Submitted to: Ecological Society of America Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: May 1, 2001
Publication Date: August 5, 2001
Citation: Halvorson, J.J., Smith, J.L. 2001. Increasing carbon and nitrogen in Mount St. Helens pyroclastic soil: Measuring soil quality and function after 20 years. Page 287 IN Abstracts of the Meetings of the Ecological Society of America, August 5-10, 2001, Madison, WI.
We revisited the Spirit Lake pyroclastic flow and other less disturbed sites near Mount St. Helens, during July 2000, to measure changes in soil C, N, biological activity and other variables during the 20 years since eruption. We hypothesized we would find 1) significantly more C and N in pyroclastic soil than our last sampling, especially near lupines; 2) evidence for increasing rates of C and N sequestration in pyroclastic soil 3) evidence of larger, more efficient populations of soil microorganisms related to substrate quantity and quality. We observed significantly more C and N in both bare and lupine-influenced pyroclastic soil than reported in 1990 and evidence of increasing rates of sequestration. The greatest proportional increases were recorded in bare soil but absolute increases were higher near lupines. Compared to bare soil, lupine-influenced soil had a similar pH, significantly higher electrical conductivity (EC), higher rmicrobial and enzyme activity. Concentrations of C and N were highest nea the soil surface and pH, EC, microbial and enzyme activities varied significantly with depth too. When compared to less disturbed sites, the pyroclastic site exhibited the highest EC, but lowest C and N. These results extend our understanding of early succession by measuring the cumulative impacts of lupine colonists on net soil C and N sequestration rates, changes in soil properties and microbial activity.