Role of decomposition of mangrove and seagrass detritus in sediment carbon and nitrogen cycling in a tropical mangrove forest

Abstract

The elemental composition and in situ decomposition of detritus of Rhizophora apiculata and Enhalus acoroides were studied in mangrove and seagrass bed sediments in the Bangrong mangrove, Phuket, Thailand, and compared with controlled laboratory flux incubations. At the field site detritus was buried in litter-boxes in the sediments and changes in particulate organic carbon and nitrogen in detritus and sediments were followed for up to 2 mo. In the flux incubations the sediments were amended with mangrove and seagrass leaves and rhizomes, and the exchange of oxygen, CO 2 , dissolved organic carbon (DOC) and inorganic nitrogen was measured across the sediment-water interface for 43 d. The decomposition of seagrass leaves was rapid both in situ and in the laboratory, whereas about 40% of the mangrove leaves remained after 43 d, and no decomposition could be detected for the seagrass rhizome detritus. There was an immediate increase in sediment oxygen uptake (SOU) in the seagrass sediments followed by an increase in CO 2 production after the addition of detritus, whereas the SOU remained low in the mangrove sediments. The C:N ratios decreased in the carbon-rich mangrove leaves and seagrass rhizome detritus, but increased in the less carbon-rich seagrass leaves during the decomposition. The decrease in C:N ratio was attributed to colonization by bacteria which incorporated nitrogen from the overlying water column or from the indigenous particulate organic nitrogen pool in the sediments. The mineralised carbon from the plant detritus was recovered as CO 2 , whereas no accumulation or release of DOC was found. The effect of amendment with mangrove detritus on the nitrogen fluxes was minor, whereas the uptake of nitrate and release of ammonium was enhanced with the seagrass leaves. About 32 to 36% of the mineralised nitrogen from the seagrass leaves was released across the sediment-water interface, where it became available for primary producers or exported to adjacent ecosystems KEY WORDS: Mangrove · Seagrass · Nutrient cycling · Decomposition · Tropical sediments Resale or republication not permitted without written consent of the publisher

Modeled CO2 Emissions from Coastal Wetland Transitions to Other Land Uses: Tidal Marshes, Mangrove Forests, and Seagrass Beds

“…Given that decomposition rates of organic matter are faster when nitrogen and phosphorus content are higher (Enríquez et al, 1993) and that belowground plant parts generally have lower nutrient content than leaves, it is not surprising that decomposition of belowground parts is much slower than that of leaves (Holmer and Olsen, 2002;Fourqurean and Schrlau, 2003), but there are few reports of decay rates of belowground biomass. In Posidonia oceanica, rhizomes decayed at a rate of 0.0001 d −1 and belowground leaf sheaths at a rate of 0.0002 d −1 , which was two orders of magnitude slower than the decomposition of leaves at the same location (Romero et al, 1992).…”

Resource availability and meiofauna in sediment of tropical seagrass beds: Local versus global trends

“…In addition, seagrass beds get carbon input from nearby coastal systems such as mangrove forests (e.g., Bouillon, Moens, & Dehairs, 2004). Several studies aimed to study the origin of carbon in these systems (e.g., Fleming, Lin, & Sternberg, 1990;Holmer & Bachmann Olsen, 2002;Marguillier, van der Velde, Dehairs, Hemminga, & Rajagopal, 1997) rather than to unravel the effects of total resource availability on consumers.…”

Grazing by the intertidal gastropod Melampus coffeus greatly increases mangrove leaf litter degradation rates

“…Despite considerable study, the linkages between mangrove forest detritus and adjacent estuarine water ecosystems are inadequately understood (Odum & Heald 1972, Fell & Master 1973, Snedaker & Lugo 1973, Cundell et al 1979, Twilley et al 1986, Boto 1992, Holmer & Olsen 2002. Proffitt et al (1993) reported that grazing by the intertidal gastropod Melampus coffeus L. (Pulmonata: Ellobiidae) in both field and laboratory trials caused very high rates of breakdown of Rhizophora mangle, Avicennia germinans and Laguncularia racemosa leaves.…”