Estimated stocks of organic carbon in mangrove roots and sediments in Hinchinbrook Channel, Australia

Abstract

Above‐ground and below‐ground root biomasses (Babove and Broot) were measured for young, isolated Rhizophorastylosa on Iriomote Island, Japan. The relationship between these two parameters was significant and given as the equation, Broot (g dry weight) = 0.394 × Babove (g dry weight) − 485  (r = 0.986). Multiple regression analyses also revealed good correlation between diameter and biomass of prop roots (Dprop and Bprop) and between prop root and root biomasses. Consequently, root biomass could be estimated from the measurements of diameter and biomass of prop roots using the multiple regression equation, Broot (g dry weight) = 80.0 ×Dprop (cm) + 0.86 ×Bprop  (g dry weight) − 251. The relationship between DBH (diameter at breast height) and prop root biomass was also adequately described using an allometric equation.

In Hinchinbrook Channel, Australia, redox potential (measured as Eh) and organic carbon stocks in the top 5 cm of mangrove sediments were measured along a 600 m transect from the frequently inundated, Rhizophora dominated zone on the creek edge, towards higher grounds, where Ceriops spp. became increasingly dominant. Eh values were about −60 mV near the creek edge and increased to 260 mV on higher grounds. Organic carbon stocks showed an opposite trend to Eh, with the values decreasing from about 360 t C ha−1 to 160 t C ha−1. At 18 sites, representing six different habitats, organic carbon stocks were also measured along with the DBH of mangrove trees. DBH was converted into above‐ground biomass and then into root biomass using the equations obtained in the study on Iriomote Island. The average organic carbon stocks in the top 50 cm of sediments, above‐ground biomass and root biomass were 296 t C ha−1, 123 t C ha−1 and 52 t C ha−1, respectively, and accounted for 64%, 25% and 11% of the total organic carbon stock.