资源环境科技发展态势分析平台

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 Be-10 (Be-10(i) and Be-10(m), respectively) along with measurements of reactive and mineral phases of Be-9 (Be-9(re)ac, and Be-9(min), respectively) to infer long-term rates of landscape change in the Potomac River basin, North America. Using these data, we directly compare results from the two different Be-10 isotope systems and contextualize modern sediment flux from the Potomac River basin to Chesapeake Bay.

Sixty-two measurements of Be-10(i) 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 2700 kg m(-3))-a rate consistent with other estimates in the mid-Atlantic region. Be-10(i) erosion rates correlate with basin latitude, suggesting that periglacial weathering increased with proximity to the former Laurentide Ice Sheet margin. Considering the ioBe l -derived erosion rate as a sediment flux over millennia, rates of sediment delivery from the Potomac River to Chesapeake Bay are up to similar to 5x lower than contemporary sediment yields implying modern land-use practices have accelerated erosion and sediment transport over background rates. However, Be-10(i) erosion rate data suggest that regulatory benchmark levels used to manage sediment export from the Potomac River basin to Chesapeake Bay are set appropriately to reduce sedimentation and restore the Bay's ecological health.