The influence of anthropogenic disturbances and watershed morphological characteristics on Hg dynamics in Northern Quebec large boreal lakes (original) (raw)
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Anthropogenic mercury enrichment in remote lakes of northern Qu�bec (Canada)
Water, Air, & Soil Pollution, 1995
In a sub-Arctic region of the province of Quebec, at sites situated 200 to 1400 km away from the closest industrial centers, we find the ubiquitous presence of anthropogenic Hg, reflected by steadily increasing concentrations of this metal in lake sediments, since about 1940, to rates averaging 2.3 times the preindustrial levels. Mercury concentrations in lake sediments were found to be proportional to the amounts of telTestrial organic carbon from the catchment area. It would, therefore, be misleading to derive continental-scale gradients of this pollutant based on Hg concentrations in oligotropbic lake sediments, unless they are normalized to their organic carbon content. Our normalized data for sediments of remote lakes along a 1200 km transect (45 to 55~ clearly indicate that the distribution pattern of long-range Hg contamination is independent of the latitude over the boreal forest domain. This uniform contamination contrasts with that of Pb, which decreases towards the north over the same latitudinal span, away from the industrial centers of the St Lawrence Valley and the U.S. Mid-West.
Environmental Pollution, 2013
Spatial and temporal changes in mercury (Hg) concentrations and organic carbon in lake sediments were examined from the Hudson Bay Lowlands to investigate whether Hg deposition to sediments is related to indicators of autochthonous production. Total organic carbon, "S2" carbon (mainly algalderived OC), C:N and v 13 C indicators suggest an increase in autochthonous productivity in recent decades. Up-core profiles of S2 concentrations and fluxes were significantly correlated with Hg suggesting that varying algal matter scavenging of Hg from the water column may play an important role in the temporal profiles of Hg throughout the sediment cores. Absence of significant relationship between total Hg and methyl Hg (MeHg) in surficial sediments suggested that inorganic Hg supply does not limit MeHg production. MeHg and OC were highly correlated across lakes in surface and deep sediment layers, indicating that sediment organic matter content explains part of the spatial variation in MeHg concentrations between lakes.
Mercury empirical relationships in sediments from three Ontario lakes
Science of The Total Environment, 2010
Total mercury (THg), methyl mercury (MeHg), total organic carbon (TOC), sediment bulk density (SBD), redox potential (Eh) and percent fines measurements were made on sediment cores collected along transects from littoral to profundal depths in Harp, Dickie, and Blue Chalk lake located on the Canadian Shield near Dorset, Ontario, Canada to determine whether empirical relationships exist among these sediment properties. MeHg was positively correlated with THg in all sediments with a MeHg:THg ratio (0.004 ±0.004) comparable to other uncontaminated profundal lakes. MeHg, MeHg:THg and TOC decreased with sediment depth within the core for all lakes, whereas THg only showed a decrease in Harp Lake. MeHg:THg ratio in surficial sediments was positively correlated with Eh and negatively correlated with TOC [MeHg:THg=−0.009⁎TOC (%)+0.001⁎Eh (mV)−1.902, p=0.026]; whereas THg was positively correlated with TOC [log THg (ppb)= 0.026⁎TOC (%)+1.400, pb 0.0001].
Chemosphere, 2018
Sediment cores from 47 inland lakes in Michigan, USA were used to assess spatial and temporal trends in loadings of mercury (Hg). Focusing/background corrected accumulation rates and inventories and concentration peaks were used to examine: 1) responses of loadings to post-1990 reductions in emissions, 2) if spatial trends are consistent with modeled Hg deposition and 3) evidence for local and distal inputs. Results showed that decreases in concentrations and anthropogenic accumulation rates of Hg were consistent with recent reductions in emissions of Hg. Most lakes exhibiting a decreasing trend were located within an area with the most emission sources. Not all lakes showed the decreasing trend with some showing increases or no change. These lakes tended to be in the northern portion of the state. In all lakes, current concentrations of Hg remain greater than long-term, historical, background concentrations. Sub-regional mean inventories and mean decadal accumulation rates exhibited a south to north gradient, consistent with previously modeled spatial trends. However, individual lake inventories and rates of accumulation compared at shorter times scales varied among lakes. Evidence for event deposition (e.g., volcanic eruptions, manufacturing) was also variable among lakes. These results suggest
Canadian Journal of Fisheries and Aquatic Sciences, 2009
Mercury (Hg) concentrations in recent (0.5-1 cm) and preindustrial (>30 cm) sediments were examined across lakes in south-central and eastern Ontario, Canada (45.538N, 82.418W to 44.158N, 76.258W), to determine whether Hg exported from watersheds is at steady state with atmospheric deposition. An examination of headwater lakes revealed that Hg enrichment was not uniform among watersheds but that the enrichment factor (EF = [Hg]present day/[Hg]preindustrial, standardized for organic matter) decreased as a function of drainage ratio (Ad /Ao, watershedarea/lakearea). Furthermore, the model fit was improved after accounting for differences in sulfate concentrations and pH among lakes: EF = (Ad /Ao) -15.96 -0.07(SO 4 2-) -(3.55(pH>8.3)) (R 2 = 0.458, p = 0.0001). Hg concentrations in preindustrial sediments of headwater lakes showed a positive linear relationship with drainage ratio (partial t = 4.83, p < 0.0001, n = 66) that was strengthened following an adjustment for mean annual runoff (MAR) ([Hg]preindustrial = 0.011 ± 0.002(Ad /Ao) + 0.0008 ± 0.0003(MAR) (R 2 = 0.108, F[1,66] = 8.01, p = 0.006)). Our results suggest that Hg export from watersheds may be currently lagging behind atmospheric Hg deposition, in which case, Hg export would increase into the future, even as Hg deposition from the atmosphere stabilizes. Résumé : Nous avons mesuré les concentrations de mercure (Hg) dans les sédiments récents (0,5-1 cm) et préindustriels (>30 cm) dans des lacs répartis dans tout le centre-sud et l'est de l'Ontario, Canada (45.538N, 82.418O à 44.158N, 76.258O) afin de déterminer si le Hg exporté des bassins versants est en équilibre avec les retombées atmosphériques. Un examen des lacs d'amont des bassins versants indique que l'enrichissement en Hg n'est pas uniforme dans tous les bassins, mais que le facteur d'enrichissement (EF) ([Hg] actuelle / [Hg] préindustrielle ; corrigé pour tenir compte de la matière organique) décroît en fonction du rapport de drainage (A d / A o ; bassin surface / lac surface ). De plus, l'ajustement du modèle s'améliore si on tient compte des différences de concentrations de sulfates et de pH entre les lacs: EF = (A d /A o ) -15.96 -0.07(SO 4
Environmental Science & Technology, 2009
Recent and historical deposition of mercury (Hg) was examined over a broad geographic area from southwestern Northwest Territories to Labrador and from the U.S. Northeast to northern Ellesmere Island using dated sediment cores from 50 lakes (18 in midlatitudes (41-50°N), 14 subarctic (51-64°N) and 18 in the Arctic (65-83°N)). Distinct increases of Hg over time were observed in 76% of Arctic, 86% of subarctic and 100% of midlatitude cores. Subsurface maxima in Hg depositional fluxes (µg m-2 y-1) were observed in only 28% of midlatitude lakes and 18% of arctic lakes, indicating little recent reduction of inputs. Anthropogenic Hg fluxes adjusted for sediment focusing and changes in sedimentation rates (∆F adj,F) ranged from-22.9 to 61 µg m-2 y-1 and were negatively correlated (r)-0.57, P < 0.001) with latitude. Hg flux ratios (FRs; post-1990)/pre-1850) ranged from 0.5 to 7.7. The latitudinal trend for Hg ∆F adj,F values showed excellent agreement with predictions of the global mercury model, GRAHM for the geographic location of each lake (r) 0.933, P < 0.001). The results are consistent with a scenario of slow atmospheric oxidation of mercury, and slow deposition of reactive mercury emissions, declining with increasing latitude away from emission sources in the midlatitudes, and support the view that there are significant anthropogenic Hg inputs in the Arctic.
Spatiotemporal patterns of mercury accumulation in lake sediments of western North America
The Science of the total environment, 2016
For the Western North America Mercury Synthesis, we compiled mercury records from 165 dated sediment cores from 138 natural lakes across western North America. Lake sediments are accepted as faithful recorders of historical mercury accumulation rates, and regional and sub-regional temporal and spatial trends were analyzed with descriptive and inferential statistics. Mercury accumulation rates in sediments have increased, on average, four times (4×) from 1850 to 2000 and continue to increase by approximately 0.2μg/m(2) per year. Lakes with the greatest increases were influenced by the Flin Flon smelter, followed by lakes directly affected by mining and wastewater discharges. Of lakes not directly affected by point sources, there is a clear separation in mercury accumulation rates between lakes with no/little watershed development and lakes with extensive watershed development for agricultural and/or residential purposes. Lakes in the latter group exhibited a sharp increase in mercury...
Water, Air, and Soil Pollution, 2006
Lake sediments are a potential source of mercury (Hg) for aquatic biota. Here, we investigated the predictive power of (a) key parameters for lake catchment morphometry and (b) organic matter composition of sediments in an effort to account for observed variations of total (THg) and methyl (MeHg) mercury concentrations in lake sediments. Using regression models we demonstrate that the morphometric parameters lake depth as well as inclination of catchment soils and lake bottoms can significantly predict variations of THg concentrations, but not MeHg, at profundal lake sediments. Although THg and MeHg concentrations in sediments could not be predicted by specific organic matter sources, as elucidated by atomic C/N ratios, our data suggest that wetland-derived total organic carbon (TOC) contained less THg concentrations than TOC derived from mostly forested watersheds. However, TOC concentrations could significantly predict MeHg concentrations and the proportion of methylated Hg at all sediment stations. Finally, from an ecotoxicological point of view, we propose that concentrations of TOC at surface lake sediments, rather than parameters of catchment morphometry, may predict dietary sources of MeHg for benthic consumers and consequently perhaps for organisms at higher trophic levels.
Water, Air, and Soil Pollution, 2008
Lake St. Pierre (LSP), constituted of a 120 km 2 stretching of the St. Lawrence River (Southern Québec), hosts the largest freshwater fishery industry in Canada. The lake drains, through its main tributaries, an important area of agrarian land and was subjected to intense industrial activities in the past century. In this paper, we present (1) an estimation of the seasonal aquatic mercury (Hg) inputs to LSP from the St-Lawrence River and two major tributaries; (2) a reconstruction, by the analysis of sediment cores, of the historic inputs of Hg into LSP and in a large riparian wetland, Bay St. François. Our results indicate that the aquatic Hg inputs to LSP (290 kg Hg between April 2003 and April 2004) are moderately elevated with most of the inputs occurring from the St. Lawrence River, either in spring or early winter, during high flow episodes. The sediment profiles suggest a recent decrease in Hg inputs, likely attributable to improvements of industrial practices. The observed perturbation of the surface sediments give evidence of an active hydrodynamic regime, suggesting that LSP could only act as a transitory system for suspended sediment and Hg, with seasonal accumulation and recurrent resuspension resulting from changes in the hydrodynam-ic regime. Finally, we observed positive MeHg fluxes from the sediment to the water at different seasons in Bay St. François. However, Hg levels in fish like walleyes of LSP are reported to be low, which could be explained by faster fish growth rates following in part intense fishing pressure in LSP.