Human activities exert great pressures on the environment which in turn cause environmental stresses of Various intensities depending on the factors involved and the sensitivity of the receiving environment. For fragile and highly sensitive environments such as the Lagoon coast, the manifestation of the stresses in the form of environmental degradation is easily noticeable. Some 50% of the world’s population live close to the coast, within about 100km of the shore [1Kremer H, Crossland C. Coastal change and the “Anthropocene”: Past and future perspectives of the IGBP-LOICZ project. In: Deutsches Nationalkomitee fur das Internationale Hydrologische Programm (IHP) der UNESCO und das Operationelle Hydrologische program (OHP) der WMO, Herausgeber, Koblenz, Germany; IHP/OHP Berichte, Sonderheft 13, 2002.]. This figure, however, would have increased drastically owing to growth, migration and preference for the coastal environment. It therefore, means that about 3.5 billion people presently rely on the coastal ecosystem including the lagoon coast ecosystems, habitats and resources. These numbers of people also use the coastal areas as a dumping ground for sewage, garbage and toxic wastes. This proportion is expected to live along the growing urbanization, industrialization and transportation systems, putting even greater pressure not only on the physical environment but also on the social environment [2Creel L. Ripple Effects: Population and Coastal Regions. Making the Link: Population Reference Bureau, 2003, 8.]. In Nigeria, about 26% of the population lives within 100 km of the coast while the population living in the coastal zone is 25% [3ACOPS - Advisory Committee on Protection of the Sea. Nigeria National Report: Phase 1: Integrated Problem Analysis Authored by Awosika, L, Osuntogun, N, Oyewo, E and Awobamise, A for the Global Environment Facility project Development and Protection of the Coastal and Marine Environment in Sub-Saharan Africa (GF/6010-0016), jointly undertaken with UNESCO-IOC 2002. e, 4Agboola J I, Odunuga S. Coastal Watershed Ecosystem Services Management in West Africa: Case of Ghana and Nigeria. Ecosystem Services and River Basin Ecohydrology, Springer 2015; 251-274.]. Understanding the pressure on the coastal lagoon environment has to involve a critical assessment of its condition using Driving force, Pressure, State, Impact and Responses (DPSIR) analysis [5Kjerfve B. Coastal Lagoon Elsevier Oceanography series, 60 1994.]. This also has to involve a consideration of both natural and anthropogenic factors that may have contributed to the current landscape. DPSIR can achieve this by using an integration of the social, economic and natural science information to understand the external forcing effects of the social and economic changes as well as the impacts of coastal resource systems on human welfare. DPSIR framework is a tool which models environmental processes in order to develop appropriate management responses. The framework evolved from the Pressure-State-Response (PSR) model which was originally developed by the Organization of Economic Co-operation and Development (OECD) in 1993, and further developed by the European Environmental Agency (EEA) in 1999 [6Jago-on KA, Kaneko S, Fujikura R, et al. Urbanization and subsurface environmental issues: an attempt at DPSIR model application in Asian cities. Sci Total Environ 2009; 407(9): 3089-104.
[http://dx.doi.org/10.1016/j.scitotenv.2008.08.004] [PMID: 18922564] ]. Since then, the DPSIR framework has been widely adopted in many environmental and coastal management studies [7Lan TD. Conclusions: Environmental pressures and conflicts in urban and periurban regions, In: Tran Dinh Lan, E. Gunilla Almered Olsson, Serin Alpokay (ed.), Environmental Stresses and Resource Use in Coastal Urban and Peri-Urban Regions DPSIR Approach to SECOA's 17 Case Studies. Cap. 10. SECOA FP7 Research Project, Rome: Sapienza Università Editrice, 2014; 7: 385-394. http://digilab-epub.uniroma1.it
[http://dx.doi.org/10.13133/978-88-98533-23-7] ]. Fig. (1) shows the basic elements of the DPSIR.

Fig. (1) Elements of the DPSIR.

Although there has been several criticisms against the DPSIR [8Bell S. DPSIR 1/4 a problem structuring method? an exploration from the “Imagine” approach. Eur J Oper Res 2012; 222: 350-60.
[http://dx.doi.org/10.1016/j.ejor.2012.04.029] , 9Karageorgis AP, Kapsimalis V, Kontogianni A, Skourtos M, Turner KR, Salomons W. Impact of 100-year human interventions on the deltaic coastal zone of the Inner Thermaikos Gulf (Greece): a DPSIR framework analysis. Environ Manage 2006; 38(2): 304-15.
[http://dx.doi.org/10.1007/s00267-004-0290-8] [PMID: 16779699] ] as a framework to analyse and understand pressure on the environment [10Gari SR, Newton A, Icely JD. A review of the application and evolution of the DPSIR framework with an emphasis on coastal social-ecological systems. Ocean Coast Manage 2014; 103: 63-77.
[http://dx.doi.org/10.1016/j.ocecoaman.2014.11.013] ], have argued that the framework is a veritable tool when focus is put on the links between the nodes of DPSIR by applying specific socio-economic and natural science-based models to understanding the cause-effect dynamics. This is more pertinent to peri-urban coastal environments with lagoon formation hydro-geomorphic systems, especially, for integrated management purpose [11Neves R, Baretta JW, Mateus M. The DSPIR frame work applied to the integrated management of coastal areas 2008.].

The sub-urban Lagoon coastal environment of Lagos, Nigeria, like any other marine environment is not immune to the problems of environmental pressures. Although largely residential oriented, rapid urbanization and commercialization have resulted in most wetlands and forested land being converted to built-up areas. This gradual invasion of rural areas by metropolitan zones (notion of continuum) constantly brings the status and very existence of rurality into play [12https://ec.europa.eu/energy/intelligent/projects/en/projects/ruraleevolution (Date visited; 22nd April, 2018)-14Frayssignes J. 2011. Special session: Territorial Governance, rural areas and local agro food systems The concept of “agro-energy district”: a pertinent tool for the sustainable development of rural areas. 51st Congress of the European Regional Science Association, Barcelona, 30th August – 3.]. Quantifying the rate of deforestation and identifying locations undergoing rapid change are key to understanding the driving forces and consequences for the Earth System [15Steffen W, Sanderson A, Tyson PD, et al. 2003. Global Change and the Earth System: a planet under pressure / IGBP Global Change Series, Springer-Verlag Berlin Heidelberg New York. ISSN 1619-2435, ISBN 3-540-40800-2.]. Also, solid waste garbage, coastal erosion, high turbidity, sediment loads and other physical alterations from increasing anthropogenic activities are continuously contributing to the pressure on the ecosystem. The land use conversion is accompanied by an intense pressure from the small to medium scale industries, sand mining activities, commercial activities, and transportation activities etc. Consequently, the environment is facing a serious pressure from anthropogenic activities, which have resulted in the reduction of qualitative traditional ecosystem services such as fish catch, recreation and water supply that the local people traditionally enjoy. Furthermore, coastal erosion and flooding have become the common phenomena causing environmental degradation. These have had great consequences on people’s health, occasioned by the contamination of drinking water and solid waste generation [16WHO. The World Health Report 2004. ISBN 92-4-156265-X., 17Vlahov D, Galea S. Urbanization, urbanicity, and health. J Urban Health 2002; 79(4)(Suppl. 1): S1-S12. [US National Library of Medicine, National Institutes of Health.].
[http://dx.doi.org/10.1093/jurban/79.suppl_1.S1] [PMID: 12473694] ] as well as inadequate water supply in the area [18Fantozzi F, Bartocci P, D’Alessandro B, Arampatzis S, Manos B. Public-private partnerships value in bioenergy projects: Economic feasibility analysis based on two case studies. Biomass Bioenergy 2014; 66: 387-97.
[http://dx.doi.org/10.1016/j.biombioe.2014.04.006] ]. proposed the adoption of the agroenergy district concept where rural areas host the production, transportation and the conversion of local biomass into energy as the way to reduce environmental pressure in the rural areas. Frayssignes, (2011) further argued that the agroenergy district approach to rural development can improve food security, local self-reliance, sustainable agricultural management, biodiversity conservation, climate change mitigation and improved energy supply and security. The benefit of the agroenergy district can be optimized through Public-Private Partnerships (PPPs) [19Manos B, Partalidou M, Fantozzi F, Arampatzis S, Papadopoulou O. Agro-energy districts contributing to environmental and social sustainability in rural areas: evaluation of a local public-private partnership scheme in Greece. Renew Sustain Energy Rev 2014; 29: 85-95.
[http://dx.doi.org/10.1016/j.rser.2013.08.080] ]. However, the land use trajectory of the study area can no longer support the production of sufficient feedstock for agroenergy district venture.

This study, therefore, examines the problems associated with environmental pressure by human footprint (anthropocene) along the Lagos lagoon coastal environment in the Ikorodu sub-urban settlement with a view to evaluate the historic trajectories of the land use change and analyse the drivers and pressures of the environmental degradation of the study area. The research hypothesis is formulated thus: “which factor is the most determining factor reducing the quality of the environment in the sub-urban lagoon coast of Ikorodu in Lagos, Nigeria”. This hypothesis will be determined by using driving force, pressure, state, impact and responses (DPSIR) analysis. Although the DPSIR analysis carried out in this study is limited by stakeholder influence [8Bell S. DPSIR 1/4 a problem structuring method? an exploration from the “Imagine” approach. Eur J Oper Res 2012; 222: 350-60.
[http://dx.doi.org/10.1016/j.ejor.2012.04.029] , 20Svarstad H, Petersen LK, Rothman D, Siepel H, Watzolde F. Discursive Biases of the Environmental Research Framework DPSIR. Land Use Policy 2008; 25(1): 116-25.
[http://dx.doi.org/10.1016/j.landusepol.2007.03.005] -22Olsson EGA. 2014.Environmental Stresses and Resource Uses Analysed by the DPSIR Framework In: Tran Dinh Lan, E. Gunilla Almered Olsson, Serin Alpokay (ed.), Environmental Stresses and Resource Use in Coastal Urban and Peri-Urban Regions DPSIR Approach to SECOA's 17 Case Studies. Cap. 10. SECOA FP7 Research Project, Vol. 7. Rome: Sapienza Università Editrice, http://digilab-epub.uniroma1.it
[http://dx.doi.org/10.13133/978-88-98533-23-7.] ] and the cause-effect relationships approach of the framework between the latent variables factors (drivers, pressures, state, impacts and response) and their observed variables, these however, were dealt with by using robust environmental and socioeconomic dataset relating observed variables together to describe the state of the environment based on multiple pressures, that create multiple impacts [19Manos B, Partalidou M, Fantozzi F, Arampatzis S, Papadopoulou O. Agro-energy districts contributing to environmental and social sustainability in rural areas: evaluation of a local public-private partnership scheme in Greece. Renew Sustain Energy Rev 2014; 29: 85-95.
[http://dx.doi.org/10.1016/j.rser.2013.08.080] , 8Bell S. DPSIR 1/4 a problem structuring method? an exploration from the “Imagine” approach. Eur J Oper Res 2012; 222: 350-60.
[http://dx.doi.org/10.1016/j.ejor.2012.04.029] ] and responses

The study area extends from about latitude 6⁰ 37^’ to 6⁰ 45^’ and longitude 3⁰ 30^’ to 3⁰ 5^’. The total land cover is about 275.85 km² with about 25% made up of lagoon. The major communities in the area includes; Ikorodu. Ipakodo, Ijede, Imota, Gbogbo and Ibeshe. Politically, the study area is within Ikorodu Local Government Area (LGA) of Lagos State. It physiographic features can be classified into mangrove and alluvial zones. The mangrove is made up of sands, which is unconsolidated and porous, while the alluvial zone is made up of low line and sandy tracts with silt and sand. The vegetation cover is deltaic swamps; made up of swamps and riparian forest as well as deciduous forest, found towards the northern edge. The area is characterised by short coastal plain, and numerous streams and tributaries of the Ogun and Osun rivers. Elevation ranges from about 2m along the lagoon coast to about 50m above the mean sea level (amsl) towards the northern end. The climate is humid tropics with dry and wet seasons. The wet season normally starts from the month of March and ends in October while the dry season comes up between November and February.

The occupations of the people include trading, farming and fishing. Other human activities in the area revolve around shopping complex, saw mill, brick and clay industry situated at Ibeshe and Igbogbo. Sand mining and other activities along its value chain of distribution are an important occupation that contributes significantly to the local economy of the area. The study area is accessible by both road and water (Lagos lagoon). In terms of development, however, the study area is a sub-urban or peri-urban area. In other words, it is a zone of transition from rural to urban land uses, located between the outer limits of the Lagos mega-city and the inland rural environment. The area encompasses both characteristics of the urban and rural world. As urbanization expands to the area in the last two decades, traditional activities are gradually declining while the green environment is being replaced by brown environment, placing pressures on the coastal Lagoon environment. Fig. (2) shows the location of the study area in Lagos State, Nigeria.

Fig. (2) Ikorodu LGA in Lagos State.

Fig. (3) shows the methodological framework employed for this study while Table 1 shows the spatial data sources. Non-spatial data were acquired through questionnaire administration, field observation and In-depth Interview (Table 2). The survey research adopted is the systematic sampling technique applied in three selected communities along the lagoon; Oreta, Ijede and Offin. The communities were selected based on their location along the Lagoon coastline, spatial efficiency along the urbanized coast of the lagoon, high level of economic activities, natural resource exploitation and direct receptor of coastal degradation. The questions in the survey covers demographic characteristics of the respondents (including but not limited to age, sex and education background), socio-economic parameters (including but not limited to income and occupation), ecosystem services (including but not limited to fishing, sand mining and housing) and economic indices of selected ecosystem services (fishing and sand mining). As shown in Table 2, the social survey sampling technique adopted in choosing the number of respondents was predicated on population density (stratified sampling) of the selected communities while questionnaire administration in these communities was random.

Fig. (3) Methodological framework.

Table 1
Spatial Data Sources and Characteristics.

Table 2
Social Survey Research Components.

The sample size was complimented with Focus Group Discussion (FGD) and Key Informant Interviews to enrich and validate the quality of feedbacks from questionnaire. Communities that are the direct receptors of the degradation were specifically selected for questionnaire interview and the sample size chosen for these communities is sufficient and representative based on their population size.

Based on the knowledge of the researchers about the localities, reconnaissance survey, ancillary information from the 1964 topographic maps and additional information from key informants interview, a classification scheme after Odunuga et al (2011) hierarchical approach was developed for the land use interpretation. Five major classes were consequently identified at the primary level (level 1) while several classes were identified for each of the primary class at the secondary level (level 2). However, the mapping exercise was carried out at the primary levels due to the small area coverage of the study area. Table 3 shows the land use classification scheme. Area calculations of the land use / land cover (LU/LC) for the three scenarios (1964, 2000, and 2015) were carried out to determine the static land uses and land cover, analyse the direction of change (pressure) and determine the rate of change (impacts) on the biophysical resources of the environment. An overlay of the generated land use (1964-2015) was conducted. This provides information in matrix format on the specific point change detection procedure that generates the nature, location, and magnitude of changes [23Caeiro S, Mourao I, Costa MH, Painho M, Ramos TB, Sousa S. 2004.Application of the DPSIR model to the Sado Estuary in a GIS context Social and Economical Pressures. In: 7th AGILE Conference on Geographic Information Science 29 April-1May 2004, Heraklion, Greece Parallel Session 4.3- Environmental/Social Modelling, 13pp.].

Table 3
Land Use and Land Cover Classification Scheme.

A combination of the data generated from LULC and the questionnaire administration were modelled using the Factor Analysis (FA) to evaluate the state of the environment. The DPSIR approach was used in this analysis. Factor Analysis (FA) is a multivariate technique that integrates various variables of many drivers and pressures of the environment to establish their respective spatial relationship. The equation for the FA is given below:

Where: a = no of variables, f = factor loadings which is constant, Y= variable with a known data and e₁ is error term.

Data were collected on relevant variables that cut across human population, socio-economic indices infrastructures development, human activities including small and medium scale industrial activities, extractive processes, land use, biodiversity issues and policy issues. Overall, forty five (45) variables were related together under the latent factors of; drivers, pressure, state, impact and response. The ‘drivers’ were defined as the underlying factors causing a variety of change. The ‘pressures’ are the variables that directly caused the changes in the initial wetland environment. The ‘state’ is a measure of the present physical conditions of the wetlands ecosystem; it identifies the current status and impacts resulting from these pressures. The ‘impacts’ describes the effect of changes especially as they affect the ecosystem services of the wetlands while the ‘response’ is defined as the measures devised by the stakeholders to proffer solution to the problems resulting from the changes in the ecosystem function. It includes the policies, plans or projects taken by the government to reduce the pressures and their negative impacts on the environment and the people. For each of the latent factors (DPSIR), the initial variables were extracted from the pool of observed variables using principal components by linear combination with maximum variance. The percentage (%) variability of the components was adopted in choosing the number of variables to retain for each of the latent factors while Orthogonal varimax approach (maximize squared loading variance across variables: sum over factors) (equation 1) was adopted in the FA rotation. Interpretation with orthogonal is simple because factors are independent while loadings are correlations. However, variables with positive PFA (Principal Factor Analysis) values close to 1 are considered as having significant but positive relationship with the environment. Variables with negative values close to 1 are considered as having significant but negative relationship with the environment. Significant in this context is the level of correlation depicted by the regression coefficients of PFA value.

The flowchart for the DPSIR-factor analysis used for this study is shown in Fig. (4) and it has five major observed variables; (1) identifying and interpreting the drivers; (2) interpreting the pressures; (3) describing the state changes; (4) describing the impacts; and (5) reviewing the human response. The latent variables (factors) that exert causal influence on these observed variables are shown in the corresponding right side of Fig. (4). Drivers were derived from the population dynamics, the socioeconomic trends and the associated anthropogenic activities that have taken place over the previous years through land use change analysis (rate and trend). The factors that exert pressure that are considered include road development, industrial activities, fishing and sand mining. The state was described in terms of physical and biological wellness of the environment. The impacts considered were assessment of changes in the ecosystem services (ecological impacts) and socioeconomic impacts. The responses were extracted from the on-going policy implementations of both the Local and State governments. Fig. (4) shows the flowchart defining the DPSIR-FA latent variables and their major components.

Fig. (4) Flowchart for the DPSIR PFA.

A comprehensive assessment of land uses was linked to a systematic environmental and economic analysis of the benefits they generate [24Odunuga S, Omojola A, Oyebande L. Urban land use dynamics of system 6c watershed, Lagos, Nigeria, Lagos Jour. of Geo-. Inf Sci 2011; 1(1): 7-18.] by evaluating the economic benefits and services of fishing and artisanal sand mining in the lagoon and surrounding wetlands. The economic valuation of these ecosystem services was based on Direct Use Method (DUM) using the Market-Price Based approach. This approach estimates the economic value for ecosystem products and services that are bought and sold in commercial markets [25Bateman IJ, Harwood AR, Mace GM, et al. Bringing ecosystem services into economic decision-making: land use in the United Kingdom. Science 2013; 341(6141): 45-50.
[http://dx.doi.org/10.1126/science.1234379] [PMID: 23828934] ]. This, in other words, shows how these respond to the forces of demand and supply. The actual service produced by each of the chosen services (fishing and artisanal sand mining) was based on the annual income generated by the producers (Fishermen and sand mining merchants). The income (producer surplus) is calculated as the difference between the total revenues earned from the goods (fish and sand), and the total cost of production. This was calculated per kilogram (kg) for fish and per ton for sand in each of the three sampled locations (Oreta, Ijede and Offin). The average income (I) for the ecosystem service was the average derived from respondents (Table 2) in each of the locations.

Equation 2 describes the economic benefit from the ecosystem services of the environment.

y = annual income derived from ecosystem for particular services by location

n = number of tons or kg derived in a year

I = average income per ton or kg.

The classification scheme used in the remote sensing technique and the socio-economics survey captured all underline factors (Natural and Socio-economics) that could contribute to environmental degradation of the study area. No environmental and socio-economic variable was ignored or over-weighted in its contribution to the problem under investigation. Therefore, the principal factors calculated in each component of the five DPSIR variables are reliable and reveal the situation in the study area.

The trajectories of land use change in the sub urban lagoon coastal environment of Ikorodu in Lagos using remote sensing technique shows a steady and continuous decrease in the riparian forest. This decrease owes largely to urbanization, forest resource exploitation and other human developmental activities. Also, the emergence and decreasing trend in wetland resources [23Caeiro S, Mourao I, Costa MH, Painho M, Ramos TB, Sousa S. 2004.Application of the DPSIR model to the Sado Estuary in a GIS context Social and Economical Pressures. In: 7th AGILE Conference on Geographic Information Science 29 April-1May 2004, Heraklion, Greece Parallel Session 4.3- Environmental/Social Modelling, 13pp.]. have created additional pressures on the area causing environmental degradation and reducing ecosystem services of the coastal environment. Drivers, Pressures, State, Impact and Response Indicators showed that pressures from human population and economic development have increased over time [44Chopin T, Buschmann AH, Halling C, et al. Integrating seaweeds into aquaculture systems: A key towards sustainability. J Phycol 2001; 37: 975-86.
[http://dx.doi.org/10.1046/j.1529-8817.2001.01137.x] ]. and as demonstrated in the land use analysis in this study, the continuous loss of the critical components of the environment such as the forest is a steady one. Resource exploitation, waste and water pollution have directly caused the degradation of the environment in both physical and biological aspects, which have consequently led to much negative ecological and socio economic impacts. Also, pressure from fishing and housing including floating houses have also caused serious damages to environment and the ecosystem. However, urbanization, deforestation, fishing, sand mining, transportation, housing, resources exploitation and land degradation have direct strong association with population. Consequently, the most determining factor reducing the quality of the environment in the sub-urban lagoon coast of Ikorodu in Lagos, Nigeria is the human population, which is on the increase in the study area. However, serious human effort to protect the environment through policy formulations amongst which include the continuous updating of the regional master plan of Lagos State have not yielded positive results. Consequent upon this, continuous data collection, analysis, interpretation and updating of data concerning environmental issues in the sub-urban lagoon coastal areas are required to curtail the possibility of the area transforming into a despicable city slum. Public awareness campaign about the environmental degradation issues identified in this study should be encouraged while strengthening the implementation of existing policies. Local communities should be involved in the planning and management of intervention projects so as to reduce resource exploitation, safeguard coastal areas and human well-being. All these, will ensure a sustainable sub-urban lagoon coastal environment of Lagos.