ABSTRACT

A study was conducted to investigate the ecological changes and socioeconomic activities in the coastal areas of Akwa Ibom State, Nigeria between February and August 2018, with the objectives of determining the mangrove cover change in the area; investigating the drivers of change in the mangroves; and assessing the impact of human activities on soil properties and vegetation structure and composition. Landsat imagery of 1983, 2003 and 2016 from United State Geological Survey were used to assess the extent of mangrove loss and the images obtained were processed using Erdas Imagine software while mapping was completed with ArcGIS software. To evaluate the human drivers to the destruction of mangrove forest, nine mangrove (9) communities were randomly selected at 10% sampling intensity resulting in the selection of 180 households. Visual observation, questionnaire administration and Focus Group Discussion (FGD) were used to obtain relevant information on anthropogenic activities occurring within the mangrove ecosystem. After research questionnaire administration, one hundred and twenty four (124) sets were retrieved. Descriptive statistics such as tables, graphs were used to analyse the data obtained. To assess the impact of human activities on soil properties, three core samples were obtained in each plot at depths of 0-15 and 15-30cm. The samples were subjected to physical and chemical analysis. Fixed Analysis of Mixed Data (FAMD) was applied to show the effect of human activities on soil properties and how this differed amongst the three physiographic habitats (Interdistributary, wooded levee and distributary channel habitats). To assess changes in vegetation structure and composition of the mangroves, two transects measuring 100m were cut in each of the three identified physiographic habitats. Two temporary plots of 20m x 20m along each transect were randomly selected for enumeration of trees (≥ 5m). Within each plot, a 5m x 5m subplot was mapped out for under storey plant species (≤ 2 ≥5m) enumeration and 1m x 1m for seedlings/saplings (< 2m). The 30 year period (1986-2016) under assessment showed a decline of 19.07% (2,147.77ha) of the mangrove forest. Fuelwood harvesting(97.6%), Nypa fruticans introduction (93.5%), oil exploration and exploitation activities (82.3%), waste disposal, stilt root (71.0%) and timber harvesting (62.1%) were the direct drivers of mangrove ecosystem change while availability of improved tool for harvesting (91.1%),  migration(87.9%) and, attitude and lifestyle(54.8%) were the indirect drivers inducing the anthropogenic drivers. Variation in soil properties appeared not to be affected by human activities. However, Wooded levee and interdistributary mangrove soils had more ammonium, organic carbon, sand, nitrate, sodium and magnesium, calcium, potassium, ECEC and redox potential than distributary channel mangroves.The mangrove ecosystem of the study area is characterized by  Rhizophora racemosa, R. harisonii, R. mangle, Avicennia africana, L. racemosa, Phoenix reclinata, N. fruticans and Acrostichum aureum and unclassified plant (akpachan)  with Rhizophora racemosa and Rhizophoraceae as the most abundant species and family respectively. The presence of Nypa fruticans was observed in all the physiographic habitats but highest relative density was observed for Distributary habitatmangroves. Highest mean heights(11.47m and 9.05m) and dbh (27.80cm and 19.75cm) was recorded for Avicennia africana in Interdistributary and Wooded habitats mangroves respectively while R. harisonnii had the highest mean height of 7m and highest mean dbh of 15.92cm in Distributary habitat mangrove. In terms of basal area, Rhizophora racemosa had the highest value of 0.11m2 in Distributary habitat mangroves and 0.02m2 for Avicennia africana in the  Wooded levee habitat.  Regular and effective monitoring of the mangrove forest of Akwa Ibom State, constitution of “Mangrove Protected Area” backed by effective government legislation to protect the remaining mangroves and restoration of degraded mangrove areas with propagules will increase mangrove forest extent and provide coastal protection.