Department or Program
Geology
Abstract
Southeast Alaska exhibits one of the fastest rates of glacier retreat, plant succession, and soil development in the world. Previous soil chronosequence studies have shown a predictable pattern of soil formation from Entisols to Spodosols and plant succession from pioneer to climax species 270 years after moraine deposition. However, little is known about plant successional controls on soil chemical weathering on post-glacial landscapes. This study aims to elucidate the connection between plant succession and soil chemical weathering in response to climate change in Southeast Alaska. To accomplish this goal a soil chronosequence was established on the moraines of the Herbert Glacier valley, an extension of the Juneau Icefield. Seven pedons were sampled and morphologically described and the proportion of different plant species was estimated and recorded at each site. Moraine age was constrained using tree cores. Soil samples were analyzed for elemental composition (XRF) and Fe enrichment (DCB extraction). XRF data were used in a chemical weathering index to evaluate weathering degree and in mass balance calculations to determine weathering rates. The ratio of pedogenic to total Fe was calculated to determine soil development over the chronosequence. Results show rapid soil development consistent with previous literature, with Spodosols forming in under 300 years. Over the chronosequence the vegetation underwent several successional stages, shifting from cottonwoods and alders to a spruce forest and eventually a mixed spruce and hemlock forest. Carbon accumulated and pH decreased over time, consistent with increasing soil development. Weathering rates did not show any trend over time nor correlation with the plant successional sequence, and this may be due to the young age of the soil, instrumental limitations, or biogeochemical cycling of nutrients. The ratio of pedogenic to total Fe increased over time, indicating weathering of Fe-bearing minerals. This ratio seems to be a more reliable metric for soil chemical weathering than the index used, potentially because Fe is not heavily taken up by plants or leached from the system as are other soil elements.
Level of Access
Restricted: Embargoed [Open Access After Expiration]
First Advisor
Castro, Raquel
Date of Graduation
5-2023
Degree Name
Bachelor of Arts
Recommended Citation
Margerum, Alana, "Plant Succession and Soil Chemical Weathering on Post-glacial Landscapes, SE Alaska" (2023). Honors Theses. 451.
https://scarab.bates.edu/honorstheses/451
Number of Pages
49