The mangrove swamps of Keneba, lower Gambia River basin. III. Seasonal variations in the chloride and water content of swamp soils, with observations on the water levels and chloride concentration of free soil water under a barren mud flat during the dry season.
Profiles in hizophora racemosa, Avicennia germinans and Sesuvium portulacastrum zones and in four barren mud flats flooded only from June to October, were examined to depths of 4|- ft. There were large variations in Cl content between different levels in one profile; the range was 26 to 77 mg/g in Avicennia soils but only 6 to 10 mg/g in sands of one barren flat. There were high concentrations of Cl in the wettest layers (as well as at the surface) especially in the dry season and in the least permeable soils. Cl concentration varied greatly between quite close localities. Except in the surface layers, Cl concentration varied little between seasons, and rainfall had little effect on total soil salts. Cl concentration reflected the state of drainage in the profiles. The impermeable but marginal soils under Rhizophora were constantly leached by tidal water and Cl content in the soil and the free water was relatively low. In permeable soils with a mobile water table but poor lateral drainage to the creeks, Cl concentration was low in the soil but high in the free soil water. In impermeable soils far from the waterways, Cl levels of soil and water were high.