Governing the Environmental Impact of Dredging: Consequences for Marine Biodiversity in the Niger Delta Region of Nigeria

The attention of most scholars and stakeholders is far drawn from the devastation of the environmental consequences caused by dredging related activities, which has necessitated sand filling and pilling including skewed national government policies, which has resulted to fundamental concern to halt species extinction, a situation which ecologist are not at ease with. Emphasis has been focused on alterations in the chemistry of the environment. They are worried with the numerous vanished creatures and saddened, often angered by their extinction. Man has directly or indirectly been the cause of the extinction, including the issues of depletion and degradation impact on the environment, thereby, leading to restrictions in the size, density, and distribution of organisms that threaten the biodiversity, resilience, or provision of ecosystem services. As soon as the functionally significant components of an ecosystem are missing, it is extremely challenging to identify and understand ecological thresholds. The extent and intensity of human disturbance to oceanic ecosystems is a significant threat to both structural and functional biodiversity and in many cases this has virtually eliminated natural systems that might serve as baselines to appraise these impacts. It is therefore recommended that effective management of dredging problems in the Niger delta will require enforcement of relevant environmental laws, environmental monitoring, as it help limits the huge expenses on habitat clean-up exercises and restoration programs and critical habitats should be banned or carried out in such a manner as to protect the area or limit dredging to the lowest ecological damage. This should be pressure on all oil companies and relevant stakeholders to discontinue with dredging related activities. Petrochemical such as oils and other hydrocarbon should not be present in the aquatic environment in concentration that can cause tainting of edible aquatic organism, form visible deposits on shoreline and bottom sediment or be detected as a visible film/sheen or discoloration.


Introduction
The Niger Delta is the life wire of the Nigerian economy, an important region that has been very seriously affected by oil exploration and production. Large channels have been dredged in many places to float oil rigs and lay pipelines. While the Niger Delta is located in the Gulf of Guinea in the Atlantic Coast of southern Nigeria precisely where River Niger divides into numerous tributaries (Figure 1). Regarded as the second largest delta in the world with a coastline spanning about 450 kilometres terminating at the Imo River entrance, the region span over 20,000 square kilometers and it has been described as the largest wetlands in Africa and among the three largest in the world. About 2,370 square kilometres of the Niger Delta area consist of rivers, creeks and estuaries and while stagnant swamp covers about 8,600 square kilometers [1][2][3][4][5][6]. In the last two decades, the Niger Delta has enjoyed rare spotlight in the Nigerian political discourse. The reasons for this are not connected to its being the second largest delta in the world or because it consists of rivers, creeks and stagnant swamp, but because the Niger Delta has been a victim of its resources.
The oil wealth and the politics of its exploration and exploitation, make the Niger Delta a study on paradox. The Niger Deltas resource oil production makes Nigeria the seventh largest producer in the world and the fifth exporter of oil in the United State. However, the region account for nearly 95% of Nigeria's foreign exchange earnings, 40% of gross domestic product (GDP), and 84 percent of government expenditure is undeniably a victim of "oil resources curse" [7]. It is the most underdeveloped region in Nigeria with widespread and entrenched poverty. The people are not only poor, but their environment has also become the most environmentally assaulted area with major impact as a result of dredging activities. With over 5200 oil wells drilled in the areas, and about 2 million barrels of crude oil per day that passed through about 275 flow station and exported through ten terminals [1,[8][9][10], the region has been subjected to the most environmental abuse recorded in sub-Saharan Africa. Hence, human activity is having a significant and escalating impact on the global environment, they also reduce the resilience and capacity of ecosystems for delivery of vital ecosystem services, including food and water provision and protection from natural disasters. Often times, environmental degradation is a major cause of productivity losses and poor human health in the Niger Delta, and environmental degradation issues are of topical concern to communities in the area. While, human altered these aquatic systems and ruin the life histories of many species, even those that he finds desirable interest. Because of their partially enclosed nature, estuaries seem especially vulnerable to this anthropogenic perturbation. As many currently experience remarkable rates of qualitative and quantitative degradation, environmental threats and impacts are associated with growing human populations; as population dynamics are key drivers of local and global environmental change. The resulting growing populations leads to increased consumption of land use natural resources, posing additional environmental pressures in terms of uses and misuses of aquatic systems that have caused considerable increase in their degradation (Table 1) [11][12][13][14]. Consequently, their importance has continually diminished and there is an overall alteration in ecological integrity. Very often, the duration, magnitude and extent of undetected anthropogenic perturbations may be so enormous that there is limited opportunity for natural recovery of impacted aquatic systems without serious restoration efforts. Moreover, species and whole communities are being lost in an alarming rate in some cases even before they can be identified and long before they can be studied (Stiassny, 1996). There is thus an obvious need for organized environmental monitoring exercises if aquatic systems and their resources are to be protected from the adverse effects of human-induced perturbations.
The aquatic ecosystem parameters that are commonly affected by anthropogenic perturbations are summarized in Table 2. The integrated impacts of these human mediated factors cause considerable perturbations of a minimum of eight major components of aquatic systems viz: ecohydrological regime, habitat area, habitat quality, water quality, substrate quality, energy source, biotic interactions and resources exploitation. These variables play critical roles in determining the ecological integrity of aquatic systems ( Figure 2).

Resources Exploitation
Overexploitation of living resources via finfish fishing, octopus fishing, shellfish collection, sea-cucumber collection, seaweed collection, coral mining, curio collection, hunting, grazing and tourism Sources: Adapted from Richard and Goodluck [39].
While, changes in wealth and age structure also alter lifestyle, consumption habits and diet, all of which can have environmental consequences [7,[15][16][17][18]. The world's population has grown from less than 4 billion in 1970 to 7 billion today. By 2050, the United Nations estimates that the global population will reach almost 9.2 billion people, an additional 2.2 billion people [19]. The world's population is now over seven billion people and is tracking toward nine billion come 2050 [19]. Many environmental problems arise from human-induced habitat modification, resource use, and disposal of waste. Examples comprise air and water pollution, impacts on biodiversity as a result of direct influences (e.g., hunting and fishing) or indirect activities (habitat clearing, pesticide use), and reduction of freshwater flows as a result of diversion (irrigation) or storage (dams) for human use [13,16,[20][21][22].
Although great emphasis has been paid to the decline in species diversity in terrestrial ecosystems, it is apparent that there have also been substantial changes in the diversity of aquatic systems, albeit changes that may not be so readily detected. A common perception of marine seafloor biodiversity reflects a disproportionate interest in hard bottoms such as coral reefs, kelp forests, and the rocky intertidal. This bias is understandable because these hard-bottom communities lend themselves to terrestrial comparisons and ecological studies. However, nearly 70% of the earth's seafloor is composed of marine soft sediments [23,24]. These soft-sediment habitats can be highly heterogeneous due to the interactions between broad-scale factors (e.g., hydrodynamic and nutrient regimes) and smaller-scale physical and biological features; nonetheless, the apparent three-dimensional habitat structure imposed by this heterogeneity may not be as obvious as that observed on hard-bottom habitats. Although these habitats are not always appearing as highly structured as some terrestrial or marine reef habitats, they support an extremely high species diversity [24][25][26]. Additionally, organisms that inhabit the sediments create much of the structure in soft-sediment habitats, ranging from the micro-scale changes around individual animal burrows to the formation of extensive biogenic reefs. As well as adding substantively to the variety of species found on earth, soft sediment marine organisms have functional roles crucial to many ecosystem processes. However, the disturbance regimes play an important role in influencing biodiversity [27].
In marine benthic habitats small-scale natural disturbance plays a remarkable role in influencing communities by generating patchiness [28,29]. Many of the small-scale disturbances that impact benthic communities and generate heterogeneity result from the biological activities of organisms that live in or feed on the seafloor. The spatial heterogeneity created by local disturbance events can account for resource patchiness [30], and ubiquity of opportunistic species in soft-sediment habitats. This heterogeneity is an important component of the functioning of ecological systems [31] and has consequences for diversity maintenance and population stability for community, and ecosystem levels [32]. The natural disturbance fact is important to soft-sediment communities that has led to the suggestion that fishing disturbance can positively affect biodiversity.
Dredging is a critical operation that is regularly carried out to preserve safe passage for boats and ships at ports and harbors [33,34]. In other words, dredging is significant for maintaining and performance of harbor operations, i.e., For the import and export of goods. However, the removal of dredged spoil at sea can potentially affect the marine environment and its ecosystems [35,36]. The dredging and dumping of spoils at sea will inevitably increase turbidity levels and settlement of fine sediment over an extended area. This can propagate to a large area around the dumped location. The impacts of this loss of land and fisheries potential has been studied at Louisiana State University [37]. It is estimated that nearly 1-2.6% of Barataria Basin (around 5,700 km 2 or 2,200 square miles) has been directly removed by dredging. If the dredged spoils area is combined (as this land also is lost from marsh production), perhaps 10% of the area could be lost due to biotic production.
The total area adversely affected is almost 20% in combination with secondary adverse effects, such as loss of sheet flow, are included. Once the canals are dug, they tend to expand each year from erosion [38] thus the effects persist even after dredging or extraction ceases. Also, dredging results in the direct removal of intact benthic sediments, the habitat upon which the survival of many species of animals, plants, and bacteria depends. A similar effect from dredging was observed on shallow-water benthos in a tropical estuary and the loss in benthic algae biomass (i.e. standing crop) was attributed to dredging. The main sources of environmental stress from dredging activities are the formation of airborne dust, solid waste, noise, and chemical discharges released into nearby bodies of waters. A well comprehensive review will cover all these impacts associated with dredging activities in other areas of the Niger Delta region of Nigeria. It also, interferes with physiological processes, suggesting that temperature is very significant in determining the rates, and in some cases even the presence of significant biological functions such as photosynthesis, respiration, enzyme activity, feeding, and reproduction. Hence, any change in water temperature affects the metabolism of aquatic plants, bacteria, and cold-blooded animals since they cannot perform their internal heat balance actively.
Henceforth, the continuous dumping of spoils can interfere with the smothering of the seabed environment, coral reefs, egglaying nests of fish and can disturb their navigations. Finally, dredging and dumping alter the topography of the seabed during dredging and dumping locations and can therefore change the local flow patterns. The impact of the dumped spoils on water quality is also affected by the concentration of suspended material. The chemical, physical, physiological, and behavioral changes can be combined to change and affect entire aquatic ecosystems through changing primary and secondary production, community respiration, species composition, biomass, and nutrient flows. As a result, dredging and its related activities should be monitored, controlled and their impacts on the marine environments should be assessed, maintained and safeguarded through appropriate and effective management strategies.
Impacts are summarized as follows: a) Introduction of hard substrata into soft-sediment ecosystems (shipwrecks, clinkers, trash, cables, pipelines, submarine structures). b) Organic enrichment (sewage dumping, organic cargo on sunken vessels, dumping of by catch).

c)
Chemical pollution (oil, drilling muds and other oil/ gas production chemicals, industrial chemicals, pharmaceuticals, munitions including chemical weapons).
d) The introduction of heavy metals and other toxins into the environment during the dredging operations. e) Excessive sediment disruption with sometimes heavy increases in turbidity-associated with the dredging of channels for tankers and drill rigs. h) Mechanical disturbance (bottom fishing, cable laying, submarine pipelines, scientific research).

i)
Light pollution (industrial activity, scientific research).

j)
Acoustic disturbance (oil and gas exploration, military activity, scientific research).
k) The provision of protein for human consumption and the ecosystems that sustain fisheries are clear examples of the products and functions of marine ecosystems that benefit humankind. Other processes in which marine benthos play important roles include their influence on sediment stability, water column turbidity, nutrient and carbon processing, and contaminant sequestering, as well as the provision of pharmaceuticals and nutraceuticals and recreational and amenity values.

l)
Suspended sediments reduce primary productivity by limiting light penetration into the water column. However, many nearshore coastal sediments are also badly polluted with a variety of hydrocarbons, metals, pesticides, etc. and the suspension and movement of such polluted sediments can pose a significant threat to biological communities [8][9][10]12,22].
m) The disposal of polluted dredge spoil alone is also a significant problem. Poorly planned and managed dredging has resulted in the death of many miles of coral reefs.
n) This loss to the ecosystem occurs when there are restrictions in the size, density, and distribution of organisms that threaten the biodiversity, resilience, or provision of ecosystem services. Once the functionally important components of an ecosystem are missing, it is extremely difficult to identify and understand ecological thresholds. The extent and intensity of human disturbance to oceanic ecosystems is a significant threat to both structural and functional biodiversity and in many cases, this has virtually eliminated natural systems that might serve as baselines to evaluate these impacts [39].

Addressing the Issues
Most of these changes have arisen as a result of the quest of man to improve his socioeconomic and technological status. Because of the fact that mankind will always continue to improve on these endeavors so as to make life meaningful and the world better to live in, the aquatic environment will for a long time be under intense pressure. Of these, the most serious present impacts arise from deep-sea bottom fisheries that target low species productivity. Low species productivity are those considered by slow growth rates, high longevity, and sporadic reproduction when they have accumulated enough energy for offspring production. Undisturbed coastal regions are uniquely rich biotic resources that are valued highly by society. They are also areas that is important and often necessary industries must be maintained and utilized. Some of these are large-scale systems for the production, processing, and distribution of commercial energy. Since dredging-related activities have been known to generate severe and persistent environmental impacts, it is important to understand how and why they affect the integrity of coastal ecosystems as they do and to determine the adequacy of attempting to mitigate their effects. This is especially imperative when the aquatic and semiaquatic systems is to continue to provide us with the various aesthetic, recreational, and fishery resources they have given us in the past. These benefits confirm some legitimate uses of the coastal zone that should be protected or safeguarded by appropriate management strategies. Much of the current negative impact connected with dredging activities in the coastal zone is unwarranted and could have been avoided by more thoughtful planning. This is a condition that has resulted from man's inability to measure or characterize ecological stress, mismanagement of our technical resources, and/or from the inadequacy of appropriate decision-making.
Likewise, the ecological consequences of human activity on marine environment require an understanding of the broad scale forcing functions as well as knowledge of the natural and life history characteristics of each individual species. There are winners and losers in responding to the ecological disturbance, but the big question is understanding the ecological heterogeneity and its role in transforming the consequences of habitat disturbance to ecosystem processes. It is necessary to better understand the implications of natural and anthropogenic habitat fragmentation and how it relates to the intensity and frequency of disturbance. Interesting empirical and theoretical studies that solves this problem should integrate biogeochemistry, hydrodynamics, and ecology. Site history and the effect of multiple stresses will be predominantly remarkable in many areas in order to address the role of the resident species assemblage and environmental context in affecting disturbance-recovery dynamics in fragmented habitats. Once the functionally important components of an ecosystem are missing, it is extremely difficult to identify and understand ecological thresholds that are violated beyond the point of recovery, at which point the anthropogenic disturbances are less evident. Some knowledge of these issues is necessary to resolve this more important question. Also, environmental impact assessment should be conducted as detailed and specified by the regulatory authority.
The study if well executed will serve all concern stakeholders in no small measure. The document will serve as a management tool to guide decision making during start up and decommissioning of dredging project. Similarly, there is need for the development of an integrated monitoring framework from dredging related activities to provide the fundamental implement for decision making through integrated multidisciplinary approach such as environmental scientists, planners and managers. Consequently, a monitoring scheme should be expedient and uncomplicated. It should involve the use of a standard monitoring team that has the expertise to investigate and evaluate the apparent or potential effects of dredging related activities. The team should be acceptable to government authorities, community stakeholders, property owners, developers and other interest groups. The team membership should include inter alia experts in the fields of ecology, geography, biology, geology, fisheries, hydrochemistry, hydrology, engineering, sociology, economics, tourism, environmental laws and policies, including hydroinformatics. Ancillary team members may perhaps include public relations officers, policymakers, representatives of affected local communities, stakeholders, coast guards, wildlife rangers and police. The selection of the team members should be based strictly on qualification and experience. Very often unqualified and inexperienced personnel are appointed in order to limit operational cost. This should be strongly discouraged. Moreover, the composition of the team should be gender biased.
As many more effort is urgently needed to save the 100 species scientist fear are being extinguished every single day as humans deliberately or inadvertently destroy the natural system that sustain life on earth. Like any inheritance, biodiversity can flourish if well managed, or it can be squandered and lost. Today massive loss of species and habitat will be slowed only when the human community understand that nature is not an inferior to be exploited or an enemy to be destroyed but an ally requiring respect and replenishment. Hence, to reduce vulnerability, there is need for collective action on environmental protection and ecosystem balance, henceforth the collective drive for environmentalism. This is because every human society depends to a large extent on the biodiversity that are within its immediate environment. Hence, an effective weighing and aggregating system of environmental evaluation could be devised.