Sulfate reduction, acetate turnover and carbon metabolism in sediments of the Ao Nam Bor mangrove, Phuket, Thailand

Abstract

Rates of sediment O2 uptake, CO2 production, sulfate reduction and acetate turnover were examined during January 1992 in the Ao Nam Bor mangrove, Phuket, Thailand. The impact of air exposure on O2 uptake was most pronounced in the intensely bioturbated high-intertidal zone (6.4 times higher than during water cover), and decreased to almost zero in the low-intertidal zone. This indcates a gradual increased area of sediment-air contact zones with tidal elevation due to changes in surface topography. Based on an average water cover for January, the diurnal O2 uptake -and thus total decay of deposited detritus -was 4 to 5 and 8 times faster in the high-intertidal compared to the mid-and low-intertidal zones, respectively. Sulfate reduction rates were generally low. The depthintegrated (0 to 30 cm) sulfate reduction was highest in the mid-intertidal zone, and supported 85 % of the estimated daily CO2 release. In the high-and low-intertidal zones, sulfate reduction supported 11 and 92%, respectively, of daily CO2 release. Rates of acetate uptake were also higher in the midthan in the low-intertidal zone (no data from high-intertidal) However, the depth-integrated acetate uptake was consistently about 2.6 times the rates of CO, release and 5 to 6 times the 0 to 11 cm integrated sulfate reduction, which suggests that pool sizes of acetate and thus uptake rates may have been overestimated. In conclusion, while benthic respiration in the mid-and low-intertidal zones of the Ao Nam Bor mangrove was dominated by sulfate reduction with acetate as carbon source. 'suboxic' conditions related to bioturbation in the active high-intertidal sediment made respiration by other electron acceptors than SO.,-more important.

Temporal variations in microbenthic metabolism and inorganic nitrogen fluxes in sandy and muddy sediments of a tidally dominated bay in the northern Wadden Sea

“…The estimates are based on integrations of the daily data, where it is assumed that the hourly net flux of CO2 is independent of tides, whereas the net flux of DIN species is 0 at low tide (DIN values should be multiplied by 3 (S), 1.8 (A) and 2.2 (M) if this assumption is not used (Table 1). Previous studies have concluded that the exchange of 02 between sediment and air (low tide) corresponds to the exchange between sediment and water (high tide) when the surface topography is relatively smooth as in most Wadden Sea sediments (Grant, 1986;Kristensen et al, 1992Kristensen et al, , 1994. However, Bodenbender & Papen (1996) found rates of dark CO2 emission from exposed K6nigs-hafen sediments around 50 % lower than the dark 02 uptake measured here.…”

Carbon and nitrogen mineralization in sediments of the Bangrong mangrove area, Phuket, Thailand

“…It was earlier thought that aerobic decomposition is much more important than anaerobic decay in mangrove sediments. More recently, it was shown that this is not always true, and that sulfate reduction may be an important electron acceptor in organic-rich deposits typical of mangrove forests (Kristensen et al 1994, Alongi et al 1998.…”

“…It was earlier thought that aerobic decomposition is much more important than anaerobic decay in mangrove sediments. More recently, it was shown that this is not always true, and that sulfate reduction may be an important electron acceptor in organic-rich deposits typical of mangrove forests (Kristensen et al 1994, Alongi et al 1998.Another feature of mangrove forests and tropical seagrass meadows is the very low levels of dissolved and particulate nutrients in the sediment and overlying water, and the forests generally appear to be N or P limited (Boto & Wellington 1983). As a consequence, they possess a high capacity for retaining and recycling nutrients by several mechanisms that reduce loss (Twilley et al 1986).…”

Transformation and exchange processes in the Bangrong mangrove forest-seagrass bed system, Thailand. Seasonal and spatial variations in benthic metabolism and sulfur biogeochemistry

“…rapid cycling between living pools and detritus (Harrison 1989, Kristensen et al 1995, Mateo & Romero 1996. Mangrove detritus has high C:N ratios and a significant fraction of the organic matter is considered to be refractory humic compounds and geopolymers (Benner et al 1990, Kristensen et al 1994. This is probably an important cause of the observed low rates of mineralization in mangrove ecosystems despite the ambient high temperatures (Knstensen et al 1992(Knstensen et al , 1995.…”