Preliminary study of benthic metabolism and sulfate reduction in a mangrove swamp of the Indus Delta, Pakistan

Abstract

The mangrove, which is characterized by large salinity fluctuations, has highly variable concentrations of Cl- and SO42- in sediment porewater. Vertical profiles of these constituents reflect the historical events of salinity changes in the overlying water. Rates of O2 uptake at intertidal creek banks were generally low and about two times higher in air-exposed than in water-covered sediment. Frequency and duration of water cover were important determinants for microbial respiration in the sediment. Highest rates during water cover were measured subtidally in creek sediment and lowest rates at intertidal creek bank sites. Desiccation may reduce overall microbial respiration at the creek banks. About half of the CO2 production measured during water cover could be accounted for by sulfate reduction in intertidal sediments, whereas only 18% of the CO2 production in subtidal creek sediments could be ascribed to sulfate reduction. The remainder may be produced by other respiration processes. The generally low fluxes of dissolved inorganic nitrogen combined with the low nitrogen content in sediment detritus (C:N ≃ 20) also indicated that nitrogen was a limiting factor for microbial activity. -from Authors