Variations in Tissue Mercury Contents in Three Species of Adult Salamanders in Streams in Western Maryland.

The purpose of this study was to improve our understanding of the relationship between mercury in three species of adult salamanders and relatively pristine first-order streams in western Maryland. We measured the tissue mercury content of 106 northern two-lined salamanders (Eurycea bislineata bislineata), 111 northern dusky (Desmognathus fuscus), and 107 Allegheny mountain dusky (Desmognathus ocrophaeus) salamanders collected during three sampling periods. Averaged over our entire data set, northern two-lined salamanders had significantly greater tissue mercury contents (29.57 ± 1.32 ng g-1) than northern dusky (20.95 ± 0.78 ng g-1) and Allegheny mountain dusky salamanders (22.84 ± 1.23 ng g-1). This may be due in part to the longer larval period of the northern two-lined salamanders (24-36 vs. 0-10 months). A longer larval period suggests that the northern two-lined larvae were consuming a fully aquatic diet for a longer time period, which is likely to be higher in mercury compared with a more terrestrial diet. The tissue mercury content in northern two-lined and northern dusky salamanders were strongly correlated with the average total mercury, methyl mercury, and dissolved organic carbon concentrations in stream water. In contrast, the tissue mercury content of the more terrestrial salamander, the Allegheny mountain dusky, was not correlated with stream water chemistry. This suggest that the mercury in the terrestrial prey consumed by the Allegheny mountain dusky salamanders is not directly linked to the mercury in stream water. Our results also suggest that the aquatic salamanders could be important bioindicators of mercury contamination of small streams.

Mercury Concentrations in Northern Two-Lined Salamanders from Stream Ecosystems in Garrett County, Maryland.

The purpose of this study was to increase our understanding of the bioaccumulation of mercury in northern two-lined salamanders (Eurycea bislineata bislineata) in freshwater stream ecosystems. We collected 111 adults and 131 larval northern two-lined salamanders from six streams in Garrett County, Maryland. These salamanders were collected in April, July, and September 2010. We measured the size and tissue mercury content in all of these salamanders. We also measured the total and methyl mercury concentrations in stream water on monthly basis from April through December 2010. Averaged over all stream ecosystems, adult northern two-lined salamanders had significantly greater total mercury concentrations than larval salamanders (29.6 vs. 23.8 ng g-1). For individual stream ecosystems, the mean tissue mercury contents in adult northern two-lined salamanders were significantly greater than the mean tissue mercury contents in larval northern two-lined salamanders for Bear Pen and Mill Run. Adult and larval salamanders from the Little Savage River and Mud Lick had 1.5-2 times greater mean tissue mercury contents than salamanders in all other streams. These two streams also had significantly greater total and methyl mercury concentrations. Despite their different life-stage feeding behaviors (terrestrial vs. aquatic), the tissue mercury contents of adult (r = 0.76) and larval (r = 0.79) northern two-lined salamanders were strongly linked to the methyl mercury concentrations in stream water. This implies that northern two-lined salamanders may be a useful bioindicator of mercury pollution in relatively pristine stream ecosystems.

The Estimated Six-Year Mercury Dry Deposition Across North America.

Dry deposition of atmospheric mercury (Hg) to various land covers surrounding 24 sites in North America was estimated for the years 2009 to 2014. Depending on location, multiyear mean annual Hg dry deposition was estimated to range from 5.1 to 23.8 µg m-2 yr-1 to forested canopies, 2.6 to 20.8 µg m-2 yr-1 to nonforest vegetated canopies, 2.4 to 11.2 µg m-2 yr-1 to urban and built up land covers, and 1.0 to 3.2 µg m-2 yr-1 to water surfaces. In the rural or remote environment in North America, annual Hg dry deposition to vegetated surfaces is dominated by leaf uptake of gaseous elemental mercury (GEM), contrary to what was commonly assumed in earlier studies which frequently omitted GEM dry deposition as an important process. Dry deposition exceeded wet deposition by a large margin in all of the seasons except in the summer at the majority of the sites. GEM dry deposition over vegetated surfaces will not decrease at the same pace, and sometimes may even increase with decreasing anthropogenic emissions, suggesting that Hg emission reductions should be a long-term policy sustained by global cooperation.

Effectiveness of Emission Controls to Reduce the Atmospheric Concentrations of Mercury.

Coal-fired power plants in the United States are required to reduce their emissions of mercury (Hg) into the atmosphere to lower the exposure of Hg to humans. The effectiveness of power-plant emission controls on the atmospheric concentrations of Hg in the United States is largely unknown because there are few long-term high-quality atmospheric Hg data sets. Here, we present the atmospheric concentrations of Hg and sulfur dioxide (SO2) measured from 2006 to 2015 at a relatively pristine location in western Maryland that is several (>50 km) kilometers downwind of power plants in Ohio, Pennsylvania, and West Virginia. Annual average atmospheric concentrations of gaseous oxidized mercury (GOM), SO2, fine particulate mercury (PBM2.5), and gaseous elemental mercury (GEM) declined by 75%, 75%, 43%, and 13%, respectively, and were strongly correlated with power-plant Hg emissions from the upwind states. These results provide compelling evidence that reductions in Hg emissions from power plants in the United States had their intended impact to reduce regional Hg pollution.

Dry deposition of gaseous oxidized mercury in Western Maryland.

The purpose of this study was to directly measure the dry deposition of gaseous oxidized mercury (GOM) in western Maryland. Annual estimates were made using passive ion-exchange surrogate surfaces and a resistance model. Surrogate surfaces were deployed for seventeen weekly sampling periods between September 2009 and October 2010. Dry deposition rates from surrogate surfaces ranged from 80 to 1512 pgm(-2)h(-1). GOM dry deposition rates were strongly correlated (r(2)=0.75) with the weekly average atmospheric GOM concentrations, which ranged from 2.3 to 34.1 pgm(-3). Dry deposition of GOM could be predicted from the ambient air concentrations of GOM using this equation: GOM dry deposition (pgm(-2)h(-1))=43.2 × GOM concentration-80.3. Dry deposition velocities computed using GOM concentrations and surrogate surface GOM dry deposition rates, ranged from 0.2 to 1.7 cms(-1). Modeled dry deposition rates were highly correlated (r(2)=0.80) with surrogate surface dry deposition rates. Using the overall weekly average surrogate surface dry deposition rate (369 ± 340 pg m(-2)h(-1)), we estimated an annual GOM dry deposition rate of 3.2 µg m(-2)year(-1). Using the resistance model, we estimated an annual GOM dry deposition rate of 3.5 µg m(-2)year(-1). Our annual GOM dry deposition rates were similar to the dry deposition (3.3 µg m(-2)h(-1)) of gaseous elemental mercury (GEM) at our site. In addition, annual GOM dry deposition was approximately 1/2 of the average annual wet deposition of total mercury (7.7 ± 1.9 µg m(-2)year(-1)) at our site. Total annual mercury deposition from dry deposition of GOM and GEM and wet deposition was approximately 14.4 µg m(-2)year(-1), which was similar to the average annual litterfall deposition (15 ± 2.1 µg m(-2)year(-1)) of mercury, which was also measured at our site.

Investigation of factors affecting gaseous mercury concentrations in soils.

The purpose of this study was to determine the effects of soil temperature, soil moisture, redox potential (Eh) and soil organic matter (SOM) on the total gaseous mercury (TGM) concentrations in background soils. Our measurements were made in a grass field and deciduous forest at the Piney Reservoir Ambient Air Monitoring Station (PRAAMS) in Garrett County, Maryland. Three plots in each area were sampled every third week from July 2009 to June 2010 at the Oe-A soil horizon interface, the A-E soil horizon interface, and 5 and 10 cm into the E soil horizon. The mean soil TGM concentration for all depths in the forest (2.3 ± 2.2 ng m(-3)) was significantly higher than the mean soil TGM concentration in the grass field (1.5 ± 1.9 ng m(-3)). Soil TGM at all depths was most strongly and consistently correlated to soil temperature. The soil TGM concentrations were highest and most variable at the forest Oe-A soil horizon interface (4.1 ± 2.0 ng m(-3)), ranging from 1.5 to 8.4 ng m(-3). This soil horizon interface had 11 to 26% more SOM and the soil Eh was 100 to 400 mV lower than the other soil depths. Our results suggest that soil temperature, soil Eh and SOM are significant factors affecting TGM concentrations in forest soils. Future studies of TGM dynamics in background soils may benefit from closely monitoring the organic soil horizon.

Relationship between wetlands and mercury in brook trout.

The purpose of this study was to determine if wetlands influence mercury concentrations in brook trout (Salvelinus fontinalis), benthic macroinvertebrates, and stream water. On September 26, 2005, water samples, benthic macroinvertebrates, and brook trout were collected from four streams in western Maryland under low-flow conditions. Water samples were also collected in these four streams under high-flow conditions in January 2006. The watersheds of Blue Lick and Monroe Run did not contain wetlands, but the watersheds of the Upper Savage River (3% of upstream area) and Little Savage River (7% of upstream area) contained wetlands. We found significantly (p = 0.05) higher average total mercury concentration in brook trout from Little Savage River (129 +/- 54 ng g(-1)); intermediate concentrations (66 +/- 19 ng g(-1)) in brook trout from Upper Savage River; and lowest concentrations in brook trout from Blue Lick (28 +/- 11 ng g(-1)) and Monroe Run (23 +/- 19 ng g(-1)). Brook trout in all streams accumulated mercury at the same rate over their lifetimes, but the youngest fish had significantly different mercury concentrations (Little Savage > Upper Savage > Blue Lick = Monroe Run), which may be due to differences in mercury concentrations in the eggs or food for the fry. Mercury concentrations in brook trout were not consistent with mercury concentrations in stream water and benthic macroinvertebrates. The Little Savage River had significantly higher total and methylmercury concentrations in stream water, but mercury concentrations in the other streams and in the benthic macroinvertebrates were not significantly different among streams. The unusually high methylmercury concentrations (0.5 to 2.1 ng L(-1)) in the Little Savage River may have been caused by production of methylmercury in the pools. The relatively low methylmercury concentrations in the Upper Savage River may be caused by a mercury concentration gradient downstream of the wetland.

Atmospheric nitrogen deposition to estuares in the mid-Atlantic and northeastern United States.

The purpose of this work was to determine the contribution made by atmospheric nitrogen (N) deposition to the total N input to 10 estuaries on the east coast of the United States. We estimated the amount of N fixed by human activities in the watersheds (N fertilization, biotic N2fixation by legumes and pastures, atmospheric N deposition, and net food and feed import of N) of these 10 estuaries and used a land-use specific approach to estimate the N available for transport to the estuary from different watershed N sources (runoff from agriculture, urban areas and upland forests, point sources, and atmospheric deposition). Total atmospheric N inputs (watershed runoff plus direct deposition to the surface of estuary) accounted for 15-42% of the total N inputs to these 10 estuaries. Direct deposition to the surface of the estuary was an important atmospheric N source for four estuaries, accounting for 35-50% of the total atmospheric N inputs. Simulated reductions of atmospheric N deposition by 25% and 50% of current deposition rates reduced the contribution made by atmospheric N deposition to the total N loads by 1-6% and 2-11%, respectively. Largest reductions occurred in estuaries with direct atmospheric N deposition contributions >35% of the total atmospheric N input. Results from our simulated reductions suggest that considerable reductions (>25%) in atmospheric N deposition will be needed to significantly reduce the contribution made by atmospheric N deposition to the total N loads to our study estuaries. In addition, reductions in atmospheric N deposition will first be detected in estuaries with relatively high direct deposition inputs of atmospheric N deposition.