Edward Swain - Academia.edu (original) (raw)
Papers by Edward Swain
Monitoring and Evaluating Trends in Methylmercury Accumulation in Aquatic Biota
Indicators of Change, 2007
Hydrologic Fluctuations Resulting From Climatic Variability Cause Methylation Events in Peatlands Impacted by Elevated Sulfate Deposition
A long-term sulfate addition experiment at the Marcell Experimental Forest of northern Minnesota ... more A long-term sulfate addition experiment at the Marcell Experimental Forest of northern Minnesota has demonstrated the stimulatory effect of sulfate on mercury methylation at the ecosystem scale. Wetland margins have been shown to be principal zones of methylmercury (MeHg) production in sulfur-limited peatlands, but this research illustrates how the hydrologically isolated center of a small peatland effectively becomes a hot
Mercury-Sulfur Interactions in an Experimental Peatland
ABSTRACT The mercury and sulfur cycles are intimately linked. For example, the production of meth... more ABSTRACT The mercury and sulfur cycles are intimately linked. For example, the production of methylmercury, the mercury species that accumulates in biota, is strongly controlled by the activity of sulfate-reducing bacteria. Of the many types of wetlands, peatlands and especially bogs are important areas of methylmercury production, partly because the hydrological and biogeochemical conditions in peatlands support anaerobes like sulfate-reducing bacteria. Given the vast coverage of peatlands in the northern U.S. and in Canada (> 1million km2), the impact of peatlands on large-scale mercury cycling could be enormous. Our current understanding of sulfur-mercury interactions in peatlands is mostly from short-duration or fine-scale experimentation, which makes extrapolation tenuous. Currently, the positive relationship between sulfate loading and methylmercury production is relatively well understood. However, the converse, how methylmercury pools are affected by reductions in sulfate loading, is entirely unknown. An important, policy-relevant question is whether reductions in sulfate deposition could lead to reductions in methylmercury loads in peatland biota, and how quickly these reductions might occur. These issues were addressed in a long-term, ecosystem-scale experiment in which sulfate loads were elevated through simulated rainfall to half of a 2-hectare peatland in northern Minnesota. Wet sulfate deposition was increased to the experimental half of a wetland from 2001 through 2006. In 2006, this increased deposition was halted in half of the experimental area (referred to as the "recovery" area thereafter), while increased deposition continued in the other half of the experimental area until the end of 2008 ("experimental"). Once increased sulfate deposition ceased, sulfate concentrations returned to background (control) levels within one year. Methylmercury concentrations in pore waters, peat, and invertebrates took three to five years to decrease to control levels once wet sulfate deposition was reduced, but important spatial patterns emerged that affected the level of impact. We believe that the impact of atmospherically-deposited sulfate on methylmercury production is relatively short-lived because sulfate is sequestered in increasingly recalcitrant organic sulfur pools over time, which reduces the activity of sulfate-reducing bacteria and tips the mercury methylation-demethylation scales in favor of demethylation. These results also suggest that further controls on atmospheric sulfur emissions and deposition could be as important as reductions in mercury emissions to arrive at significant reductions in the mercury load of peatland biota.
Atmospheric Mercury Deposition to Lakes and Watersheds
Advances in Chemistry, 1994
Environmental science & technology, Jan 17, 2014
Human activities over the last several centuries have transferred vast quantities of mercury (Hg)... more Human activities over the last several centuries have transferred vast quantities of mercury (Hg) from deep geologic stores to actively cycling earth-surface reservoirs, increasing atmospheric Hg deposition worldwide. Understanding the magnitude and fate of these releases is critical to predicting how rates of atmospheric Hg deposition will respond to future emission reductions. The most recently compiled global inventories of integrated (all-time) anthropogenic Hg releases are dominated by atmospheric emissions from preindustrial gold/silver mining in the Americas. However, the geophysical evidence for such large early emissions is equivocal, because most reconstructions of past Hg-deposition have been based on lake-sediment records that cover only the industrial period (1850-present). Here we evaluate historical changes in atmospheric Hg deposition over the last millennium from a suite of lake-sediment cores collected from remote regions of the globe. Along with recent measurement...
Lessons from the Silica "Decline" in Lake Michigan
Science, 1983
A new analysis of data obtained from water treatment plants on Lake Michigan fails to support pub... more A new analysis of data obtained from water treatment plants on Lake Michigan fails to support published contentions, based on such data, that the silica content of the lake has declined during the last five decades. The purported silica decline appears to have been due to changes in analytical methods and laboratories. Had such changes been avoided, an invaluable record of the silica content of the lake could have been obtained.
Review of Lake Management in Minnesota
Lake and Reservoir Management, 1989
Lake management practices in Minnesota have included holistic Clean Lakes Projects, extensive rem... more Lake management practices in Minnesota have included holistic Clean Lakes Projects, extensive remedial methods to control excessive phytoplankton and macrophyte growth, and fisheries improvement projects. Clean Lakes projects have had varying degrees of success, but there has been no systematic evaluation of the overall success of the program. Remedial methods and fisheries management have narrow objectives, and the broader water
USE OF EXCLOSURES TO ASSESS THE IMPACT OF COPPER SULFATE TREATMENTS ON PHYTOPLANKTON
Lake and Reservoir Management, 1986
The impact of a whole-lake copper sulfate treatment is difficult to assess because it is uncertai... more The impact of a whole-lake copper sulfate treatment is difficult to assess because it is uncertain how the lake would have behaved if the copper had not been added, that is, no control exists. However, control can be created by isolating lake water in an enclosure prior to the copper sulfate treatment. The enclosure, by excluding copper, functions as an
The chemistry of lake sediments in time and space
Hydrobiologia, 1986
Five short cores (1.0–1.5 m) representing different depositional zones of an isolated bay of Lake... more Five short cores (1.0–1.5 m) representing different depositional zones of an isolated bay of Lake Minnetonka, Minnesota (USA), were independently dated by 210Pb and pollen analysis and were analyzed stratigraphically for elemental chemistry (following sediment fractionation) and sedimentary pigments (including myxoxanthophyll and oscillaxanthin). Because of good dating control, short-interval time-stratigraphic units could be traced across the basin, and lake-wide accumulation
Fuel Processing Technology, 2000
0378-3820r00r$ -see front matter q 2000 Elsevier Science B.V. All rights reserved.
Methylmercury Declines in a Boreal Peatland When Experimental Sulfate Deposition Decreases
Environmental Science & Technology, 2012
Between 2001 and 2008 we experimentally manipulated atmospheric sulfate-loading to a small boreal... more Between 2001 and 2008 we experimentally manipulated atmospheric sulfate-loading to a small boreal peatland and monitored the resulting short and long-term changes in methylmercury (MeHg) production. MeHg concentrations and %MeHg (fraction of total-Hg (Hg(T)) present as MeHg) in the porewaters of the experimental treatment reached peak values within a week of sulfate addition and then declined as the added sulfate disappeared. MeHg increased cumulatively over time in the solid-phase peat, which acted as a sink for newly produced MeHg. In 2006 a "recovery" treatment was created by discontinuing sulfate addition to a portion of the experimentally treated section to assess how MeHg production might respond to decreased sulfate loads. Four years after sulfate additions ceased, MeHg concentrations and %MeHg had declined significantly from 2006 values in porewaters and peat, but remained elevated relative to control levels. Mosquito larvae collected from each treatment at the end of the experiment exhibited Hg(T) concentrations reflective of MeHg levels in the peat and porewaters where they were collected. The proportional responses of invertebrate Hg(T) to sulfate deposition rates demonstrate that further controls on sulfur emissions may represent an additional means of mitigating Hg contamination in fish and wildlife across low-sulfur landscapes.
Sulfate Addition Increases Methylmercury Production in an Experimental Wetland
Environmental Science & Technology, 2006
Atmospheric mercury is the dominant Hg source to fish in northern Minnesota and elsewhere. Howeve... more Atmospheric mercury is the dominant Hg source to fish in northern Minnesota and elsewhere. However, atmospherically derived Hg must be methylated prior to accumulating in fish. Sulfate-reducing bacteria are thought to be the primary methylators of Hg in the environment. Previous laboratory and field mesocosm studies have demonstrated an increase in methylmercury (MeHg) levels in sediment and peatland porewaters following additions of sulfate. In the current ecosystem-scale study, sulfate was added to half of an experimental wetland at the Marcell Experimental Forest located in northeastern Minnesota, increasing annual sulfate load by approximately four times relative to the control half of the wetland. Sulfate was added on four separate occasions during 2002 and delivered via a sprinkler system constructed on the southeast half (1.0 ha) of the S6 experimental wetland. MeHg levels were monitored in porewater and in outflow from the wetland. Prior to the first sulfate addition, MeHg concentrations (filtered, 0.7 microm) were not statistically different between the control (0.47 +/- 0.10 ng L(-1), n = 12; mean +/- one standard error) and experimental 0.52 +/- 0.05 ng L(-1), n = 18) halves. Following the first addition in May 2002, MeHg porewater concentrations increased to 1.63 +/- 0.27 ng L(-1) two weeks after the addition, a 3-fold increase. Subsequent additions in July and September 2002 did not raise porewater MeHg, but the applied sulfate was not observed in porewaters 24 h after addition. MeHg concentrations in outflow from the wetland also increased leading to an estimated 2.4x increase of MeHg flux from the wetland. Our results demonstrate enhanced methylation and increased MeHg concentrations within the wetland and in outflow from the wetland suggesting that decreasing sulfate deposition rates would lower MeHg export from wetlands.
Environmental Science & Technology, 1997
ABSTRACT Historic increases in atmospheric mercury deposition caused by anthropogenic emissions h... more ABSTRACT Historic increases in atmospheric mercury deposition caused by anthropogenic emissions have been well documented from sediment cores from lakes and peatlands in North America and Europe. Few previous studies have addressed the question of whether mercury deposition has increased continuously to the present or whether it has declined in recent decades. We present stratigraphic data from a suite of Minnesota lakes that indicate mercury deposition peaked in the 1960s and 1970s, at least for the upper Midwest. Recent declines, which appear in both rural and urban lakes, are not evident in sediment cores from remote coastal lakes in southeastern Alaska. Because the Alaskan sites provide an integrated sample of mercury pollution in the Northern Hemisphere, these results imply that global mercury emissions have not abated and that decreased inputs to Midwestern lakes are caused by reduced emissions from regional sources. U.S. inventory data suggest that decreased emissions likely resulted from reduced industrial use of mercury, use of pollution-control technologies that incidentally capture mercury, a shift from coal to natural gas for commercial and residential heating, and a decrease in uncontrolled waste incineration. Increased stack height and other factors that favor long-distance transport could be partially responsible for the trend.
Monitoring the Response to Changing Mercury Deposition
Environmental Science & Technology, 2005
Page 1. Monitoring the Response toChanging MERCURY DEPOSITION Page 2. Because advisories have bee... more Page 1. Monitoring the Response toChanging MERCURY DEPOSITION Page 2. Because advisories have been posted for so many water bodies against consumption of fish with elevated concentrations of potentially dan-gerous ...
Redox Chemistry in Minnesota Streams during Episodes of Increased Methylmercury Discharge
Environmental Science & Technology, 2004
Mercury (Hg) and methylmercury (MeHg) are flushed from watersheds during hydrological events, con... more Mercury (Hg) and methylmercury (MeHg) are flushed from watersheds during hydrological events, contaminating downstream surface waters and resident fish populations. We monitored total mercury (THg), MeHg, and ancillary water chemistry parameters in two streams (Cedar Creek and Trott Brook) in east-central Minnesota on a weekly or semiweekly basis from April through October 2003. Heavy precipitation in late June resulted in discrete episodes of high concentrations (>1.2 ng/L) of MeHg in both streams in early July. The MeHg/THg ratio increased from 0.15 to 0.36 in Cedar Creek and from 0.13 to 0.46 in Trott Brook during the event. The high MeHg concentrations were accompanied by low dissolved oxygen concentrations and increased concentrations of dissolved organic carbon, Mn, Fe, and orthophosphate. A prolonged absence of precipitation during August and early September brought stream levels back to baseflow values, and MeHg concentrations decreased to less than 0.1 ng/L. These results suggest that warm-weather, high-discharge events are the primary route of export of MeHg from these watersheds, and baseflow contributes much less MeHg to downstream waters. The redox water chemistry during the,events sampled here suggests that MeHg in these streams is discharged from wetland areas where anoxic/anaerobic conditions prevail.
Environmental Pollution, 2012
Data from 104 sediment cores from the Great Lakes and "inland lakes" in the region were 37 compil... more Data from 104 sediment cores from the Great Lakes and "inland lakes" in the region were 37 compiled to assess historical and recent changes in mercury (Hg) deposition. The lower Great 38
Characteristics of mercury speciation in Minnesota rivers and streams
Environmental Pollution, 2008
Patterns of mercury (Hg) speciation were examined in four Minnesota streams ranging from the main... more Patterns of mercury (Hg) speciation were examined in four Minnesota streams ranging from the main-stem Mississippi River to small tributaries in the basin. Filtered phase concentrations of methylmercury (MeHg), inorganic Hg (IHg), and dissolved organic carbon (DOC) were higher in all streams during a major summertime runoff event, and DOC was enriched with MeHg but not with IHg. Particulate-phase MeHg and IHg concentrations generally increased with total suspended solids (TSS) concentrations but the event data did not diverge greatly from the non-event data, suggesting that sources of suspended sediments in these streams did not vary significantly between event and non-event samplings. The dissolved fractions (filtered concentration/unfiltered concentration) of both MeHg and IHg increased with increasing DOC concentrations, but varied inversely with TSS concentrations. While MeHg typically constitutes only a minor portion of the total Hg (THg) in these streams, this contribution is not constant and can vary greatly over time in response to watershed inputs.
Mercury in fish from northeastern Minnesota lakes: Historical trends, environmental correlates, and potential sources
Journal of the Minnesota Academy of Science;( …, 1989
Description/Abstract High mercury concentrations in fish of some Minnesota lakes and rivers were ... more Description/Abstract High mercury concentrations in fish of some Minnesota lakes and rivers were first noted in 1971. Major anthropogenic sources of mercury to Minnesota rivers generally have been identified and controlled, but it has been difficult to identify mercury ...
Monitoring and Evaluating Trends in Methylmercury Accumulation in Aquatic Biota
Indicators of Change, 2007
Hydrologic Fluctuations Resulting From Climatic Variability Cause Methylation Events in Peatlands Impacted by Elevated Sulfate Deposition
A long-term sulfate addition experiment at the Marcell Experimental Forest of northern Minnesota ... more A long-term sulfate addition experiment at the Marcell Experimental Forest of northern Minnesota has demonstrated the stimulatory effect of sulfate on mercury methylation at the ecosystem scale. Wetland margins have been shown to be principal zones of methylmercury (MeHg) production in sulfur-limited peatlands, but this research illustrates how the hydrologically isolated center of a small peatland effectively becomes a hot
Mercury-Sulfur Interactions in an Experimental Peatland
ABSTRACT The mercury and sulfur cycles are intimately linked. For example, the production of meth... more ABSTRACT The mercury and sulfur cycles are intimately linked. For example, the production of methylmercury, the mercury species that accumulates in biota, is strongly controlled by the activity of sulfate-reducing bacteria. Of the many types of wetlands, peatlands and especially bogs are important areas of methylmercury production, partly because the hydrological and biogeochemical conditions in peatlands support anaerobes like sulfate-reducing bacteria. Given the vast coverage of peatlands in the northern U.S. and in Canada (> 1million km2), the impact of peatlands on large-scale mercury cycling could be enormous. Our current understanding of sulfur-mercury interactions in peatlands is mostly from short-duration or fine-scale experimentation, which makes extrapolation tenuous. Currently, the positive relationship between sulfate loading and methylmercury production is relatively well understood. However, the converse, how methylmercury pools are affected by reductions in sulfate loading, is entirely unknown. An important, policy-relevant question is whether reductions in sulfate deposition could lead to reductions in methylmercury loads in peatland biota, and how quickly these reductions might occur. These issues were addressed in a long-term, ecosystem-scale experiment in which sulfate loads were elevated through simulated rainfall to half of a 2-hectare peatland in northern Minnesota. Wet sulfate deposition was increased to the experimental half of a wetland from 2001 through 2006. In 2006, this increased deposition was halted in half of the experimental area (referred to as the "recovery" area thereafter), while increased deposition continued in the other half of the experimental area until the end of 2008 ("experimental"). Once increased sulfate deposition ceased, sulfate concentrations returned to background (control) levels within one year. Methylmercury concentrations in pore waters, peat, and invertebrates took three to five years to decrease to control levels once wet sulfate deposition was reduced, but important spatial patterns emerged that affected the level of impact. We believe that the impact of atmospherically-deposited sulfate on methylmercury production is relatively short-lived because sulfate is sequestered in increasingly recalcitrant organic sulfur pools over time, which reduces the activity of sulfate-reducing bacteria and tips the mercury methylation-demethylation scales in favor of demethylation. These results also suggest that further controls on atmospheric sulfur emissions and deposition could be as important as reductions in mercury emissions to arrive at significant reductions in the mercury load of peatland biota.
Atmospheric Mercury Deposition to Lakes and Watersheds
Advances in Chemistry, 1994
Environmental science & technology, Jan 17, 2014
Human activities over the last several centuries have transferred vast quantities of mercury (Hg)... more Human activities over the last several centuries have transferred vast quantities of mercury (Hg) from deep geologic stores to actively cycling earth-surface reservoirs, increasing atmospheric Hg deposition worldwide. Understanding the magnitude and fate of these releases is critical to predicting how rates of atmospheric Hg deposition will respond to future emission reductions. The most recently compiled global inventories of integrated (all-time) anthropogenic Hg releases are dominated by atmospheric emissions from preindustrial gold/silver mining in the Americas. However, the geophysical evidence for such large early emissions is equivocal, because most reconstructions of past Hg-deposition have been based on lake-sediment records that cover only the industrial period (1850-present). Here we evaluate historical changes in atmospheric Hg deposition over the last millennium from a suite of lake-sediment cores collected from remote regions of the globe. Along with recent measurement...
Lessons from the Silica "Decline" in Lake Michigan
Science, 1983
A new analysis of data obtained from water treatment plants on Lake Michigan fails to support pub... more A new analysis of data obtained from water treatment plants on Lake Michigan fails to support published contentions, based on such data, that the silica content of the lake has declined during the last five decades. The purported silica decline appears to have been due to changes in analytical methods and laboratories. Had such changes been avoided, an invaluable record of the silica content of the lake could have been obtained.
Review of Lake Management in Minnesota
Lake and Reservoir Management, 1989
Lake management practices in Minnesota have included holistic Clean Lakes Projects, extensive rem... more Lake management practices in Minnesota have included holistic Clean Lakes Projects, extensive remedial methods to control excessive phytoplankton and macrophyte growth, and fisheries improvement projects. Clean Lakes projects have had varying degrees of success, but there has been no systematic evaluation of the overall success of the program. Remedial methods and fisheries management have narrow objectives, and the broader water
USE OF EXCLOSURES TO ASSESS THE IMPACT OF COPPER SULFATE TREATMENTS ON PHYTOPLANKTON
Lake and Reservoir Management, 1986
The impact of a whole-lake copper sulfate treatment is difficult to assess because it is uncertai... more The impact of a whole-lake copper sulfate treatment is difficult to assess because it is uncertain how the lake would have behaved if the copper had not been added, that is, no control exists. However, control can be created by isolating lake water in an enclosure prior to the copper sulfate treatment. The enclosure, by excluding copper, functions as an
The chemistry of lake sediments in time and space
Hydrobiologia, 1986
Five short cores (1.0–1.5 m) representing different depositional zones of an isolated bay of Lake... more Five short cores (1.0–1.5 m) representing different depositional zones of an isolated bay of Lake Minnetonka, Minnesota (USA), were independently dated by 210Pb and pollen analysis and were analyzed stratigraphically for elemental chemistry (following sediment fractionation) and sedimentary pigments (including myxoxanthophyll and oscillaxanthin). Because of good dating control, short-interval time-stratigraphic units could be traced across the basin, and lake-wide accumulation
Fuel Processing Technology, 2000
0378-3820r00r$ -see front matter q 2000 Elsevier Science B.V. All rights reserved.
Methylmercury Declines in a Boreal Peatland When Experimental Sulfate Deposition Decreases
Environmental Science & Technology, 2012
Between 2001 and 2008 we experimentally manipulated atmospheric sulfate-loading to a small boreal... more Between 2001 and 2008 we experimentally manipulated atmospheric sulfate-loading to a small boreal peatland and monitored the resulting short and long-term changes in methylmercury (MeHg) production. MeHg concentrations and %MeHg (fraction of total-Hg (Hg(T)) present as MeHg) in the porewaters of the experimental treatment reached peak values within a week of sulfate addition and then declined as the added sulfate disappeared. MeHg increased cumulatively over time in the solid-phase peat, which acted as a sink for newly produced MeHg. In 2006 a "recovery" treatment was created by discontinuing sulfate addition to a portion of the experimentally treated section to assess how MeHg production might respond to decreased sulfate loads. Four years after sulfate additions ceased, MeHg concentrations and %MeHg had declined significantly from 2006 values in porewaters and peat, but remained elevated relative to control levels. Mosquito larvae collected from each treatment at the end of the experiment exhibited Hg(T) concentrations reflective of MeHg levels in the peat and porewaters where they were collected. The proportional responses of invertebrate Hg(T) to sulfate deposition rates demonstrate that further controls on sulfur emissions may represent an additional means of mitigating Hg contamination in fish and wildlife across low-sulfur landscapes.
Sulfate Addition Increases Methylmercury Production in an Experimental Wetland
Environmental Science & Technology, 2006
Atmospheric mercury is the dominant Hg source to fish in northern Minnesota and elsewhere. Howeve... more Atmospheric mercury is the dominant Hg source to fish in northern Minnesota and elsewhere. However, atmospherically derived Hg must be methylated prior to accumulating in fish. Sulfate-reducing bacteria are thought to be the primary methylators of Hg in the environment. Previous laboratory and field mesocosm studies have demonstrated an increase in methylmercury (MeHg) levels in sediment and peatland porewaters following additions of sulfate. In the current ecosystem-scale study, sulfate was added to half of an experimental wetland at the Marcell Experimental Forest located in northeastern Minnesota, increasing annual sulfate load by approximately four times relative to the control half of the wetland. Sulfate was added on four separate occasions during 2002 and delivered via a sprinkler system constructed on the southeast half (1.0 ha) of the S6 experimental wetland. MeHg levels were monitored in porewater and in outflow from the wetland. Prior to the first sulfate addition, MeHg concentrations (filtered, 0.7 microm) were not statistically different between the control (0.47 +/- 0.10 ng L(-1), n = 12; mean +/- one standard error) and experimental 0.52 +/- 0.05 ng L(-1), n = 18) halves. Following the first addition in May 2002, MeHg porewater concentrations increased to 1.63 +/- 0.27 ng L(-1) two weeks after the addition, a 3-fold increase. Subsequent additions in July and September 2002 did not raise porewater MeHg, but the applied sulfate was not observed in porewaters 24 h after addition. MeHg concentrations in outflow from the wetland also increased leading to an estimated 2.4x increase of MeHg flux from the wetland. Our results demonstrate enhanced methylation and increased MeHg concentrations within the wetland and in outflow from the wetland suggesting that decreasing sulfate deposition rates would lower MeHg export from wetlands.
Environmental Science & Technology, 1997
ABSTRACT Historic increases in atmospheric mercury deposition caused by anthropogenic emissions h... more ABSTRACT Historic increases in atmospheric mercury deposition caused by anthropogenic emissions have been well documented from sediment cores from lakes and peatlands in North America and Europe. Few previous studies have addressed the question of whether mercury deposition has increased continuously to the present or whether it has declined in recent decades. We present stratigraphic data from a suite of Minnesota lakes that indicate mercury deposition peaked in the 1960s and 1970s, at least for the upper Midwest. Recent declines, which appear in both rural and urban lakes, are not evident in sediment cores from remote coastal lakes in southeastern Alaska. Because the Alaskan sites provide an integrated sample of mercury pollution in the Northern Hemisphere, these results imply that global mercury emissions have not abated and that decreased inputs to Midwestern lakes are caused by reduced emissions from regional sources. U.S. inventory data suggest that decreased emissions likely resulted from reduced industrial use of mercury, use of pollution-control technologies that incidentally capture mercury, a shift from coal to natural gas for commercial and residential heating, and a decrease in uncontrolled waste incineration. Increased stack height and other factors that favor long-distance transport could be partially responsible for the trend.
Monitoring the Response to Changing Mercury Deposition
Environmental Science & Technology, 2005
Page 1. Monitoring the Response toChanging MERCURY DEPOSITION Page 2. Because advisories have bee... more Page 1. Monitoring the Response toChanging MERCURY DEPOSITION Page 2. Because advisories have been posted for so many water bodies against consumption of fish with elevated concentrations of potentially dan-gerous ...
Redox Chemistry in Minnesota Streams during Episodes of Increased Methylmercury Discharge
Environmental Science & Technology, 2004
Mercury (Hg) and methylmercury (MeHg) are flushed from watersheds during hydrological events, con... more Mercury (Hg) and methylmercury (MeHg) are flushed from watersheds during hydrological events, contaminating downstream surface waters and resident fish populations. We monitored total mercury (THg), MeHg, and ancillary water chemistry parameters in two streams (Cedar Creek and Trott Brook) in east-central Minnesota on a weekly or semiweekly basis from April through October 2003. Heavy precipitation in late June resulted in discrete episodes of high concentrations (>1.2 ng/L) of MeHg in both streams in early July. The MeHg/THg ratio increased from 0.15 to 0.36 in Cedar Creek and from 0.13 to 0.46 in Trott Brook during the event. The high MeHg concentrations were accompanied by low dissolved oxygen concentrations and increased concentrations of dissolved organic carbon, Mn, Fe, and orthophosphate. A prolonged absence of precipitation during August and early September brought stream levels back to baseflow values, and MeHg concentrations decreased to less than 0.1 ng/L. These results suggest that warm-weather, high-discharge events are the primary route of export of MeHg from these watersheds, and baseflow contributes much less MeHg to downstream waters. The redox water chemistry during the,events sampled here suggests that MeHg in these streams is discharged from wetland areas where anoxic/anaerobic conditions prevail.
Environmental Pollution, 2012
Data from 104 sediment cores from the Great Lakes and "inland lakes" in the region were 37 compil... more Data from 104 sediment cores from the Great Lakes and "inland lakes" in the region were 37 compiled to assess historical and recent changes in mercury (Hg) deposition. The lower Great 38
Characteristics of mercury speciation in Minnesota rivers and streams
Environmental Pollution, 2008
Patterns of mercury (Hg) speciation were examined in four Minnesota streams ranging from the main... more Patterns of mercury (Hg) speciation were examined in four Minnesota streams ranging from the main-stem Mississippi River to small tributaries in the basin. Filtered phase concentrations of methylmercury (MeHg), inorganic Hg (IHg), and dissolved organic carbon (DOC) were higher in all streams during a major summertime runoff event, and DOC was enriched with MeHg but not with IHg. Particulate-phase MeHg and IHg concentrations generally increased with total suspended solids (TSS) concentrations but the event data did not diverge greatly from the non-event data, suggesting that sources of suspended sediments in these streams did not vary significantly between event and non-event samplings. The dissolved fractions (filtered concentration/unfiltered concentration) of both MeHg and IHg increased with increasing DOC concentrations, but varied inversely with TSS concentrations. While MeHg typically constitutes only a minor portion of the total Hg (THg) in these streams, this contribution is not constant and can vary greatly over time in response to watershed inputs.
Mercury in fish from northeastern Minnesota lakes: Historical trends, environmental correlates, and potential sources
Journal of the Minnesota Academy of Science;( …, 1989
Description/Abstract High mercury concentrations in fish of some Minnesota lakes and rivers were ... more Description/Abstract High mercury concentrations in fish of some Minnesota lakes and rivers were first noted in 1971. Major anthropogenic sources of mercury to Minnesota rivers generally have been identified and controlled, but it has been difficult to identify mercury ...