Podzolized soils on hilly and steep land near Tennyson Inlet, Marlborough Sounds, New Zealand - Classification and relation to Landform, Slope and Altitude

Abstract

Eight soil profiles ranging in altitude from 30 m to 820 m at Tennyson Inlet in the Marlborough Sounds, New Zealand, are described, classified and discussed in terms of morphology, chemistry and clay mineralogy. The soils are formed from greywacke on forested hilly and steep land under a superhumid climate. Profiles show eluvial and/or illuvial features typical of podzols and podzolized soils. Within the study morphological, chemical and mineralogical properties show patterns in weathering, leaching and podzolization. Differences in weathering are related mainly to geomorphic history and topography. The most strongly weathered soils occur at altitudes below about 200 m where parent materials were probably inherited from Late Pleistocene interglacial or interstadial weathering. Less weathered soils occur at higher altitudes where parent materials were derived from widespread periglacial erosion during the last glaciation, and from periodic erosion during the Holocene. Weathering and also leaching is least on soils on very steep slopes (>38°) at altitudes above 200 m, where rejuvenation by slope movement has been more active than on less steep slopes. Patterns in weathering are clearly shown by clay mineralogy, with strongly weathered soils dominated by kaolinite, and less weathered soils dominated by vermiculite. Differences in podzolization are attributed mainly to greater effective rainfall, leaching and accumulation of amorphous minerals and mineral-organic complexes with increasing altitude. The combination of field and laboratory data shows that at altitudes below about 200-300 m profiles are relatively weakly podzolized, while podzolized soils and podzols occur at higher altitudes. Podzolization patterns are clearly shown by subsoil values of acid-oxalate and pyrophosphate Fe and Al, NaF, pH and P retention. The profile at highest altitude is dominated by smectite clays and the greyish-coloured solum is interpreted mainly as a relatively thick (80 cm) eluvial horizon resting directly on bedrock. Neither the New Zealand Genetic Classification nor Soil Taxonomy satisfactorily classifies all the soils.