Paper No. 8
Presentation Time: 10:45 AM


NEILSON, Thomas B., Department of Geology, University of Vermont, 180 Colchester Ave, Department of Geology, UVM, Burlington, VT 05401, SCHMIDT, Amanda H., Geology, Oberlin College, 52 West Lorain Street, Oberlin, OH 44074-1044, SOSA-GONZALEZ, Veronica, The Rubenstein School, University of Vermont, Aiken Center, 81 Carrigan Drive, Burlington, VT 05405, ROTHENBERG, Miriam, Anthropology, Oberlin College, King Building 305, 10 N. Professor St, Oberlin, OH 44074-1019, BIERMAN, Paul, Department of Geology and Rubenstein School of Environment and Natural Resources, University of Vermont, Delehanty Hall, 180 Colchester Ave, Burlington, VT 05405 and ROOD, Dylan H., AMS Laboratory, Scottish Universities Environmental Research Centre (SUERC), East Kilbride, G75 0QF, United Kingdom,

We measured 137Cs and meteoric 10Be in 35 samples previously measured for in situ 10Be (Henck et al., 2011) in the Salween, Mekong, and Yangtze river systems in SW China to better understand long-term landscape behavior and effects of human-induced landscape change. Samples were collected from basins spanning ~10 to 105 km2. Meteoric 10Be concentration varied by an order of magnitude, from 3.4 to 76 x 106 atoms/g. There was no systematic spatial patterning in meteoric 10Be values. 137Cs activity was only measureable in five samples.

No significant relationships were found between meteoric 10Be concentrations and mean local relief, mean annual rainfall, or basin area. Areas with high erosion rates (>0.4 mm/yr) had low meteoric 10Be values (R2= 0.34, p= 0.0002). While meteoric 10Be and basin size did not strongly correlate, basins <104 km2 had highly variable meteoric 10Be values, while basins >104 km2 had significantly less variability (p= 0.11). Analysis of meteoric 10Be, mean annual rainfall, and mean local relief grouped by stream order suggests high variability in small basins may mask relationships found in large basins.

Erosion indices (EI) were calculated for each sample using in situ 10Be erosion rates to calculate long-term sediment flux and ranged from 0.11 to 1.48 (median = 0.55). The EI represents the ratio of total meteoric 10Be leaving the basin on sediment grains over the total estimated atmospheric delivery of 10Be. The highest EI’s were in the northern portion of the Yangtze drainage, and corresponded to moderate erosion rates of 0.06 – 0.13 mm/yr. Variability in EI was significantly higher in basins <104 km2 (p= 0.14).

EI’s calculated from long-term sediment yield allow modern events, such as land-use change, to be isolated from long-term geomorphic trends. A median EI of 0.55, with 91% of measurements below 1, suggests that less meteoric 10Be is exported than is incident upon the landscape. The absence of measureable 137Cs in the majority of samples indicates that significant erosion has occurred since 1954. EI and 137Cs activity suggest that there is a “disconnect” between long-term sediment yield estimates and modern erosion rates, potentially caused by human impact changing the style and/or distribution of erosion.