging impact on the ecosystem is low and temporary as nutrients and resources lost as a result of dredging can be regained when the activities is stopped.
In view of the above, a more collaborative work should be encouraged in the area of monitoring, enforcement and environmental regulation amongst relevant Ministries, Departments and Agencies (MDAs) to achieve sustainable dredging operations and relatively stable aquatic ecosystem.
The Ministry of Waterfront Infrastructure and Development saddled with the responsibility to regulate and monitor dredging and other activities along shorelines in Lagos State should ensure the proper management of dredging operations in waterways. This should be accomplished by granting of approvals for dredging operations in accordance with the principles of Ecologically Sustainable Development.
We immensely appreciate Late Dr J.I. Agboola and Mr J.Y. Appia of the University of Lagos and Nigerian Institute for Oceanography and Marine Research respectively for their contributions to this paper.
Adekunbi, F.O., Elegbede, I.O., Akhiromen, D.I., Oluwagunke, T.O. and Oyatola, O.O. (2018) Impact of Sand Dredging Activities on Ecosystem and Community Survival in Ibeshe Area of Lagos Lagoon, Nigeria. Journal of Geoscience and Environment Protection, 6, 112-125. https://doi.org/10.4236/gep.2018.62008