Source, transport and fate of soil organic matter inferred from microbial biomarker lipids on the East Siberian Arctic Shelf

The Siberian Arctic contains a globally significant pool of organic carbon (OC) vulnerable to enhanced warming and subsequent release by both fluvial and coastal erosion processes. However, the rate of release, its behaviour in the Arctic Ocean and vulnerability to remineralisation is poorly understood. Here we combine new measurements of microbial biohopanoids including adenosylhopane, a lipid associated with soil microbial communities, with published glycerol dialkyl glycerol tetraether (GDGTs) and bulk δ13C 5 measurements to improve knowledge of the fate of OC transported to the East Siberian Arctic Shelf (ESAS). The microbial hopanoid-based soil OC proxy R'soil ranges from 0.0 to 0.8 across the ESAS, with highest values near shore and decreases offshore. Across the shelf R'soil displays a negative linear correlation with bulk δ13C measurements (r2 = −0.73, p = < 0.001). When compared to the GDGT based OC proxy, the Branched and Isoprenoid tetraether (BIT) index, a decoupled (non-linear) behaviour on the shelf was observed, particularly in the Buor-Khaya Bay where the R'soil shows limited 10 variation, whereas the BIT index shows a rapid decline moving away from the Lena River outflow channels. This reflects a balance between delivery and removal of OC from different sources. The good correlation between the hopanoid and bulk terrestrial signal suggests a broad range of hopanoid sources, both fluvial and via coastal erosion whilst GDGTs appear to be primarily sourced via fluvial transport. Analysis of ice complex deposits (ICDs) revealed an average R'soil of 0.5 for the Lena delta, equivalent to that of the Buor-Khaya Bay sediments, whilst ICDs from further East showed higher values (0.6–0.85). Al15 though R'soil correlates more closely with bulk OC than the BIT, our understanding of the endmembers of this system is clearly still incomplete with east-west variations potentially reflecting differences in environmental conditions (e.g. temperature, pH) but other physiological controls on microbial BHP production under psychrophilic conditions are as yet unknown

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)

Mercury dynamics in a San Francisco estuary tidal wetland : assessing dynamics using in situ measurements

© The Author(s), 2012. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Estuaries and Coasts 35 (2012): 1036-1048, doi:10.1007/s12237-012-9501-3.We used high-resolution in situ measurements of turbidity and fluorescent dissolved organic matter (FDOM) to quantitatively estimate the tidally driven exchange of mercury (Hg) between the waters of the San Francisco estuary and Browns Island, a tidal wetland. Turbidity and FDOM—representative of particle-associated and filter-passing Hg, respectively—together predicted 94 % of the observed variability in measured total mercury concentration in unfiltered water samples (UTHg) collected during a single tidal cycle in spring, fall, and winter, 2005–2006. Continuous in situ turbidity and FDOM data spanning at least a full spring-neap period were used to generate UTHg concentration time series using this relationship, and then combined with water discharge measurements to calculate Hg fluxes in each season. Wetlands are generally considered to be sinks for sediment and associated mercury. However, during the three periods of monitoring, Browns Island wetland did not appreciably accumulate Hg. Instead, gradual tidally driven export of UTHg from the wetland offset the large episodic on-island fluxes associated with high wind events. Exports were highest during large spring tides, when ebbing waters relatively enriched in FDOM, dissolved organic carbon (DOC), and filter-passing mercury drained from the marsh into the open waters of the estuary. On-island flux of UTHg, which was largely particle-associated, was highest during strong winds coincident with flood tides. Our results demonstrate that processes driving UTHg fluxes in tidal wetlands encompass both the dissolved and particulate phases and multiple timescales, necessitating longer term monitoring to adequately quantify fluxes.This work was supported by funding from the California Bay Delta Authority Ecosystem Restoration and Drinking Water Programs (grant ERP-00- G01) and matching funds from the United States Geological Survey Cooperative Research Program

Duffy blood group gene polymorphisms among malaria vivax patients in four areas of the Brazilian Amazon region

<p>Abstract</p> <p>Background</p> <p>Duffy blood group polymorphisms are important in areas where <it>Plasmodium vivax </it>predominates, because this molecule acts as a receptor for this protozoan. In the present study, Duffy blood group genotyping in <it>P. vivax </it>malaria patients from four different Brazilian endemic areas is reported, exploring significant associations between blood group variants and susceptibility or resistance to malaria.</p> <p>Methods</p> <p>The <it>P. vivax </it>identification was determined by non-genotypic and genotypic screening tests. The Duffy blood group was genotyped by PCR/RFLP in 330 blood donors and 312 malaria patients from four Brazilian Amazon areas. In order to assess the variables significance and to obtain independence among the proportions, the Fisher's exact test was used.</p> <p>Results</p> <p>The data show a high frequency of the <it>FYA/FYB </it>genotype, followed by <it>FYB/FYB, FYA/FYA</it>, <it>FYA/FYB-33 </it>and <it>FYB/FYB-33</it>. Low frequencies were detected for the <it>FYA/FY</it>^<it>X</it>, <it>FYB/FY</it>^<it>X</it>, <it>FYX/FY</it>^{<it>X </it>}and <it>FYB-33/FYB-33 </it>genotypes. Negative Duffy genotype (<it>FYB-33/FYB-33</it>) was found in both groups: individuals infected and non-infected (blood donors). No individual carried the <it>FY</it>^<it>X</it><it>/FYB-33 </it>genotype. Some of the Duffy genotypes frequencies showed significant differences between donors and malaria patients.</p> <p>Conclusion</p> <p>The obtained data suggest that individuals with the <it>FYA/FYB </it>genotype have higher susceptibility to malaria. The presence of the <it>FYB-33 </it>allele may be a selective advantage in the population, reducing the rate of infection by <it>P. vivax </it>in this region. Additional efforts may contribute to better elucidate the physiopathologic differences in this parasite/host relationship in regions endemic for <it>P. vivax </it>malaria, in particular the Brazilian Amazon region.</p