Anthropogenic Mercury Deposition to Arctic Lake Sediments

The history of atmosheric mercury inputs to remote arctic regions can be measured in lake sediment cores using lead-210 chronology. In this investigation, total mercury deposition is measured in sediments from Imitavik and Annak Lakes on the Belcher Islands in southeastern Hudson Bay, an area in the southern Canadian Arctic with no history of local industrial or agricultural sources of contamination. Both lakes received background and atmospheric inputs of mercury while Annak also received mercury from raw domestic sewage from the Hamlet of Sanikiluaq, a growing Inuit community of about 550 established in the late 1960's. Results from Imitavik show that anthropogenic mercury inputs, apparently transported through the atmosphere, began to appear in the mid-eighteenth century, and continued to the 1990's. Annak had a similar mercury history until the late 1960's when disposal of domestic sewage led to increased sediment and contaminant accumulation. The high input of mercury to Annak confirms that Sanikiluaq residents are exposed to mercury through native food sources.     

Numerical simulation model of fatty acids in lake sediments

The finite element model was successfully applied to predict the Pb-210 and total extractable fatty acid concentrations at different depths in two sediment cores from Lake Ontario by using different transport parameters. The transport parameters were computed from Pb-210 data. These parameters were used to simulate the total extractable fatty acid concentrations at different depths. The computed results were compared with observed data and results were compared by statistical methods. Good agreement was achieved though improved results were observed in a two layer model accounting for bioturbation in the upper 4–6 cm of sediment. By modifying this model is useful to apply the contaminant transport in lake sediments, industrial waste disposal ponds, and fish ponds with different geological, physical, chemical and biological parameters at different depths.     

Historical sediment mercury deposition for select South Dakota,USA, lakes: implications for watershed transport and flooding

Purpose

Select South Dakota, USA water bodies, including both natural lakes and man-made impoundments, were sampled and analyzed to assess mercury (Hg) dynamics and historical patterns of total Hg deposition.

Materials and methods

Sediment cores were collected from seven South Dakota lakes. Mercury concentrations and flux profiles were determined using lead (²¹⁰Pb) dating and sedimentation rates.

Results and discussion

Most upper lake sediments contained variable heavy metal concentrations, but became more consistent with depth and age. Five of the seven lakes exhibited Hg accumulation fluxes that peaked between 1920 and 1960, while the remaining two lakes exhibited recent (1995–2009) Hg flux spikes. Historical sediment accumulation rates and Hg flux profiles demonstrate similar peak and stabilized values. Mercury in the sampled South Dakota lakes appears to emanate from watershed transport due to erosion from agricultural land use common to the Northern Great Plains.

Conclusions

For sampled South Dakota lakes, watershed inputs are more significant sources of Hg than atmospheric deposition.

     

Mercury concentrations in fish in a remote Canadian Arctic lake

Lac Ste. Thérèse, a remote Canadian Arctic lake in the Northwest Territories, Canada, has high natural (non-point source) mercury concentrations in fish. The high mercury levels have persisted for over 18 years. Lac Ste. Thérèse has had consistently higher mercury concentration in fish than the other three lakes sampled within the basin, regardless of species tested.     

Historical and Geographical Trends in Sediment Chronology from Lakes and Marine Sites Along the Norwegian Coast

Sediment cores collected from 12 lakes and eight marine sites along the Norwegian and Svalbard coast as part of a project investigating polycyclic aromatic hydrocarbons (PAH) in sediments were dated radiometrically using ²¹⁰Pb, ¹³⁷Cs and ²⁴¹Am fallout radionuclides. In all lake cores, except on Svalbard, the ¹³⁷Cs activity versus depth profile appears to have been significantly modified by post-depositional migration within the sediment column. The relatively low ¹³⁷Cs inventories suggest that these sites were not significantly impacted by fallout from the 1986 Chernobyl accident. All the marine cores have ¹³⁷Cs inventories that are substantially lower than in lake sediments almost certainly due to leaching of ¹³⁷Cs from the marine sediments due to higher solubility in the seawater. In the marine surface sediments, the unsupported ²¹⁰Pb concentrations are up to an order of magnitude lower than in the corresponding lake sediments reflecting the higher (dry mass) sedimentation rate at the marine sites. Five of the cores including marine sites and lakes have unusual high ²¹⁰Pb flux most likely due to sediment focusing. Most of the irregularities in the ²¹⁰Pb records seem to be due to slump events but some patterns are also due to possibly increased accumulation rates. Three of the marine cores show systematic increase in their sedimentation rate from c.1960 towards the present while only one lake shows the same systematic increase.     

Mercury in vegetation and lake sediments from the U. S. arctic

Global atmospheric concentrations of mercury (Hg) appear to be increasing and with it the potential for ecosystem exposure and ecological effects. From 1990 to 1993 we examined U. S. arctic ecosystems over a broad spatial scale to develop baseline information on current concentrations of trace elements, heavy metals (including Hg), persistent organic compounds, and radionuclides in various components of the terrestrial and freshwater biosphere. Matrices reported here include, vegetation (lichens and mosses) and lake sediments. Total Hg in two lichen and two moss species from Alaska were generally low (0.02–0.112 μg/g dw), compared to reported values from other arctic locations and showed a statistically significant negative relationship between total Hg content and distance from the marine coastline.²¹⁰Pb dated sediment cores indicated that average preindustrial total Hg accumulation rates were over four times greater in arctic Schrader lake than in subarctic Wonder Lake. Both lakes indicated a small increase (5–8%) in total Hg flux to the sediments during the last 145 years, much smaller than similar increases in total mercury for lakes in the north central U. S. The likely source of recent increases in Hg in these Alaskan ecosystems is long range atmospheric transport. While we can detect increases in mercury in lake sediments likely due to anthropogenic activities, values are low and there appears to be no immediate threat to terrestrial environments and inland freshwaters of arctic Alaska from long range atmospheric transport and deposition of Hg.     

Distribution and background levels of mercury in sediment cores from selected wisconsin lakes

The vertical distribution of Hg in sediment cores from a range of hard- and soft-water lakes in Wisconsin was evaluated in terms of potential sources of Hg during the nineteenth and twentieth centuries. For the Madison lakes, the trends in Hg distribution were related to variations in sewage inputs during the last 80 yr. It is unlikely that either inputs of sewage or erosional products are responsible for the observed accumulation of Hg in the most recent sediments from three lakes in northeastern Wisconsin. Background levels varied from 0.01 to 0.24 ppm of Hg (intact sediment basis) in precultural sediments from the Wisconsin lakes investigated. There was no consistent relationship between the concentration of Hg and other sediment components of potential importance in the retention of Hg.     

Mercury accumulation trends in Florida Everglades and Savannas Marsh flooded soils

Global and regional increases in atmospheric mercury (Hg) concentrations have previously been identified as the cause of increased mercury accumulation rates in north temperate lakes in Sweden, Wisconsin, and Minnesota. Atmospheric deposition can often account for elevated Hg concentrations in fish from these systems. Mercury levels in sportfish collected from some areas of the Florida Everglades and Savannas Marsh exceed limits that are acceptable for human consumption. Forty five soil cores and soil grab samples were retrieved from the Everglades and Savannas Marsh wetlands. Eighteen sediment cores were dated radiochemically with²¹⁰Pb and¹³⁷Cs using γ-ray spectroscopy to determine modern and historic mercury accumulation rates for these subtropical wetland systems. Recent (“post-1985”) Hg accumulation rates averaged 53 μg m^?2 y^?1 (23 to 141, n=18) corresponding to an average rate increase of 4.9 times (1.6 to 19.1) over those observed around the turn of the century. This accumulation seems to result more from either global or regional atmospheric deposition rather than from lateral transport via overlying surface water. The trends for mercury accumulation match those reported for lakes in Sweden and the northern United States, even though these systems are distinctly different in their climate, vegetational composition, and location. We provide the first data on accumulation of mercury in subtropical wetland systems, and demonstrate the feasibility of radiochemical dating of wetland sediment.     

MERCURY ACCUMULATION IN DEVILS LAKE,NORTH DAKOTA – EFFECTS OF ENVIRONMENTAL VARIATION IN CLOSED-BASIN LAKES ON MERCURY CHRONOLOGIES

Sediment cores were collected from lakes in the Devils Lake Basin in North Dakota to determine if mercury (Hg) accumulation chronologies from sediment-core data are good indicators of variations in Hg accumulation rates in saline lakes. Sediment cores from Creel Bay and Main Bay, Devils Lake were selected for detailed analysis and interpretation. The maximum Hg concentration in the Creel Bay core was 0.15 micrograms per gram at 8 to 9 centimeters. The maximum Hg concentration in the Main Bay core was 0.07 micrograms per gram at 5 to 7 centimeters. The general decreases in Hg concentrations with depth are attributed to historic variations in atmospheric Hg deposition rate. Hg stratigraphies combined with²¹⁰Pb and¹³⁷Cs dating analyses yield Hg chronologies that indicate a general increase in Hg accumulation rates in Devils Lake since the middle of the 19th century. Mean modern Hg accumulation rates in Creel Bay were 4.9 nanograms per square centimeter per year, and rates in Main Bay were 1.8 nanograms per square centimeter per year. Mean preindustrial Hg accumulation rates in Creel Bay were 1.2 nanograms per square centimeter per year, and rates in Main Bay were 1.6 nanograms per square centimeter per year. Relatively low Hg concentrations in recent sediments in the Devils Lake Basin, along with similarities in Hg accumulation rates between lakes in the Devils Lake Basin and other lakes in the northern interior of North America, indicate that local sources of Hg are not important sources of Hg. Results of the study indicate that accurate Hg chronologies are discernible in sediment cores collected from saline lakes. However, spatial and temporal variations in lake level and water chemistry common to saline lakes make interpretation of radioisotopic and geochemical chronologies difficult. Hg geochemistry in Devils Lake, and presumably in other saline lakes, is dynamic. The results of this study indicate that the absolute amount of sediment transported to Devils Lake, along with the associated Hg and total organic carbon, and the distribution of sedimentation patterns in Devils Lake may be affected by changing lake levels.     

Mercury Sedimentation in Lakes in Western Whatcom County, Washington, USA and its Relation to Local Industrial and Municipal Atmospheric Sources

Concentrations of mercury (Hg) were measured in six dated cores from four lakes in western Whatcom County, Washington, USA, that were at various bearings from a chlor-alkali plant, two municipal waste incinerators and a municipal sewage sludge incinerator. The importance of atmospheric emissions of Hg from these local municipal and industrial sources was evaluating by comparing the temporal trends in sedimentation of the lake cores with the emission history of each Hg species and by examining the geographical distribution of Hg sedimentation in relation to the region’s primary wind pattern. Local municipal and industrial sources of atmospheric Hg were not responsible for the majority of the Hg in the upper layer of sediments of Whatcom County lakes because of (1) the significant enrichment of Hg in lake sediments prior to emissions of local industrial and municipal sources in 1964, (2) smaller increases in Hg concentrations occurred after 1964, (3) the similarity of maximum enrichments found in Whatcom County lakes to those in rural lakes around the world, (4) the inconsistency of the temporal trends in Hg sedimentation with the local emission history, and (5) the inconsistency of the geographic trends in Hg sedimentation with estimated deposition. Maximum enrichment ratios of Hg in lake sediments between 2 and 3 that are similar to rural areas in Alaska, Minnesota, and New England suggest that global sources of Hg were primarily responsible for increases of Hg in Whatcom County lakes beginning about 1900.     

Historical sedimentary trends of mercury and other trace elements from two saltmarshes of the Marano and Grado lagoon (northern Adriatic Sea)

Purpose

Previous research conducted in the Marano and Grado lagoon (northern Adriatic Sea) has shown that this environment has been affected by trace metal contamination, especially by mercury (Hg), from both industrial (the chlor-alkali plant) and mining activities (Idrija mine, Slovenia). Sediment cores were collected from two different saltmarshes of this lagoon environment to evaluate the degree of the anthropogenic enrichments and the geochronology of Hg accumulation.

Materials and methods

Core subsampling was performed by cutting 1-cm thick slices at discrete intervals. Mercury determination was done differently from the other parameters in that the two long cores were subsampled at 1-cm intervals to obtain continuous concentration profiles. Samples were completely decomposed, using a mixture of mineral acids in a closed microwave system before being analysed for trace metal content using ICP-OES. Total Hg content in the solid phase was determined by DMA-80. ¹³⁷Cs was measured via gamma spectrometry. ²¹⁰Pb activity was measured via alpha-counting of its daughter, ²¹⁰Po, assuming secular equilibrium between the two isotopes.

Results and discussion

In saltmarsh sediments, Fe, Co, Li, Sc and V show no enrichment at both sites thus suggesting that they are essentially lithogenic elements. Conversely, enrichments are minimal (EF = <2) for As, Cd, Cr, Ni, Pb and Zn and moderate (EF = 2–5) for Cu and Mn and also for Pb and Zn but only in some levels of the sedimentary sequences. An exception is Hg, as expected due to the long-term input proceeding from the historical mining activity which has especially affected the eastern sector of the lagoon.

Conclusions

The core collected from the saltmarsh in the eastern lagoon (Grado) displays a better time resolution during the last century although the Hg background level has not been reached. Conversely, the core collected in the western sector (Marano) has recorded a longer and more complete history of Hg contamination, from the beginning of the peak of Hg extraction activity at the Idrija mine (1850). Both saltmarshes still receive Hg inputs and the sediment accumulation rates in the upper section appear to have increased over the last 10–20 years (from 0.30 to 0.45 cm year^?1 at Marano and from 0.30 to 0.74 cm year^?1 at Grado). Many of these morphological structures suffer erosive processes thus representing a potential source of contaminants associated with sediments, in particular Hg. Conservation and monitoring of saltmarshes should be taken into consideration also from this environmental point of view.

     

In-lake alkalinity generation by sulfate reduction: A paleolimnological assessment

The generation of alkalinity by SO₄ reduction and net storage of reduced S in lake sediments has been estimated from an analysis of sediment cores from 16 lakes in ME, VT, NY, MI, MN, and WY. The cores have been dated by ²¹⁰Pb. The rate of pre-1850 (background) storage of S in lake sediments suggests that alkalinity contribution to lake water from this process ranged from 0.2 to 9.3 geq L^?1, with an average of 4 geq L^?1, Background values are similar for all lakes and remain low in the WY lakes up to the present. Maximum alkalinity contributions recorded in sediment, from upper mid-west and eastern lakes, dated between 1850 and 1985 are between 0.4 and 33 geq L^?1, with a lake mean maximum of 9.9 geq L^?1, Significant increases in recent S storage only occur in eastern lakes. Average values for net S accumulation in the sediment of most lakes for post-1850 sediment are typically less than half of maximum values.     

Diatom and Chrysophyte Algal Response to Long-Term PCB Contamination from a Point-Source in Northern Labrador,Canada

The long-term response of diatom and chrysophyte communities to local PCB contamination was examined in an impacted and referencelake in northern Labrador. Beginning in the late 1950s, lake Saglek-2 (SK-2) received direct inputs of the contaminant in runoff, leaving a record of rising PCB concentrations in lake sediments. An examination of sediment samples spanning the past～ 150 yr revealed chrysophyte and diatom assemblages characteristic of clear, slightly acidic, oligotrophic lakes, butsurprisingly little change in either community was observed through time. The lack of response may be explained by severalfactors. For example, elevated PCB concentrations in lake sediments may not reflect bioavailable concentrations in lakewater. Therefore, realized concentrations may be too low to exhibit detrimental effects in phytoplankton communities. Our findings do, however, have important implications for studies ofclimate change in circumpolar regions. First, we provide additional evidence that climatic change has been minimal in northern Labrador, in contrast to changes observed in other Arctic and sub-Arctic regions. Second, our findings support thenotion that recent, marked changes in species composition observed in other Arctic lakes are the result of recent climatechange and not caused by the contamination of lakes from the long-range transport of pollutants.     

Neutralization of acidic groundwater inputs and control of metal mobility by a near-shore adirondack lake sediment

Biogeochemical processes contributing to the neutralization of acidic groundwater passing through near-shore sediments of an acidified lake (Dart's Lake) were investigated in a controlled laboratory experiment. Three intact sediment cores collected from the near-shore region of the lake were connected to a system that simulated groundwater flow through lake sediments in a temperature controlled laboratory environment. The effect of sediment biogeochemical processes on groundwater chemistry was determined by evaluating changes in acid/base and metal chemistry for solutions entering and leaving the cores. Aluminum mobilization represented the most significant source of neutralization for each core and contributed up to 99% of H⁺ removal. Although the sediment cores were collected parallel to the shoreline and over a linear distance of only 0.3 m, significant differences in sediment chemistry were apparent and contributed to variations in the chemistry of water transported from the cores. For one core that exhibited retention of Al from the influent groundwater, retention of Pb by the sediment was similarly observed. Following acidification of this groundwater, Pb was readily remobilized. These results suggest that near-shore lake sediments may be effective at influencing seasonal variations in Al, Pb and base cations in lakes receiving groundwater inputs.     

Impact of man's activities on the chemical composition of the sediments of lakes superior and Huron

The concentrations of organic matter, major elements and trace elements were determined at 15 core locations in Lake Superior and Huron. The chemical compositions of the cores are related to sediment particle size, Eh, pH, chronology and location. Concentrations of Si, Al, Ca, Mg, K, Na, and Ti, which represent the major mineral species in the sediments, are generally uniform in each core. Surface enrichments of Hg, Pb, Zn, Cu, Ni, Co, Cd, Cr, Be, V, As, Org-C, and N at many of the locations are attributed to anthropogenic inputs of these elements in recent years. Concentration profiles of Fe, Mn, P, and S are influenced by migration of these elements in the pore waters. High anthropogenic Cu loadings in Lake Superior were related to Cu mining activities in the lake basin, while high anthropogenic inputs of Ni to the Lake Huron sediments were related to Ni contamination from the Sudbury area. Sediment loading calculations show that the anthropogenic inputs of trace and nutrient elements are related to the sedimentation rate, that the inputs are dispersed over wide areas of the lakes and that inputs to Lake Superior have increased significantly since 1955. Evidence is presented that atmospheric inputs are an important source of contaminants.     

Temporal and spatial trends in metal loads to sediments of Lake Simcoe,Ontario

Metal loads to sediments of Lake Simcoe were partitioned into three components, which were attributable to natural background, accelerated erosion, and point + atmospheric sources. These loads were calculated over time using metal concentration profiles together with pre-settlement sedimentation rates based on sonar and time-variable sedimentation rates based on ²¹⁰Po profiles in cores. Concentrations of metals significantly higher than pre-settlement concentrations were observed in all cores in the case of Pb, back to 80 yr BP on average, and in at least 75% of cores, back to 60 yr BP for Cd and Zn and 30 to 45 yr BP for Cu, Ni, and Cr. Total metal loads increased 3 × for Cu and Ni, 4 × for Zn and Cr, 11 × for Cd and nearly 20 × for Ph from pre-1800 to 0 to 10 yr BP. At present about 90% of the anthropogenic loads of Pb and Cd, and 60 to 70% of the anthropogenic Cu, Ni, Zn, and Cr, are from point + atmospheric sources, the balance being from increased erosion. The direct atmospheric input of Cd is relatively high, approximately 77% of point + atmospheric inputs, while inputs of Cr and Ni are low at 1% and 9%, and inputs of Cu, Zn, and Pb are intermediate at 20 to 40% of point + atmospheric inputs. Two significant findings on spatial distribution of metals were the large increases in metal loads to Cook Bay following the drainage of 33 km² of marshes for agricultural use and the widespread dispersal of Cr from point source(s) in Kempenfelt Bay.     

Long distance transport of anthropogenic lead as measured by lake sediments

Long-term atmospheric deposition of Pb has been measured using lake sediment cores. The average ‘whole-lake’ Pb burden was measured for several lakes in each of four regions located throughout Ontario and Quebec, Canada. Since the regions were remote to any point source of Ph, large scale variation in atmospheric transport could be studied. The results indicate that Pb deposition is highest in South-Central Ontario, where lake burdens ranged from 312 to 432 mg m^?2, and that it decreases in an eastward direction into Quebec. Lowest deposition was at the site farthest north, Schefferville, Quebec, where fallout was 31 to 42 mg m^?2, less than one-tenth of that previously observed in South-Central Ontario. Lead-210 dating of sediment cores from the northern site showed that input to these remote lakes has occurred over the same time period as in the southern sites.     

Sediment Records of Fallout Radionuclides and their Application to Studies of Sediment-Water Interactions

The fallout radionuclides 210Pb and 137Cs are widely used to date environmental records contained in lake sediments. Since the radionuclide records are themselves the outcome of the transformation of atmospheric fallout by mediating transport processes from the catchment, through the water column and post-depositional migration via pore waters, reliable models of these processes are crucial to accurate dating. The large quantities of data on 210Pb and 137Cs in lake sediments accumulated through their widespread dating applications may be used to study transport models. Their advantages as tracers of transport processes include widespread dispersal through the environment, relatively simple and well known input functions, and ease of measurement. One of the principle factors controlling the transport of any species through the water column is its distribution between aqueous and particulate phases. The relatively solubility of 137Cs in the water column is demonstrated by the reduced 137Cs/210Pb inventory ratios in sediments compared to values expected from direct fallout. Using sediment records from a wide range of Cumbrian lakes, calculations based on simple models indicate that the particulate fraction of weapons fallout 137Cs in the water column ranged from 5-22%, and was proportional to the square root of the sedimentation rate (determined by 210Pb). The KD value for weapons 137Cs in the water column is estimated to be in the range 1-2×105 L kg-1. This is comparable with KD values for Chernobyl 137Cs in these lakes (Smith et al. in press) obtained from direct measurements in the water column.     

Relationship between mercury and organic carbon in sediment cores from Lakes Qinghai and Chenghai, China

Purpose

Factors such as organic matter can significantly influence the distribution of mercury (Hg) in aquatic environments. Recent studies in Arctic and sub-Arctic lakes in Canada have investigated whether scavenging of Hg by phytoplankton significantly affects distributions of Hg in sediments. This study examined the relationships between Hg and organic components in two contrasting lakes (Lakes Qinghai and Chenghai) in low and middle latitudes of China.

Materials and methods

Sediment cores from the less-polluted, oligotrophic Lake Qinghai (QH) and from the polluted, eutrophic Lake Chenghai (CH) were collected by a gravity corer. The cores were sectioned and transported on ice to the laboratory where they were stored at ?20 °C. Subsamples were dried in a vacuum freeze dryer and grounded with a mortar and pestle prior to analyses. Total concentrations of Hg were quantified using cold vapor atomic absorption spectrometry. Total organic carbon (TOC) was quantified using an elemental analyzer after removal of carbonate. The Rock-Eval 6 pyrolysis technique (Vinci Technologies, Rueil-Malmaison, France) was used to deconvolute TOC in sediments into S1, S2, and RC components; S2 was further separated into S2a and S2b.

Results and discussion

Different relationships between Hg and TOC were found in the two lakes, which suggest that different types of organic compounds might play completely different roles in the distribution of Hg in lakes. S1 (the soluble organic matter (SOM)) was found to significantly control distributions of Hg in sediments of both lakes, while S2 and S2a were not. Combining the synchronous fluctuations of Hg and the oxygen index in the QH sediment core and in recent sections of CH suggested that allochthonous SOM derived from the terrestrial environment had an important influence on the distribution of Hg in both lakes and a large portion of Hg that originated from the lake catchment.

Conclusions

This study provides further evidence that organic matter is one of the most important factors that influences distributions of Hg in lake sediments and that SOM was the primary form of carbon associated with sedimentation of Hg. The results also suggest that Hg in lake sediments might not accurately represent its pollution history as it could also be influenced by land use, such as agriculture or other human activities in the catchment.     

Evidence of deposition of anthropogenic pollutants in remote rocky mountain lakes

Thirteen trace elements, the PAH fluoranthene and PCBs were measured in the sediments of four remote high altitude lakes in Rocky Mountain National Park. PCBs were found in the sediments of all four lakes providing substantial evidence of anthropogenic inputs, most likely through atmospheric transport. The results were less certain, but still suggestive as to the anthropogenic origins for the elements As, Cd, Pb, and Sb and the PAH fluoranthene. Several of these elements, as well as fluoranthene and the PCBs, were found to be elevated in surface sediments compared to samples taken at greater depths, inferring that loadings of these substances into Rocky Mountain National Park region have increased with time.