Impact of Sand Dredging Activities on Ecosystem and Community Survival in Ibeshe Area of Lagos Lagoon , Nigeria

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.


Introduction
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 [1].
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 [2].Other impacts may result from the dredging of polluted areas with an associated release of anoxic bottom sediments to the surface, leading to the oxidation of metal sulphides [3].Biologically available cations are released in this process, a common phenomenon observed in estuaries subjected to dredging [3] [4] [5] [6].This mobilisation process impacts estuarine water systems due to the persistent toxicity effects of a number of trace elements [6] [7].
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 [8].Phytoplankton are efficient and easily detectable indicators of water and ecological change due to their sensitivity to several environmental stressors [9].
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 [10] [11] [12] [13].The socio-economic functions of coastal environments are also often hampered by dredging operations thus creating ecosystem imbalance.
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 [14].Sediments retain nutrients, including N and P [15].Metals; Zn, Hg, Cd, As, Pb, Cu and Ni are retained and transported by sediments.Transportation of contaminants by sediments is dependent on several factors, primarily particle size [16].Ocean and wetland systems, tides, currents and waves can be attributed to sediments transportation [17] [18].
Mangrove zones bordering estuarine environments are characterized by sediments and soils rich in iron sulphides [19].Exposing these sulphide-containing sediments through dredging initiate oxidative reactions results in acidification of estuarine environments [20].Acidifications of estuarine systems have been implicated as the cause of death in fish, vegetation, and change in water quality, and contamination by heavy metals [21] [22] [23].
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 [24].Phytoplankton community structure has been found to be reconfigured, favouring the dominance of benthic diatoms thriving in water column as a result of suspended particulate matter that occur during dredging.High benthic: pelagic diatom ratio has been found to be prevalent in perturbed areas [25].
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.

Study Area
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˚ (Figure 1).The lagoon has a wide catchment with its Journal of Geoscience and Environment Protection

Sample Collection and Analyses
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 [26] method and [27] methods respectively.
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.

Questionnaire Administration
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).

Statistical Analysis
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
Water quality parameters of Dredged and Undredged area of the lagoon are

Sediment Samples
Sediment samples showed similar trend as in water samples with values of tem-Journal of Geoscience and Environment Protection perature, 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 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.
Table 2 gives the descriptive statistics of the results of the investigated heavy metals in the sediments from the study area.Nine ( 9) heavy metals were considered for indicator of pollution, and Pb was the most abundant with average value of 9.68 mg/kg as against recorded average value of 6.45 mg/kg lead metal during pre-dredging phase from this environment.
Water quality parameters of Dredged and Undredged area of the lagoon is presented in Table

Discussion
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 showed that fishes will be negatively affected due to dredging activities, Table 1.
The people living around the place pay little or no attention to conservation of the area due to unawareness.The sand dredging operators' activities influence negatively on the ecological resources and water composition of the Lagoon.
In comparison to LASEPA standard, physico-chemical parameter except for turbidity and nitrate contents were within acceptable standards as illustrated in Table 2. From the results of the samples analysed, it is therefore apparent that the impact of dredging on water quality is localized and short-term, hence there is no significant change in water composition compared to standard water quality concentrations.
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 [28].A plausible factor for this high level is associated with deposition of petroleum products from motorised out board engines by artisanal fishing folks into the water in both Dredge and Undredged areas.
As COD and BOD results varied strongly with TSS (Table 3) results in this study for both Dredged and Undreged areas were well below permissible limits, apparently an indication that dredging has little influence in organic pollution of the water body, a relatively low COD values was also recorded for the dredging of Bay in Egypt [29] 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, Figure 2(e).Hence, there is the need to better information on the essence of environmental 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, [30] opined that decrease in light penetration by between 25% -50% for over a distance of about 12 km could emanate and this effect could remain persistent for a period of 18 months after dredging activities.Thus, the extent of turbidity impact on the study area established that there are significant changes in fishery distribution.

Figure 1 .
Figure 1.Map of study area showing sampling sites (Source: Nigerian institute for oceanography and marine research).

Table 1 .
Values of water quality parameters in dredged and undredged areas in Ibeshe section of Lagoon, Lagos in relation to LASEPA standard.

Table 2 .
Values of parameters in sediments of dredged and undredged areas in Ibeshe section of Lagoon, Lagos in relation to LASEPA standard.

Table 3 .
Pearson correlation matrix of water quality parameters in dredged and undredged area.