Short-lived radionuclides (7Be and 210Pb) as tracers of particle dynamics in a river system in southeast Michigan

Jweda, Jason, Mark Baskaran, Ed van Hees, Linda Schweitzer

Limnol. Oceanogr., 53(5), 2008, 1934-1944 | DOI: 10.4319/lo.2008.53.5.1934

ABSTRACT: Riverine water samples (dissolved and particulate), surficial bottom sediments, and trapped sediments were collected mostly monthly from three stations along the Clinton River, in southeastern Michigan, over a period of ~1 yr and analyzed for 7Be and 210Pb to elucidate the types and rates of processes affecting particle dynamics in a riverine system. Using a simple irreversible scavenging box model approach, sources and sinks for dissolved and particulate 7Be and 210Pb were quantified to estimate their residence times in the dissolved and particulate phases. Resuspension rates of surficial bottom sediments calculated from the mass balance of particulate 7Be varied from 0.50 to 1.34 (geometric mean: 0.83 ± 0.34) g cm-2 yr-1, while corresponding values varied from 0.16 to 1.48 (GM: 0.38 ± 0.38) g cm-2 yr-1 using particulate 210Pb. Based on the 210Pb mass balance, it appears that only ~2% of 210Pb was derived from direct atmospheric deposition, while ~98% was derived from resuspension of bottom sediments. Additionally, there was a large discrepancy between mass flux collected in the trap (GM: 8.9 g cm-2 yr-1) compared to net sediment accumulation rates (GM: 0.88 ± 0.38 g cm-2 yr-1), which was attributed to sediment resuspension; this may provide insight into the frequency of particle-recycling events. Furthermore, desorption of particle-reactive species during resuspension events could result in the mobility of contaminants to farther distances from the contaminated site. Therefore, this study has direct relevance to the uptake of particle-reactive species in a riverine system and thereby the water quality of rivers.

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