PARENT SESSION
Oral Session #76: Ecosystem Ecology: Larger scale processes, geomorphology, soils.
Presiding: W. Straw
Thursday, August 8. 9:00 AM to 11:30 AM. Gila Meeting Room, TCC.
Impacts of erosion on biogeochemistry: preliminary results from the Hawaiian Islands.
Porder, Stephen*,1, Vitousek, Peter1, Paytan, Adina1, 1 Stanford University, Stanford, CA
ABSTRACT- Erosion has long been recognized as a pathway of nutrient loss, but its potential to increase soil nutrient pools by removing nutrient-depleted soils and exposing fresh rock to weathering has received less attention. We compared 87Sr/86Sr in plants on two actively eroding slopes to values from adjacent ~150ky constructional surfaces in the Hawaiian Islands. Sr is a useful tracer of cation inputs because Hawaiian rocks and atmospheric deposition have easily distinguishable, discrete 87Sr/86Sr . Each shield/slope pair has similar climate, vegetation, and bedrock. We also assessed the impact of erosion on the effective age of slope ecosystems by comparing our sites to a well studied, 4.1ma chronosequence in Hawaii (LSAG). 87Sr/86Sr analyses show that plants on these slopes derive up to 80% of their Sr from rock weathering, while plants on adjacent uneroded surfaces derive ≤ 20% of their Sr from rock weathering. The range of 87Sr/86Sr along the ~100m slopes is similar to the variation seen in the 150ky of ecosystem development on constructional surfaces. This is consistent with the idea of rejuvenation through erosion, and has important implications for landscape-level variation of soil fertility in ecosystems.
KEY WORDS: Hawaii, strontium, erosion