Abstract:
The Haast chronosequence on the west coast of the South Island of New Zealand consists of a series of coastal dune ridges formed by periodic earthquake disturbance over the last 6500 years. It approximates an ideal chronosequence, because soils are under the same climate and vegetation, have similar topography, and are developed in the same parent material. We assessed soil development and the changes in nutrients at eleven sites along the sequence to determine rates of nutrient transformations and the potential for limitation of biological activity by nitrogen and phosphorus availability. Soils develop rapidly to podzols (Spodosols) under the super-humid climate, involving acidification and depletion of base cations in the first few hundred years, development of a bleached eluvial horizon under a thick organic horizon within 2000 years, and formation of a continuous cemented iron pan within 4000 years. Soil phosphorus concentrations decline markedly in the first few hundred years in both the organic and upper mineral soil horizons, with rapid depletion of primary mineral phosphate and the accumulation of organic phosphorus to ~ 80% of the total phosphorus in the upper mineral soil. These changes lead to an increasing degree of phosphorus limitation along the sequence, as indicated by an increase in C:P and N:P ratios and a decline in available phosphate. The rates of soil development and phosphorus depletion are more rapid than at the nearby Franz Josef post-glacial chronosequence, where glacial moraine derived from graywacke contains a relatively high phosphorus concentration and weathers into fine-textured soils. The Haast chronosequence therefore provides an important additional example of soil development linked to long-term depletion of soil phosphorus under a perudic moisture regime.
