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Timber harvest has many effects on aquatic ecosystems, including changes in hydrological, biogeochemical, and ecological processes that can influence mercury (Hg) cycling. Although timber harvest's influence on aqueous Hg transformation and transport are well studied, the effects on Hg bioaccumulation are not. We evaluated Hg bioaccumulation, biomagnification, and food web structure in 10 paired catchments that were either clear-cut in their entirety, clear-cut except for an 8-m wide riparian buffer, or left unharvested. Average mercury concentrations in aquatic biota from clear-cut catchments were 50% higher than in reference catchments and 165% higher than in catchments with a riparian buffer. Mercury concentrations in aquatic invertebrates and salamanders were not correlated with aqueous THg or MeHg concentrations, but rather treatment effects appeared to correspond with differences in the utilization of terrestrial and aquatic basal resources in the stream food webs. Carbon and nitrogen isotope data suggest that a diminished shredder niche in the clear-cut catchments contributed to lower basal resource diversity compared with the reference of buffered treatments, and that elevated Hg concentrations in the clear-cut catchments reflect an increased reliance on aquatic resources in clear-cut catchments. In contrast, catchments with riparian buffers had higher basal resource diversity than the reference catchments, indicative of more balanced utilization of terrestrial and aquatic resources. Further, following timber harvest THg concentrations in riparian songbirds were elevated, suggesting an influence of timber harvest on Hg export to riparian food webs. These data, coupled with comparisons of individual feeding guilds, indicate that changes in organic matter sources and associated effects on stream food web structure are important mechanisms by which timber harvest modifies Hg bioaccumulation in headwater streams and riparian consumers. Image 1 • Biota Hg differed between clear-cuts, riparian buffers, and unharvested forests. • Biota Hg was not related to aqueous THg or MeHg. • Biota Hg was related to changes in reliance on terrestrial resources. • Hg was higher in riparian songbirds following timber harvest. Hg concentrations in aquatic biota were highest in clear-cuts, intermediate in unharvested forests, and lowest in catchments with riparian buffers, likely due to differences in basal resource use. [ABSTRACT FROM AUTHOR]

Mercury is a potent contaminant that can disrupt an organism's behavior and physiology, ultimately affecting reproductive success. Over the last 100 years, environmental deposition of anthropogenic sourced mercury has increased globally, particularly in the U.S. Northeast region. Marine birds are considered effective bioindicators of ecosystem health, including persistent marine contaminants. Goodale et al. (2008) found that mercury exposure exceeded adverse effects levels in some marine bird species breeding across the Gulf of Maine. We re-examined mercury contamination in four species identified as effective bioindicators. Compared with the previous sampling effort, inshore-feeding species showed significant increases in mercury exposure, while one pelagic-feeding species remained stable. This suggests that a major shift may have occurred in methylmercury availability in inshore waters of the Gulf of Maine. Understanding environmental mercury trends in the Gulf of Maine, and its significance to marine birds and other taxa will require a dedicated, standardized, long-term monitoring scheme. [ABSTRACT FROM AUTHOR]

Mercury (Hg) is a globally-distributed pollutant, toxic to humans and animals. Emissions are particularly high in Asia, and the source of exposure for humans there may also be different from other regions, including rice as well as fish consumption, particularly in contaminated areas. Yet the threats Asian wildlife face in rice-based ecosystems are as yet unclear. We sought to understand how Hg flows through rice-based food webs in historic mining and non-mining regions of Guizhou, China. We measured total Hg (THg) and methylmercury (MeHg) in soil, rice, 38 animal species (27 for MeHg) spanning multiple trophic levels, and examined the relationship between stable isotopes and Hg concentrations. Our results confirm biomagnification of THg/MeHg, with a high trophic magnification slope. Invertivorous songbirds had concentrations of THg in their feathers that were 15x and 3x the concentration reported to significantly impair reproduction, at mining and non-mining sites, respectively. High concentrations in specialist rice consumers and in granivorous birds, the later as high as in piscivorous birds, suggest rice is a primary source of exposure. Spiders had the highest THg concentrations among invertebrates and may represent a vector through which Hg is passed to vertebrates, especially songbirds. Our findings suggest there could be significant population level health effects and consequent biodiversity loss in sensitive ecosystems, like agricultural wetlands, across Asia, and invertivorous songbirds would be good subjects for further studies investigating this possibility. [ABSTRACT FROM AUTHOR]

We investigated the relation between environmental mercury exposure and corticosterone concentrations in free-living adult common loons ( Gavia immer ). We determined blood and feather mercury concentrations and compared them to testosterone, estradiol, and stress-induced plasma corticosterone concentrations. Although neither testosterone nor estradiol correlated with Hg levels, there was a robust positive relation between blood Hg and stress-induced corticosterone concentrations in males, but not in females. The lack of an effect in females may have been due to overall less contamination in females. There were no significant correlations between feather Hg and stress-induced corticosterone in either sex. To help determine whether Hg had a causal effect on corticosterone, we investigated the impact of experimental Hg intake on the corticosterone stress response in captive juvenile loons. Juveniles were subjected to three different feeding regimes: 0, 0.4 and 1.2 μg Hg (as MeHgCL)/g wet weight (ww) fish. We then measured baseline and 30 min post-solitary confinement stressor corticosterone concentrations. The Hg fed chicks exhibited a decreased ability to mount a stress response. From these data, we conclude that Hg contamination does appear to alter the corticosterone response to stress, but not in a consistent predictable pattern. Regardless of the direction of change, however, exposure to mercury contamination and the resulting impact on the corticosterone stress response in common loons may substantially impact health, fitness and survival. [ABSTRACT FROM AUTHOR]

Mercury bioaccumulation is frequently observed in marine ecosystems, often with stronger effects at higher trophic levels. We compared total mercury (THg) and methylmercury (MeHg) from muscle with length, comparative isotopic niche, and diet (via δ 13 C and δ 15 N) among four sympatric coastal sharks in Florida Bay (USA): blacknose, blacktip, bull, and lemon. Mercury in blacknose and blacktip sharks increased significantly with size, whereas bull and lemon sharks had a high variance in mercury relative to size. Both δ 13 C and δ 15 N were consistent with general resource use and trophic position relationships across all species. A significant relationship was observed between δ 13 C and mercury in blacktip sharks, suggesting an ontogenetic shift isotopic niche, possibly a dietary change. Multiple regression showed that δ 13 C and δ 15 N were the strongest factors regarding mercury bioaccumulation in individuals across all species. Additional research is recommended to resolve the mechanisms that determine mercury biomagnification in individual shark species. [ABSTRACT FROM AUTHOR]

An introduction is presented in which the authors discuss the beginnings of loon research and conservation in North America, including papers within the issue that include topics on loon movements and migrations, habitat and landscape requirements, and the impact of environmental contaminants.

The article discusses the detection of polycyclic aromatic hydrocarbons in common loons wintering off in coastal Louisiana after an oil spill in the Gulf of Mexico in April 2010. Results from an experiment to test loon blood samples show that the concentrations and frequency of the chemical appear to increase among loons annually, but concentrations from petroleum-based petrogenic alkyl polycyclic hydrocarbons were significantly higher than combustion-based pyrogenic polycyclic hydrocarbons.

The article discusses the wildlife criterion values for common loons in Adirondack Park, New York based on a study to determine mercury concentrations in Adirondack lakes, and in blood, feather and egg samples of loons. Study results show that the values obtained were small enough to affect behavior and reproductive activity of loons, thus providing an estimate of reasonable mercury thresholds in lakes. The results will also assist environmental legislators to better protect aquatic ecosystems.

The article discusses the migration pathway of common loons from the state of Louisiana to the province of Saskatchewan in Canada where they breed during the winter season. Based on a pilot study using platform terminal transmitters to track bird sightings, the common loons wintering off Louisiana migrated to Saskatchewan. Conversely, previous research findings also indicate that common loons from breeding areas in Saskatchewan overwinter in several North American sites and the Pacific Ocean.

The article discusses the relationship of body mass of common loons with migration distance, based on a study to examine body mass, tarsal width, and bill length of common loons from satellite tracking data in breeding territories in North America. Study results show that body mass is inversely proportional to migration distance, and differences in body mass between male and female loons increase with decreasing migration distance. Males, for example, were larger than females in coastal areas.

The article discusses the effect of size and retention of territories for yellow-billed loons based on a study using satellite transmitters that quantified the habit limitations of three loon breeding populations in Alaska and Canada. Study results show that the range of territory size corresponded to the size of lakes in the areas, and loons who lost their habitats did not occupy new territories. The study also suggests that the lake sizes suitable for breeding may limit population size.

The article presents a study which examined the impact of mercury exposure on the population of the piscivorous common loon in Adirondack Park, New York. Topics discussed include the spatial distibution of mercury, a model for assessing the long-term effect of mercury on common loon reproduction and growth, and the extent of mercury contamination of aquatic ecosystems in the area.

The article discusses mercury exposure affecting the breeding grounds of yellow-billed loons in Alaska and Canada, based on an experimental study to determine the risks posed by mercury originating from waters in eastern Asia. Study results show that mercury concentrations in blood, feather, and egg tissues from live loons and museum specimens have lowered the species' productivity. Findings also indicate that mercury is an environmental stressor for yellow-billed loons in the Arctic habitats.

The article discusses a research study which investigated the impact of mercury exposure on the breeding population of Common Loon, Gavia immer, in the Adirondack Park in New York from 1998-2007. Topics discussed are the correlation of lake acidity with mercury concentrations in Common Loons, the risk for behavioral and reproductive impacts in male and female Common Loons based on mercury body burden, and the link between high mercury levels and reduced number of chicks fledged annually.

The article discusses a study which detected the presence of polycyclic aromatic hycrocarbons (PAH) in blood samples from Common Loons, Gavia immer, wintering off the coast of Louisiana from 2011-12 after the Deepwater Horizon oil drilling rig explosion in the Gulf of Mexico. Topics covered are the changes in the concentration levels and frequency of petrogenic alkyl PAH derived from petroleum and pyrogenic PAH derived from combustion and anthropogenic sources.

The article discusses a study on the development of wildlife criterion values (WCV) for the Common Loon, Gavia immer, in the Adirondack Park in New York based on estimates of wildlife population viability through measurements of contaminant stressors. Topics covered are the level of water mercury concentrations required to protect the Common Loon population and the accuracy of WCV within the park. Also discussed is the impact of mercury levels on the reproductive success and behavior of loons.

The article discusses a research study which examined the association of the body mass in Common Loons, Gavia immer, with migration distance. Topics covered are the clinal variation in body mass, tarsal width and bill length in loons from populations in the upper Great Lakes and central Canada, and the resulting three migration groups based on band return and satellite tracking. Also discussed is the male and female pair differences related to migration distance.

The article discusses a research study which examined the size and retention of breeding territories of Yellow-billed Loons, Gavia adamsii, in Alaska and Canada. Topics covered are the mean territory radius for the breeding populations within the Seward Peninsula in northwest Alaska, within the Arctic Coastal Plain of Alaska, and within Daring Lake in mainland Canada, as well as the relationship of territory retention to early arrival dates at the breeding site.

The article discusses a research study which tracked the migration of Common Loons, Gavia immer, wintering off the Louisiana Coast to Saskatchewan during the breeding season. Topics covered are the link between the wintering and breeding locations of Common Loons from coastal Louisiana, and the spring and fall migration routes with location and flight distance estimates between locations for a male and female Common Loon caught in Adams Bay, Louisiana on March 29, 2001.

An introduction to several papers on loon research and conservation in North America is presented that include the behavior, life-history, population ecology, movements and migrations, habitat and landscape requirements of Gavia species, and the impacts contaminants have had on loon populations.

Rusty blackbirds are undergoing rapid population decline and have elevated Hg concentrations while breeding in the Acadian ecoregion of North America. Factors regulating the bioavailability of methyl-Hg (MeHg) within this population's habitat were determined using water, invertebrates, and blood from adult rusty blackbirds collected for Hg-speciation, along with additional water column parameters: MeHg and THg, dissolved organic carbon, pH, dissolved oxygen, conductivity, redox potential, and temperature. Both DO2 and pH were negatively related to biota MeHg, while water MeHg concentrations were positively related. Both invertebrate MeHg concentration and %MeHg increased with trophic level. Invertebrate MeHg concentrations were among the greatest reported when compared with those reported elsewhere for wetlands and waterbodies—often several times greater for similar taxa—while percent MeHg of THg were similar. An environment with high bioavailability of MeHg in combination with a high trophic position best explains elevated Hg concentrations for this species regional population. [Copyright &y& Elsevier]

We assessed the risks of mercury in yellow perch, a species important in the trophic transfer of methylmercury, in the Great Lakes region. Mean concentrations in whole perch from 45 (6.5%) of 691 waters equaled or exceeded 0.20 μg/g w.w., a threshold for adverse effects in fish. In whole perch within the size range eaten by common loons (<100 g), mean concentrations exceeded a dietary threshold (0.16 μg/g w.w.) for significant reproductive effects on loons in 19 (7.3%) of 260 waters. Mean concentrations in fillets of perch with length ≥ 15.0 cm, the minimum size retained by anglers, exceeded the USEPA criterion (0.3 μg/g w.w.) in 26 (6.4%) of 404 U.S. waters and exceeded the Ontario guideline (0.26 μg/g w.w.) in 35 (20%) of 179 Ontario waters. Mercury levels in yellow perch in some waters within this region pose risks to perch, to common loons, and to mercury-sensitive human populations. [Copyright &y& Elsevier]

The Laurentian Great Lakes region of North America contains substantial aquatic resources and mercury-contaminated landscapes, fish, and wildlife. This special issue emanated from a bi-national synthesis of data from monitoring programs and case studies of mercury in the region, here defined as including the Great Lakes, the eight U.S. states bordering the Great Lakes, the province of Ontario, and Lake Champlain. We provide a retrospective overview of the regional mercury problem and summarize new findings from the synthesis papers and case studies that follow. Papers in this issue examine the chronology of mercury accumulation in lakes, the importance of wet and dry atmospheric deposition and evasion to regional mercury budgets, the influence of land–water linkages on mercury contamination of surface waters, the bioaccumulation of methylmercury in aquatic foods webs; and ecological and health risks associated with methylmercury in a regionally important prey fish. [Copyright &y& Elsevier]

Mercury (Hg) is a persistent environmental contaminant found in many freshwater and marine ecosystems. Historical Hg contamination in rivers can impact the surrounding terrestrial ecosystem, but there is little known about how far downstream this contamination persists. In 2009, we sampled terrestrial forest songbirds at five floodplain sites up to 137 km downstream of an historical source of Hg along the South and South Fork Shenandoah Rivers (Virginia, USA). We found that blood total Hg concentrations remained elevated over the entire sampling area and there was little evidence of decline with distance. While it is well known that Hg is a pervasive and long-lasting aquatic contaminant, it has only been recently recognized that it also biomagnifies effectively in floodplain forest food webs. This study extends the area of concern for terrestrial habitats near contaminated rivers for more than 100 km downstream from a waterborne Hg point source. [Copyright &y& Elsevier]

Abstract: Changes in deposition of gaseous divalent mercury (Hg(II)) and particulate mercury (Hg(p)) in New Hampshire due to changes in local sources from 1996 to 2002 were assessed using the Industrial Source Complex Short Term (ISCST3) model (regional and global sources and Hg atmospheric reactions were not considered). Mercury (Hg) emissions in New Hampshire and adjacent areas decreased significantly (from 1540 to 880kgyr−1) during this period, and the average annual modeled deposition of total Hg also declined from 17 to 7.0μgm−2 yr−1 for the same period. In 2002, the maximum amount of Hg deposition was modeled to be in southern New Hampshire, while for 1996 the maximum deposition occurred farther north and east. The ISCST3 was also used to evaluate two future scenarios. The average percent difference in deposition across all cells was 5% for the 50% reduction scenario and 9% for the 90% reduction scenario. [Copyright &y& Elsevier]

Three pairs of color-marked Common Loons (Gavia immer) nesting on the Lake Superior shoreline of Isle Royale National Park, Michigan, were observed from mid-May to early August of 1992 and 1993 to develop atime-activity budget which could be compared with that of loons nesting on inland lakes elsewhere. Lake Superior loons spent significantly more time moving about their territories during the pre-nesting stage than at any other time during the breeding season and significantly more time resting during the post-nesting stage than at any other time (P< 0.05). We present evidence that the optimal time budget for aloon in its given habitat may be relatively flexible and subject to environmental influence. Differences in loon behavior over time may reflect changing environmental conditions (e.g., changes in the prey base or water quality) and provide valuable information for conservation efforts. [ABSTRACT FROM AUTHOR]