Wetland Depletion Assessment in Marine Local Government Areas of Rivers State

Wetlands are considered to be one of the most productive yet disappearing ecosystems, providing critical ecological, social (livelihood, water supply, floods regulation) and economic services. But once depleted these vital supporting functions are lost or diminished to a great degree. The prime aim of this paper is therefore to provide cost-effective, accurate and spatially-explicit information that supports appropriate policy decisions and actual wetland conservation in the Marine LGAs of Rivers State, Nigeria. Three specific questions were addressed: (i) Spatial identification and delineation of wetlands in the LGAs based on Landsat-7 images from 2004–2024 in ≥5-year period; (ii) Quantification of the variation of their spatial extent and depletion rate; and (iii)Examination of the spatio-temporal variation of land use/land cover (LULC). Preprocessed multi-temporal Landsat-7 imageries were spectral-enhanced using indices (NDVI, NDWI), digested with DEM, classified into wetlands and non-wetlands based on threshold technique and changes were spatio-temporally quantified through image differencing; while status, distribution and dynamics of LULC were analyzed. Classifications schemes for the selected LULC categories; built-up, vegetation, water bodies and bare earth were derived according to the nature of the area, spectral characteristics of Landsat-7 image and their potential roles in the hydrological and Ecological functioning of the wetlands. These schemes were respectively rooted on indices, boundaries, spectral characteristics, and extent of the variables. The maximum likelihood supervised classification was consecutively employed on the focused area for the multi-temporal datasets image-sets for the years (2004, 2009, 2014, 2019 and 2024) to ensure homogeneity in classification and accordingly, consistency in change detection accuracy. The temporal prevalence of wetland extent in years (2004, 2009, 2014 and 2024) indicated gain of +153% just before the onset of observed decline within the period (2014–2024) by ≈51%, which explained the trend of increase in exploitation of wetlands in the last decade. The classification of LGAs landsat images revealed a significant gain in built-up lands area between the two endpoints (2004 and 2024) from 1000km² to 3420Km² (341% increase), which is indicative of a significant increase in anthropogenic intervention. A significant loss was observed between 2004 and 2009 (N=−61%), before a recovery period with a gain of 37% in 2019, followed by an accelerated depletion with a loss in area of −73% in 2024 (N=−73%). Intermedium-year variations were affected by the clouds ratio and scanning errors of Landsat 7 visible bands, which induced inaccuracies in imagery classification. Nonetheless, these findings did also report a relative stability in water body surface areas in the study area. This was countered with fluctuations in bare lands with a magnitude of −99%, from 651 km ²in 2004 to 6 km ²in 2024 as well as a continuous increase in urbanized lands from 1000 km2 in 2004 to 3420 Km ²in 2024. It was concluded that the loss in the values of 2004 exhibited wetlands dynamic could be tackled to ensure sustainable development if immediate actions are taken. These could include setting up GIS-based monitoring and controlling framework, establishing effective regulations on land uses & implementation, and providing participatorily active role for local communities & authorities in wetland conservation.