Soil characteristics and nutrient status in a mangrove forest at Hinchinbrook Island, north Queensland

Soil characteristics and nutrient status were monitored monthly, over the period April 1979 to June 1980, at 9 sites along a 370 m vegetated transect between Coral Creek and Priest Creek, Hinchinbrook Island. The elevation of the sites ranged between 0 and 1.4 m (Australian High Datum). Tree species composition and canopy height varied along the transect.

At the beginning of the study, basic soil properties along the transect were determined. Particle size analyses over the size range 2 µm to 2 mm were performed on 10 cm lengths of single cores collected using a 1 m long and 6 cm diameter stainless steel sediment corer at sites 2, 5 and 9. The amount of organic material in the size ranges 250 µm was also calculated. Bulk density measurements for all 9 sites were made from duplicate core samples of 40 cm length. Analysis of total C, N and P, were carried out on duplicate 5 cm lengths of core section, collected from the surface and at 95 cm depth from all 9 sites.

Monthly soil samples were collected at all 9 sites using a 1 m long, 6 cm diameter corer with PVC slides at 5 cm intervals, which could be removed to allow sampling. Redox potentials were measured by immediate insertion of a Pt/SCE combination electrode into the soil. The measured potentials were corrected to EH (vs. hydrogen electrode reference) by addition of +244 mV to the reading. The pH was measured by direct insertion of a glass electrode through the port into the soil. Interstitial salinities were measured using a chloride selective electrode and SCE reference lightly touched upon the soil surface exposed at any given port.

Soil subsamples were taken at 10 cm intervals from each core, (10 samples per core), by insertion of open-ended polythene tubes through the ports. The tubes were then quickly sealed with septum caps and immediately stored in ice until analysis. Analyses for extractable nitrogen (ammonium, nitrate + nitrite) and phosphorus were carried out in the laboratory within 2-3 days after collection.

Crude estimates of above ground biomass for 5 m sectors of the transect were calculated using previously collected transect data. Litter fall was monitored monthly for 12 catchers (6 pairs) placed near the sampling sites.