Mercury and Organic Matter Concentrations in Lake and Stream Sediments in relation to One Another and to Atmospheric Mercury Deposition and Climate Variations across Canada

Mina Nasr,Paul A Arp

doi:10.1155/2017/8949502

Abstract

This article focuses on analyzing the Geological Survey of Canada (GSC) data for total mercury concentrations (THg) in lake and stream sediments. The objective was to quantify how sediment THg varies by (i) sediment organic matter, determined by loss on ignition (LOI) at 500∘C, (ii) atmospheric Hg deposition (atm.Hgdep) as derived from the Global/Regional Atmospheric Heavy Metals Model GRAHM2005, and (iii) mean annual precipitation and mean monthly July and January temperatures (TJuly,TJan). Through regression analyses and averaging by National Topographic System tiles (NTS, 1:250,000 scale), it was found that 40, 70, and 80% of the sediment THg, LOI, and atm.Hgdepvariations were, respectively, related to precipitation,TJuly, andTJan. In detail, lake sediment THg was related to atm.Hgdepand precipitation, while stream sediment THg was related to sediment LOI andTJuly. Plotting sediment THg versus sediment LOI revealed a curvilinear pattern, with highest Hg concentrations at intermediate LOI values. Analysing the resulting 10th and 90th log10THg percentiles within each 10% LOI class from 0 to 100% revealed that (i) atm.Hgdepcontributed to the organic component of sediment THg and (ii) this was more pronounced for lakes than for streams.

Highlights

Mercury (Hg) concentrations in lake and stream sediments vary by many factors pertaining to geology, atmospheric Hg deposition, climate, vegetation, topography, and soil and sediment composition [2,3,4,5]
Once incorporated into organic matter, reevaporation of Hg is limited by the extent of sunlit surface exposure and biological activity [24, 25], with overall turnover times increasing from decades to thousands of years with increasing soil and sediment depth
High to very high THg concentrations are generally associated with bedrock formations with mineral Hg exposures, such that they occur within the Selwyn Basin of the Yukon Territory [47] and in combination with sulfide mineral exposures due tectonic uplift (e.g., British Columbia [48,49,50]; Nova Scotia [51]; Quebec [52, 53]), rift (Labrador Trough, [54]), mafic volcanic extrusions (Quebec [55]; Labrador [56]), and meteor impacts (Sudbury, Ontario [57])

Summary

Introduction

Mercury (Hg) concentrations in lake and stream sediments vary by many factors pertaining to geology, atmospheric Hg deposition, climate, vegetation, topography, and soil and sediment composition [2,3,4,5]. Once incorporated into organic matter, reevaporation of Hg is limited by the extent of sunlit surface exposure and biological activity [24, 25], with overall turnover times increasing from decades to thousands of years with increasing soil and sediment depth. This extended retention is due to strong Hg-S bonds in the form of organic sulfide groups and S-containing minerals, including HgS such as cinnabar [26,27,28]. Due to decomposition and humification processes, this affinity leads to a gradual increase of organically bound Hg concentrations in soils and sediments, as occurs with other elements such as S and N [29]

Methods

Results

Conclusion