A Geospatial Analysis of Wetland Cultivated Areas in Ile-Ife, Osun State, Nigeria

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Journal of Earth Science and Engineering 2 (2012) 97-104

DAVID

PUBLISHING

A Geospatial Analysis of Wetland Cultivated Areas in Ile-Ife, Osun State, Nigeria Nathamiel Olugbade Adeoye1 and A. Dami2 1. Department of Geography, Obafemi Awolowo University, Ile-Ife 220005, Osun State, Nigeria 2. Department of Geography, University of Maiduguri, Maiduguri 610004, Borno State, Nigeria Received: August 30, 2011 / Accepted: February 6, 2012 / Published: February 20, 2012. Abstract: Wetlands are among the world’s most productive environment. They are cradles of bio-diversity, providing the water and primary productivity upon which large numbers of plant and animal species depend for survival. Unfortunately, they are also among the world’s most threatened ecosystems, owing mainly to continued drainage, urbanization, pollution, over-exploitation or other unsustainable uses of their resources. The lack of baseline wetland inventory and limited accessibility to the available ones have been identified as major limitations for sustainable use and management of wetland resources. This study therefore utilized multispectral remote sensing data and global positioning system (GPS) for mapping and assessing the spatial pattern of wetlands, particularly the cultivated ones. The images were processed using ILWIS 3.2 Academic. The combined digital image processing and visual image interpretation were used to identify and segment wetlands in the image data. The coordinates of all identified wetlands and various anthropogenic activities on them were taken using GPS. Questionnaire forms were designed and randomly administered on the households residing around the wetland areas to enable the study to assess the anthropogenic factors, which are capable of destroying the ecosystem. The result indicated that the original size of wetlands in the study area has been modified as there has been reduction in their area extent. Various anthropogenic factors such as, the conversion of wetlands to agricultural, residential and commercial land uses were majorly responsible for the modification. In conclusion, remote sensing data and GIS technology were found useful in mapping and assessing wetlands for sustainable use. Key words: Wetlands, multispectral images, geospatial technology, anthropogenic factors, southwestern Nigeria.

1. Introduction  A wetland is land that is seasonally or permanently covered by shallow water, as well as land where the water table is close to or at the surface [1]. In either case, the presence of abundant water has caused the formation of hydric soils and favoured the dominance of either hydrophytic or water tolerant plants. These unique areas represent a combination of terrestrial and aquatic characteristics, and are further categorized by type as marsh, swamp, fen and bog. The water found in wetlands can be saltwater, freshwater, or brackish. Wetlands are considered the most biologically diverse of all ecosystems. Plant life found in wetlands includes Corresponding author: Nathamiel Olugbade Adeoye, lecturer, Ph.D., main research fields: environmental issues, land resource planning and analysis. E-mail: [email protected], [email protected].

mangrove, water lilies, cattails, sedges, tamarack, black spruce, cypress, gum, and many others. Animal life includes many different amphibians, reptiles, birds, and furbearers [2]. In the last few decades wetlands have come under intensive scientific study owning to the knowledge and appreciation of its benefits. For instance, studies on the value of wetlands revealed that wetlands provide food, water, and shelter for fish, shellfish, birds, and mammals, and they serve as a breeding ground and nursery for numerous species [3-6]. As Tiner et al. [7] asserted, wetlands are among the most productive habitats in the world. Richard [8] reported that many endangered plant and animal species are dependent on wetland habitats for their survival. They further revealed that wetlands simultaneously produce a

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A Geospatial Analysis of Wetland Cultivated Areas in Ile-Ife, Osun State, Nigeria

number of benefits-from clean water and nutrient cycling to flood control and recreation (hunting, fishing, bird watching). But in spite of the benefits wetlands offer to waterfowl, wildlife and people; limited knowledge on the benefits of resources and their associated functions and values resulted into their reclamation in many countries, and the impact of their loss is being realized in different forms. Studies revealed that wetlands are among the world’s most threatened ecosystems, owing mainly to continued drainage, urbanization, pollution, over-exploitation or other unsustainable uses of their resources [9-13]. Report also shows that in Canada, up to 70 per cent of the wetlands have been lost in settled areas, and more are lost every day [14]. The situation is not different in Nigeria. The wetland areas are disappearing due to increase in human population and the urbanization process is adversely affecting the size of wetland areas in the cities. Report of Ref. [15] estimated Nigeria population at 126.9 million with a growth rate of about 2.4%. Besides, Ref. [16] categorized Nigeria among those nations that are at the moment technically unable to meet their food

needs from rain fed production at a low level of inputs and appear likely to remain so even at intermediate levels of inputs at some point in time between 2000 and 2025. Presently, there is no adequate support, management and monitoring of wetland areas, which led to frequent conversion for agricultural use and industrial development. An inventory of wetlands is essential for proper management and sustainable use. This study therefore, examined the location and size of wetlands in a city in southwestern Nigeria. It analyzed the spatial pattern of the ecosystem and recorded the activities around them with the view of assessing the sustainable and unsustainable activities around the valuable resource.

2. The Study Area The study area is Ile-Ife in Osun State, southwestern Nigeria (Fig. 1). It lies within latitude 7°25′ and 7°33′ north of equator and longitude 4°28′ and 4°36′ east of the Greenwich. The study area falls within the tropical rain forest that is characterized by wet and dry seasons. Both seasons are used for farming. While rainy (wet) season is used for rainfed agriculture the wetlands are

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A Geospatial Analysis of Wetland Cultivated Areas in Ile-Ife, Osun State, Nigeria

cultivated in dry season as irrigated agriculture. The wetlands used for cropping are located within the city and are farmed by both men and women of varying ages and diverse origins. The rainfall is heavy ranging from 1,200 to 1,500 mm and falls for about 8 months with the peak period in September. Temperature is high throughout the year and it aids the process of photosynthesis. This in effect favours the growth of dense forest. The temperature ranges from 27 C to 32 C with the maximum temperature occurring around April. Generally, the dry season is short, lasting from December to February. The study area is found within Osun State, Nigeria and overlies metamorphic rocks of the basement complex, the great majority of which dates back to ancient Pre-Cambrian era. These rocks show great variation in grain size and in mineral composition, which enhanced the growth of dense vegetation. The soils belong to the highly ferruginous tropical red soils associated with basement complex rocks. The population of the study area has been increasing steadily since 1967 till date when the University of Ife (now Obafemi Awolowo University) was sited there. The population of the town was 36,200 in 1911, dropped to 22,000 in 1921 due to the communal crisis that rocked the town. It later rose to 24,200 in 1931, then to 130,000 in 1963 [17]. In 1991 the population of the town increased to 185,256 and 355,818 in 2006 [18]. The area is well drained and the fertility of the soil makes farming a prominent economic activity in the area. The drainage system over the areas of basement complex rocks is usually marked by a proliferation of many small river channels, which favour the growth of many wetlands around the underlying area. The drainage system of the area is strongly influenced by the slope inclination and the drainage pattern is dendritic. Agriculture is one of the economic activities of people with wetland cropping solely practiced in dry season when wetland areas are accessible. The area has a well-developed social amenities; the development of which improved the social and economic life of people

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but negatively affected wetland resources.

3. Materials and Methods This study utilized Landsat ETM+ acquired on March 1st 2002 and Landsat ETM+ obtained on January 1st 2007 of 30 metres spatial resolution respectively (Figs. 2 and 3). These were used to map and assess the spatial pattern of wetlands in the study area. The images were processed using ILWIS 3.2 Academic. The combined digital image processing and visual image interpretation were used to identify and segment wetlands in the image data. Handheld GARMIN III global positioning system (GPS) was used to capture the coordinates of all identified wetlands in the study area. Various anthropogenic activities on them were recorded along with the coordinates of the wetlands (Table 1). Base map of the study area was used as a guide to the locations of the wetland areas. The GPS readings were interpolated on the map to assess the spatial pattern of the wetlands.

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Landsat ETM+ 2002.

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Landsat ETM+ 2007.

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A Geospatial Analysis of Wetland Cultivated Areas in Ile-Ife, Osun State, Nigeria

Table 1 GPS reading of wetland locations in the study area. S/No. Wetland location 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

Coconut, Ede road Beside Bethel, Ede road Ede road Ita Agbon Ita Agbon Ita Agbon Ita Agbon Apana Str., Modakeke Ogunsua Str Ogunsua Str Olorunsogo Mkt Area Olorunsogo Mkt Area Ondo Rd, Modakeke Ondo Rd, Modakeke Ondo Rd, Modakeke Ondo Rd, Modakeke Itasin str, Modakeke Isale Agbara Area Isale Agbara Area Oduduwa College area Oduduwa College area Arubiewe, Fajuyi area Arubiewe, Fajuyi area Arubiewe, Fajuyi area Arubiewe/Oduduwa College Arubiewe/Oduduwa College Arubiewe Area Arubidi Area Omi-Okun Omi-Okun area Omi-Okun Omi-Okun Oke Malaika, Ondo Rd, Ile Ife Apata 2, Ondo road, Ile Ife Ondo road area, Ile Ife Egbedore, Olugbodo layout, Ondo Rd, Ife Onireke street Onireke street Ibadan Rd, Idi-Omo area Ibadan Rd, AP fillindg station area Ilode area Awominure area, Ilode Awominure area, Ilode Awominure area, Ilode Ayelabowo off moore rd Ayelabowo off moore rd Ayelabowo off moore rd Ayelabowo off moore rd

Anthropogenic activities on/ around wetlands Houses Houses, farmland Farmland Houses, farmland, dump site Church, houses Farmland Farmland Farmland Farmland, trading stores Saw Mill Farmland Farmland Petrol station, school, block industry Church, school Quarry, stream Mechanic workshop, car wash Farmland Police station, stream, slaughter slab Farmland, houses, church Farmland Farmland Farmland, church Farmland Farmland Farmland Farmland Farmland, houses, stream School Mechanic workshop Farmland, petrol station Mechanic workshop, farmland Houses Houses Farmland House Farmland Farmland House Car Wash Farmland, mechanic workshop Farmland Farmland Farmland Farmland House, farmland Farmland Farmland, houses Farmland

X

Y

668406 668455 668570 671310 671320 671320 671213 670563 670565 670519 670459 670462 669780 669551 669516 669447 670789 670590 670804 672408 672423 672623 672667 672641 672638 672552 672676 671892 671944 671856 671910 671867 671932 671856 671758 671056 671127 671152 669719 669651 673297 673263 673233 673243 673123 673219 673263 673238

828741 828669 828610 827105 826903 826903 826920 826500 826450 826404 826459 826564 826803 827393 827333 827473 827256 827568 827414 828600 828666 828709 828658 828624 828541 828496 828790 825995 825619 825625 825499 825278 824820 824619 824291 824388 828621 828259 828054 828116 827467 827812 827731 827607 827825 827897 823216 827915

Elevation (metres) 240.5 241.2 240.7 276.1 270.1 275.7 271.9 268.6 264.5 275.0 265.2 267.3 257.7 263.3 255.5 256.4 267.0 270.9 280.2 276.7 272.9 261.1 265.6 263.7 262.1 264.9 258.9 277.8 286.3 279.5 282.9 287.2 286.9 286.4 297.7 297.6 267.1 265.4 258.4 255.1 268.5 271.8 265.5 268.1 267.4 265.1 267.2 261.5

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A Geospatial Analysis of Wetland Cultivated Areas in Ile-Ife, Osun State, Nigeria Table 1 (continued) Anthropogenic activities on/ around wetlands Oke-Ogbo Rd, Ilode area Houses Opp Diganga hotel, Ife-Ibadan express way Houses Adesanmi area, Ife-Ibadan express way Farmland, church Ajebamidele area, Ife-Ibadan express way Farmland Ajebamidele area, Ife-Ibadan express way Farmland Ajebamidele area, Ife-Ibadan express way Farmland Opp. OAU Campus gate Shops, cinema, houses Aladanla area, Ilesha Rd Carpentry workshop, stream, car wash Aladanla Layout, Ilesha Rd, Ile Ife Car wash, mechanic workshop Aladanla area, Ilesha Rd Block Industry Iredapo area, Ilesha Rd School, stream Off Ilesha road, Ile-Ife Petrol station, shopping mall, Block Industry, stream Ife City area, Ilesha road, Ile Ife Church, houses Erinta Quarters, Ife City area, Ilesha Rd, Ife Farmland

S/No. Wetland location

X

Y

49 50 51 52 53 54 55 56 57 58 59 60

673456 667637 667070 666720 666646 666705 667846 673234 673193 673303 673823 673921

827272 828838 828716 828858 828795 828992 828841 829090 829164 829216 830175 830139

Elevation (metres) 269.8 239.6 234.7 244.1 241.8 236.9 249.1 257.4 259.2 263.3 266.9 272.3

674066 674996

830266 830856

272.6 263.2

61 62

Questionnaire forms were designed and randomly administered on the households residing around the wetland areas to enable the study assess the anthropogenic factors, which are capable of destroying the ecosystem.

4. Results and Discussion Throughout the study area, 62 wetlands were identified and these were captured by handheld GARMIN III global positioning system. The coordinates of all these wetlands and their attributes are presented in Table 1. It is obvious from the table that there are many unsustainable land uses around wetlands in the study area, which are capable of destroying the value of the ecosystem. Among them are residential quarters, commercial centres, farmlands, workshops, sawmills, block industries, schools, car wash, religious centres, slaughter slab and filling stations. Besides, the field observation shows that many of the wetlands have been modified and their areal extents have been reduced. The result of field survey show that 53.2% of the wetlands in the study area were used for farming while 46.8% have residential quarters and other land uses on them. Various crops grown on them include maize, vegetables, okro, sugar cane and plantain. Mixed cropping was the major farming technique. An estimated measurement of the size of the wetlands was

carried out during the field work. It was discovered that majority of the wetlands are less than 60 metres in length and 40 metres in breadth. The landsat ETM+ 2002 and 2007 were segmented through the combined digital image processing and visual image interpretation to show the spatial pattern of the wetlands and the water bodies in the study area (Figs. 4 and 5). The figures show that the study area is well served with the water bodies. Close examination of the maps revealed that many of the streams and rivers took their sources from somewhere within the city and formed second order stream where they join the dam. Only few of them are third order stream. Comparing the two maps, it was discovered that the urban expansion is having negative effect in terms of reducing the size of the wetlands and the water bodies in the study area. Although the wetlands are not clearly visible in the image data due to their spatial resolution, observation during the field survey shows that the wetlands in the study area are being converted into other land uses. The GPS readings of the wetlands were linked with the base map using GIS technology to show the spatial pattern of the ecosystem. As shown in Fig. 6, wetlands are scattered all over the study area and are accessible to road. This informed the reason for their encroachment as observed during the survey. Some of

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A Geospatial Analysis of Wetland Cultivated Areas in Ile-Ife, Osun State, Nigeria

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A Geospatial Analysis of Wetland Cultivated Areas in Ile-Ife, Osun State, Nigeria

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Distribution patterns of wetlands in lle-Ife.

the wetlands were found in the built up areas and this affirms the claims of Refs. [10-12, 19] that the loss of wetlands were as a result of the continued drainage, urbanization, pollution, over-exploitation or other unsustainable uses.

5. Conclusion The study observed human modification in terms of the reduction in the size of the original wetlands in the study area. This is as a result of the conversion of the wetlands into another land uses, which supports various findings of the existing studies. For instance, the study discovered various social and economic activities and land uses going on around wetlands in the study area. These include residential quarters, farmlands and small scale industries among others. There is therefore need to protect this valuable ecosystem since unprotected wetlands will disappear faster than the protected one. Demarcating wetland zones in the cities could do this. The approach of geo-spatial technology and remote sensing data in this

study was found useful and adequate for regular and up-to-date monitoring of earth resources.

Acknowledgments The authors acknowledged Sunday Adewumi Adefioye, a final year student of the Department of Geography, Obafemi Awolowo University, 2009/2010 academic session, who assisted in capturing the coordinates of all the wetlands in the study area.

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