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Xue P.,Michigan Technological University | Pal J.S.,Loyola Marymount University | Ye X.,Michigan Technological University | Lenters J.D.,LimnoTech | And 3 more authors.
Journal of Climate | Year: 2017

Accurate representations of lake-ice-atmosphere interactions in regional climatemodeling remain one of themost critical and unresolved issues for understanding large-lake ecosystems and their watersheds. To date, the representation of theGreat Lakes two-way interactions in regional climatemodels is achieved with one-dimensional (1D) lake models applied at the atmospheric model lake grid points distributed spatially across a 2D domain. While some progress has beenmade in refining 1D lake model processes, such models are fundamentally incapable of realistically resolving a number of physical processes in the Great Lakes. In this study, a two-way coupled 3D lake-ice-climate modeling system [Great Lakes-Atmosphere Regional Model (GLARM)] is developed to improve the simulation of large lakes in regional climate models and accurately resolve the hydroclimatic interactions. Model results are compared to a wide variety of observational data and demonstrate the unique skill of the coupled 3D modeling system in reproducing trends and variability in the Great Lakes regional climate, as well as in capturing the physical characteristics of the Great Lakes by fully resolving the lake hydrodynamics. Simulations of the climatology and spatiotemporal variability of lake thermal structure and ice are significantly improved over previous coupled, 1D simulations. At seasonal and annual time scales, differences inmodel results are primarily observed for variables that are directly affected by lake surface temperature (e.g., evaporation, precipitation, sensible heat flux) while no significant differences are found in other atmospheric variables (e.g., solar radiation, cloud cover). Underlying physical mechanisms for the simulation improvements using GLARM are also discussed. © 2017 American Meteorological Society.

Szymczycha B.,Polish Academy of Sciences | Szymczycha B.,U.S. Geological Survey | Kroeger K.D.,U.S. Geological Survey | Crusius J.,U.S. Geological Survey | Bratton J.F.,LimnoTech
Water Research | Year: 2017

We investigated biogeochemical conditions and watershed features controlling the extent of nitrate removal through microbial dinitrogen (N2) production within the surficial glacial aquifer located on the north and south shores of Long Island, NY, USA. The extent of N2 production differs within portions of the aquifer, with greatest N2 production observed at the south shore of Long Island where the vadose zone is thinnest, while limited N2 production occurred under the thick vadose zones on the north shore. In areas with a shallow water table and thin vadose zone, low oxygen concentrations and sufficient DOC concentrations are conducive to N2 production. Results support the hypothesis that in aquifers without a significant supply of sediment-bound reducing potential, vadose zone thickness exerts an important control of the extent of N2 production. Since quantification of excess N2 relies on knowledge of equilibrium N2 concentration at recharge, calculated based on temperature at recharge, we further identify several features, such as land use and cover, seasonality of recharge, and climate change that should be considered to refine estimation of recharge temperature, its deviation from mean annual air temperature, and resulting deviation from expected equilibrium gas concentrations. © 2017 Elsevier Ltd

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.

Fakhraei H.,Syracuse University | Driscoll C.T.,Syracuse University | Selvendiran P.,LimnoTech | DePinto J.V.,LimnoTech | And 3 more authors.
Atmospheric Environment | Year: 2014

Acidic deposition has impaired acid-sensitive surface waters in the Adirondack region of New York by decreasing pH and acid neutralizing capacity (ANC). In spite of air quality programs over past decades, 128 lakes in the Adirondacks were classified as "impaired" under Section 303(d) of the Clean Water Act in 2010 due to elevated acidity. The biogeochemical model, PnET-BGC, was used to relate decreases in atmospheric sulfur (S) and nitrogen (N) deposition to changes in lake water chemistry. The model was calibrated and confirmed using observed soil and lake water chemistry data and then was applied to calculate the maximum atmospheric deposition that the impaired lakes can receive while still achieving ANC targets. Two targets of ANC were used to characterize the recovery of acid-impaired lakes: 11 and 20μeqL-1. Of the 128 acid-impaired lakes, 97 currently have ANC values below the target value of 20μeqL-1 and 83 are below 11μeqL-1. This study indicates that a moderate control scenario (i.e., 60% decrease from the current atmospheric S load) is projected to recover the ANC of lakes at a mean rate of 0.18 and 0.05μeqL-1yr-1 during the periods 2022-2050 and 2050-2200, respectively. The total maximum daily load (TMDL) of acidity corresponding to this moderate control scenario was estimated to be 7.9meqSm-2yr-1 which includes a 10% margin of safety. © 2014 Elsevier Ltd.

Kaur J.,CH2M HILL | DePinto J.V.,LimnoTech | Atkinson J.F.,State University of New York at Buffalo | Verhamme E.,LimnoTech | Young T.C.,Clarkson University
Journal of Great Lakes Research | Year: 2012

A linked hydrodynamic-hydrophobic organic chemical mass balance and food chain bioaccumulation model, LOTOX2, was developed to support the Lake Ontario Lakewide Management Plan (LaMP) for establishing contaminant load reduction strategies. This paper describes the development of LOTOX2, including the linkage with a relatively finer-scale hydrodynamic model (the Princeton Ocean Model, POM). An important component of this development was the reconstruction of PCB loading history (1930-2005), which was used to understand historic trends and to conduct model calibration/confirmation for total PCBs (tPCBs) in the lake water, sediments, and adult lake trout using data for the last 25years. A separate mass balance was conducted for the radioisotope cesium-137 (137Cs) in order to develop a sorbent mass balance model for the system. Following calibration and confirmation, a diagnostic application of the model showed that the lake is not yet at steady-state with current loads. It will take more than 50years for tPCB concentration in lake trout to decrease to a steady-state value of about 0.4ppm if year 2005 loads remain constant. If all external loads were instantaneously eliminated in 2005, it would take approximately 40years for the adult lake trout tPCB concentration to reach 0.05ppm (the uniform Great Lakes protocol value for unrestricted consumption) from its current level of 0.74ppm. © 2012 Elsevier B.V..

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.

Van Cleave K.,University of Nebraska - Lincoln | Lenters J.D.,LimnoTech | Wang J.,National Oceanic and Atmospheric Administration | Verhamme E.M.,LimnoTech
Limnology and Oceanography | Year: 2014

Significant trends in Lake Superior water temperature and ice cover have been observed in recent decades, and these trends have typically been analyzed using standard linear regression techniques. Although the linear trends are statistically significant and contribute to an understanding of environmental change, a careful examination of the trends shows important nonlinearities. We identify a pronounced step change that occurred in Lake Superior following the warm El Niño winter of 1997–1998, resulting in a ‘‘regime shift’’ in summer evaporation rate, water temperature, and numerous metrics of winter ice cover. This statistically significant step change accounts for most of the long-term trends in ice cover, water temperature, and evaporation during the period 1973–2010, and it was preceded (and followed) by insignificant linear trends in nearly all of the metrics examined. The 1998 step change is associated with a decrease in winter ice duration of 39 d (a 34% decline), an increase of, 2–3uC in mean surface water temperature (July–September averages), and a 91% increase in July–August evaporation rates, reflecting an earlier start to the summer evaporation season. Maximum wintertime ice extent decreased by nearly a factor of two, from an average of 69% of the lake surface area (before 1997–1998) to 36% after the step change. This reassessment of long-term trends highlights the importance of nonlinear regime shifts such as the 1997–1998 break point—an event that may be related to a similar shift in the Pacific Decadal Oscillation that occurred around the same time. These pronounced changes in Lake Superior physical characteristics are likely to have important implications for the broader lake ecosystem. © 2014, by the Association for the Sciences of Limnology and Oceanography, Inc.

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.

Larson W.M.,LimnoTech | Freedman P.L.,LimnoTech | Passinsky V.,University of Michigan | Grubb E.,University of Michigan | Adriaens P.,University of Michigan
Water Alternatives | Year: 2012

A decision framework for business water-risk response is proposed that considers financial instruments and supply management strategies. Based on available and emergent programmes, companies in the agricultural, commodities, and energy sectors may choose to hedge against financial risks by purchasing futures contracts or insurance products. These strategies address financial impacts such as revenue protection due to scarcity and disruption of direct operations or in the supply chain, but they do not directly serve to maintain available supplies to continue production. In contrast, companies can undertake actions in the watershed to enhance supply reliability and/or they can reduce demand to mitigate risk. Intermediate strategies such as purchasing of water rights or water trading involving financial transactions change the allocation of water but do not reduce overall watershed demand or increase water supply. The financial services industry is playing an increasingly important role, by considering how water risks impact decision making on corporate growth and market valuation, corporate creditworthiness, and bond rating. Risk assessment informed by Conditional Value-at-Risk (CVaR) measures is described, and the role of the financial services industry is characterised. A corporate decision framework is discussed in the context of water resources management strategies under complex uncertainties.

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