Mangrove species zonation and soil redox state, sulphide concentration and salinity in Gazi Bay (Kenya), a preliminary study

Abstract

The relationship between soil redox state, sulphide concentration, salinity and spatial patterns of mangrove species distribution was investigated in the mangrove forest of Gazi Bay (Kenya). Field measurements were conducted to examine the relationship between species distribution along a band transect of 280 m and soil redox potential (Eh) and sulphide patterns, as well as the indirectly related (through flooding regimes) soil salinity. Of the three major. species Avicennia marina, Ceriops tagal and Rhizophora mucronata present along the transect, only the distribution of the latter correlated with the measured soil variables, R. mucronata being absent from the less-reduced zone with high salinity. Bruguiera gymllorhiza and Heritiera littoralis occur in minor populations, they are restricted to the saline, sulphide-poor and less-reduced substrates. From the results it is concluded that soil redox potential (Eh), sulphide concentration and salinity may contribute to structure mangroves through the distribution of dominant species, however in combination with other environmental conditions and processes of vegetation dynamics.