A Review of Environmental Implications of Dredging Activities

Dredging is a global anthropogenic excavation activity of removing sediments from water bodies and depositing it elsewhere. It is a mixed blessing as it has both beneficial and adverse impacts. This paper is on a review of environmental implications of dredging. The objective of the paper is to review previous works by researchers on the environmental consequences of dredging. The method used is a review of academic/journal articles, internet materials, conference / workshop papers, textbooks, bulletins and publicly available materials on dredging activities. The results of the study revealed that previous authors whose works were reviewed have a convergent view that apart from the beneficial impacts of dredging (e.g. keeping waterways navigable, flood and storm protection and provision of materials for road construction and building), it has lots of adverse environmental impacts, including environmental pollution, erosion, widespread hydrological changes, reduction in the population of aquatic lives like destruction of fish spawning grounds and benthic organisms and resuspension of particulate matter column that has elevated levels of lead, copper, zinc and nickel in Phytoplankton. Recommendations of the study include: (1) establishment of environmental legislations and regulations for dredging operation; (2) use of green technology in dredging activities to minimize suspension of sediments and contamination/pollution of dredging environments; and (3) creation of awareness among dredging contractors, regulators and marine communities where dredging take place on the economic and ecological values of the marine ecosystems that are usually very sensitive, fragile and productive. Keywords— Dredging, Environmental Implications, Marine Ecosystems, Review Sediment, Sustainable


INTRODUCTION
Dredging is a worldwide excavation activity that involves removing sediment from a sea, river, or lakebed and depositing it at a new location ( Brunn, Gayes, and Eiser, 2005; Thomsen, McCully, Wood, Pace and White, 2009).They further reported that uses of dredged materials are vast and include construction of ports, waterways, dykes, and other marine infrastructure, land reclamation, flood and storm protection, extraction of the construction industry (e.g for road construction and buildings) and in environmental remediation of contaminated sediments.International Association of Dredging Company (IADC) (2012) opined that population growth and increasing number and size of infrastructure projects mean that demand for dredging, volume of aggregate, and turnover will most likely increase.Since dredging impacts the marine environment, sustainable management of the activity is required, based on in-depth understanding of how dredging affects marine habitats and associated fauna and flora (Thrush and Dayton, 2002; David, Hitchcock and Bell ,2004; Erftemeijer and Lewis, 2006).Globally, dredging activities certainly affect the global economy and in fact still plays a huge role in global trade (Bob, 2015).IADC (2012), reported an estimated 11.68 billion of dredging work.In Nigeria, dredging activities are a major environmental problem (Abubaker, Alzubi and Alzyond, 2011).They further noted that mining industries and dredging practices in particular are vastly known for their hazardous working condition and the unstable nature of the earth-crust which minerals are extracted is causing threat to life and properties of the society.According to Robbins (2006), dredging is an excavation activity of operations usually carried out at least partly under water, in shallow seas or fresh water areas with purpose of gathering up bottom sediments and disposing them at a different location.He further asserted that dredging helps to keep waterway navigable, and also a way of replenishing sand on some public beaches, where sand has been lost because of coastal erosion.Walker, Hillman, Kendrick and Lavery (2001) defined dredging as an activity that is done or carried out using a device, machine or vessel that is used to excavate and remove materials from the bottom of a body of water, for example, a scoop is attached to the rope or pole by which a man can draw sediments up from the bottom of a pond, or river.In the view of Watson, Revenga and Kura (2006), dredging involves the excavation and relocation of sediments from lakes, rivers, estuaries or seabed and is a critical component of most major marine infrastructure development along the coast.Despite the necessity of

Objective of the Study
The objective of this paper is to review environmental implications of dredging activities.

II. CONCEPTUAL FRAMEWORK:
SUSTAINABLE DEVELOPMENT This paper adopts the concept of sustainable development as its framework.The World Conference on Environment and Development (WCED) (1987) defined sustainable development as the development that meets the needs of the present without compromising the ability of future generations to meet their own needs.Morelli and Greenwood (2010) claimed that sustainable development is meeting the resource and service needs for current and future generations without compromising the health of the ecosystems that provide them and more specifically as a condition of balance, residence and interconnection that allows human society to satisfy its needs while neither exceeding the capacity of its supporting ecosystems to continue to regenerate the services necessary to meet those needs by our actions diminishing biological diversity.This study is focused on a review of the environmental implications of dredging so as to build in sustainability into the management of the phenomenon.

III.
METHOD This research made use of a review of academic articles, journals, internet materials, textbooks, conference papers and publicly available materials on dredging activities.The researchers assembled thirty of these materials for this research, but summarized the characteristics of 10 deemed more relevant to environmental implications of dredging for the review.This enabled the researchers to make a synthesis of various researchers' views on implications of dredging activities.

IV.
REVIEW OF RELATED LITERATURE Watson, Ravenga and Kura (2006) conducted a study on Trawling and Dredging in Western Australia and asserted that dredging involves the excavation and relocation of sediment from lakes, rivers, estuaries or seabed and is a critical component of most major marine infrastructure development along the coast.Hitchcock and Bell ( 2004) carried out a study on marine aggregate dredging in Florida and reported that sediment plumes cannot be under estimated as it is a phenomenon that has the capacity to extend the footprint of impact beyond the limits of the dredging activity itself.Copper, Curtis, Hussain, Barrio Fajon, Defew and Nye (2011) studied implications of dredging in United Kingdom and claimed that changes in sediment composition can have implications for residents and recolonizing fauna, resulting in the establishment of fauna community that differs from the assemblage present before the dredging.They also asserted that marine aggregate dredging is to identify those locations where it is more and less important to try to preserve sediment particle size composition, and to determine whether there is a rational scientific justification for the active restoration of sediment particle size composition at site of former marine aggregate dredging.2007) were of the view that dredging of channel and excavation of the banks exposed the underlying layer of historically contaminated sediments, compromising partially decomposed organic matter from dredging activities, resuspension of sediment partially accounted for higher concentrations of organic carbon in water column, in their study on impacts of dredging in Singapore.A research by Nayar, Goh and Chou (2004) on heavy metals from dredging in Singapore revealed that dredging operations potentially released toxins into the marine environment.They further claimed that in Zeebrugge and Singapore dredging, operations led to resuspension of particulate matter column that has elevated levels of lead, copper, zinc and nickel recorded in phytoplankton.

International Journal of
Walker, Hillman, Kendrick and Lavery (2001) researched on ecological significance of dredging in Western Australia and asserted that dredging in shallow nearshore waters associated with significant conservation values, adverse effects on marine habitats due to direct seabed disturbance and indirect effects could offset shipping movements and seabed shoreline stability.A research by Desprez (2000) on impact of marine aggregate dredging in France indicated that extraction of marine aggregate has its impact on the seabed as dredging activity has conventionally targeted bottom substrate associated with benthic fauna.
Mmom and Chukwu-Okeah (2012), in their study on sand dredging in Calabar, opined that increasing anthropogenic disturbances have imposed considerable impacts on river channel.They further reported that high dredging activities had resulted to serious incision of the river channel deepening the river bed and increasing velocity of flow.Rinaldi, Wyzga and Surian (2005) conducted a study on sediment mining in Italy and claimed that channel incision of alluvial river as a result of sediment depletion arising from dredging had series of detrimental effects on the river channel, including ground water table lowering, flood flow increase, the destabilization of infrastructures, sea water encroachment in the area.Michael et al (2015) carried out a research on potential dredging impact in Vicksburg and reported that dredging is a complex activity, and its impact on aquatic ecosystems is poorly understood, over long-time scales.Muyideen, Abiodun and Ismaila (2013), in their study on impacts of dredging in Awoyaya Lagos, claimed that dredging activity pollutes the environment and the water source of the area, thereby endangering the life of people and aquatic animal in the area.2013) asserted that dredging activity pollutes the environment and water source of the area as well endangering the life of people and aquatic animal in the area.Michael et al (2015) reported that dredging is a complex activity which has impact on aquatic ecosystem over long-time scales.They were of the divergent view that dredging is done to maintain water ways navigable.
David, Hitchcock and Bell (2004) reported that dredging disturbance will likely result to geological conditions.Mmom and Chukwu-Okeah (2011) deduced that high dredging activities have resulted to serious incision of river channel, deepening the river bed and increasing the velocity of flow.Generally, dredging activities have a lot of environmental implications that tend to pollute the environment as well as endangering life of people and aquatic animals.For example, in Zeebrugge and Singapore dredging operations led to resuspension of particulate matter column in phytoplankton (Nayar, Goh and Chou, 2004).VII.CONCLUSION This paper discussed environmental implications of dredging activities through a review of works of pervious authors.Generally, the authors agreed that dredging is the excavation and relocation of sediment from river, lakes, estuaries and seabed.Dredging activities potentially because disturbance to aquatic ecosystem, changes in topography by creation of spoils, short term increase in turbidity which can affect aquatic species metabolism, environmental pollution and flooding of coastal areas and erosion.This study therefore, concludes that although dredging is beneficial in socio-economic terms, its adverse environmental consequences call for proper management to avoid a situation where they undermine the positive impacts.

ACKNOWLEDGEMENT
We appreciate the grace and empowerment of God Almighty who has been our source of strength from beginning to completion of this work.We also commend the effort of the relations, friends and well-wishers of the authors who contributed both financially and otherwise for making this review a success.Our gratitude extends to the Vice chancellor and the entire stakeholders of Chukwuemeka Odumegwu Ojukwu University, Uli, Anambra State, Nigeria for providing a platform for the study of Environmental Management.To all the lecturers, head of department and dean of the Environmental Sciences, we appreciate their collective efforts in making sure that the goal of environmental management is achieved in the institution.We are highly indebted to the chief author, Mr. Igwe, P.U. for his tireless effort towards an extensive research on the materials used for the review.

Table . 1
: Summary of Characteristic of some Studies on Environmental Implications of Dredging Activities.

Table 1 ,
Nayar et al (2007)u (2004)andNayar et al (2007)are of the convergent view that resuspension of sediment partially accounted for higher concentrations of organic carbon, as dredging activity potentially release toxins into the marine environment.Mmom and Chukwu-okeah (2012) and Rinaldi et al (2005) were of the view that dredging activities have resulted to serious incision of river channel including ground water table lowering, flood flow increase, destabilization of infrastructures and sea water encroachment in the area.Muyideenn et al (