Plutonium Isotopes: An Effective Tool for Fluvial Sediment Sourcing in Urbanized Catchments. Issue 2 (12th January 2022)

• Record Type: Journal Article
• Authors: Percich, Abigal; Husic, Admin; Ketterer, Michael E.
• Is Part Of: Geophysical research letters. Volume 49:Issue 2(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-01-12
• Subjects: Bayesian mixing -- erosion -- land use -- plutonium -- radionuclides -- sediment fingerprinting; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2021GL094497
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: Sediment management is currently limited by uncertainties in the applicability of existing radionuclide tracers and the effects of urbanization. Here, we use plutonium isotopes ( 239+240 Pu) from weapons‐testing fallout to trace sediment transport across five watersheds in an urbanizing landscape in Kansas, USA. Historic flooding in the region provided an opportunity to assess extreme connectivity of sediment sources. 239+240 Pu activity of transported sediment decreased as catchments urbanized, indicating a greater contribution from subsurface bank sediment; Bayesian modeling predicted 50% (8%–80%) bank sourcing in the most rural watershed, which rose to 93% (73%–100%) in the most urban catchment. 239+240 Pu activity provides explanatory information on the superposition of sediment sources, which is beyond that given by traditional organic and geochemical tracers that primarily infer vegetative and geologic sourcing, respectively. Our study demonstrates the utility of 239+240 Pu as a sediment tracer for managing erosion under anthropogenic change. Plain Language Summary: Sediment is one of the most common contaminants in rivers around the globe. The susceptibility of soil to erosion increases as humans convert natural landscapes into rural and urban systems. Uncertainties remain regarding how urbanization alters sediment pathways and what tools are appropriate for quantifying this alteration. Radioactive isotopes, generated from nuclear weapons testing in the 1950s, have proven useful in this regard, although the most prominent tracer, for example, cesium, is losing some utility due to a short half‐life and extensive radioactive decay. We suggest that plutonium isotopes, which have longer half‐lives, are a viable option for tracing sediment in modern landscapes. Plutonium results suggest that in rural basins the source of sediment transitions from upland soil during low‐flows to bank material at high‐flows. On the other hand, urban streams always deliver bank sediment, regardless of storm intensity. Our study demonstrates the utility of plutonium as an alternate sediment tracer and highlights how urbanization changes the pathways and mechanisms of fluvial sediment transport. Key Points: 239+240 Pu activity is a robust tracer for describing sediment sources and fluvial mixtures in a rapidly urbanizing landscape Frequentist and Bayesian models were consistent in estimating increased bank erosion with increasing urban land use Sediment sourcing is dependent on discharge in rural watersheds whereas it is independent of discharge in urban watersheds