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Our study focused on the seasonal dynamics of total Hg in the phytoplankton (living and dead) of two dystrophic shield lakes (Mouse, and Ranger). Phytoplankton samples were taken from metalimnetic and hypolinmetic depths in the euphotic zone and were collected and analyzed using ultraclean techniques. In both lakes, phytoplankton Hg (PHYTO-Hg) levels (pg/L) in the metalimnion did not significantly change amongdates over the season, although Ranger Lake exhibited significant differences between Hg values measured at the beginning and end of the season. In contrast, PHYTO-Hg significantly increased in the hypolimnia of both lakes by the end of the season. Combined influences of external Hg inputs, remineralization, phytoplankton sedimentation, and increased methylmercury production in the hypolimnia over the season may have contributed to these trends. A highly significant positive relationship existed between PHYTO-Hg levels and whole-water Hg-levels (r2 = 0.90), and the mean bioconcentration factor for Hg between the water column and phytoplankton was significantly higher inthe hypolimnion compared to the metalimnion for both lakes. In most cases, parameters associated with algal biomass had significant positive correlationss with PHYTO- Hg levels. Weight-specific PHYTO-Hg (pg/mg dry weight) varied significantly over the season, and there were interlake differences with respect to seasonal trends. On the basis of these results, we recommend that future sampling regimes include collection of phytoplankton at different limnetic depths throughout theseason to account for spatial and temporal variations. Weight-specific Hg levels in phytoplankton could not be explained well by the parameters tested, and the only significant regressions were with parameters reflecting algal biomass. This study provides in situ evidence ofHg accumulation in lake phytoplankton as a function of algal biomasson a seasonal basis (as opposed to biodilution) and stresses the need to [ABSTRACT FROM AUTHOR]

Formation rates of dissolved gaseous mercury (DGM) were measured in three high (740.N) Arctic lakes and one wetland. The rate of formation of DGM was controlled by (1) the intensity of solar radiation, particularly ultraviolet-B (280--320 nm) and ultraviolet-A (320--400 nm) wavebands and (2) the concentration of available photoreducible Hg(II) complexes. Additions of hydrogen peroxide and of fulvic acids did not enhance DGM formation rates in our experiments. This study illustrates that photoreduction of mercury occurs in a wide range of aquaticsystems even in the high arctic where radiation levels are lower butcontinue for the entire day during the summer. [ABSTRACT FROM AUTHOR]

We collected and analysed 113 leeches (Hirudinea) from 17 small lakes in the acid-stressed Muskoka region of central Ontario, Canada to examine the relationship between lake chemistry and mercury (Hg) concentrations in leeches, and thus determine whether leeches and other benthic invertebrates posed a dietary risk of Hg exposure for non-piscivorous waterfowl. Hg concentrations in leeches were generally low andonly a few-fold above the detection limit (0.78 ng g- 1 wet weight (ww)). Mean Hg concentration in the bloodsucker Macrobdelladecora was 6.94 q0.78 SE ng g-1 ww (n = 49) and was 5.98 q 0.46 ng g-1 ww (n = 64) in the scavenger Percymoorensis marmoratis. Leech Hg concentrations were correlated with calcium and dissolved organic carbon concentrations in the water, respectively. These data suggest that leeches are not suitable monitors of Hg (usually as methylmercury) biomagnification in central Ontario lakes, and do not pose a dietary risk to non-piscivorous waterfowl. [ABSTRACT FROM AUTHOR]

The distribution of total mercury (THg) within common deciduous trees and the applicability of tree cores as biomonitors of historical environmental THg trends were assessed for both contaminated and reference sites around Kingston, Ontario. Samples were collected from Acer spp., Quercus spp. Populus spp. and Salix spp. Bark and wood THg concentrations were found to be highly correlated whereas soil and wood THg concentrations were not. There were no temporal relationships for THg in dated tree rings corresponding with any other known environmental Hg trends. The shoreline species, Populus and Salix spp., had the greatest bark and wood Hg concentrations reaching 18 ng/g, significantly higher than for inland trees Quercus and Acer spp. with maximum values of 7 and 1.2 ng/g for bark and wood respectively. While tree cores cannot be reliably used as temporal THg biomonitors, there is promise for tree species such as Populus spp and Salix spp as spatial indicators of local long-term Hg contamination., (Copyright 2010 Elsevier Ltd. All rights reserved.)

This study focused on the value of deciduous leaves as biomonitors of total mercury (THg). Leaf samples were collected from a range of deciduous species from five sampling sites in the province of Ontario, Canada. These included a site in the northwest (the Experimental Lakes Area, ELA), two sites in central Ontario (the town of Dorset and the Centre for Atmospheric Research Experiments, CARE), and two sites in the southeast (Sandbanks Provincial Park, SBPP and the City of Kingston). The sampled species exhibited distinctive species-specific differences with red oaks consistently having lower leaf THg concentrations than all maple species, while black and white ash leaves had the highest concentrations. Spatially, leaves collected across the distance between ELA and SBPP (approximately 1500 km apart) had overlapping THg concentrations between 20 and 40 ng/g. Unexpectedly, leaves from urban parks of Kingston had considerably lower THg concentrations (<25 ng/g) than the other sites, which suggested leaves may not reflect subtle gradients of atmospheric THg found under field conditions. Leaf THg increased with the growing season, with highest THg leaf concentrations found in early autumn just before senescence. Microspatial differences within a single tree, such as position on a branch are important, since higher mercury concentrations were associated with leaves positioned deeper into the canopy relative to outer leaves more exposed to wind turbulence and sunlight. Within any single leaf, THg concentrations were highest in the leaf tissue, and consistently distributed, while the vein and petiole tissue had lower THg concentrations. There was no relationship between THg concentrations and leaf area. Using deciduous tree leaves as regional temporal monitors of bioavailable mercury may be feasible, but careful selection of leaf sampling sites on the tree itself and the timing is of utmost importance for ensuring consistent and high quality biomonitoring data.

Total mercury concentration was analyzed in 171 lakes from pre-industrial (>30 cm depth; Hg(pre-industrial)) and present-day sediments (0.5-1 cm; Hg(present-day)). Numerous hot or cold spots of sediment mercury enrichment (Hg EF; Hg(pre-industrial)/Hg(present-day)) were evident as determined by local tests of autocorrelation, although in most cases, the maximum correlation among sites was not the nearest neighbor, indicating a strong influence of watershed characteristics. Hg EF was correlated with the area of open water (ha) (r = 0.91, p = 0.035), mine tailings (r = 0.94, p = 0.019), and organic deposits in surficial geology of the watershed (r = -0.91, p = 0.034). Through use of local rather than global regression coefficients, R(2) increased from 0.20 (p = 0.005) to 0.60 (p = 0.013). A broad spatial pattern (>500 km) observed only in Hg(pre-industrial) was best explained by mean annual precipitation (shared variance = 3.5%), while finer spatial patterns only observed in Hg(present-day) and Hg EF were best explained by pH (average shared variance = 10.8%).

Mass budgets for total mercury, major ions and nutrients were calculated for Amituk Lake, located on Cornwallis Island, Nunavut, Canada. Total mercury in two distinct snowpacks averaged 1.25 and 4.21 ng L(-1); the discharge-weighted concentration of influent streams averaged 0.76 ng L(-1). The recent and pre-industrial Hg(T) fluxes in atmospheric deposition to the catchment were estimated to be 0.57 and 0.23 microg m(-2) but through retention within the catchment and/or re-volatilization from the melting snowpack, these decreased by 69% in the lake inflow. The spring freshet was the prime conduit for transporting Hg(T) into Amituk Lake. Because of limited mixing of surface runoff with the lake water column during snowmelt, 59% of the Hg(T) input was directly discharged through the outflow, 16% entered the lake water column where concentrations increased from 0.23 to 0.33 ng L(-1) from June to August and 25% was deposited to the bottom sediments producing a sediment Hg(T) flux of 3.1 microg m(-2).

Selenastrum capricornutum was grown in two lake waters of differing dissolved organic carbon content (1.8 vs. 9.1 mg DOCl(-1)) to determine the responses of population dynamics and photosynthesis to Cu, and to assess the modifying effects of varying ultraviolet radiation (UVR) exposure. In the absence of UVR, the mean EC(50) for Cu effect on population growth rate was 2.3-2.6 microg l(-1) in the low DOC water and 17.4-26.2 microg l(-1) in the high DOC water. The variable chlorophyll a fluorescence ratio, F(v)/F(m), decreased approximately in parallel with the diminished growth rates. Exposure of the higher DOC lake water to full spectrum artificial radiation caused an increase of Cu(2+) concentration, compared to samples held in darkness or in photosynthetically active radiation (PAR) only. Full spectrum exposures also resulted in a lower (although not significantly so) EC(50) for Cu effect on growth rate, consistent with response to the moderately elevated Cu(2+) concentration. Cu(2+) concentration was unaffected by radiation exposure in the low DOC water, and EC(50)s for growth were also unaffected except in the most severe UVR treatment, which was >40% inhibited even in the absence of added Cu. Using F(v)/F(m) as an end-point, there was no evidence of interactions between UVR and Cu under the relatively low PAR exposures used here. Algal growth and photosynthesis was extremely sensitive to Cu in these soft lake waters, with EC(50)s close to current water quality standards in the low DOC water.