Evolution of Soils and Erosion Rates on Recent Post-glacial Landscapes in the Coastal Temperate Rainforest of Southeast Alaska

The coastal temperate rainforest of Southeast Alaska presents one of the fastest rates of glacier retreat, plant succession, and soil development in the world. Glacial till deposits are rapidly colonized by plants and soils evolve from Entisols to Spodosols in less than 270 years. Soil formation plays an important role in controlling chemical weathering and soil erosion processes. However, the interplay between soil formation and erosion rates on recently deglaciated surfaces in temperate rainforests remains unknown. Our objective was to evaluate soil evolution and soil erosion rates on the complex moraines of the Mendenhall Glacier, southeast Alaska. We hypothesized that erosion rates decrease with soil development, and surfaces stabilize before 270 years of soil formation. We evaluated soil chemical, physical and morphological properties in five moraines spanning from 69 to 270 years in age. For soil erosion assessment using 239+240Pu and stable carbon isotopes, we sampled four replicates on backslopes (erosion sites) and at the crest (reference sites) of the oldest moraines. Pedons show a trend of increasing podzolization intensity and profile differentiation with surface age. The first morphological evidence of podzolization is found in the 69-year-old pedon, showing a sequence of Oi/AE/Bs/C horizons while the 158-year-old pedon shows a distinct E horizon, and after 270 years of soil development, a Spodosol with Oe/E/Bhs/BC/C horizons is formed. The 239+240Pu and stable carbon isotopes will provide more information to shed light on the interplay between soil development and surface stability on recent post-glacial surfaces in a temperate rainforest.