Sulfide Concentration and Redox Potential Patterns in Mangrove Forests of Dar es Salaam: Effects on Avicennia Marina and Rhizophora Mucronata Seedling Establishment

Abstract

The mangrove species Avicennia marina and Rhizophora mucronata occur in coastal areas with reducing sediment that contain high sulfide concentrations. However, in this study a glasshouse experiment demonstrated that the establishment of seedlings from these species did not occur in sediment with high sulfide concentration (0.5-6 mM) and low redox potential (-27 to -198 mV). In situ measurements, conducted at Mtoni and Mbweni, Dar es Salaam, showed similar ranges. However, sediments with mangrove roots had significantly lower (P = 0.03) sulfide concentrations than the adjacent areas without roots. Corresponding redox potential was higher in the sediment with roots than without roots. At Mtoni, the sulfide concentrations ranged between 0.0025 to 0.96 mM and 1.5 to 24.5 mM in sediment with roots and without roots, respectively. At Mbweni, sulfide concentrations between 0.01-0.97 mM and 1.09-16.59 mM were detected in sediment with roots and without roots, respectively. The conclusion of these results is that spatial and temporal variation in the soil redox potential and sulfide concentrations, which are results of microbial activities in the sediment, influence mangrove seedling establishment. These soil factors are modified by the root systems, whereby sediments in areas with plenty of mangrove roots are oxidized and thus conducive for mangrove regeneration.

Keywords: Mangrove seedling, sulfide concentration, redox potential, sulfate reducing bacteria

West Indian Ocean Journal of Marine Science Vol. 4 (2) 2005: pp. 163-174