Contemporary Mobilization of Legacy Pb Stores by DOM in a Boreal Peatland

Abstract

We examined how different landscape areas in a catchment containing a northern ombrotrophic peatland and upland mineral soils responded to dramatic decreases in atmospheric deposition of lead (Pb). Pb concentrations in the outflow stream from the peatland measured from 2009-2015 indicated continued mobilization and export of Pb derived from historic inputs to the bog. In contrast, Pb concentrations in surface peat and runoff from upland mineral soils have declined in response to reductions in atmospheric deposition. Relative to the early 1980s, Pb concentrations in the streamflow decreased only ∼50%, while Pb in surface peat and upland subsurface runoff decreased by more than 90%. Water level fluctuations in the slow-accumulating peat have allowed dissolved organic matter (DOM) to continue mobilizing Pb deposited in the peatland decades earlier. Strong correlations between dissolved organic carbon (DOC) and Pb concentrations in outflow from the peatland and in bog porewaters demonstrate Pb mobility related to DOM production. Peat stores of Pb in 2016 were less than or equal to those reported in the early 1980s despite the dry mass inventory increasing by 60-80%. Much of the loss in Pb stored in peat can be accounted for by stream runoff from the peatland.

A Review of the Impact on Aquatic Communities of Inputs from Peatlands Drained for Peat Extraction

“…Streams draining degraded peatlands have been shown to export significantly higher concentrations of heavy metals such as aluminium (Al), iron (Fe), lead (Pb), arsenic (As), nickel (Ni) and cadmium (Cd) compared to undrained peatland (Gandois et al 2020;Ramchunder et al 2009) with Fe, As, Cd and zinc (Zn) being strongly linked with the presence of dissolved organic matter (DOM) from degraded peatlands (Gandois et al 2020). Atmospherically deposited Pb from an eroding peatland in the UK showed inputs of 30.0 ± 6.0g ha − ¹ a −1 , with 85% of mobilised Pb associated with particulate matter from the peatland (Rothwell et al 2008), in keeping with subsequent research from the USA linking changes in water table depth to the mobilisation of Pb by DOM (Jeremiason et al 2018). The export of mercury-containing peat particles has also been reported (Surette et al 2002).…”

Methylmercury Export From a Headwater Peatland Catchment Decreased With Cleaner Emissions Despite Opposing Effect of Climate Warming

“…Droughts and subsequent hydrological recovery are commonly linked to increased concentrations of metals, such as Hg or lead, from peatlands (Jeremiason et al., 2018; Szkokan‐Emilson et al., 2013) and MeHg concentrations can increase within peatlands (Coleman Wasik et al., 2015). There were several droughts (1967/1968, 1976/1977, 1990/1991, and 2006/2007) with annual precipitation <603 mm (<77% of the 1962–2017 mean) during the long‐term record.…”

The distribution and behaviour of Fe, Al, Si, Mn, Cu and Ni in ombrotrophic tropical peat draining blackwater estuaries on Borneo Island

“…In particular, the close association between trace elements and DOM could affect trace element fluxes from the land to the ocean in these regions. The export of major elements and trace elements from peat swamps to surface ocean waters has been reported (Weiss et al, 2002;Rothwell et al, 2007;Broder and Biester, 2017;Jeremiason et al, 2018). There is substantial literature to facilitate a better understanding of the biogeochemistry of major and trace elements in high-latitude peatlands, peaty riparian zones (Broder and Biester, 2017), peatlands and bogs in the UK and Europe (Rothwell et al, 2007), but to the best of our knowledge scant information exists on transport of trace elements in low latitude peatlands, despite increasing destruction of peat swamps in southeast Asia.…”

“…Trace element export from such a dynamic and diverse ecosystem is considered to be regulated by biological, chemical and physical conditions (Rothwell et al, 2007). Specific contributing factors include pH, ionic strength, fluvial regime, suspended particulate matter (SPM) levels, concentration of complexing agents and DOM (Achterberg et al, 2003;Broder and Biester, 2017;Jeremiason et al, 2018).…”