68 research outputs found
Evaluation of chemical assays for determining hydroperoxides levels in oxidized lipids
No full textThis thesis re-evaluated current analyses for hydroperoxides, the first stable product of lipid oxidation. The objective was to compare linearity of response, accuracy, limits of detection, active concentration range, reproducibility, and required conditions and handling for six commonly-used hydroperoxide assays, using cumene (lipid-soluble) and tert-butyl (water-soluble) hydroperoxides as test standards; optimized procedures were then applied to oxidized methyl linoleate. Traditional iodometric titration method with thiosulfate is the most accurate assay chemically. It is stoichiometric, linear, and useful for high peroxide concentrations, but unclear endpoints limits sensitivity and many handling issues must be controlled to provide reproducible results. It is the only method providing absolute quantitation of hydroperoxides. PeroxySafeTM and PeroxoQuantTM commercial kits based on the xylenol orange assay detected nanomoles of hydroperoxides, but samples with more than trace levels of hydroperoxides (the usual case with foods) must be diluted extensively before analysis. Variation of reaction response varied with hydroperoxide structure is a major disadvantage for this assay, and the Fe3+-xylenol orange complex was readily bleached by excess hydroperoxide, thus reducing apparent hydroperoxide levels. Reaction stoichiometry cannot be determined due to proprietary reagents of unspecified concentration. The ferric thiocyanate method (chemical reaction or Cayman LPOTM kit) is extremely sensitive, detecting as low as 5 nanomoles, but the reaction stoichiometry varies with solvent and hydroperoxide structure and concentration. Fe3+-SCN complexes bleached at high hydroperoxide concentrations, causing underestimation of peroxide values. Extensive dilution of samples is thus required for analyses of lipid extracts from most foods. Due to these complications, xylenol orange and Fe3+-thiocyanate assays may be useful for monitoring changes of single materials over time or comparing extracts with comparable fatty acid composition, but they cannot determine absolute hydroperoxide concentrations. No optical assay tested matched peroxide values determined by iodometric assay. Finally, hydroperoxides oxidize triphenylphosphine selectively and stoichiometrically to triphenylphosphine oxide that can be detected and quantitated by HPLC, detecting as low as 5 picomoles of hydroperoxide. The reaction has promise, but needs further investigation before adoption. Results for all methods highlight the importance of excluding oxygen during the assays and understanding the correct concentration range for each assay.M.S.Includes bibliographical referencesby Elah Tamar Steltze
pgbrodrick/conifer_modeling: v1.0.0
No full textThis release represents the code used in the final version of the manuscript:
K. Dana Chadwick, Philip Brodrick, Kathleen Grant, Tristan Goulden, Amanda Henderson, Nicola Falco, Haruko Wainwright, Kenneth H. Williams, Markus Bill, Ian Breckheimer, Eoin L. Brodie, Heidi Steltzer, C. F. Rick Williams, Benjamin Blonder, Jiancong Chen, Baptiste Dafflon, Joan Damerow, Matt Hancher, Aizah Khurram, Jack Lamb, Corey Lawrence, Maeve McCormick. John Musinsky, Samuel Pierce, Alexander Polussa, Maceo Hastings Porro, Andea Scott, Hans Wu Singh, Patrick O. Sorensen, Charuleka Varadharajan, Bizuayehu Whitney, Katharine Maher. Integrating airborne remote sensing and field campaigns for ecology and Earth system science. Methods in Ecology and Evolution, 2020. doi: 10.1111/2041-210X.13463
kdchadwick/east_river_trait_modeling: v1.0.0
No full textThis release represents the code used in the final version of the manuscript:
K. Dana Chadwick, Philip Brodrick, Kathleen Grant, Tristan Goulden, Amanda Henderson, Nicola Falco, Haruko Wainwright, Kenneth H. Williams, Markus Bill, Ian Breckheimer, Eoin L. Brodie, Heidi Steltzer, C. F. Rick Williams, Benjamin Blonder, Jiancong Chen, Baptiste Dafflon, Joan Damerow, Matt Hancher, Aizah Khurram, Jack Lamb, Corey Lawrence, Maeve McCormick. John Musinsky, Samuel Pierce, Alexander Polussa, Maceo Hastings Porro, Andea Scott, Hans Wu Singh, Patrick O. Sorensen, Charuleka Varadharajan, Bizuayehu Whitney, Katharine Maher. Integrating airborne remote sensing and field campaigns for ecology and Earth system science. Methods in Ecology and Evolution, 2020
pgbrodrick/shade-ray-trace: v1.0.0
No full textThis release represents the code used in the final version of the manuscript:
K. Dana Chadwick, Philip Brodrick, Kathleen Grant, Tristan Goulden, Amanda Henderson, Nicola Falco, Haruko Wainwright, Kenneth H. Williams, Markus Bill, Ian Breckheimer, Eoin L. Brodie, Heidi Steltzer, C. F. Rick Williams, Benjamin Blonder, Jiancong Chen, Baptiste Dafflon, Joan Damerow, Matt Hancher, Aizah Khurram, Jack Lamb, Corey Lawrence, Maeve McCormick. John Musinsky, Samuel Pierce, Alexander Polussa, Maceo Hastings Porro, Andea Scott, Hans Wu Singh, Patrick O. Sorensen, Charuleka Varadharajan, Bizuayehu Whitney, Katharine Maher. Integrating airborne remote sensing and field campaigns for ecology and Earth system science. Methods in Ecology and Evolution, 2020
pgbrodrick/acorn_atmospheric_correction: v1.0.0
No full textThis release represents the code used in the final version of the manuscript:
K. Dana Chadwick, Philip Brodrick, Kathleen Grant, Tristan Goulden, Amanda Henderson, Nicola Falco, Haruko Wainwright, Kenneth H. Williams, Markus Bill, Ian Breckheimer, Eoin L. Brodie, Heidi Steltzer, C. F. Rick Williams, Benjamin Blonder, Jiancong Chen, Baptiste Dafflon, Joan Damerow, Matt Hancher, Aizah Khurram, Jack Lamb, Corey Lawrence, Maeve McCormick. John Musinsky, Samuel Pierce, Alexander Polussa, Maceo Hastings Porro, Andea Scott, Hans Wu Singh, Patrick O. Sorensen, Charuleka Varadharajan, Bizuayehu Whitney, Katharine Maher. Integrating airborne remote sensing and field campaigns for ecology and Earth system science. Methods in Ecology and Evolution, 2020
Earth and Water: Landcover and River Health on the Missouri River
No full textThe Missouri River Research Endeavor (MRRE ‘mɜr i’) set out to conduct an empirical study of the Missouri River. Our team canoed from the official headwaters near Three Forks, MT to the confluence with the Mississippi River in Saint Louis, MO. The MRRE sought greater understanding of the river, its health, and how human practices on and near the river affect it. Dams, nutrients, and pollution can have dramatic impacts on rivers. The river was broken up into twelve reaches because of the effects of damming. Reaches were defined as a length of river from headwaters to the first dam, between dams, and from the final dam to confluence with the Mississippi River. At three sites per reach water was sampled at 1 m depth and analyzed in the field. From these samples seston was collected by filtration, while pH, total dissolved solids, conductivity, salinity, dissolved oxygen, nitrate (NO3-), nitrite (NO2-), phosphate (PO4-) were measure from the filtrate. The seston samples were combusted to determine organic mass. Land cover was determined within 50 km of the river and its reservoirs using the USGS National GAP Land Cover dataset. Most phosphate measurements were outside 2.75 mgL-1 range of the colorimeter used, but the few low sites suggest a relationship between phosphate, conserved lands, and impoundment deltas. Nitrate levels showed no significant pattern and , while nitrite levels were within natural back ground levels. River modification, in the form of damming and channelization, severely reduce sediment load in the river and is disruptive to native riparian areas. Within 50 km of the river, 35% of the land is cropland and is the largest contributor of excess nutrients to the river system
Lepidoptera Larvae as an Indicator of Multi-Trophic Level Responses to Changing Seasonality in an Arctic Tundra Ecosystem
No full textEarlier snowmelt and warming temperatures in the Arctic will impact multiple trophic levels through the timing and availability of food resources. Lepidoptera are a vital link within the ecosystem; their roles include pollinator, parasitized host for other pollinating insects, and essential food source for migrating birds and their fledglings. Multiple environmental cues including temperature trigger the emergence of Lepidoptera. In response to changes in seasonality, including earlier snowmelt and warming, we expect caterpillar abundance to increase. We determined the abundance of caterpillar larvae in relation to the timing of snowmelt through two approaches: 1) a climate change experiment in which we accelerated snowmelt by 15 days through the use of radiation-absorbing fabric and warmed air and soil temperatures using open-top chambers, individually and in combination and 2) an observational 50 km transect study with 4 sites that naturally vary in the timing of snowmelt. Caterpillar abundance was determined by pitfall traps in all study plots, and we also did visual searches for caterpillars in the climate change experiment. In the climate change experiment, observations began one to three weeks after snowmelt. In the observational study, observations began prior to when study sites were completely snowfree. We characterized caterpillars by skin type (hairy, spiked, or smooth). The animals were examined for braconid wasp and tachinid fly parasites.
Where snowmelt was experimentally accelerated and temperatures were warmed, caterpillar abundance was greatest and more were seen earlier in June. Within the transect study, we observed two seasonal peaks in caterpillar abundance. One occurs within two weeks of snowmelt and one occurs four to six weeks following snowmelt at all four sites. In both studies, we found that caterpillars found soon after snowmelt were hairy or spiky, and smooth skinned caterpillars were most abundant later in the season. Proportion of parasitism was up to 54% of the observed animals and was greatest for caterpillars observed visually in the climate change experiment compared to those observed in pitfall traps in the experiment and across the transect. An earlier, warmer Arctic summer will alter the timing of Lepidoptera and pollinator-dependent life cycles, which could then affect food availability for migrating birds and their offspring
Diverse values, philosophies and ideas beget innovation and resilience in ecology and for our world
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