Mangrove forests along the tidal flats and lagoons of Ngomeni, Ungwana Bay
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Publication EditorHoorweg, J.
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AbstractThe study was carried out from November 1995 to March 1996 during the dry season period, and concentrated on mangrove forest under different anthropogenic pressures. A total of six stations with 13 sub-stations were demarcated representing five biotopes; mangrove forest, degraded mangrove areas, saltwork ponds, sandflat, and aquaculture ponds. Macroflora and macrofauna composition, soil characteristics, extent and status of mangrove forests at Ngomeni, Kenya are presented and discussed. There are no statistically significant differences between the various biotopes for epifauna; differences in fauna densities and species diversity in different biotopes were statistically significant. Mangrove forest biotope had the highest infaunal densities, while no infauna were recorded for sandflat and the saltworks ponds. Species diversity (no. of species or taxa/station) was highest in the mangrove forest and lowest in the saltworks ponds. Sediment texture was mainly sand (>50% sand) in all the biotopes, temperature and salinity were moderate in mangrove forest biotope (28.1 degree C and 41.1 ppt, respectively) and extreme in the sandflat (30.8 degree C and 6.1 ppt respectively) the pH was highest in saltworks and aquaculture ponds (9.5 and 7.9 respectively) and lowest in the mangrove forest (6.4). Percentage organic and water content were highest in mangrove forests (13.45% and 43.7%) and saltwork ponds (12.12% and 40.6% respectively) and lowest in sandflats (5.14% and 21.1% respectively). There are statistically significant differences in the nutrient status between the biotopes: Ammonium-nitrogen 0.066 mu g/g of wet sediment in the sandflat to 0.783 in saltworks ponds; nitrate-nitrogen ranged between 0.022 in saltworks to 0.047 in degraded areas; phosphates ranged between 0.007 in aquaculture ponds to 0.021 in saltworks ponds; and sulphate areas; phosphates ranged between 1.022 in aquaculture ponds to 3.174 in saltworks ponds. Biotopes with moderate temperature and salinity levels, and high levels of organic matter and water content had greater species diversity. Simple correlation analysis was performed. A great deal of mangrove forest cover has been lost to aquaculture and saltworks developments, on comparison between earlier (1960s) and recent (1992) aerial photographs. Destruction of mangroves has led to decline in both forestry output and macroinvertebrate diversity, and changes in soil physical and chemical parameters. Rehabilitation conservation, and sustainable of the mangrove forest resources is highly recommended.
Title of Parent Book or ReportDunes, groundwater, mangroves and birdlife in coastal Kenya
Publisher or UniversityActs Press
Series : NrCoastal Ecology Series;No. 4