Metropolitan Council Environmental Services

Saint Paul, MN, United States

Metropolitan Council Environmental Services

Saint Paul, MN, United States
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Engstrom D.R.,St. Croix Research | Fitzgerald W.F.,University of Connecticut | Cooke C.A.,Yale University | Lamborg C.H.,Woods Hole Oceanographic Institution | And 4 more authors.
Environmental Science and Technology | Year: 2014

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 measurements of Hg in the deep ocean, these archives indicate that atmospheric Hg emissions from early mining were modest as compared to more recent industrial-era emissions. Although large quantities of Hg were used to extract New World gold and silver beginning in the 16th century, a reevaluation of historical metallurgical methods indicates that most of the Hg employed was not volatilized, but rather was immobilized in mining waste. © 2014 American Chemical Society.

Coleman Wasik J.K.,University of Wisconsin - River Falls | Engstrom D.R.,St. Croix Research | Mitchell C.P.J.,University of Toronto | Swain E.B.,Minnesota Pollution Control Agency | And 6 more authors.
Journal of Geophysical Research G: Biogeosciences | Year: 2015

A series of severe droughts during the course of a long-term, atmospheric sulfate-deposition experiment in a boreal peatland in northern Minnesota created a unique opportunity to study how methylmercury (MeHg) production responds to drying and rewetting events in peatlands under variable levels of sulfate loading. Peat oxidation during extended dry periods mobilized sulfate, MeHg, and total mercury (HgT) to peatland pore waters during rewetting events. Pore water sulfate concentrations were inversely related to antecedent moisture conditions and proportional to past and current levels of atmospheric sulfate deposition. Severe drying events caused oxidative release of MeHg to pore waters and resulted in increased net MeHg production likely because available sulfate stimulated the activity of sulfate-reducing bacteria, an important group of Hg-methylating bacteria in peatlands. Rewetting events led to increased MeHg concentrations across the peatland, but concentrations were highest in peat receiving elevated atmospheric sulfate deposition. Dissolved HgT concentrations also increased in peatland pore waters following drought but were not affected by sulfate loading and did not appear to be directly controlled by dissolved organic carbon mobilization to peatland pore waters. Peatlands are often considered to be sinks for sulfate and HgT in the landscape and sources of MeHg. Hydrologic fluctuations not only serve to release previously sequestered sulfate and HgT from peatlands but may also increase the strength of peatlands as sources of MeHg to downstream aquatic systems, particularly in regions that have experienced elevated levels of atmospheric sulfate deposition. ©2015. American Geophysical Union. All Rights Reserved.

Novak P.J.,University of Minnesota | Arnold W.A.,University of Minnesota | Henningsgaard B.,Minnesota Pollution Control Agency | Hozalski R.M.,University of Minnesota | And 10 more authors.
Environmental Science and Technology | Year: 2015

Environmental, social/societal, and economic sustainability should be the ultimate goal of regulation, and this is more achievable if regulations are implemented in a flexible manner to allow for protection via a variety of technical and management approaches. Flexibility in regulation should also lead to the adoption of new technologies that provide corollary benefits such as energy efficiency, resource recovery, and ultimately, a move toward greater sustainability and a reduced human footprint on the Earth. © 2015 American Chemical Society.

Tsui M.T.K.,University of Minnesota | Finlay J.C.,University of Minnesota | Balogh S.J.,Metropolitan Council Environmental Services | Nollet Y.H.,Metropolitan Council Environmental Services
Environmental Science and Technology | Year: 2010

Natural stream ecosystems throughout the world are contaminated by methylmercury, a highly toxic compound that bioaccumulates and biomagnifies in aquatic food webs. Wetlands are widely recognized as hotspots for the production of methylmercury and are often assumed to be the main sources of this neurotoxin in downstream ecosystems. However, many streams lacking wetlands in their drainage basins (e.g., montane and semiarid regions in the western United States) have significant methylmercury contamination, and the sources of methylmercury in these streams remain largely unknown. In this study, we observed substantial production of methylmercury within a highly productive stream channel in northern California (South Fork Eel River) within a drainage basin lacking wetlands. We found that in situ methylmercury production is positively related to phosphorus removal and water temperature within the stream channel, supporting hypothesized biological mediation of in situ mercury transformation. Moreover, our data suggest that epiphytic microbial communities on a dominant filamentous alga (Cladophora glomerata) could play a role in in situ methylmercury production. Because peak in situ methylmercury production coincides with the period of the highest biological productivity during summer baseflow, methylmercury produced internally may be efficiently routed into local stream food webs. Our study provides strong evidence that stream channels, especially those associated with high primary productivity, can be important for regulating the bioavailability and toxicity of this global contaminant. © 2010 American Chemical Society.

Tsui M.T.-K.,University of North Carolina at Greensboro | Blum J.D.,University of Michigan | Finlay J.C.,University of Minnesota | Balogh S.J.,Metropolitan Council Environmental Services | And 3 more authors.
Environmental Science and Technology | Year: 2014

Mercury (Hg) is widely distributed in the environment, and its organic form, methylmercury (MeHg), can extensively bioaccumulate and biomagnify in aquatic and terrestrial food webs. Concentrations of MeHg in organisms are highly variable, and the sources in natural food webs are often not well understood. This study examined stable isotope ratios of MeHg (mass-dependent fractionation, as δ202HgMeHg; and mass-independent fractionation, as Δ199HgMeHg) in benthic invertebrates, juvenile steelhead trout (Oncorhynchus mykiss), and water striders (Gerris remigis) along a stream productivity gradient, as well as carnivorous terrestrial invertebrates, in a forested watershed at the headwater of South Fork Eel River in northern California. Throughout the sampling sites, δ202HgMeHg (after correction due to the effect of MeHg photodegradation) was significantly different between benthic (median = -1.40% range, -2.34 to -0.78% total number of samples = 29) and terrestrial invertebrates (median = +0.51% range, -0.37 to +1.40% total number of samples = 9), but no major difference between these two groups was found for Δ199HgMeHg. Steelhead trout (52 individual fishes) have MeHg of predominantly aquatic origins, with a few exceptions at the upstream locations (e.g., 1 fish collected in a tributary had a purely terrestrial MeHg source and 4 fishes had mixed aquatic and terrestrial MeHg sources). Water striders (seven pooled samples) derive MeHg largely from terrestrial sources throughout headwater sections. These data suggest that direct terrestrial subsidy (e.g., terrestrial invertebrates falling into water) can be important for some stream predators in headwater streams and could represent an important means of transfer of terrestrially derived MeHg (e.g., in situ methylation within forests, atmospheric sources) to aquatic ecosystems. Moreover, these findings show that terrestrial subsidies can enhance MeHg bioaccumulation of consumers in headwater streams where aqueous MeHg levels are very low. © 2014 American Chemical Society.

Blumentritt D.J.,University of Minnesota | Engstrom D.R.,St. Croix Research | Balogh S.J.,Metropolitan Council Environmental Services
Journal of Paleolimnology | Year: 2013

It can be advantageous to revisit coring locations in lakes years after an initial paleolimnological study is completed, to assess environmental changes in the intervening time interval. We revisited sediment core sites in Lake Pepin (Minnesota, Wisconsin) more than a decade after an original set of 10 cores was collected, dated radiometrically, and studied in 1996. Prominent magnetic susceptibility features were used to align the new core set with the older set, such that traditional radiometric dating was not necessary to obtain a chronology for the new cores. The procedure used to align the two core sets accounted for compaction of former surface sediments by burial with new sediment. The amount of new sediment, mercury, and phosphorus accumulated at each core site was determined and extrapolated to the depositional area of the lake to estimate recent (1996-2008) whole-basin loads. Recent sediment accumulation in Lake Pepin compared well (within 3%) with monitored inflow data from a gauging station on the upper Mississippi River just before it enters the lake. Bulk sediment accumulation rate remained very high (772,000 t/year) for the recent period (1996-2008), down slightly from the peak in 1990-1996 (876,000 t/year), and almost an order of magnitude above pre-settlement rates. Total phosphorus deposition remained constant since a peak in the 1960s, but was also well above pre-settlement rates. Mercury continued its precipitous decline since peaking in the 1960s. © 2013 Springer Science+Business Media Dordrecht.

Tsui M.T.K.,University of Michigan | Blum J.D.,University of Michigan | Finlay J.C.,University of Minnesota | Balogh S.J.,Metropolitan Council Environmental Services | And 2 more authors.
Limnology and Oceanography | Year: 2013

Photodegradation is an important sink for highly toxic methylmercury (MeHg) in aquatic ecosystems. Lakes have been extensively studied for MeHg photodegradation, but much less is known about streams, mainly because of the heterogeneity in sunlight availability along stream reaches and because there has been a lack of tools with which to integrate this longitudinal variability. We utilize odd-mass anomalies of stable Hg isotopes (i.e., Δ199Hg) as a proxy for estimating the relative extent of MeHg photodegradation in streams. In a northern California stream network, levels of MeHg in water and biota increased with increasing stream size in headwater and intermediate streams (drainage areas ranging from 0.6 to 150 km2), but MeHg levels decreased substantially in larger streams (drainage areas up to 1212 km2). In smaller streams, the increase of MeHg levels is attributed to increasing in situ MeHg production and is accompanied by only a small increase in Δ199Hg, indicating that the rate of MeHg photodegradation is low relative to the rate of in situ MeHg production. In larger streams, decreasing MeHg levels coincided with significant increases in Δ199Hg of MeHg (an average increase of 1.5% 6 0.5%, n 5 4), indicating that increasing MeHg photodegradation reduced MeHg levels in these wider, more open channels. Our findings clearly indicate that increasing sunlight availability in stream channels substantially increases MeHg photodegradation, which can reduce MeHg contamination in stream food webs. © 2013, by the Association for the Sciences of Limnology and Oceanography, Inc.

Tsui M.T.K.,University of Michigan | Blum J.D.,University of Michigan | Kwon S.Y.,University of Michigan | Finlay J.C.,University of Minnesota | And 2 more authors.
Environmental Science and Technology | Year: 2012

Nearly all ecosystems are contaminated with highly toxic methylmercury (MeHg), but the specific sources and pathways leading to the uptake of MeHg within and among food webs are not well understood. In this study, we report stable mercury (Hg) isotope compositions in food webs in a river and an adjacent forest in northern California and demonstrate the utility of Hg isotopes for studying MeHg sources and cross-habitat transfers. We observed large differences in both δ202Hg (mass-dependent fractionation) and Δ199Hg (mass-independent fractionation) within both food webs. The majority of isotopic variation within each food web could be accounted for by differing proportions of inorganic Hg [Hg(II)] and MeHg along food chains. We estimated mean isotope values of Hg(II) and MeHg in each habitat and found a large difference in δ202Hg between Hg(II) and MeHg (∼2.7‰) in the forest but not in the river (∼0.25‰). This is consistent with in situ Hg(II) methylation in the study river but suggests Hg(II) methylation may not be important in the forest. In fact, the similarity in δ202Hg between MeHg in forest food webs and Hg(II) in precipitation suggests that MeHg in forest food webs may be derived from atmospheric sources (e.g., rainfall, fog). Utilizing contrasting δ202Hg values between MeHg in river food webs (-1.0‰) and MeHg in forest food webs (+0.7‰), we estimate with a two-source mixing model that ∼55% of MeHg in two riparian spiders is derived from riverine sources while ∼45% of MeHg originates from terrestrial sources. Thus, stable Hg isotopes can provide new information on subtle differences in sources of MeHg and trace MeHg transfers within and among food webs in natural ecosystems. © 2012 American Chemical Society.

Alm R.,Metropolitan Council Environmental Services | Sealock A.W.,Metropolitan Council Environmental Services | Nollet Y.,Metropolitan Council Environmental Services | Sprouse G.,Metropolitan Council Environmental Services
Water Environment Research | Year: 2016

Metropolitan Council Environmental Services has observed poorer than expected dewatering performance at its Empire Plant. This plant has both anaerobic digestion and enhanced biological phosphorus removal in its treatment train. A research program using pilot-scale anaerobic digesters investigated potential solutions to the plant's poor dewaterability. The dewaterability goal was to increase the cake solids from 12% total solids (TS) to 16% TS or higher. This research investigated 20 different reactor conditions including chemical, feed sludge, and digested sludge treatments. At the pilot scale, unaerated storage of waste activated sludge prior to thickening and addition of ferric chloride to digestion was found to achieve dewatered cake solids of nearly 17% TS with the added benefit of reducing polymer demand. Issues including the amount of chemical required and the resulting volatile solids destruction influence the viability of the process change, so a full-scale pilot and financial analysis is recommended before making permanent process changes. © 2016, Water Environment Federation. All rights reserved.

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