Using cosmogenic 10Be in detrital quartz to quantify erosion rates in the Des Moines Lobe region of Iowa

Abstract:

Surface erosion in agricultural and other landscapes can lead to a multitude of deleterious effects including decreased soil fertility, crop yields, and water quality as well as contributing to increased sedimentation and downstream flood hazards. It has been widely recognized that modern agricultural practices in the midwestern U.S., one of the world’s most productive agricultural regions, have led to increased rates of surface erosion. However, pre-agricultural erosion rates remain poorly quantified – particularly at the watershed scale, hence it is difficult to quantify the magnitude of the increase in erosion rates during the Anthropocene. Cosmogenic nuclides measured in river sediment, such as in situ ¹⁰Be, are commonly used to measure long-term erosion rates at the watershed scale. However, major agricultural regions tend to be co-located with glacially-derived sediments that may have considerable ¹⁰Be inherited from prior exposure, hindering application of the method. Here we present basin averaged erosion rate estimates derived from ¹⁰Be in detrital quartz for watersheds draining the Des Moines Lobe region of Iowa. We account for inheritance by measuring ¹⁰Be in samples at depth, shielded from cosmic rays, collected from sediment cores and exposures in quarries. We compare the ¹⁰Be erosion rates against estimates of modern erosion from river sediment yields, dam and lake sedimentation, and modeled rates from the Iowa Daily Erosion Project. The millennial -averaged erosion rates presented here are essential for placing modern rates of landscape denudation in a broader geologic context and for assessing the magnitude of anthropogenic acceleration of erosion.