Academic journal article Journal of Sustainable Development

Spatial Changes in the Wetlands of Lagos/Lekki Lagoons of Lagos, Nigeria

Academic journal article Journal of Sustainable Development

Spatial Changes in the Wetlands of Lagos/Lekki Lagoons of Lagos, Nigeria

Article excerpt

Abstract

Lagos metropolis, the current economic capital of Nigeria is a low-lying coastal city endowed with a number of lagoons and wetland ecological assets. Lagos/Lekki Lagoons being the largest with a combined size of 646km[sup]2[/sup] are fringed on many sides by wetlands. Many of these wetlands have undergone severe spatial changes from rapid urbanization in the past three decades. The precise nature of these changes is largely unknown and unreported. As the area is experiencing intense development pressure, this study therefore examined the spatial changes in the wetlands fringing these lagoons using the integrated approach of remote sensing data and GIS with topographic maps providing baseline data. The objective is to quantify and establish the precise location and magnitude of these changes over the years from 1984 to 2006. Two types of wetlands are prevalent in the Lagos area namely: the swamps and mangroves. ENVI software was used along with parallelepiped supervised classification in processing the Landsat images. Results show that the mangrove wetlands decreased from 88.51km[sup]2[/sup] to 19.95km[sup]2[/sup] at -3.12km[sup]2[/sup] annually while swamps decreased from 344.75km[sup]2[/sup] to 165.37km[sup]2[/sup] at - 8.15km[sup]2[/sup] annually both between 1984 and 2006. Results further show that mangroves which were widespread in seven council areas around these lagoons in 1984, have dwindled to only four councils in 2006. These decreases are attributable to urban development pressures. Some of the implications of these losses and conservation issues are briefly highlighted.

Keywords: lagoons, wetlands, spatial changes, remote sensing, GIS

1. Introduction

1.1 Background

As part of natural ecosystem, wetlands where they occur in the landscape are valued for their contribution to ecological balance and biodiversity. Also, they are valued for the numerous goods and functions delivered freely to the ecosystem and human habitats which include flood storage and distribution, retention of sediments and nutrients, aquifer recharge, water quality improvement, aesthetic and educational benefits among others (Kindscher et al., 1998; USEPA, 2009). Unrestrained degradation of wetlands and ecosystem will inevitably lead to a loss or diminution of some or all of these functions.

Wetlands are land areas covered with water or where water is present at or near the soil surface all year or varying periods of the year. These areas support the prevalence of hydrophytes or aquatic plants that are typically adapted to life in water saturated (hydric) conditions (USEPA, 2009). Wetlands include a variety of habitats such as marshes, peat lands, flood plains, rivers and lakes, coastal salt marshes, mangroves and sea grass beds, coral reefs and other marine areas no deeper than six meters (6m) at low tide. They also include human-made wetlands such as waste-water treatment ponds and reservoirs (Ramsar Convention Secretariat. 2007a). Urban populations and wetlands are said to have been engaged in a turbulent, somewhat symbiotic marriage since the dawn of civilization. Being essential for human well - being, wetlands have been progressively lost and degraded from human activities since then. The rate of their loss is known to be greater than for any other type of ecosystem (UN - Habitat, 2010).

Metropolitan Lagos, the current economic capital of Nigeria and some of its suburbs have developed on a coastal environment characterized by low-lying tidal flats, estuaries, wetlands and sandy barrier beaches, some of which were reclaimed haphazardly for development (Abegunde, 1988). Spurred by demand for land for rapid urbanization, Abegunde (1988) further suggested that this unplanned and extensive reclamation of wetlands, sand filling of lagoon shores, excessive dredging, encroachment on natural drainage channels and unrestrained deforestation have all been significant features of metro Lagos. Adeniyi (1980) had earlier observed that over 87% of vacant wetlands in metro Lagos between 1962 and 1974 had been converted to high density unplanned residential housing. …

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