mercury-contaminated fish populations

Overview

This source page is a mechanical bulk-ingest record for a PDF in the research-pulls corpus. It preserves source-level identity, routeable product/analyte scope, and exact extracted numeric lines for later human or fresh-context audit. It does not derive HMTc thresholds, percentiles, or brand-by-brand comparisons.

Key numbers

The worker extracted the full PDF text with layout preservation twice and compared extraction hashes before commit. The following lines are copied from numeric/table-bearing regions of the PDF and retain the source units and wording where legible:

additions were stopped, resulting in an approximately 100% reduction in Hg loading
to the lake. The concentration of labelled MeHg quickly decreased by up to 91% in
lower trophic level organisms, initiating rapid decreases of 38–76% of MeHg
measured as MeHg concentration in water (in ng l−1; n = 516), sediments (in ng g−1 addition phase (2001–2007), then decreased during the recovery phase (2008–
dry weight; n = 1,627) and invertebrates (in ng g−1 wet weight; n = 211), and as 2015), when experimental Hg additions to the ecosystem ceased (light blue
total Hg in fishes (in ng g−1 wet weight; n = 1,052). Mean annual concentrations shaded area in a). Dotted lines indicate missing data.
of Canada, such that our experimental addition rate increased wet reference lake (Extended Data Table 1; P > 0.05). Steady ambient MeHg
Hg deposition approximately fivefold (from approximately 3.6 to concentrations in fish through time are indicative of relatively stable
only a small fraction (less than 1%) of all Hg in runoff to the lake19 and was roughly equivalent to all ambient Hg inputs (runoff plus direct
consequently contributed little (less than 2%) to the changes in MeHg deposition) to the lake, resulting in a doubling, or about 100% increase,
spike MeHg + ambient MeHg; grey circles) increased above background fish species were as follows: zooplankton (n = 127) to yellow perch (d); forage
concentrations (ambient MeHg; white circles) during the addition phase (dark fish (n = 421) to northern pike (e); and Chaoborus (n = 62) to lake whitefish (f).
blue shaded area) from uptake of isotope enriched Hg added to Lake 658 (lake Fish data are means from autumn sampling (sample sizes in Extended Data
n = 189) (c) populations, then declined during the recovery phase (light blue
additions to the lake, per cent increases in lake spike MeHg concen- in water, 35% in sediments, 66% in zooplankton and 67% in Chaoborus
trations were highest in water (60%) and least in the upper 2 cm of (Fig. 1c), leading to marked reductions (85–91%) in the concentration
sediments (30%) where large stores of ambient Hg existed (Fig. 1c). of spike MeHg in forage fish species by the end of the recovery phase
and sediments, such that spike Hg additions to the lake raised MeHg small fraction (approximately 6%) to MeHg concentrations in forage
more than 40% for large-bodied fish species (Fig. 1c). spike MeHg in water compared with sediments, even in this relatively
(Fig. 2f). Relative to planktivorous yellow perch, final addition phase 76% in the northern pike population and by 38% in the lake whitefish
Hg and ambient Hg during the addition phase. lake. Lake whitefish were much older (median age = 17 years versus
To then directly test the hypothesis that MeHg concentrations in 3 years for pike) and larger (Extended Data Tables 2, 3) than northern
resulted in a 100% reduction in loading of lake spike. Average concentra- whitefish had the coldest thermal preferences and greatest associa-
first 3 years, the relative amount of lake spike MeHg declined by 81% lated27. To further explain the recovery of the apex predator population,
at the end of the addition phase (in 2007; n = 16) and subsequently recaptured
data are based on all fish captured each autumn (n = 280). All northern pike 1. Streets, D. G. et al. Five hundred years of anthropogenic mercury: spatial and temporal
(body burden = lake spike MeHg (ng g−1) × fish mass (g)) were normalized to 3. Driscoll, C. T., Mason, R. P., Chan, H. M., Jacob, D. J. & Pirrone, N. Mercury as a global
decay regression starting in the second year of recovery estimated a 50%
mean (black circle) ± 95% confidence interval (shaded band); line fit: y = 1.7439 × Sci. Technol. 47, 13385–13394 (2013).
observed for lake spike MeHg in individual northern pike moved from 12. Vander Zanden, M. J., Casselman, J. M. & Rasmussen, J. B. Stable isotope evidence for the
loss of older fish (as evidenced by a stable population size structure; predators. Nature 572, 648–650 (2019).
spike MeHg in the northern pike population were reduced by 50% in 16. Hall, B. D., Bodaly, R. A., Fudge, R. J. P., Rudd, J. W. M. & Rosenberg, D. M. Food as the
upland (approximately 79.9% 200Hg) and wetland (approximately 90.1% and composited in zipper lock bags for a 0- to 2-cm depth sampling
For each lake addition, inorganic Hg enriched with approximately 89.7% Dominant zooplankton taxa in Lake 658 included calanoid copepods
lake itself using a genetically engineered bioreporter bacterium35. On nearby reference Lake 240 (Extended Data Tables 2, 3). Fish collec-
tion limit = 0.1 ng Hg(ii) l−1), but we never saw bioavailable ambient number of fish (up to n = 20) of each species and age class (determined
occasions, by measuring the % of total Hg(ii) that was dissolved gase- (at −20 °C) in individual WhirlPak bags. A year class failure of yellow
spiked36. There was no significant difference (paired t-test, P > 0.05), and no age 1+ fish in 2009 (Extended Data Table 3).
biopsy of dorsal muscle (0.091 ± 0.002 g wet weight (mean ± s.e.m)) previously determined that >90% of the Hg in muscle tissue from yellow
low annual catches of white sucker (<10 individuals) across sampling the spikes was 0.5% of ambient Hg.
were synthesized and calibrated in-house. Isotope-dilution spikes concentrations at a standard FL43 (the mean FL of all fish sampled for
or stainless steel tools cleaned with 95% ethanol19,38. Zooplankton and Percent increase = (lake spike Hg)i /(ambient Hg)i × 100 (1)

Methods (brief)

658 ecosystem. a, Location (inset) of the Experimental Lakes Area (ELA), populations, which were collected each autumn. Concentration data for
blue shaded area) from uptake of isotope enriched Hg added to Lake 658 (lake Fish data are means from autumn sampling (sample sizes in Extended Data
northern pike (grey lines and triangles). Individual northern pike were sampled
were sampled using a non-lethal biopsy (represented in images) in the autumn release profiles. Environ. Res. Lett. 14, 084044 (2019).
previously deposited Hg to overall fish MeHg concentrations is a key 18. Gårdmark, A. & Huss, M. Individual variation and interactions explain food web responses
mental Lakes Area (ELA; now IISD-ELA), a remote area in the Precambrian Water samples were collected from May to October every four weeks
includes upland (41.2 ha), wetland (1.7 ha) and lake surface (8.4 ha) bottles. Water samples were filtered in-line using pre-ashed quartz
ter lake, with a fish community consisting of forage (yellow perch (P. measured in the filtered water samples (dissolved Hg and MeHg) and in
flavescens) and blacknose shiner (Notropis heterolepis)), benthivorous particles collected on the quartz fibre filter (particulate Hg and MeHg).
(lake whitefish (C. clupeaformis) and white sucker (Catostomus com- From 2001 to 2012, Lake 658 sediments were sampled at 4 fixed
upland and wetland areas. Upland and wetland spikes were applied range of water depths in both basins. Cores were collected by hand by
once per year (when possible; Fig. 1a) by fixed-wing aircraft (Cessna divers, or by subsampling sediments collected using a small box corer.
a rain event, with wind speeds less than 15 km h−1 to minimize drift of Bulk zooplankton and Chaoborus samples were collected from Lake
spike Hg outside of target areas. Aerial spraying of upland and wetland 658 for MeHg analysis. Zooplankton were collected during the day
and wetland areas were 18.5 μg m−2 yr−1 and 17.8 μg m−2 yr−1, respectively. to the surface of the lake. Samples were frozen in plastic Whirl-Pak
lake water (pH 4). Nine lake additions were conducted bi-weekly at pulicaria and Daphnia mendotae). Chaoborus samples were collected
year (2001–2007) by injecting at 70-cm depth into the propeller wash Chaoborus were picked from the sample using forceps and frozen in
lake that this approach evenly distributed spike added in the evening fundal chironomids were sampled at the deepest part of the lake using

Implications

This page makes the source discoverable for category-level evidence routing. Values remain source-native and should be used only with the stated matrix, species, basis, geography, and censoring context from the paper. The page does not convert total mercury to methylmercury or use total arsenic as inorganic arsenic.

Wiki pages this source may touch

Verification notes

Identity check: DOI, raw handle, candidate cite-key, and SHA-256 were compared against existing wiki/sources/ pages before creation.
Full-PDF read: pdftotext -layout was run on the full PDF twice; extracted text hashes matched before the page was written.
Numeric verification: numeric/table-bearing lines were selected mechanically from the verified extraction and preserved without unit conversion or rounding.
Brand firewall: the worker skips PDFs when extracted numeric lines appear brand/manufacturer-sensitive; this page contains category-level or species-level evidence only.
HMTc firewall: no threshold, percentile, pass/fail, clean/dirty, or certification math is stated.

Update history

The five most recent substantive edits to this page, classified major (evidence or structure moved), correction (a published value or statement was wrong and has been fixed), or minor (narrative rewritten without changing the underlying evidence). Each description is derived from what the edit did to this page; the linked commit is the authoritative record, routine regeneration passes are excluded, and the full version history lives in git. When DOI minting comes online (see schema docs), each entry below will also link to a version-pinned DataCite DOI.

Commit	Date	Change	Description
b01ec52c	2026-08-04	major	2 sections added
d49e450f	2026-08-03	major	5 sections added; narrative text revised