Simultaneous spectrophotometric determination of chromium(VI) and iron (III) by H-point standard addition method

In this work the possibility of simultaneous spectrophotometric determination of chromium (VI) and iron (III) in alloys with help of the mixed organic reagent (diphenylcarbazide and 1,10-phenanthroline) is studied. We have applied Н-point standard addition method to determine concentrations of chromium (VI) and iron (III) from the mixture. The pure signals of complexes of chromium (VI) with diphenylcarbazide and iron (III) with the 1,10-phenanthroline and their calibration plots are previously carried out. We established the possibility of simultaneous determination of chromium (VI) and iron (III) in the different concentration ranges by Н-point standard addition method. Correctness of determination of concentration by means of the offered technique is proved by "added-found" method for a series of mixtures with different ratios of concentration of chromium (VI) and iron (III). It is founded that the error of determination of concentration doesn't exceed 33 %.

Simultaneous spectrophotometric determination of chromium (VI) and iron (III) in alloys

In this work the possibility of simultaneous spectrophotometric determination of chromium (VI) and iron (III) in alloys with help of the mixed organic reagents (diphenylcarbazide and 1,10-phenanthroline, diphenylcarbazide and sulphosalicylic acid) is studied. We have applied curve fitting method to separate individual signals of chromium (VI) and iron (III) from overlapped absorption spectrum. Peak shape analysis of pure signals of complexes of chromium (VI) with diphenylcarbazide and iron (III) with the 1,10-phenanthroline and sulphosalicylic acid is previously carried out. For adequate application of curve fitting method we chose the optimal empirical models of signals taking into account preliminary information on their shape. Correctness of determination of concentration by means of the offered technique is proved by "added-found" method for a series of mixtures with different ratios of concentration of chromium (VI) and iron (III). It is founded that the error of determination of concentration doesn't exceed 11%

Flux and Seasonality of Dissolved Organic Matter From the Northern Dvina (Severnaya Dvina) River, Russia

Pan‐Arctic riverine dissolved organic carbon (DOC) fluxes represent a major transfer of carbon from land‐to‐ocean, and past scaling estimates have been predominantly derived from the six major Arctic rivers. However, smaller watersheds are constrained to northern high‐latitude regions and, particularly with respect to the Eurasian Arctic, have received little attention. In this study, we evaluated the concentration of DOC and composition of dissolved organic matter (DOM) via optical parameters, biomarkers (lignin phenols), and ultrahigh resolution mass spectrometry in the Northern Dvina River (a midsized high‐latitude constrained river). Elevated DOC, lignin concentrations, and aromatic DOM indicators were observed throughout the year in comparison to the major Arctic rivers with seasonality exhibiting a clear spring freshet and also some years a secondary pulse in the autumn concurrent with the onset of freezing. Chromophoric DOM absorbance at a350 was strongly correlated to DOC and lignin across the hydrograph; however, the relationships did not fit previous models derived from the six major Arctic rivers. Updated DOC and lignin fluxes were derived for the pan‐Arctic watershed by scaling from the Northern Dvina resulting in increased DOC and lignin fluxes (50 Tg yr−1 and 216 Gg yr−1, respectively) compared to past estimates. This leads to a reduction in the residence time for terrestrial carbon in the Arctic Ocean (0.5 to 1.8 years). These findings suggest that constrained northern high‐latitude rivers are underrepresented in models of fluxes based from the six largest Arctic rivers with important ramifications for the export and fate of terrestrial carbon in the Arctic Ocean

Seasonal hydrology drives rapid shifts in the flux and composition of dissolved and particulate organic carbon and major and trace ions in the Fraser River, Canada

© The Author(s), 2015. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Biogeosciences 12 (2015): 5597-5618, doi:10.5194/bg-12-5597-2015.Rapid changes in the volume and sources of discharge during the spring freshet lead to pronounced variations in biogeochemical properties in snowmelt-dominated river basins. We used daily sampling during the onset of the freshet in the Fraser River (southwestern Canada) in 2013 to identify rapid changes in the flux and composition of dissolved material, with a focus on dissolved organic matter (DOM). Previous time series sampling (at twice monthly frequency) of dissolved inorganic species in the Fraser River has revealed smooth seasonal transitions in concentrations of major ions and tracers of water and dissolved load sources between freshet and base flow periods. In contrast, daily sampling reveals a significant increase in dissolved organic carbon (DOC) concentration (200 to 550 μmol L−1) occurring over a matter of days, accompanied by a shift in DOM optical properties, indicating a transition towards higher molecular weight, more aromatic DOM composition. Comparable changes in DOM composition, but not concentration, occur at other times of year, underscoring the role of seasonal climatology in DOM cycling. A smaller data set of total and dissolved Hg concentrations also showed variability during the spring freshet period, although dissolved Hg dynamics appear to be driven by factors beyond DOM as characterized here. The time series records of DOC and particulate organic carbon (POC) concentrations indicate that the Fraser River exports 0.25–0.35 % of its annual basin net primary productivity. The snowmelt-dominated hydrology, forested land cover, and minimal reservoir impoundment of the Fraser River may influence the DOC yield of the basin, which is high relative to the nearby Columbia River and of similar magnitude to that of the Yukon River to the north. Anticipated warming and decreased snowfall due to climate changes in the region may cause an overall decrease in DOM flux from the Fraser River to the coastal ocean in coming decadesThis work was partially supported by a WHOI Ocean Ventures Fund award to BMV and NSF grants EAR-1226818 to BPE, OCE-0851015 to TIE, BPE, and VG, and OCE-0851101 to RGMS, and support to BPE from Jane and James Orr

High biolability of ancient permafrost carbon upon thaw

Ongoing climate warming in the Arctic will thaw permafrost and remobilize substantial terrestrial organic carbon (OC) pools. Around a quarter of northern permafrost OC resides in Siberian Yedoma deposits, the oldest form of permafrost carbon. However, our understanding of the degradation and fate of this ancient OC in coastal and fluvial environments still remains rudimentary. Here, we show that ancient dissolved OC (DOC, &gt;21,000 (14)Cyears), the oldest DOC ever reported, is mobilized in stream waters draining Yedoma outcrops. Furthermore, this DOC is highly biolabile: 34 +/- 0.8% was lost during a 14 day incubation under dark, oxygenated conditions at ambient river temperatures. Mixtures of Yedoma stream DOC with mainstem river and ocean waters, mimicking in situ mixing processes, also showed high DOC losses (14 days; 17 +/- 0.8% to 33 +/- 1.0%). This suggests that this exceptionally old DOC is among the most biolabile DOC in any previously reported contemporary river or stream in the Arctic.</p

Seasonal and annual fluxes of nutrients and organic matter from large rivers to the Arctic Ocean and surrounding seas

Author Posting. © The Author(s), 2011. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Estuaries and Coasts 35 (2012): 369-382, doi:10.1007/s12237-011-9386-6.River inputs of nutrients and organic matter impact the biogeochemistry of arctic estuaries and the Arctic Ocean as a whole, yet there is considerable uncertainty about the magnitude of fluvial fluxes at the pan-arctic scale. Samples from the six largest arctic rivers, with a combined watershed area of 11.3 x 106 km2, have revealed strong seasonal variations in constituent concentrations and fluxes within rivers as well as large differences among the rivers. Specifically, we investigate fluxes of dissolved organic carbon, dissolved organic nitrogen, total dissolved phosphorus, dissolved inorganic nitrogen, nitrate, and silica. This is the first time that seasonal and annual constituent fluxes have been determined using consistent sampling and analytical methods at the pan arctic scale, and consequently provide the best available estimates for constituent flux from land to the Arctic Ocean and surrounding seas. Given the large inputs of river water to the relatively small Arctic Ocean, and the dramatic impacts that climate change is having in the Arctic, it is particularly urgent that we establish the contemporary river fluxes so that we will be able to detect future changes and evaluate the impact of the changes on the biogeochemistry of the receiving coastal and ocean systems.This work was supported by the National Science Foundation through grants OPP-0229302, OPP-0519840, OPP-0732522, and OPP-0732944. Additional support was provided by the U. S. Geological Survey (Yukon River) and the Department of Indian and Northern Affairs (Mackenzie River)

Anti-Apoptotic Protein Bcl-xL Expression in the Midbrain Raphe Region Is Sensitive to Stress and Glucocorticoids.

Anti-apoptotic proteins are suggested to be important for the normal health of neurons and synapses as well as for resilience to stress. In order to determine whether stressful events may influence the expression of anti-apoptotic protein Bcl-xL in the midbrain and specifically in the midbrain serotonergic (5-HT) neurons involved in neurobehavioral responses to adverse stimuli, adult male rats were subjected to short-term or chronic forced swim stress. A short-term stress rapidly increased the midbrain bcl-xl mRNA levels and significantly elevated Bcl-xL immunoreactivity in the midbrain 5-HT cells. Stress-induced increase in glucocorticoid secretion was implicated in the observed effect. The levels of bcl-xl mRNA were decreased after stress when glucocorticoid elevation was inhibited by metyrapone (MET, 150 mg/kg), and this decrease was attenuated by glucocorticoid replacement with dexamethasone (DEX; 0.2 mg/kg). Both short-term stress and acute DEX administration, in parallel with Bcl-xL, caused a significant increase in tph2 mRNA levels and slightly enhanced tryptophan hydroxylase immunoreactivity in the midbrain. The increasing effect on the bcl-xl expression was specific to the short-term stress. Forced swim repeated daily for 2 weeks led to a decrease in bcl-xl mRNA in the midbrain without any effects on the Bcl-xL protein expression in the 5-HT neurons. In chronically stressed animals, an increase in tph2 gene expression was not associated with any changes in tryptophan hydroxylase protein levels. Our findings are the first to demonstrate that both short-term stress and acute glucocorticoid exposures induce Bcl-xL protein expression in the midbrain 5-HT neurons concomitantly with the activation of the 5-HT synthesis pathway in these neurons

Effects of stress-induced glucocorticoid signal on Bcl-xL expression.

<p>The levels of the midbrain <i>bcl-xl</i> mRNA at 2 h after second forced swim: Stress-induced glucocorticoid signal was blocked by MET and substituted by DEX in MET+DEX treated animals. *p < 0.05 vs. Intact (untreated animals), ^#p < 0.05 vs. VEH1.</p

Effects of DEX on Bcl-xL in adult rats.

<p>Bcl-xL protein expression in the 5-HT cell bodies located in the dorsal (DRNd) and ventral (DRNv) parts of the dorsal raphe nucleus, and in the median raphe nucleus (MRN) at 6 h after the drug (VEH or DEX) injection. *p < 0.05 vs. Intact (untreated animals).</p

Representative photomicrographs of immunofluorescent staining.

<p>Bcl-xL (red), TPH (green) and double immunofluorescence for TPH and Bcl-xL are shown in the rat ventral part of the dorsal nucleus (DRNv), and at higher magnification in the random insets 1 and 2 as indicated in the DRNv TPH picture.</p