Geospatial assessment of ecosystem health of coastal urban wetlands in Ghana

Abstract

A comprehensive assessment of ecosystem health of wetlands is needed to guide protection and restoration activities. However, the conventional methods used in evaluating ecosystem health of wetlands largely rely on field observational data which often do not provide spatio-temporal perspectives to the assessment. Geospatial assessment of remotely sensed data has enormous potentials for assessing ecosystem health of wetlands at different temporal and spatial scales. This study employed geospatial techniques to assess ecosystem health of Densu Delta, Sakumo II and Muni-Pomadze Ramsar Sites over a 32-year period using structure, function and resilience indicators. Landsat satellite images of 1985, 2002 and 2017 were obtained for this study. Analytic hierarchy process (AHP) was used to weight the indicators. The importance of the ecosystem health indicators in decreasing order was as follows: Structure > Resilience > Function. The findings of the study also indicated that ecosystem health of the wetlands progressively deteriorated in 2002 and 2017 compared to the reference year of 1985. In 2002, the Densu Delta experienced the least decline (11.8%) from the 1985 state among the three wetlands and Sakumo II recorded the highest deterioration (38.0%). Unlike 2002, in 2017 the health of the Densu Delta experienced the worse deterioration (46.3%) whereas Sakumo II recorded the least decline (26.2%). Ecosystem health of Muni-Pomadze Ramsar Site deteriorated at a similar magnitude, 27.0% and 29.1% in 2002 and 2017, respectively. The critical underlying factor for the degradation of the wetlands is urbanization largely due to increase in human population which led to the expansion of built-up areas in the wetlands, fragmentation of natural land use and land cover (LULC) classes and reduction of vegetation cover.