Beryllium‐7 wet deposition variation with storm height, synoptic classification, and tree canopy state in the mid‐Atlantic USA

• Published in: Hydrological processes 2016, Vol.30 (1), p.75-89
• Main Authors: Karwan, D. L., Siegert, C. M., Levia, D. F., Pizzuto, J., Marquard, J., Aalto, R., Aufdenkampe, A. K.
• Format: Article
• Language: English
• Subjects: beryllium-7; Deposition; Fluxes; Hydrology; Isotopes; precipitation; Precipitation (chemistry); Precipitation (meteorology); sediment fingerprinting; Sediments; storm type; Storms; throughfall; wet deposition
• ISSN: 0885-6087; 1099-1085
• DOI: 10.1002/hyp.10571

Short‐lived fallout isotopes, such as beryllium‐7 (⁷Be), are increasingly used as erosion and sediment tracers in watersheds. ⁷Be is produced in the atmosphere and delivered to the Earth's surface primarily in precipitation. However, relatively little has been published about the variation in ⁷Be wet deposition caused by storm type and vegetation cover. Our analysis of precipitation, throughfall, and sediments in two forested, headwater catchments in the mid‐Atlantic USA indicates significant variation in isotope deposition with storm type and storm height. Individual summer convective thunderstorms were associated with ⁷Be activity concentrations up to 5.0 Bq l⁻¹ in precipitation and 4.7 Bq l⁻¹ in throughfall, while single‐event wet depositional fluxes reached 168 Bq m⁻² in precipitation and 103 Bq m⁻² in throughfall. Storms originating from the continental USA were associated with lower ⁷Be activity concentrations and single‐event wet depositional fluxes for precipitation (0.7–1.2 Bq l⁻¹ and 15.8–65.0 Bq m⁻²) and throughfall (0.1–0.3 Bq l⁻¹ and 13.5–98.9 Bq m⁻²). Tropical systems had relatively low activity concentrations, 0.2–0.5 Bq l⁻¹ in precipitation and 0.2–1.0 Bq l⁻¹ in throughfall, but relatively high single‐event depositional fluxes due to large rainfall volumes, 32.8–67.6 Bq m⁻² in precipitation and 25.7–134 Bq m⁻² in throughfall. The largest sources of ⁷Be depositional variation were attributed to storm characteristics including precipitation amount and maximum storm height. ⁷Be activity associated with fluvial suspended sediments also exhibited the highest concentration and variability in summer (175–1450 Bq kg⁻¹). We conclude the dominant source of variation on event‐level ⁷Be deposition is storm type. Our results illustrate the complex relationships between ⁷Be deposition in precipitation and throughfall and demonstrate event‐scale relationships between the ⁷Be in precipitation and on suspended sediment. Copyright © 2015 John Wiley & Sons, Ltd.