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

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 7 Be and 210 Pb 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 7 Be and 210 Pb 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 7 Be varied from 0.50 to 1.34 (geometric mean: 0.83 6 0.34) g cm 22 yr 21 , while corresponding values varied from 0.16 to 1.48 (GM: 0.38 6 0.38) g cm 22 yr 21 using particulate 210 Pb. Based on the 210 Pb mass balance, it appears that only ,2% of 210 Pb 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 22 yr 21 ) compared to net sediment accumulation rates (GM: 0.88 6 0.38 g cm 22 yr 21 ), 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.

Interconnected riverine–lacustrine systems as sedimentary repositories: Case study in southeast Michigan using 210Pb and 137Cs-based sediment accumulation and mixing models

“…However, erosional input of 210 Pb and 137 Cs to sediments is controlled by their partitioning coefficients (K d ) between particulate and dissolved phases. Since the K d of 210 Pb is~1-2 orders of magnitude higher than that of 137 Cs (Oughton et al, 1997;Smith et al, 2000;Standring et al, 2002) in riverine systems, the estimated watershed residence time (4100 yr) for 210 Pb (Jweda, 2008) will be significantly longer than that of 137 Cs (Smith et al, 1987). Due to this difference in chemical affinities (K d ( 210 Pb) N K d ( 137 Cs)), it is expected that the erosional input flux of 137 Cs is greater than that of 210 Pb.…”

Problems with the dating of sediment core using excess 210Pb in a freshwater system impacted by large scale watershed changes

“…The constant rate of supply model assumes constant flux and efficient transfer from the water to the surficial sediments. In coastal areas and shallow freshwater systems where suspended particle concentrations and fluxes are high, the transfer of 210 Pb from the water column to the sediments could take place in less than a month (e.g., Jweda et al, 2008). The depositional flux from the precipitation is variable, although the timescale involved in the transfer from water to sediment remains constant.…”

Depositional fluxes and concentrations of7Be and210Pb in bulk precipitation and aerosols at the interface of Atlantic and Mediterranean coasts in Spain

“…Utility of 7 Be (half‐life = 53.3 days) and 210 Pb (half‐life = 22.1 yrs) as tracers for quantifying sediment dynamics in estuarine, coastal, lacustrine and riverine systems, soil erosion studies and in other environmental studies require the depositional fluxes of these nuclides [ Robbins , 1978; Krishnaswami et al , 1980; Dominik et al , 1989; Baskaran et al , 1997; Sommerfield et al , 1999; García‐Orellana et al , 2006; Church and Sarin , 2008; Jweda et al , 2008; Kaste and Baskaran , 2011; Matisoff and Whiting , 2011]. The variations in the concentrations of 7 Be and 210 Pb in aerosols have been modeled using modified versions of the global circulation models to determine the vertical transport and residence times of aerosols [ Turekian et al , 1977; Brost et al , 1991; Balkanski et al , 1993; Koch et al , 1996].…”