Physical aspects of coral reef lagoon sediments in relation to detritus processing and primary production

Abstract

Physico-chemical analysis of sediments showed there to be 4 main sediment types in One Tree Lagoon (Southern Great Barrier Reef) ranging from coarse sand to very fine sand. These sediments showed characteristic depth profiles of dissolved oxygen and E sub(h). Oxygen was depleted within the top 5 to 10 mm of the sediment and redox values were correspondingly low. These values showed seasonal differences. The sediments were generally oxidized in winter (E sub(h) values greater than or equal to -38 mV) but reduced in summer (E sub(h) less than or equal to -100 mV). Sediment concentrations of total organic carbon (TOC) and total nitrogen (TN) were typically 0.28 and 0.06% respectively with no significant difference between seasons. A significant difference was observed, however, for TOC levels between sediment types with highest concentrations observed in the very fine sand (0.29 plus or minus 0.005%). Mean values for community primary production (P) and net community production (P sub(n)) over all seasons were higher in the coarse sand (P = 0.44 gC m/d; P sub(n) = 0.05 gC m/d) than in the very fine sand (P = 0.26 gC m/d; P sub(n) = -0.003 gC m/d).