Erosion rates and sediment flux within the Potomac River basin quantified over millennial timescales using beryllium isotopes

Abstract

Beryllium isotopes measured in detrital river sediment are often used to estimate rates of landscape change at a basin scale, but results from different beryllium isotope systems have rarely been compared. Here, we report measurements of in situ and meteoric 10 Be (10 Bei and 10 Bem, respectively) along with measurements of reactive and mineral phases of 9 Be (9 Bereac and 9 Bemin, respectively) to infer long-term rates of landscape change in the Potomac River basin, North America. Using these data, we compare directly results from the two different 10 Be isotope systems and contextualize modern sediment flux from the Potomac River basin to Chesapeake Bay. Sixty-two measurements of 10 Bei in river sand show that the Potomac River basin is eroding on average at 29.6 ± 14.1 Mg km-2 yr-1 (11 ± 5.2 m m.y.-1 assuming a rock density of 2,700 kg m-3)-a rate consistent with other estimates in the mid-Atlantic region. 10 Bei erosion rates correlate with basin latitude, suggesting that periglacial weathering increased with proximity to the former Laurentide Ice Sheet margin. Considering the 10 Bei-derived erosion rate as a sediment flux over millennia, rates of sediment delivery from the Potomac River to Manuscript Click here to access/download;Manuscript;B31543_Portenga-type_13October2018.docx

Sediment dynamics and implications for management: State of the science from long‐term research in the Chesapeake Bay watershed, USA

“…2.1.1. | Pre-colonial period before European arrival Geologic (pre-European) rates of erosion varied across the Chesapeake watershed with greater erosion in basins that are steeper and have more precipitation (Portenga et al, 2019). Notably, the Piedmont physiographic province, located between the mountains and Coastal Plain, had low natural sediment yields compared to current high yields (Gellis et al, 2009).…”

Comparison of basin-scale in situ and meteoric <sup>10</sup>Be erosion and denudation rates across a rainfall, slope, and elevation gradient at George River, northeast Tasmania, Australia

“…Bioturbation homogenizes 10 Bei concentrations in soils (Brown et al, 1995;Granger et al, 1996;Schaller et al, 2018), and 10 Bei erosion rates are therefore considered to be insensitive to widespread shallow erosion. This insensitivity allows 10 Bei erosion rates to be a useful gauge of pre-disturbance rates of landscape change (Ferrier et al, 2005;Portenga et al, 2019;Schmidt et al, 2018;Vanacker et al, 2007); exceptions have been noted where human land use is intensive (i.e. Schmidt et al, 2016) or the effects of human land use are exacerbated by climate extremes (i.e.…”

“…Recently derived equations allow erosion rates and denudation rates to be calculated from measurements of 10 Bem and the chemically-similar, non-cosmogenic 9 Be, which is weathered out of mineral grains ( 9 Bereac; Willenbring and von Blanckenburg, 2010;von Blanckenburg et al, 2012). 10 Bem erosion and 10 Bem/ 9 Bereac denudation rates have been used to quantify landscape evolution over a variety of spatial scales for long-established river basins (Dannhaus et al, 2018;Deng et al, 2020;Harrison et al, 2021;Portenga et al, 2019;Rahaman et al, 2017;Wittmann et al, 2012Wittmann et al, , 2015 and has shown particular promise in quantifying landscape dynamics in quartz-poor landscapes (Deng et al, 2020;Rahaman et al, 2017).…”

Calibrating a long-term meteoric <sup>10</sup>Be delivery rate into Western US glacial deposits through a comparison of complimentary meteoric and in situ-produced <sup>10</sup>Be depth profiles

“…10 Bemet is then delivered to Earth's surface via precipitation or as dry deposition at a flux of 0.1 -2 x 10 6 atoms cm -2 yr -1 followed by dissolved export in runoff, or depending on retentivity, adsorption onto fine-grained, reactive surfaces, typically clays and Fe-oxyhydroxides, in soil horizons at the Earth's surface (Willenbring and von Blanckenburg, 2010). 10 Bemet 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 von Blanckenburg, 2010;von Blanckenburg and Bouchez, 2014;Wittman et al, 2015;von Blanckenburg et al, 2015;Portenga et al, 2019;Jelinski et al, 2019). Prerequisites to interpreting the concentrations and isotope ratios (i.e.…”