Meteoric Beryllium‐10 as a Tracer of Erosion Due to Postsettlement Land Use in West‐Central Minnesota, USA

Abstract

Meteoric beryllium‐10 (10Bem, t1/2 = 1.4 Myr) is a cosmogenic radionuclide that remains largely underutilized for deriving hillslope‐scale estimates of erosion on uplands under conditions of land use change. We applied two different models for estimating erosion rates from observed 10Bem concentrations (a one‐dimensional model predicting vertical profiles of 10Bem within hillslope soils [loss only, diffusion only, LODO] and a two‐dimensional model predicting the concurrent evolution of hillslope topography and 10Bem distributions via bioturbation, chemical mobility, and surface erosion [Be2D]). Both models were used to derive pre‐European and post‐European settlement erosion rates (Enat and Epost, respectively) across paired cultivated and uncultivated hillslopes in west‐central Minnesota, USA. Epost estimates from 10Bem were compared to Epost estimates derived from 137Cs inventories and the process‐based Water and Tillage Erosion Model (WaTEM). The results from these models suggest that erosion rates from upper positions on the cultivated hillslope have increased from an average of 0.047 mm/year under natural conditions to Epost values of 3.09 mm/year. The Be2D and LODO models, on average, produced Epost estimates that were similar in magnitude to WaTEM and 137Cs conversion models. This numerical convergence does not imply absolute 10Bem model accuracy, particularly when considering the uncertainties inherent in each approach, but it does suggest that the orders of magnitude increase in estimated erosion rates from Enat to Epost is robust. Additionally, the pattern of Epost estimates produced using 10Bem conversion models is supported by the distribution of soil inorganic carbon at the study site. Our results demonstrate that 10Bem can provide reasonable estimates of both predisturbance and postdisturbance erosion rates in landscapes that have undergone extensive human modification.

Parameterization of river incision models requires accounting for environmental heterogeneity: insights from the tropical Andes

“…Consequently, the relative role of climate variability and tectonic processes could only be deduced from sediment archives (e.g., Hay et al, 1988). However, whether sediment archives offer reliable proxies remains contested because sediment sources and transfer times to depositional sites are often obscured by stochastic processes that shred environmental signals (Bernhardt et al, 2017;Jerolmack and Paola, 2010;Romans et al, 2016;Sadler, 1981).…”

Calibrating a long-term meteoric <sup>10</sup>Be delivery rate into eroding western US glacial deposits by comparing meteoric and in situ produced <sup>10</sup>Be depth profiles

“…(1) to nearby Fish Lake Mountain contained within the same Heikkilä and von Blanckenburg (2015) grid cell as this study site with a modern precipitation rate of 128 cm yr −1 (WRCC, 2005), the F ( 10 Be met ) would be 2.5 × 10 6 atoms cm −2 yr −1 , substantially higher than that predicted from Heikkilä and von Blanckenburg (2015). Considering this alone, it is not surprising that such a discrepancy exists between methods, nor is this a unique occurrence (e.g., Jungers et al, 2009;Schoonejans et al, 2017;Dixon et al, 2018;Deng et al, 2020).…”

“…10 Be met is then delivered to the Earth's surface via precipitation or as dry deposition at a flux of 0.1-2 × 10 6 atoms cm −2 yr −1 , followed by dissolved export in runoff or, depending on retentivity, adsorption onto finegrained reactive surfaces, typically clays and Fe and Al oxyhydroxides in soil horizons at the Earth's surface Willenbring and von Blanckenburg, 2010). 10 Be met has been used as a tracer of Earth surface processes, including estimating erosion rates at the soil profile and river catchment scales, soil residence times, ages of landforms over millennial to million-year timescales, and paleo-denudation rates from marine sedimentary records (Pavich et al, 1986;McKean et al, 1993;Jungers et al, 2009;Willenbring and T. Clow et al: Calibrating a long-term meteoric 10 Be delivery rate von von Blanckenburg et al, 2012;von Blanckenburg and Bouchez, 2014;Wittmann et al, 2015;von Blanckenburg et al, 2015;Portenga et al, 2019;Jelinski et al, 2019). Prerequisites for interpreting the concentrations and isotope ratios (i.e., 10 Be met / 9 Be) as erosion or denudation (the sum of erosion and weathering) rates, respectively, include knowing the delivery rate of 10 Be met (Pavich et al, 1986;Reusser et al, 2010;Graly et al, 2011;Heikkilä and von Blanckenburg, 2015;Dixon et al, 2018, Deng et al, 2020 and quantifying the mobility or retention of beryllium in soils (e.g., Bacon et al, 2012;Boschi and Willenbring, 2016a, b;Maher and von Blanckenburg, 2016;Dixon et al, 2018), not all of which was possible in many previous studies.…”

Lithology and orographic precipitation control river incision in the tropical Andes

“…The NS-coefficient has been developed in the framework of hydrological modelling but has been applied in wide range of geomorphologic studies (e.g. Jelinski et al, 2019;Nearing et al, 2011).…”