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Lofton D.D.,LimnoTech. | Whalen S.C.,University of North Carolina at Chapel Hill | Hershey A.E.,University of North Carolina at Greensboro
Polar Biology | Year: 2015

Methanogenesis (MG) occurs in anaerobic lake sediments during the terminal step of organic matter degradation. Methane is typically produced via two primary catabolic pathways (acetoclastic or hydrogenotrophic) in which the primary substrates are acetate or H2/CO2, respectively. The acetoclastic pathway has been shown to dominate in a 2:1 ratio over the hydrogenotrophic pathway in freshwater sediments. Rates of methane production from each pathway are regulated primarily by the quantity and quality of organic matter. As acetate and H2 are produced through decomposition of organic matter, increased terrestrially derived organic matter loading can fuel sediment MG. Increased delivery of terrestrially derived organic matter to arctic lakes is expected under future climate change scenarios. Therefore, we compared unamended rates of MG in anaerobic sediment slurries to those amended with acetate or hydrogen. We also evaluated the vertical sediment distribution of MG pathways in 1-cm increments to a final depth of 5 cm using an inhibitor for the acetoclastic pathway, methyl fluoride. In both lakes, unamended rates of MG decreased with increasing sediment depth. Additions of acetate or hydrogen stimulated rates of MG at all depths in both lakes resulting in rates 1–3 orders of magnitude greater than MG rates in unamended slurries. The ratio of the acetoclastic to the hydrogenotrophic pathway decreased with increasing sediment depth in both lakes. Our findings suggest that increased delivery of terrestrial organic matter to shallow arctic lakes may increase sediment methane production. © 2015, Springer-Verlag Berlin Heidelberg.

Buser A.M.,ETH Zurich | MacLeod M.,University of Stockholm | Scheringer M.,ETH Zurich | Mackay D.,Trent University | And 4 more authors.
Integrated Environmental Assessment and Management | Year: 2012

Multimedia mass balance models of chemical fate in the environment have been used for over 3 decades in a regulatory context to assist decision making. As these models become more comprehensive, reliable, and accepted, there is a need to recognize and adopt principles of Good Modeling Practice (GMP) to ensure that multimedia models are applied with transparency and adherence to accepted scientific principles.We propose and discuss 6 principles of GMP for applying existing multimedia models in a decision-making context, namely 1) specification of the goals of the model assessment, 2) specification of the model used, 3) specification of the input data, 4) specification of the output data, 5) conduct of a sensitivity and possibly also uncertainty analysis, and finally 6) specification of the limitations and limits of applicability of the analysis. These principles are justified and discussed with a view to enhancing the transparency and quality of model-based assessments. © 2012 SETAC.

Denkenberger J.S.,Syracuse University | Driscoll C.T.,Syracuse University | Branfireun B.A.,University of Western Ontario | Eckley C.S.,Environment Canada | And 2 more authors.
Environmental Pollution | Year: 2012

Rates of surface-air elemental mercury (Hg 0) fluxes in the literature were synthesized for the Great Lakes Basin (GLB). For the majority of surfaces, fluxes were net positive (evasion). Digital land-cover data were combined with representative evasion rates and used to estimate annual Hg 0 evasion for the GLB (7.7 Mg/yr). This value is less than our estimate of total Hg deposition to the area (15.9 Mg/yr), suggesting the GLB is a net sink for atmospheric Hg. The greatest contributors to annual evasion for the basin are agricultural (∼55%) and forest (∼25%) land cover types, and the open water of the Great Lakes (∼15%). Areal evasion rates were similar across most land cover types (range: 7.0-21.0 μg/m 2-yr), with higher rates associated with urban (12.6 μg/m 2-yr) and agricultural (21.0 μg/m 2-yr) lands. Uncertainty in these estimates could be partially remedied through a unified methodological approach to estimating Hg 0 fluxes. © 2011 Elsevier Ltd. All rights reserved.

Lofton D.D.,LimnoTech. | Whalen S.C.,University of North Carolina at Chapel Hill | Hershey A.E.,University of North Carolina at Greensboro
Hydrobiologia | Year: 2014

Large uncertainties exist regarding the influence of ongoing climate change to microbially mediated methane cycling in arctic lakes. Specifically, the coupled response of methanogenesis (MG) and methane oxidation (Mox) to increased temperature is poorly understood. Therefore, the effect of temperature on rates of sediment MG and water column Mox in two shallow Arctic Alaskan lakes were evaluated in 2010. To understand the capacity of Mox to offset potential increases in dissolved methane concentrations, kinetics of water column Mox were also determined. Rates of MG responded positively to increased temperature with a greater influence exerted at higher incubation temperatures. Substrate-saturated Mox significantly increased with temperature and was controlled by substrate and temperature interactions. In contrast, substrate-limited Mox was not influenced by temperature and was controlled by substrate supply. Analysis of Mox kinetics pointed to a community of water column dwelling methane oxidizing bacteria that are capable of oxidizing dissolved methane concentrations far in excess of observed levels. Assuming no diffusion limitation, our results suggest that Mox will likely offset increased MG in response to elevated temperature regimes as a function of ongoing climate change. © 2013 Springer Science+Business Media Dordrecht.

News Article
Site: www.biosciencetechnology.com

Some of the world's biggest temperature jumps are happening in lakes - an ominous sign that suggests problems such as harmful algae blooms and low-oxygen zones hazardous to fish will get worse, says a newly released scientific report. An analysis of 235 lakes that together hold more than half the earth's fresh surface water found they have warmed an average of 0.61 degrees Fahrenheit or 0.34 degrees Celsius per decade, the report said. While seemingly insignificant, the increase is bigger than those recorded in the oceans or the atmosphere. Such rapid swings can affect aquatic ecosystems in profound ways, raising concerns about the quality of waters that people rely on for drinking supplies, crop irrigation and energy production. "The message we're getting from our lakes is that they're getting more and more stressed," Catherine O'Reilly, an Illinois State University geologist who led the study, said Thursday. "With these rates of warming, the problems we're seeing will become increasingly common." Dozens of scientists in six continents took part in the project, funded partly by NASA and the National Science Foundation. The results, made public this week during a meeting of the American Geophysical Union in San Francisco, were based on a first-of-its-kind combination of temperature data from satellites and ground measurements over 25 years. They are being published in the group's journal, Geophysical Research Letters. Lakes warming at the average worldwide rate or higher were widespread, including the Dead Sea, Lake Tahoe, Lake Baikal in Siberia and Lake Fracksjon in Sweden. But deep lakes in cold regions had the most rapid changes, said John Lenters of LimnoTech, a water science consulting firm in Ann Arbor, Michigan. They included four of the five U.S. Great Lakes - Superior, Huron, Michigan and Ontario. Only Lake Erie, the shallowest and warmest of the Great Lakes, was below average. Superior, the deepest and coldest, warmed three times faster than the global average. In addition to rising air temperatures, factors causing lakes to warm vary among regions, scientists said. The Great Lakes and others in northern climates are losing winter ice earlier, and some areas are getting less cloud cover, exposing their surfaces to more sunlight. Algae blooms flourish in warmer waters. The report predicted a 20 percent boost in lake algae over the next century, including a 5 percent increase in blooms that are toxic to fish and animals. An outbreak of toxic algae left more than 400,000 residents of Toledo, Ohio, and southeastern Michigan without usable tap water for two days in August 2014. Such an increase would expand "dead zones" with so little oxygen that fish cannot survive, O'Reilly said. It also would boost emissions of methane, a greenhouse gas even more potent than carbon dioxide, the leading cause of climate change. Warming causes a different problem for some lakes. In eastern Africa, Lake Tanganyika is less able to blend warm water near the surface with colder layers farther down, reducing distribution of nutrients for algae on which fish feed. Donald Uzarski, director of the Institute for Great Lakes Research at Central Michigan University, who was not involved with the study, said its findings were consistent with other water temperature measurements in places such as the Great Lakes and Poyang Lake in China. Other likely results of warmer lakes, he said, include lower lake levels, damaged coastal wetlands and exotic species invasions. "What seems to be nothing more than a small change in water temperature produces a domino effect that drastically impacts the ecosystem," Uzarski said.

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