River export of nutrients and organic matter from the North Slope of Alaska to the Beaufort Sea

Author Posting. © American Geophysical Union, 2014. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Water Resources Research 50 (2014): 1823–1839, doi:10.1002/2013WR014722.While river-borne materials are recognized as important resources supporting coastal ecosystems around the world, estimates of river export from the North Slope of Alaska have been limited by a scarcity of water chemistry and river discharge data. This paper quantifies water, nutrient, and organic matter export from the three largest rivers (Sagavanirktok, Kuparuk, and Colville) that drain Alaska's North Slope and discusses the potential importance of river inputs for biological production in coastal waters of the Alaskan Beaufort Sea. Together these rivers export ∼297,000 metric tons of organic carbon and ∼18,000 metric tons of organic nitrogen each year. Annual fluxes of nitrate-N, ammonium-N, and soluble reactive phosphorus are approximately 1750, 200, and 140 metric tons per year, respectively. Constituent export from Alaska's North Slope is dominated by the Colville River. This is in part due to its larger size, but also because constituent yields are greater in the Colville watershed. River-supplied nitrogen may be more important to productivity along the Alaskan Beaufort Sea coast than previously thought. However, given the dominance of organic nitrogen export, the potential role of river-supplied nitrogen in support of primary production depends strongly on remineralization mechanisms. Although rivers draining the North Slope of Alaska make only a small contribution to overall river export from the pan-arctic watershed, comparisons with major arctic rivers reveal unique regional characteristics as well as remarkable similarities among different regions and scales. Such information is crucial for development of robust river export models that represent the arctic system as a whole.Funding for this project was provided by a grant from the National Science Foundation Office of Polar Programs (NSF-OPP-0436118) as part of the Arctic System Science (ARCSS) Study of the Northern Alaska Coastal System (SNACS) effort.2014-08-2

Using stable isotopes of hydrogen to quantify biogenic and thermogenic atmospheric methane sources: A case study from the Colorado Front Range

Global atmospheric concentrations of methane (CH4), a powerful greenhouse gas, are increasing, but because there are many natural and anthropogenic sources of CH4, it is difficult to assess which sources may be increasing in magnitude. Here we present a data set of δ2H-CH4 measurements of individual sources and air in the Colorado Front Range, USA. We show that δ2H-CH4, but not δ13C, signatures are consistent in air sampled downwind of landfills, cattle feedlots, and oil and gas wells in the region. Applying these source signatures to air in ground and aircraft samples indicates that at least 50% of CH4 emitted in the region is biogenic, perhaps because regulatory restrictions on leaking oil and natural gas wells are helping to reduce this source of CH4. Source apportionment tracers such as δ2H may help close the gap between CH4 observations and inventories, which may underestimate biogenic as well as thermogenic sources

New genetic loci link adipose and insulin biology to body fat distribution.

Body fat distribution is a heritable trait and a well-established predictor of adverse metabolic outcomes, independent of overall adiposity. To increase our understanding of the genetic basis of body fat distribution and its molecular links to cardiometabolic traits, here we conduct genome-wide association meta-analyses of traits related to waist and hip circumferences in up to 224,459 individuals. We identify 49 loci (33 new) associated with waist-to-hip ratio adjusted for body mass index (BMI), and an additional 19 loci newly associated with related waist and hip circumference measures (P < 5 × 10(-8)). In total, 20 of the 49 waist-to-hip ratio adjusted for BMI loci show significant sexual dimorphism, 19 of which display a stronger effect in women. The identified loci were enriched for genes expressed in adipose tissue and for putative regulatory elements in adipocytes. Pathway analyses implicated adipogenesis, angiogenesis, transcriptional regulation and insulin resistance as processes affecting fat distribution, providing insight into potential pathophysiological mechanisms

Carbon and nitrogen cycling in the Peruvian Andean Amazon

textThis dissertation consists of several studies conducted at various spatial and temporal scales designed to identify the important processes that affect organic matter (OM) inputs from the Andes mountains to the Amazon headwaters, as well as carbon (C) and nitrogen (N) cycles in the rivers themselves. Andean rivers supplied approximately equal amounts of fine and coarse sediments to the Amazon, but most coarse sediments were retained in the Andean foreland while fine sediments continued downstream. Terrestrial plant δ¹³C increased with elevation, but terrestrial soil δ¹³C did not and was enriched by 1-3% over plants. Particulate organic matter (POM) concentrations were generally low, with periodic high concentrations during storms. There were significant differences in the isotopic composition of POM between seasons (wet vs. dry), reflecting changes in sediment source. During high flow, POM resembled terrestrial materials, but during drier periods there was evidence for a resuspended bottom sediment or algal source. During wet periods, OM content of soils and river POM decreased downstream, but the POM trend was complicated during drier months. Δ¹⁴C of POM decreased downstream, suggesting that young, fresh OM introduced in small headwater streams was respired preferentially in rivers or diluted with older material downstream. Fine suspended POM was higher in δ¹⁵N and δ¹³C than coarse POM, indicating either greater degradation in the fine fraction or sorption of isotopically enriched dissolved OM. Deforestation is reflected in suspended POM in small headwaters, with enrichment in both ¹³C (due to introduced C₄ grasses) and ¹⁵N. Epiphytic plants living in forest canopies were δ¹⁵N-deplete compared to rooted plants, and the biomass of these epiphytes was so high that their δ¹⁵N was reflected in stream POM. Precipitation was a major source of isotopically enriched dissolved organic N (DON) to cloudforests in the central Andes. Inorganic N export from these systems in streams was very low, but this seems to be the result of high demand for DIN by microbes and fine roots in riparian soils, not a high reactivity of dissolved inorganic N (DIN) in the stream. Low deposition of and demand for inorganic N in these forests appear to explain low ambient stream DIN concentrations.Marine Scienc