Litter fall and energy flux in a mangrove ecosystem

Abstract

Production, elemental composition and In situ decomposition of litter of Rhizophora apiculata, R. mucronata, Sonneratia alba and Avicennia offcinalis were studied in a mangrove ecosystem fringing Mandovi-Zuari Estuaries on the Central West Coast of India, Litter yield ranged from 10.2 tonnes ha sup(-1) in A. officinalis through 11.8 (R. apiculata and R. mucronata) to 17 tonnes ha sup(-1) year sup(-1) in S. alba. Seasonally maximum litter fall was in pre and post-monsoon months, with the lowest production in the monsoon. Modelling of litter fall as a function of Julian day and six environmental parameters showed that the observed changes can be explained in terms of dry/wet season and wind speed, with a less than 10% difference between calculated and observed annualo averages. C, N and P contents of 13 litter fractions in the four species were 41.9-43.4, 0.66-1.15 and 0.054-0.105% N:P, C:N and C:P ratios were less than 30, 30-100 and greater than 1000. Total decomposition (98-100% loss in dry weight and C, and greater than 90% loss in N and P) of yellow leaves was within 15 weeks in the two Rhizophora spp. and S. alba, and within 8 weeks in A.officinalis. In all four species, mass changes during decomposition obeyed first-order kinetics. Comparison of C, N and P fluxes from the decomposing mangrove litter with phytoplankton, bacterial and secondary production in the estuarine waters showed that mangrove production is important mainly for the C budget of the Estuaries and in sustaining the microbial food chain and nutrient regeneration, rather than the particulate food chain directly