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Earth SALTWATER - FRESHWATER WETLAND ECOSYSTEM AND URBAN LAND USE CHANGE IN PORT HARCOURT METROPOLIS, NIGERIA

Urban development in wetland ecosystems for human settlement, transport networks, exploration /exploitation of natural resources, agriculture and industrial development is one of the biggest menace to wetland change and management. To estimate future urban expansion is very crucial for urban planners and environmental managers in fastest growing cities. This study aims to examine the saltwater/freshwater ecosystem and urban land use change in Port Harcourt metropolis, Nigeria. Sources of data for this study were acquired from a time series of landsat Thematic Mapper (TM) and Enhanced Thematic Mapper plus (ETM+) with Thermal Infrared Sensor (TIRS) images were used to derive land use and land cover maps of the Port-Harcourt metropolis. This study revealed that both freshwater wetland and saltwater wetlands ecosystem occupied 46.99% (18837.1 Ha) of the total classes. This may be the result of wetland being in an undisturbed nature without any conversion or alteration for use. The urban land use change of Port- Harcourt metropolis had changed dramatically during the period of 29 years. The two wetlands (saltwater and freshwater wetland) sum up to a total of 40% (16497.5 Ha) which indicates that there is pressure on wetland use such as plant products harvested from fuel wood, human settlement, urban agriculture, sand dredging, sanitation, water pollution and industrial activities from oil companies within the metropolis. Efforts should be made to increase knowledge, sensitization, consultation, stakeholder’s particip ation and awareness on the wetlands values and wise use economy through dissemination of information, using appropriate techniques and training of adequate staff as well as the need for sound wetland policies, laws and legislation for sustainable use, management and control in conservation of wetland.


INTRODUCTION
In the context of Convention adopted by Ramsar, Convention (Article 1.1), wetlands are defined as areas of marsh, fen, peat land or water, whether natural or artificial, permanent or temporary, with water that is static or flowing, fresh, brackish or salt, including areas of marine water the depth of which at low tide does not exceed six meters [1,2]. In addition, the convention (Article 2.1) also provide that they may incorporate riparian and coastal zones adjacent to the wetlands, and islands or bodies of marine water deeper than six meters at low tide lying within the wetland [1,2].
Wetland ecosystems are among the most important in the world, providing a diverse range of ecosystem services vital to human well-being [2,[3][4][5]. They gave rise to the first modern global nature-conservation convention and remain the only single group of ecosystems with their own International Convention [6][7][8]. Urbanization is a major cause of loss of coastal wetlands.
Urbanization impacts wetlands in numerous direct and indirect ways. For example, construction reportedly impacts wetlands by causing direct habitat loss, suspended solids additions, hydrologic changes and altered water quality. Indirect impacts include changes in hydrology and sedimentations which substantially alter wetlands. It also exerts significant influences on the structure and function of coastal wetlands, mainly through modifying the hydrological and sedimentation regimes, and the dynamics of nutrients and chemical pollutants [9].
Wetland ecosystems are important natural habitat, which must be conserved [10,11]. They are associated with a diverse and complex array of direct and indirect uses. Direct uses include the use of the wetland for water supply and harvesting of wetland products such as fish and plants resources, while indirect benefits are derived from environmental functions such as flood water retention, ground water recharge/discharge, nutrient abatement etc. Human activities in the wetland themselves may be fairly related to alternations; they may also be caused by activities in the wetland watersheds and predominantly by agricultural ones i.e. crop and livestock's production [12]. Changes in wetland area may significantly affect the ecosystem processes and services.
Concern about changes in the size and quality of many of the world's wetlands ecosystem has been growing as more and more wetlands are being converted to agricultural or urban land use and as a result of natural factors like drought [13][14][15]. This study therefore aims at developing a spatial data base on land use and land cover change, with an emphasis on land use classes, assess the ecological and socio-economic effects of wetland use, to map and generate the inventory of wetlands within the Port-Harcourt metropolis between 1984 and 2013, and to explore the causes of degradation of the wetlands.
of State of Colonies. The main City of Port Harcourt is the Port-Harcourt City Local Government Area. It serves as the Headquarters of Rivers State [18]. Today, the Port-Harcourt metropolis is made up of two Local Government Areas, namely Port-Harcourt L.G.A. and Obio-Akpor LGA ( Figure 1). The Port-Harcourt metropolis features within a tropical monsoon climate of transitional zone of KoppenAf climatic types with prolonged and heavy rainy season and very short dry season months in the city. Only the months of December and January truly qualifies as dry season months in the city. The harmattan, which climatically influences many cities in West Africa, is less pronounced in Port-Harcourt. The heaviest precipitation in Port-Harcourt occurs between March and October [17]. The mean annual rainfall is put at 2,000mm [19]. The Port-Harcourt metropolis usually has a temporary cessation of rain commonly known as "August Break" (a dry spell) that comes in between the middle of the rainy season. The area has an average monthly temperature above 27 0 C and there is adequate moisture in virtually all the months.
The relief of the area is low-lying, and the rivers are influenced by tidal fluctuation. The Port-Harcourt metropolis lies at an average altitude of about 12m above mean sea level. In terms of general surface features, the Port-Harcourt metropolis is very unique. The area falls within the coastal belt dominated by low-lying coastal plains which structurally belong to the sedimentary formation of the recent Niger Delta [20]. It consists mainly of muddy deposit pushed out of the River Niger into a relatively tide-less salt sea. The Port-Harcourt metropolis is drained by many rivers such as, Ntawogba, New Calaber, Amadi creek, Dockyard creek, Dick Fiberesima creek, Isaka River, Mini Apalugo, Elechi creek, Primose River, MgbuodohiaRiver,etc.

Data Acquisition and Sources
Sources of data for this study were acquired from a time series of landsat Thematic Mapper (TM) and Enhanced Thematic Mapper plus (ETM+) with Thermal Infrared Sensor (TIRS) images were used to derive land use and land cover maps of the Port-Harcourt metropolis. The data set includes a notable period of four years for, 1984, 1999, 2003 and 2013 (Table 1). The raw satellite data were obtained from the archive of the United States Geological Survey and Earth Explorer. The maps were projected using Universal Transverse Mercator (UTM) and datum WGS 84 of zone 32. These data sets sensors have repeat cycles of 20 days, ground pixel dimension of 57 x 79m (TM), 16-bit pixel for values TIRS and the spectral range includes seven spectral bands in the visible/near infrared (VNIR)-Bands 1, 2, 3 and 4), shortwave infrared (SWIR -Bands, 5 and 7) and thermal infrared TIR -Band 6) parts of the electromagnetic (EM) spectrum. The spectral resolution of Landsat TM and ETM+ (30m) data makes it very useful for land use change and land cover classification and general mapping.

Geo-Referencing Properties of the Images
The Geo-referencing properties of 1984, 1999, 2003 and 2013 made up of Universal Transverse Mercator (UTM) projection, and datum WGS 84, zone 32. Based on the prior knowledge of the study area for over 30 years and a brief ground-routing with additional information from previous research in the study area, a classification scheme was developed [21]. The classification scheme developed gives a rather broad classification where the land use/land cover was identified by a single digit. Table 2 Shows the five-land use/land cover classification identified in the Port Harcourt metropolis considering the scale and resolution of the remote sensor data, interpretation of more elements of the image such as color, texture, shadow, pattern, association, shape and size of the data (resource data), research objectives, field visit and the physical nature of the wetlands terrain in the Port Harcourt metropolis. This involved identifying a set of sample locations and conducting field visit to the study site on Monday 22 nd June and Tuesday 7 th July 2015 to validate these locations. The land use and land cover found were compared to that which was mapped in the image for the same locations. Photographs and coordinates of the various land-use land-cover were obtained with a hand-held GPS.

Saltwater Wetland Ecosystem
The saltwater wetland is mainly salt-water ecosystems (Plates 1 -3). They are primarily associated with floodplains of estuaries of large rivers and water courses [5,22]. In the study conducted in Nigeria, some groups researchers identify two major types of wetlands in Nigeria; they are freshwater wetlands and saltwater wetlands [23]. Saltwater wetlands mean all tidal and sub-tidal lands, including all areas below any identifiable debris line left by tidal action; all areas with vegetation present that is tolerant of salt water and occurs primarily in salt water or estuarine habitat; and any swamp, marsh, bog, beach, flat or other contiguous lowland which is subject to tidal action.
The saltwater ecosystem wetland over the study years has the size shown in the results. Table 4

Freshwater Wetland Ecosystem
Freshwater wetlands are mainly fresh water ecosystems (Plates 4 -6). They occur wherever ground water, surface spring, streams or run-off courses, saturated soils or frequent flooding creates temporary and/or permanent shallow water bodies. Freshwater wetlands include swamps, marshes, bogs and similar areas that are inundated or saturated by surface or groundwater at a frequency and for duration sufficient to support the ecosystem. The size of fresh water ecosystem from our review in    Table 3 and Figures 6-13. The total area under study is 40066.59 (Ha).  ). The 1999 image scene shows a cloud cover during the period of image acquisition, and this led to an increase in figure instead of decrease. It remains the only single image that was clean and clear in the nineties.
As shown in Table 3, byin the year 2003, built up area (urban land use) occupied 39.72% (15915.6 Ha) of the total class with a high increase. The two wetlands (saltwater and freshwater wetland) sum up to atotal of 40% (16497.5 Ha) which indicates that there is pressure on wetland use such as plant products harvested from fuel wood, urban agriculture, sand dredging, sanitation, water pollution and industrial activities from oil companies within the metropolis.
The year 2013 witnessed an expansion of cities in terms of developmental activities in all facets. Here, built up area recorded a two-fold increase in size. The pattern of land cover distribution in 2013 indicated that built-up areas were occupied by the development of greater Port-Harcourt city, as there was not enough space for development in the Port-Harcourt metropolis. People therefore tended to develop towards wetland ecosystem. Table 3 shows that both wetlands (saltwater and freshwater wetland) occupied 37.82% (15159.07 Ha). This is to say that there is a reduction in the size of both wetlands ecosystem due to rapid conversion of wetlands for housing development and excessive urban sprawl and its associated problems of inefficient use of land, urban space and the development of shanty towns/slums.
Other classes such as water bodies and fallow land in Table 3

Result of Accuracy Assessment of Land use/Land Cover Map of the Study Area.
A supervised classification of the satellite imagery was adopted to produce land use and land cover classes. The study made use of Maximum likelihood classification technique to perform its task, there by using all relevant spectral bands in each image. This is the most widely used classification algorithm [24,25]. To generate land cover classes, images of the study areas were taken in three stages: feature extraction, selection of training data (signatures), and selection of suitable classification approaches. The following five land use and land cover classes were identified and mapped: fallow land, saltwater wetland, built-up area, freshwater wetland and water bodies. After the classification, 20 sample points were generated to determine accuracy assessment, except in accuracy total report of 1999 where point generated was 25 points due to cloud cover.
In order to ascertain classification accuracy assessment, it is necessary to systematically compare two sources of information, the first one is pixels or polygon in remote sensing-derived classification map and the second one is ground reference test information. The relation between these two sets of data is usually summarized in an error matrix. The error matrix compares, on a category-by-category basis, the relation between known reference data and the corresponding result of an automated classification [26]. A researcher has proposed that two ways to evaluate and validate error matrix are descriptive statistical and multivariate analytical statistical methods [27].
Kappa Analysis is a multivariate analytical statistical method used and introduced to the remote sensing community in 1981 and was first published in remote sensing journal in 1983 [28,29]. It measures accuracy between the remote sensing-derived classification map (in this study LULC map of the study area) and the ground-truther data by the major diagonal of the error matrix, as well as the chance agreement, which is indicated by the row and column total referred to as marginal [30,31].
According to a studies, Kappa value >0.80 represents a strong agreement or accuracy between the classification map and the ground reference, a Kappa value between 0.40 and 0.80 is considered moderate, and a Kappa value < 0.4 represents a poor agreement.

CONCLUSION
Since it is impossible to avoid change in time and space there is a crucial need for planning in the Port Harcourt metropolis. This study revealed a very alarming rate of wetland reduction and expansion of built-up area. Sound planning is needed to protect and preserve wetland ecosystem. If no adequate measures are taken, wetland resources in the Port Harcourt Metropolis may grossly become extinct. This is because of the following: • Wetlands and fallow land experienced both absolute and relative losses between 1984 and 1999. • Drivers of the land use and land cover change in Port-Harcourt metropolis include demographic factors, urbanization, infrastructural development and oil and gas activity.
It is recommended that: -Efforts should be made to increase knowledge, sensitization, consultation, stakeholder's participation and awareness on the wetlands values and wise use economy through dissemination of information, using appropriate techniques and training of adequate staff.
-There is need for sound wetland policies, laws and legislation for sustainable use, management and control in conservation of wetland.
-There is need for improvement of institutional arrangement so that wetland policies can be fully integrated into the urban planning process across all departments.