A detailed description of the methods for determining in situ 210Pb, 210Bi, and 210Po activities is given by Waples (2020).

A second manuscript describing the use of Pb-210, Bi-210, and Po-210 as particle tracers in aquatic systems is currently in review for Limnology and Oceanography (March/2020).

Water samples collected by submersible pump were weighed and filtered through nitrocellulose filters (0.45 um, 293 mm, Millipore) within two hours of sample collection to separate dissolved and particle-bound nuclide fractions of 210Pb, 210Bi, and 210Po. Yield monitors of 207Bi and 209Po (Eckert & Ziegler Isotope Products) were then added to both fractions. No lead monitor was required. Dissolved nuclide fractions (< 0.45 um) of 210Pb, 210Bi, and 210Po were co-precipitated onto newly formed ferric hydroxide and collected by filtration. Both particle-bound and dissolved nuclide fractions were then digested in concentrated nitric acid. Bismuth and polonium were completely separated from lead on EmporeTM anion solid phase extraction (SPE) disks (3M, 47 mm, product number 2252, now manufactured by CDS Analytical). Eluate from the particle-bound fraction was re-spiked with 207Bi and set aside for ~one month for the determination of particle-bound 210Pb (via 210Bi in secular equilibrium with its parent). Anion SPE disks were then counted– first for 210Bi via b-decay on a low background gas-flow proportional detector with anticoincidence circuitry (G542 System, Gamma Products), then for 207Bi via g-emission to determine yield. Polonium was then removed from the SPE disks, plated to copper, and a-counted for 210Po and the yield monitor 209Po. Total 210Pb was determined in a separate water sample via 210Bi that had grown into secular equilibrium with its parent. Activity calculations including uncertainty propagation and decay corrections are all fully described by Waples (2020).

Rainwater was collected at ground level (43.017719, -87.903000) in a large plastic barrel fitted with a funnel (0.216 m2 collection area) over a 40-h period during an extended rain event beginning at 17:20 (CST) on 03 November 2018. The funnel and barrel were rinsed before and after the collection event with a total of 0.4 L of 1 M HCl.

Lake water samples (~ 50 L) for radionuclide analyses were collected from the slip (43.017835, -87.903521) with a submersible pump from a depth of 2 m on 08 November, 15 November, and 20 November 2018.

Quagga mussels (Dreissena rostriformis bugensis) were collected from the slip wall (43.017829, -87.904407) on 29 November 2018. Each mussel was measured for shell length and sorted into two groups of large (range: 18–22 mm; geometric mean: 19 mm; n = 10) and small (10–16 mm; geometric mean: 13 mm; n = 20) mussels. Mussel tissue was separated from the shell, pooled by group into two glass beakers, and digested in concentrated HNO3. Shell-free biomass was estimated using the allometric equation m = 0.0018 × L3.11, where m is the tissue dry weight in mg (DW mg) and L is the mussel shell length in mm (Waples et al. 2017).

Software used:
- Maestro software (v. 6.04 and 6.06, Advanced Measurement Technology)
- SigmaPlot (v. 11, Systat Software)
- Excel (v. 2002, Microsoft)