To understand the impact reduced mercury (Hg) loading and invasive species have had on methylmercury bioaccumulation in predator fish of Lake Michigan, we reconstructed bioaccumulation trends from a fish archive (1978 to 2012). By measuring fish Hg stable isotope ratios, we related temporal changes in Hg concentrations to varying Hg sources. Additionally, dietary tracers were necessary to identify food web influences. Through combined Hg, C, and N stable isotopic analyses, we were able to differentiate between a shift in Hg sources to fish and periods when energetic transitions (from dreissenid mussels) led to the assimilation of contrasting Hg pools (2000 to present). In the late 1980s, lake trout δ 202 Hg increased (0.4‰) from regulatory reductions in regional Hg emissions. After 2000, C and N isotopes ratios revealed altered food web pathways, resulting in a benthic energetic shift and changes to Hg bioaccumulation. Continued increases in δ 202 Hg indicate fish are responding to several United States mercury emission mitigation strategies that were initiated circa 1990 and continued through the 2011 promulgation of the Mercury and Air Toxics Standards rule. Unlike archives of sediments, this fish archive tracks Hg sources susceptible to bioaccumulation in Great Lakes fisheries. Analysis reveals that trends in fish Hg concentrations can be substantially affected by shifts in trophic structure and dietary preferences initiated by invasive species in the Great Lakes. This does not diminish the benefits of declining emissions over this period, as fish Hg concentrations would have been higher without these actions.
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An assessment of temporal trends in mercury concentrations in fish
The importance of fish consumption as the primary pathway of human exposure to mercury and the establishment of fish
consumption advisories to protect human health have led to large fish tissue monitoring programs worldwide. Data on fish
tissue mercury concentrations collected by state, tribal, and provincial governments via contaminant monitoring programs
have been compiled into large data bases by the U.S. Environmental Protection Agency’s Great Lakes National Monitoring
Program Office (GLNPO), the Ontario Ministry of the Environment’s Fish Contaminants Monitoring and Surveillance
Program (FMSP), and many others. These data have been used by a wide range of governmental and academic investigators
worldwide to examine long-term and recent trends in fish tissue mercury concentrations. The largest component of the trend
literature is for North American freshwater species important in recreational fisheries. This review of temporal trends in fish
tissue mercury concentrations focused on published results from freshwater fisheries of North America as well as marine
fisheries worldwide. Trends in fish tissue mercury concentrations in North American lakes with marked overall decreases
were reported over the period 1972–2016. These trends are consistent with reported mercury emission declines as well as
trends in wet deposition across the U.S. and Canada. More recently, a leveling-off in the rate of decreases or increases in fish
tissue mercury concentrations has been reported. Increased emissions of mercury from global sources beginning between
1990 and 1995, despite a decrease in North American emissions, have been advanced as an explanation for the observed
changes in fish tissue trends. In addition to increased atmospheric deposition, the other factors identified to explain the
observed mercury increases in the affected fish species include a systematic shift in the food-web structure with the
introduction of non-native species, creating a new or expanding role for sediments as a net source for mercury. The
influences of climate change have also been identified as contributing factors, including considerations such as increases in
temperature (resulting in metabolic changes and higher uptake rates of methylmercury), increased rainfall intensity and
runoff (hydrologic export of organic matter carrying HgII from watersheds to surface water), and water level fluctuations that
alter either the methylation of mercury or the mobilization of monomethylmercury. The primary source of mercury exposure
in the human diet in North America is from the commercial fish and seafood market which is dominated (>90%) by marine
species. However, very little information is available on mercury trends in marine fisheries. Most of the data used in the
published marine trend studies are assembled from earlier reports. The data collection efforts are generally intermittent, and
the spatial and fish-size distribution of the target species vary widely. As a result, convincing evidence for the existence of
fish tissue mercury trends in marine fish is generally lacking. However, there is some evidence from sampling of large, longlived commercially-important fish showing both lower mercury concentrations in the North Atlantic in response to reduced
anthropogenic mercury emission rates in North America and increases in fish tissue mercury concentrations over time in the
North Pacific in response to increased mercury loading.
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- Award ID(s):
- 1634024
- NSF-PAR ID:
- 10130153
- Date Published:
- Journal Name:
- Ecotoxicology
- ISSN:
- 1573-3017
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Because herbivore growth and reproduction scale with protein intake, declining foliar [N] may be contributing to widely reported declines in insect populations and may be negatively affecting the growth of grazing livestock and herbivorous wild mammals. Spatial and temporal patterns in N availability are not yet fully understood, particularly outside of Europe and North America. Developments in remote sensing, accompanied by additional historical reconstructions of N availability from tree rings, herbarium specimens, and sediments, will show how N availability trajectories vary among ecosystems. Such assessment and monitoring efforts need to be complemented by further experimental and theoretical investigations into the causes of declining N availability, its implications for global carbon sequestration, and how its effects propagate through food webs. Responses will need to involve reducing N demand via lowering atmospheric CO 2 concentrations, and/or increasing N supply. Successfully mitigating and adapting to declining N availability will require a broader understanding that this phenomenon is occurring alongside the more widely recognized issue of anthropogenic eutrophication. Intercalibration of isotopic records from leaves, tree rings, and lake sediments suggests that N availability in many terrestrial ecosystems has steadily declined since the beginning of the industrial era. Reductions in N availability may affect many aspects of ecosystem functioning, including carbon sequestration and herbivore nutrition. Shaded areas indicate 80% prediction intervals; marker size is proportional to the number of measurements in each annual mean. Isotope data: (tree ring) K. K. McLauchlan et al. , Sci. Rep. 7 , 7856 (2017); (lake sediment) G. W. Holtgrieve et al. , Science 334 , 1545–1548 (2011); (foliar) J. M. Craine et al. , Nat. Ecol. Evol. 2 , 1735–1744 (2018)more » « less
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Abstract Aim Anthropogenic warming of marine systems has caused biological and physiological responses that are fundamentally altering ecosystem structure. Because estuaries exist at the land‐ocean interface, they are particularly vulnerable to the effects of ocean warming as they can undergo rapid biogeochemical and hydrological shifts due to climate and land‐use change. We explored how multiple components of estuarine fish diversity—turnover, richness, and abundance—have changed in the North Atlantic and Gulf of Mexico estuaries across space and time and the drivers of change.
Location North Atlantic and Gulf of Mexico.
Taxa Fish.
Method We compiled long‐term (>30 years), continent‐wide fisheries independent trawl surveys conducted in estuaries—from the Gulf of Maine to the Gulf of Mexico (U.S. waters)—and combined these with climate and land‐use‐land‐cover data to examine trends and ecological drivers of fish richness, abundance and turnover using mixed‐effect models.
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1007/s10646-019-02112-3
