Lead biogeochemistry in a central Ontario Forested watershed

Abstract

To determine the sources and sinks of atmospherically deposited Pb at a forested watershed (Plastic Lake) in central Ontario, Canada, Pb pools and fluxes through upland, wetland and lake compartments were measured during 2002/ 2003 and compared with previous measurements taken between , annual bulk deposition of Pb was 0.49 mg m À2 compared with 1.90-1.30 mg m À2 in 1989-1991. Annual Pb concentrations in stream water draining the upland part of the catchment were very low (0.04 mg l À1 ) and were approximately half those measured in 1989-1991 (0.11-0.08 mg l À1 ). Leaching losses in stream water were small and mass balance estimates indicate almost complete retention (>95%) of atmospherically deposited Pb in upland soils. In contrast, annual Pb concentrations in stream water draining a wetland were between 0.38 and 0.77 mg l À1 , with the highest concentration occurring in 2002/2003 and mass balance calculations indicate that the wetland is a net source of Pb in all measured years. Lead concentrations in the lake outflow were low and the average Pb concentration measured in 2002/2003 (0.09 mg l À1 ) was approximately half the value recorded in 1989-1991 (0.19 mg l À1 both years). Annual mass balance estimates indicate that the lake retained between 2.47 mg m À2 (1989/1990) and 1.42 mg m À2 (2002/2003) and that in 2002/2003 68% of the Pb input to the lake is derived from the terrestrial catchment. These estimates are higher than sediment core records, which indicate around 18 mg m À2 Pb was retained in sediment during the 1990s. Nevertheless, Pb concentrations decrease with sediment depth and 206 Pb/ 207 Pb concentrations increase with depth, a pattern also observed in mineral soils that reflects the substantial contribution of anthropogenic Pb to the watershed. Lead isotope data from soil and sediment indicate a recent anthropogenic Pb signal ( 206 Pb/ 207 Pb * 1.185) in upper soils and sediments and an older anthropogenic signal ( 206 Pb/ 207 Pb * 1.20) in deeper soil and sediment. Lead isotope data in sediment and vegetation indicate that practically all the Pb cycled in the forest at Plastic Lake is anthropogenic in origin.

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

“…The significance of atmospheric industrial metals across the wider landscape is likely to be more complex, reflecting rates of atmospheric deposition relative to sediment generation (by physical, biological and chemical weathering) and sediment transport rates (by aeolian, fluvial and colluvial processes). A substantial body of literature has focussed on quantifying the inputs, flows and retention of atmospherically derived industrial metals through watersheds using a mass balance approach, often in areas experiencing relatively high rates of industrial metal enrichment (Landre et al, 2010;Lindberg and Turner, 1988;Watmough and Dillon, 2007). However, despite collected aerosol samples universally recording industrial metal enrichment (e.g.…”

“…Arimoto et al, 1995;Huang et al, 2001;Marx et al, 2014b;Witt et al, 2006) there are few studies which examine the relative significance of the deposition of industrial metals across a variety of environmental archives (e.g. Landre et al, 2010;Rose et al, 2012;Starr et al, 2003;Watmough and Dillon, 2007), where they may potentially concentrate or dilute depending on the behaviour of individual metals (e.g. their particle reactivity) and hydrological and geomorphic processes.…”

The fate of atmospheric metal pollutants in the landscape, Snowy Mountains, south-eastern Australia

“…At a landscape scale, however, the distribution and abundance of anthropogenic metals in the terrestrial environment is known to be moderated by post-depositional processes which can remobilise metals originally derived from the atmosphere or cause metals to become more concentrated or diluted within surface sediments (Bacardit et al, 2012;Balogh et al, 2000;Brännvall et al, 2001b;Foster and Charlesworth, 1996;Klaminder et al, 2006b;Kober et al, 1999;Landre et al, 2010;Lidman et al, 2014;Lindberg and Turner, 1988;Salomons and Förstner, 1984a;Salomons and Förstner, 1984b;Starr et al, 2003;Steinnes and Friedland, 2006;Sutherland, 2000;Swain et al, 1992;Watmough and Dillon, 2007;Yang and Rose, 2005;Young, 2013). These processes are important because they control the degree to which atmospheric metals are incorporated into the environment and therefore determine their ecological impact (Kabata-Pendias and Mukherjee, 2007).…”

“…The significance of atmospheric industrial metals across the wider landscape is likely to be more complex, reflecting rates of atmospheric deposition relative to sediment generation (by physical, biological and chemical weathering) and sediment transport rates (by aeolian, fluvial and colluvial processes). A substantial body of literature has focussed on quantifying the inputs, flows and retention of atmospherically derived industrial metals through watersheds using a mass balance approach, often in areas experiencing relatively high rates of industrial metal enrichment (Landre et al, 2010;Lindberg and Turner, 1988;Watmough and Dillon, 2007).…”

“…Arimoto et al, 1995;Huang et al, 2001;Marx et al, 2014a;Witt et al, 2006) there are few studies which examine the relative significance of the deposition of industrial metals across a variety of environmental archives (e.g. Landre et al, 2010;Rose et al, 2012;Starr et al, 2003;Watmough and Dillon, 2007), where they may potentially concentrate or dilute depending on the behaviour of individual metals (e.g. their particle reactivity) and hydrological and geomorphic processes.…”