Dissecting the spatial scales of mercury accumulation in Ontario lake sediment (original) (raw)
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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...
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
Deconstruction of Historic Mercury Accumulation in Lake Sediments, Northeastern United States
2005
Total atmospheric contribution of mercury (Hg T) to lake sediment was estimated using 210 Pbdated sediment cores. Algorithms based on estimates of lake and watershed processes were applied to more accurately assess anthropogenic contributions of Hg to the environment and Hg T. Factors addressed include: lake-specific background accumulation rates of Hg (Hg B), variability of sediment accumulation rates that caused variation in Hg accumulation during the last 100-150 years (Hg V), and variable flux of anthropogenic Hg from the atmosphere (Hg A). These fluxes were normalized for sediment focusing using a regional, unsupported 210 Pb correction factor to yield Hg A,F. Time series maps of Hg A,F allow for comparison across time and space, and are provided for 1900, 1950, 1975 and 1990 across eastern New York and New England, USA. Deconstruction algorithms reduce inter-/intra-lake variability in Hg accumulation rates and improve temporal coherence. Hg A,F started to increase near the end of the 19th century to a maximum between 1970 and 1990, depending on the lake. Maximum Hg T across the region ranges from 27.1 to 175 lg/m 2 year. Maximum Hg A,F ranged from 10.4 to 66.3 lg/m 2 year. The timing of Hg A,F declines in response to decreased atmospheric deposition may be controlled by in-lake and in-watershed storage and transport of Hg-bearing sediment.
Journal of Geophysical Research, 2012
1] The aim of this study was to determine the spatial variability for total-and methylmercury in surface sediments (0-2 cm) across a single whole-lake basin, and to relate this variability to the sediment's geochemical composition. 83 surface sediment samples from Stor-Strömsjöna lake with multiple sub-basins located in northern Swedenwere analyzed for geochemical composition as well as total-mercury (total-Hg) and methylmercury (methyl-Hg; 35 samples) concentrations. Our results indicate that variations in fine-grained mineral matter (36%) and organic matter (34%) explain an equal amount of the total-Hg variation, but that their relative importance varies between different parts of the lake. Total-Hg concentrations were similar in locations controlled by organic matter or fine-grained mineral matter (average 109 ng g À1 ); however, total-Hg inventories (mass per unit area) were significantly higher in the latter (35 and 53 mg m À2 , respectively). Methyl-Hg concentrations are largely (55% of variance) controlled by water depth and sulfur concentration, which supports the importance of within lake methylation reported from other studies. Both for concentrations and inventories the spatial distribution for methyl-Hg in surface sediments is patchy, and interestingly the highest methyl-Hg inventory (1.4 mg m À2 ) was found in a shallow location with coarse-grained minerogenic sediment (very low organic matter). A large spatial variability, even within a single lake, is something that needs to be recognized, e.g., when studying processes affecting mercury cycling, mercury loadings and when using lake sediments to reconstruct historic mercury deposition.
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.
Factors Influencing Mercury in Freshwater Surface Sediments of Northeastern North America
Ecotoxicology, 2005
We report on an inventory and analysis of sediment mercury (Hg) concentrations from 579 sites across northeastern North America. Sediment Hg concentrations ranged from the limit of detection ca. 0.01-3.7 lg g )1 (dry weight, d.w.), and the average concentration was 0.19 lg g )1 (d.w.) Sediment methylmercury concentrations ranged from 0.15 to 21 ng g )1 (d.w.) and the mean concentration was 3.83 ng g )1 (d.w.). Total Hg concentrations (HgT) were greatest in lakes > reservoirs > rivers, although the proportion of Hg as methylmercury showed an inverse pattern. Total Hg was weakly and positively correlated with the sediment organic matter and percent of watershed as forested land, and weakly and negatively correlated with sediment solids content, drainage area, and agricultural land. Sediment methylmercury concentrations were weakly and positively correlated to wetland area, and weakly and negatively correlated to drainage area. Methylmercury, expressed as a percentage of HgT was positively correlated to agricultural land area. For sites with co-located sediment and fish-tissue sampling results, there was no relationship between sediment Hg and fish-tissue Hg. Finally, our data indicate that at least 44% of waters across the region have sediment HgT concentrations in excess of Canadian and United States minimum sediment contaminant guidelines for the protection of aquatic biota.
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
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 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.