Bulk density, particle density, and porosity of two species of <i>Sphagnum</i> : Variability in measurement techniques and spatial distribution
Pete Whittington, Alexander J. Koiter, Dia Watts, Alyssa A. Brewer, Vitaly Golubev
Abstract
Abstract Peatlands store more carbon than the world's forests combined, despite covering only 3% of Earth's surface. Governing the sequestration of carbon are biogeochemical processes which are controlled largely by hydrology, which is influenced by the physical properties of the soils, such as bulk density, particle density, and porosity. Reliable values for these properties for peat can be found in the literature; however, values for Sphagnum litter, particularly particle density, are often not measured or reported. The values that do exist for Sphagnum litter rarely report the depth or any spatial differences within the peatland that might exist. Particle density of soil organic material (i.e., humus) is often assumed to be 1.4 g cm –3 and is used for litter. We sampled numerous hummocks of S. capillifolium (Ehrh.) Hedw. and S. magellanicum Brid. (now either S. divinum Flatberg & Hassel or S. medium Limpr.) at a midlatitude continental peatland and determined the bulk density, particle density, and porosity at 5‐cm intervals from the surface to 25‐cm depth. Bulk density and porosity values were similar to values reported in the literature; difference between species and location within the peatland were observed, with the largest difference being found between Sphagnum growing in open and treed areas. Particle density, however, averaged 0.75 g cm –3 , or nearly half that of the assumed value from the literature, suggesting strongly that assuming 1.4 g cm –3 is incorrect for Sphagnum litter and that peatland practitioners should use a locally obtained value, or 0.75 g cm –3 instead.