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

Brief description

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. This study was undertaken to investigate whether variations in soil redox potential, pH, salinity and extractable ("available") nitrogen and phosphorus occurred with time and elevation within the tidal zone, for a mangrove forest in North Queensland.

Lineage

Maintenance and Update Frequency: notPlanned

Statement: Statement: Particle size analysis:Wet core sections were washed through a series of standard sieves ranging from 2 mm to 53 µm. The fraction passing the 53 µm mesh was then well mixed and diluted further for analysis over the 2 µm to 50 µm range using a Coulter Counter model TAII. The amount of organic material in the size ranges 250 µm was estimated by ashing dried samples at 450°C for 12 hours. Bulk density measurements were made using techniques described in: Allen SE, Grimshaw HM, Parkinson JA and Quarmby C (1974) Chemical Analysis of Ecological Materials. John Wiley and Sons, New York. The values quoted refer to the dry weight per total volume of wet soil. Total C, N and P:Duplicate core sections, 5 cm long, from the surface and at 95 cm depth for each site were dried at 90°C for 3 days and ground to pass a 50 µm mesh in a Wiley mill. Subsamples of the ground material were analysed for C and N using a Perkin Elmer model 240 elemental analyser. Duplicate subsamples from any given core section gave very good agreement to within ±0.05% C and ±0.02% N. However, the replicate samples for a given site and depth showed a much greater variability (up to ±1.5% C and ±0.05% N) due to the heterogeneous distribution of fine root material. Total P was measured by standard colorimetric methods following a mixed acid digestion of a finely ground sample as described in Allen et al. (1974) above.Pore water salinity:Extracted pore water salinities were also measured using a conductivity meter in the laboratory. This check revealed errors of up to ±4%, however the use of the chloride selective electrode and SCE reference was continued because of its simplicity for field use. Electrodes were calibrated with appropriate standards just before each core was taken.Ammonium, nitrate, nitrite and phosphorus analyses:A 0.5-1.0 g sample of wet soil was weighed into a 10 ml capacity centrifuge tube and 6.0 ml of a 1 M sodium acetate-acetic acid buffer solution, pH4, added. After capping and shaking for 30 minutes, the solution was cleared by centrifugation and the supernatant analyzed using a Technicon autoanalyzer and standard colorimetric methods as described in Allen et al. (1974) above.Estimates of above ground biomass:Crude estimates of above ground biomass were calculated using previous data for the transect (Duke and Bunt, unpublished) in which trees within 1 m of each side of the transect were described by species, height and girth. For a given 5 m sector of the transect, the biomass was estimated by summation of the trunk volumes (m³) calculated for each tree within the 5 m by 2 m area, the final result being expressed as trunk volume (m³) per 10 m² land area. Biomass was then calculated in terms of average values over 20 m sectors in order to simplify the data. For the statistical analyses and to obtain estimates of variance, the biomass for each site was calculated from the average of 5 by 5 m sectors bordering each site. Logarithmic transformations of biomass were used in the final analyses in order to satisfy the assumptions of the statistical methods, i.e., normal distribution and homoscedasticity.

Notes

Credit
Boto, Kevin G, Dr (Principal Investigator)