LEACHING LOSSES DURING DECOMPOSITION OF MANGROVE LEAF LITTER

Two experiments were conducted in the laboratory to determine leaching losses from submerged mangrove leaves: the first, on freshly-picked and air-dried senescent Avicennia marina (Forrsk.) Vierh. leaves submerged in water of different salinities (16 and 32 parts-per-thousand) for up to 14 days; the second, on freshly-picked senescent leaves of A. marina and Bruguiera gymnorrhiza (L.) Lam. submerged in water of 16 parts per thousand for up to 7 days. In both experiments, loss of dry mass and changes in nitrogen, phosphorus, potassium and tannins of the leaves were monitored. In the initial experiment there was a mean loss in dry mass of 24.6% after 14 days. The chemical analyses revealed that, although there was no significant decline in nitrogen concentration, there were sharp decreases in the other constituents. The greatest total loss relative to the amount initially present in the litter was in potassium (83 - 95%), while the losses for phosphorus and tannins were 57 - 87% and 74 - 85%, respectively. In general, losses were greater at 16 parts per thousand than at 32 part per thousand, and air-dried leaves showed greater initial losses than fresh leaves. In the second experiment, trends in leaching losses of both species were similar to those of the first experiment. With the exception of nitrogen, the concentrations of phosphorus and potassium (expressed as percentage oven-dry mass) had decreased significantly after 6 h in both species, while the concentrations of tannins showed a significant decrease only after 24 and 48 h in A. marina and B. gymnorrhiza, respectively. This work has confirmed that significant losses take place in the leaf litter as a result of leaching. It is suggested that those losses could have important consequences for the estuarine ecosystem.