Estimating the Mean Residence Time of Lead in the Organic Horizon of Boreal Forest Soils using 210-lead, Stable Lead and a Soil Chronosequence

Abstract

Knowledge about the residence time of lead in the organic horizon (mor layer; O-horizon) overlaying forest mineral soils is important for the prediction of past and future lead levels in the boreal environment. To estimate the mean residence time (MRT) of lead in the mor layer, we use in this study from Northern Sweden three different approaches: (1) lead-210 is applied as a tracer of lead migration; (2) estimations of loss rates of stable lead (concentrations and 206 Pb/ 207 Pb ratios) from the mor layer at an undisturbed forest setting, and (3) a study of lead in a soil series with sites of different age (a chronosequence of 20-220 years). In the last two approaches we compared measured inventories in the soil with estimated inventories derived using analyses of lake sediments. The results suggested a MRT of about 250 years in the mor layer in the mature forest and in the older parts of the chronosequence it was at least >170 years. The agreement between the three different approaches gives good credibility to this estimate. It is also supported by a modeling of trends in the 206 Pb/ 207 Pb ratio both between single cores and with depth in the mor layer. Our results suggest that it will take centuries for the deeper parts of the mor layer of undisturbed boreal forest soils to fully respond to decreased atmospheric lead pollution. However, data from the chronosequence indicate that the response could be much faster (MRT<50 years) in the mor layer at early stages of forest succession where graminoid and broadleaved litter fall dominates over conifer litter.

Contaminated lead environments of man: reviewing the lead isotopic evidence in sediments, peat, and soils for the temporal and spatial patterns of atmospheric lead pollution in Sweden

“…Lower panel 206 Pb/ 207 Pb ratios in the two peat cores along with the moss data from Norway environment, these emissions must be placed into a longer context. Over the past 3,500 years, the total cumulative burden of atmospherically deposited pollution lead is estimated from the peat and lake sediment records (as well as in soils, but this is discussed further on) to be about 2-5 g Pb m -2 in southern Sweden and about 1 g Pb m -2 in northern Sweden Brännvall et al 2001a, b;Klaminder et al 2005Klaminder et al , 2006. About half of this lead was deposited from 3500 BP until AD 1800 and the remainder over the past 200 years.…”

“…6). In the upper weathered part of the mineral soil, the isotopic composition of the bulk soil in relation to the parent material is altered by atmospherically derived lead leached from the mor layer and transport downward along with particulate and colloidal organic matter (Dörr and Münnich 1991;Wang and Benoit 1997;Watmough et al 2004;Klaminder et al 2006), as well as by the selective (Brännvall et al 2001b) in comparison with the temporal changes in 206 Pb/ 207 Pb ratios in 3 peat records from southern Sweden , 2 varved lake sediment records from northern Sweden ), herbaria mosses from Scotland (Farmer et al 2002) and forest mosses (Steinnes et al 2005a), and ice (Rosman et al 2000), peat and herbaria (Weiss et al 1999) from Switzerland and the Alps Fig. 6 Temporal changes in the 206 Pb/ 207 Pb ratios in Swedish lake sediments (left) (Brännvall et al 2001a) and the stratigraphic changes in the 206 Pb/ 207 Pb ratio in 12 podzol soil profiles from southern and northern Sweden (Brännvall et al 2001b), along with the 206 Pb/ 207 Pb composition of alkyl lead and industrial/ historical ore lead in Europe, soil mor layers (11 sites) and the surface layers of six ombrotrophic bogs (see references cited in the aforementioned papers) weathering of soil minerals (Erel et al 1994;Harlavan and Erel 2002).…”

Tracing depositional consequences of environmental radionuclides (137Cs and 210Pb) in Slovenian forest soils

“…Among many factors generally affecting pedological characteristics, the geological foundation and the relief are important factors in Slovenia [11]. Table 1 shows the predominant soil type at each site investigated in this study.…”

“…Large fluctuations were reported in atmospheric Pb deposition, which has declined markedly during the last three decades resulting from the phasing out of Pb in gasoline [11]. Table 3 gives the results of 210 Pb inventories, which were obtained by assuming a constant flux of 210 Pb from the atmosphere as of the year 2009.…”

A landscape-scale approach to examining the fate of atmospherically derived industrial metals in the surficial environment

“…Typically, however, these studies have focussed on those parts of the landscape which receive high relative rates of atmospheric input such as peat mires Shotyk et al, 2002) and snow and ice McConnell and Edwards, 2008). Enrichment has also been demonstrated in soil (Brännvall et al, 2001;Klaminder et al, 2006) and lake sediments (Brännvall et al, 1999;Stromsoe et al, 2013;Wong et al, 1984;Yang et al, 2007) although these records maybe more complex due to the influence of catchment and in situ soil processes (e.g. Augustsson et al, 2010;Shotyk and Krachler, 2010).…”