Relating Fish Hg to Variations in Sediment Hg, Climate and Atmospheric Deposition

Mina Nasr,Paul A Arp

doi:10.4236/ajcc.2018.73024

Abstract

This article addresses total fish Hg concentrations (THg) by variations in lake Sediment THg, atmospheric Hg deposition (atmHgdep), and climate, i.e., mean annual precipitation (ppt) and air temperature. The Fish THg data were taken from the 1967-to-2010 Fish Mercury Datalayer (FIMDAC). This compilation was standardized for 12-cm long Yellow Perch in accordance with the USGS National Descriptive Model for Mercury in Fish (NDMMF [1]), and documents Fish THg across 1936 non-contaminated lakes in Canada. About 40% of the standardized Fish THg variations related positively to increasing ppt and Sediment THg, but negatively to increasing mean annual July temperature (TJuly). Only 20% of the Fish THg variations related positively to atmHgdep alone. Increasing TJuly likely influences Fish Hg through increased lake and upslope Hg volatilization, in-fish growth dilution, and temperature-induced demethylization. FIMDAC Fish THg effectively did not change over time while atmHgdep decreased. Similarly, the above Fish Hg trends would likely not change much based on projecting the above observations into the future using current 2070 climate-change projections across Canada and the continental US. Regionally, the projected changes in Fish Hg would mostly increase with increasing ppt. Additional not-yet mapped increases are expected to occur in subarctic regions subject to increasing permafrost decline. Locally, Fish THg would continue to be affected by upwind and upslope pollution sources, and by lake-by-lake changes in water aeration and rates of lake-water inversions.

Highlights

There is much uncertainty about how climate and atmospheric Hg deposition affect Fish total fish Hg concentrations (THg) [2] [3] [4] [5]
The total amount of Hg generally increases with increasing organic matter transfer [12], which in turn leads to increasing Hg accumulations in stream and lake sediments [13] [14] [15] [16]
These variables differ across Canada in range, such that the lake-by-lake entries for Fish THg have a wider maximum to minimum ratio (i.e. 38) than the corresponding model-derived entries for Sediment THg (i.e. 15) and for atmHgdep (i.e. 12) For mean annual precipitation, the maximum/minimum ratio is 20

Summary

Introduction

There is much uncertainty about how climate and atmospheric Hg deposition affect Fish THg [2] [3] [4] [5]. The presence and accumulation of Hg and MeHg in fish and sediments starts with the sequestration of atmospheric Hg deposition on land and water, and with the release of surface-exposed geogenic Hg minerals. A part of land-retained Hg is gradually released into streams and lakes through 1) direct Hg-containing litter inputs (detritus), 2) upslope soil and stream bank erosion, and 3) transfer of Hg bound by water-carried particulate and dissolved Hg-containing matter [6] [7] [8] [9]. The total amount of Hg generally increases with increasing organic matter transfer [12], which in turn leads to increasing Hg accumulations in stream and lake sediments [13] [14] [15] [16]. Due to particulate Hg retention in wet areas and wetlands, first-order stream and lake sediments downslope from forested and wetland dominated watersheds have higher THg and organic matter contents than elsewhere [17]-[22]

Methods

Results

Discussion

Conclusion