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Portland, ME, United States

Sackmann B.S.,Integral Consulting Inc. | Becker D.S.,719 2 Avenue
Marine Ecology Progress Series | Year: 2015

Haney et al. (2014a,b; Mar Ecol Prog Ser 513:225-237, 239-252) developed probability models to estimate seabird mortality from oil exposure during the Deepwater Horizon oil spill. Although frequently used to characterize avian mortality following oil spills, probability models often yield uncertain results when developed without spill- and/or region-specific data. Models based on observations of beached carcasses or exposure/mortality scenarios are sensitive to variations in assumptions and methods used to summarize data sets for model parameterization and validation. Here we present alternative parameter estimates derived from spill- and Gulf of Mexico (GoM)-specific data, and offer suggestions for reducing model uncertainty. As a primary example, we evaluate the carcass transport probability to shorelines using GoM-specific data collected in 2011 to show that Haney et al. underestimated this probability by more than an order of magnitude, thus inflating mortality estimates. © Integral Consulting Inc. 2015. Source

Jensen P.D.,Integral Consulting Inc. | Dively G.P.,University of Maryland University College | Swan C.M.,University of Maryland Baltimore County | Lamp W.O.,University of Maryland University College
Environmental Entomology | Year: 2010

Corn (Zea mays L.) transformed with a gene from the bacterium Bacillus thuringiensis (Bt) comprises 49% of all corn in the United States. The input of senesced corn tissue expressing the Bt gene may impact stream-inhabiting invertebrates that process plant debris, especially trichopteran species related to the target group of lepidopteran pests. Our goal was to assess risk associated with transgenic corn debris entering streams. First, we show the input of corn tissue after harvest was extended over months in a stream. Second, using laboratory bioassays based on European corn borer [Ostrinia nubilalis (Hbner)], we found no bioactivity of Cry1Ab protein in senesced corn tissue after 2 wk of exposure to terrestrial or aquatic environments. Third, we show that Bt near-isolines modify growth and survivorship of some species of invertebrates. Of the four nontarget invertebrate species fed Bt near-isolines, growth of two closely related trichopterans was not negatively affected, whereas a tipulid crane fly exhibited reduced growth rates, and an isopod exhibited reduced growth and survivorship on the Cry1Ab near-isoline but not on the stacked Cry1Ab + Cry3Bb1 near-isoline. Because of lack of evidence of bioactivity of Bt after 2 wk and because of lack of nontarget effects on the stacked near-isoline, we suggest that tissue-mediated differences, and not the presence of the Cry1Ab protein, caused the different responses among the species. Overall, our results provide evidence that adverse effects to aquatic nontarget shredders involve complex interactions arising from plant genetics and environment that cannot be ascribed to the presence of Cry1Ab proteins. © 2010 Entomological Society of America. Source

Ruby M.V.,Integral Consulting Inc. | Lowney Y.W.,Exponent, Inc.
Environmental Science and Technology | Year: 2012

Over the last 30 years, there has been extensive research designed to quantify the extent of oral bioavailability and bioaccessibility of organic and inorganic contaminants in soil. One aspect of this research is the soil particle size selected to represent environmental exposures, which may affect study results and comparability across studies. Different research groups have studied soil particle sizes ranging from <45 μm to <2000 μm. This article reviews the historical and technical considerations that pertain to the selection of an appropriate particle size fraction for evaluating the relative oral bioavailability of chemicals from soil, which include (1) how the resultant data will be used in human health risk assessment, (2) soil fractions historically used in oral bioavailability studies, (3) studies of soil adherence to human hands, (4) the distribution of contaminants in soils as a function of particle size, and (5) the effect of differential bioavailability as a function of soil particle size and geochemical matrix. These factors are first discussed from a general perspective, applicable to all contaminants in soil, and then more specifically for polycyclic aromatic hydrocarbons (PAHs) in soil. Based on this review, a specific soil particle size of <150 μm is recommended for future studies on the oral bioavailability and bioaccessibility of PAHs in soil. © 2012 American Chemical Society. Source

Kadish S.J.,Brown University | Kadish S.J.,Integral Consulting Inc. | Head J.W.,Brown University | Fastook J.L.,University of Maine, United States | Marchant D.R.,Boston University
Planetary and Space Science | Year: 2014

Fan-shaped deposits (FSDs) extending to the northwest of the Tharsis Montes on Mars are the remnants of Amazonian-aged, cold-based, tropical mountain glaciers. We use high-resolution images to perform new impact crater size-frequency distribution (CSFD) analyses on these deposits in an effort to constrain the timing and duration of ice accumulation at tropical latitudes on Mars. This analysis revises the current understanding of the chronology regarding the formation of the glaciers and of the ridged facies in the Arsia Mons deposit, a deposit interpreted to be formed from recessional cold-based drop moraines. We develop a conceptual model that illustrates the effect of moving glacial ice on superposed impact craters of various sizes, including the buffering of underlying geologic units from impacts caused by the presence of the ice for extended periods of time, and the interpretation of crater retention ages of the subsequent glacial deposits following the periods of active glaciation. The new CSFD analyses establish best-fit crater retention ages for each entire Tharsis Montes FSD; these are ~220 Ma for the Ascraeus FSD at 8.35 S, ~125 Ma for the Pavonis FSD at 1.48 N, and ~210 Ma for the Arsia FSD at 11.92 N. Because the age for each deposit represents a combination of the stratigraphically older ridged facies and the younger knobby and smooth facies, the crater retention ages are most likely to represent dates subsequent to the onset of glaciation and prior to its final cessation. Estimates of the time necessary to build the deposits using net accumulation rates from atmospheric general circulation models and emplacement rates from glacial flow models suggest durations of ~45-150 Ma, depending on the specific obliquity history. These surface crater retention ages and related age estimates require that massive volumes of ice (on the order of 105 km3) were emplaced at tropical latitudes on Mars during the Middle to Late Amazonian. Additionally, we determined CSFD ages of three adjacent drop moraine units at Arsia Mons (725 Ma, 475 Ma and 345 Ma) and used these to calculate the average amount of time needed to form one of the approximately 185 drop moraines forming these deposits; we found that a typical drop moraine formation time in the Arsia FSD ridged facies to be on the order of ~106 years. These formation ages are considerably longer than that required for typical moraine systems alongside dynamic, wet-based glaciers on Earth, but are in approximate accord with recent geomorphological and geochemical data that document long-term, ice-margin stability for several cold-based glaciers in interior Antarctica. The difference in the ages of the ridged facies and non-ridged portion of the Arsia FSD suggests that the tropical mountain glaciers may have been emplaced over a period spanning many hundreds of millions of years. CSFD measurements for lava flows predating and postdating the Arsia Mons FSD suggest a maximum possible age of <750 Ma and a minimum age for the late stage, post FSD lava flows of ~105 Ma. Taken together, this evidence supports a scenario in which ice has been present and stable in substantial quantities (~10 5-106 km3) at tropical latitudes during extended periods of the Middle to Late Amazonian history of Mars. This implies that during this time, Mars sustained periods of spin-axis obliquity in the vicinity of 45, during which time polar ice deposits were substantially reduced in volume or perhaps even absent. © 2013 Elsevier Ltd. Source

Kadish S.J.,Brown University | Kadish S.J.,Integral Consulting Inc. | Head J.W.,Brown University
Planetary and Space Science | Year: 2014

There is significant geomorphologic evidence for the past presence of longitudinally widespread, latitudinally zoned deposits composed of ice-rich material at the northern and southern mid latitudes on Mars (lobate debris aprons, lineated valley fill, concentric crater fill, pedestal craters, etc.). Among these features, pedestal craters (Pd) are impact craters interpreted to have produced a protective layer on top of decameters-thick ice deposits now missing in intercrater regions. The time during which these various deposits were present is still highly debated. To address this question we have analyzed the distribution and characteristics of pedestal craters; here, we use a population of 2287 pedestal craters (Pd) to derive a crater retention age for the entire population, obtaining a minimum timescale of formation of ~90 Myr. Given that the ice-rich deposit has not been continuously present for this duration, the timescale of formation is necessarily longer than ~100 Myr. We then compiled impact crater size-frequency distribution dates for 50 individual pedestal craters in both hemispheres to further assess the frequency distribution of individual ages. We calculated pedestal crater ages that ranged from ~1 Myr to ~3.6 Gyr, with a median of ~140 Myr. In addition, 70% of the pedestal ages are less than 250 Myr. During the 150 Myr period between 25 Ma and 175 Ma, we found at least one pedestal age every 15 Myr. This suggests that the ice-rich paleodeposit accumulated frequently during that time period. We then applied these results to the relationship between obliquity and latitudinal ice stability to suggest some constraints on the obliquity history of Mars over the past 200 Myr. Atmospheric general circulation models indicate that ice stability over long periods in the mid latitudes is favored by moderate mean obliquities in the ~35 range. Models of spin-axis/orbital parameter evolution predict that the average obliquity of Mars is ~38. Our data represent specific observational evidence that ice-rich deposits accumulated frequently during the past 200 Myr, supporting the prediction that Mars was characterized by this obliquity range during an extensive part of that time period. Using these results as a foundation, the dating of other non-polar ice deposits will permit the specific obliquity history to be derived and lead to an assessment of volatile transport paths in the climate history of Mars. © 2013 Elsevier Ltd. Source

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