Oxygen isotope ratios of waters and respired CO2 in Amazonian forest and pasture ecosystems

Journal ArticleThe oxygen isotope ratio (d18O, SMOW) of atmospheric CO2 is a powerful indicator of large-scale CO2 exchange on land. Oxygen isotopic exchange between CO2 and water in leaves and soils controls the d18O of atmospheric CO2. Currently there is little empirical information on the spatial and temporal variation in the d18O of leaf and stem water in tropical ecosystems. We measured the seasonal dynamics of d18O in atmospheric CO2 and water in different ecosystem compartments in both primary forest and pasture ecosystems in three different regions of the Amazonian Basin of Brazil (Ji-Paraná, Manaus, and Santarém)

Responses of boreal conifers to climate fluctuations: indications from tree-ring widths and carbon isotope analyses

Journal ArticleSpatial distribution and species composition of the boreal forest are expected to change under predicted climate change scenarios. Current research indicates that water limitations control the southern boundary of the central Canadian boreal forest and temperature limitations control the northern boundary. As part of Boreal Ecosystem ? Atmosphere Study (BOREAS), we examined this idea by comparing annual variation in tree-ring widths and carbon isotope ratios (d13C) of tree-ring cellulose with annual climatic parameters in the northern and southern boreal forest

Combining tower mixing ratio and community model data to estimate regional-scale net ecosystem carbon exchange by boundary layer inversion over 4 flux towers in the U.S.A.

We evaluated an idealized boundary layer (BL) model with simple parameterizations using vertical transport information from community model outputs (NCAR/NCEP Reanalysis and ECMWF Interim Analysis) to estimate regional-scale net CO2 fluxes from 2002 to 2007 at three forest and one grassland flux sites in the United States. The BL modeling approach builds on a mixed-layer model to infer monthly average net CO2 fluxes using high-precision mixing ratio measurements taken on flux towers. We compared BL model net ecosystem exchange (NEE) with estimates from two independent approaches. First, we compared modeled NEE with tower eddy covariance measurements. The second approach (EC-MOD) was a data-driven method that upscaled EC fluxes from towers to regions using MODIS data streams. Comparisons between modeled CO2 and tower NEE fluxes showed that modeled regional CO2 fluxes displayed interannual and intra-annual variations similar to the tower NEE fluxes at the Rannells Prairie and Wind River Forest sites, but model predictions were frequently different from NEE observations at the Harvard Forest and Howland Forest sites. At the Howland Forest site, modeled CO2 fluxes showed a lag in the onset of growing season uptake by 2 months behind that of tower measurements. At the Harvard Forest site, modeled CO2 fluxes agreed with the timing of growing season uptake but underestimated the magnitude of observed NEE seasonal fluctuation. This modeling inconsistency among sites can be partially attributed to the likely misrepresentation of atmospheric transport and/or CO2gradients between ABL and the free troposphere in the idealized BL model. EC-MOD fluxes showed that spatial heterogeneity in land use and cover very likely explained the majority of the data-model inconsistency. We show a site-dependent atmospheric rectifier effect that appears to have had the largest impact on ABL CO2 inversion in the North American Great Plains. We conclude that a systematic BL modeling approach provided new insights when employed in multiyear, cross-site synthesis studies. These results can be used to develop diagnostic upscaling tools, improving our understanding of the seasonal and interannual variability of surface CO2 fluxes

ENSO effects on primary productivity in Southern Atacama desert

International audienceIn the winter-rain southern Atacama Desert of the Coquimbo Region of Chile, El Niño - Southern Oscillation (ENSO) events modulate primary productivity. In this region, there are important changes in water availability between La Niña (dry) and El Niño (rainy) years. Using inter-annual comparisons of LANDSAT images from 30° to 31° S latitude, we observed changes in primary productivity between dry and rainy years at the regional level. There were also significant, negative correlations between productivity and elevation, with changes occurring first at low elevation during rainy years. The limiting factors to dryland vegetation primary productivity is different in regard to elevation. Rain during an El Niño year is the main factor that explains the increase in primary productivity at low elevation, while lower temperatures reduce and delay the net primary productivity at mid elevation

Breath Stable Isotope Analysis Serves as a Non-invasive Analytical Tool to Demonstrate Dietary Changes in Adolescent Students Over Time

Concern about adolescent diets, obesity, and the associated health risks have been growing in the United States. This inspired former First Lady Michelle Obama to spearhead the Healthy Hunger-Free Kids Act (HHFKA), which made changes to the national school lunch program by increasing servings of whole grains, fruits, and vegetables. Our study examined the variability of student carbohydrate sources throughout the day and before and after the implementation of HHFKA using a stable isotope dietary biomarker. This method uses carbon stable isotope values of exhaled CO2 breath (δ13Cbreath) and provides a quantitative, non-invasive measure. δ13Cbreath samples were collected throughout the day from students (n = 31) that attended a public high school in Salt Lake City, UT. δ13Cbreath measurements reflected the short-term carbohydrate inputs from the previous meal. Carbohydrate sources were not consistent throughout the day; most students had their lowest inputs of corn/sugar-based carbohydrates after lunch. We compared our results with an earlier study that had been conducted pre-HHFKA. After-lunch δ13Cbreath values decreased significantly between the two time points, suggesting an increase in whole grain, fruit, and vegetable carbohydrates in the lunch program. Our results demonstrated that δ13Cbreath measurements provide a valuable tool to examine carbohydrate sources in an individual's diet throughout the day. We believe that this tool could be beneficial to studies examining the relationship between sugar sweetened beverages, added sugars, and refined carbohydrates and health outcomes like diabetes and obesity in both adolescent and adult populations.Fil: Mancuso, Christy J.. University of New Mexico. Department of Biology; Estados UnidosFil: Cornwall, Collette M.. Highland High School; Estados UnidosFil: Robinson, Swede. Highland High School; Estados UnidosFil: Valenzuela, Luciano Oscar. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Ciencias Sociales. Departamento de Arqueología. Laboratorio de Ecología Evolutiva Humana (Sede Quequén); Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tandil; ArgentinaFil: Ehleringer, James R.. University Of Utah. Department Of Biology; Estados Unido

Detection and variability of combustion-derived vapor in an urban basin

Water emitted during combustion may comprise a significant portion of ambient humidity (>  10 %) in urban areas, where combustion emissions are strongly focused in space and time. Stable water vapor isotopes can be used to apportion measured humidity values between atmospherically transported and combustion-derived water vapor, as combustion-derived vapor possesses an unusually negative deuterium excess value (d-excess, d  =  δ2H − 8δ18O). We investigated the relationship between the d-excess of atmospheric vapor, ambient CO2 concentrations, and atmospheric stability across four winters in Salt Lake City, Utah. We found a robust inverse relationship between CO2 excess above background and d-excess on sub-diurnal to seasonal timescales, which was most prominent during periods of strong atmospheric stability that occur during Salt Lake City winter. Using a Keeling-style mixing model approach, and assuming a molar ratio of H2O to CO2 in emissions of 1.5, we estimated the d-excess of combustion-derived vapor in Salt Lake City to be −179 ± 17 ‰, consistent with the upper limit of theoretical estimates. Based on this estimate, we calculate that vapor from fossil fuel combustion often represents 5–10 % of total urban humidity, with a maximum estimate of 16.7 %, consistent with prior estimates for Salt Lake City. Moreover, our analysis highlights that changes in the observed d-excess during periods of high atmospheric stability cannot be explained without a vapor source possessing a strongly negative d-excess value. Further refinements in this humidity apportionment method, most notably empirical validation of the d-excess of combustion vapor or improvements in the estimation of the background d-excess value in the absence of combustion, can yield more certain estimates of the impacts of fossil fuel combustion on urban humidity and meteorology

Stable isotopes in hair reveal dietary protein sources with links to socioeconomic status and health

Carbon and nitrogen isotope ratios in hair sampled from 65 communities across the central and intermountain regions of the United States and more intensively throughout 29 ZIP codes in the Salt Lake Valley, Utah, revealed a dietary divergence related to socioeconomic status as measured by cost of living, household income, and adjusted gross income. Corn-fed, animal-derived proteins were more common in the diets of lower socioeconomic status populations than were plant-derived proteins, with individual estimates of animal-derived protein diets as high as 75%; United States towns and cities averaged 57%. Similar patterns were seen across the socioeconomic status spectrum in the Salt Lake Valley. It is likely that corn-fed animal proteins were associated with concentrated animal-feeding operations, a common practice for industrial animal production in the United States today. Given recent studies highlighting the negative impacts of animal-derived proteins in our diets, hair carbon isotope ratios could provide an approach for scaling assessments of animal-sourced foods and health risks in communities across the United States.Fil: Ehleringer, James R.. University Of Utah. Department Of Biology; Estados UnidosFil: Covarrubias Avalos, Stephannie. University Of Utah. Department Of Biology; Estados UnidosFil: Tipple, Brett J.. University Of Utah. Department Of Biology; Estados UnidosFil: Valenzuela, Luciano Oscar. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Ciencias Sociales. Departamento de Arqueología. Laboratorio de Ecología Evolutiva Humana (Sede Quequén); Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tandil; ArgentinaFil: Cerling, Thure E.. University Of Utah. Department Of Biology; Estados Unido

Convergence in Nitrogen Deposition and Cryptic Isotopic Variation Across Urban and Agricultural Valleys in Northern Utah

The extent to which atmospheric nitrogen (N) deposition reflects land use differences and biogenic versus fossil fuel reactive N sources remains unclear yet represents a critical uncertainty in ecosystem N budgets. We compared N concentrations and isotopes in precipitation-event bulk (wet + dry) deposition across nearby valleys in northern Utah with contrasting land use (highly urban versus intensive agriculture/low-density urban). We predicted greater nitrate (NO3−) versus ammonium (NH4+) and higher δ15N of NO3− and NH4+ in urban valley sites. Contrary to expectations, annual N deposition (3.5–5.1 kg N ha−1 yr−1) and inorganic N concentrations were similar within and between valleys. Significant summertime decreases in δ15N of NO3− possibly reflected increasing biogenic emissions in the agricultural valley. Organic N was a relatively minor component of deposition (~13%). Nearby paired wildland sites had similar bulk deposition N concentrations as the urban and agricultural sites. Weighted bulk deposition δ15N was similar to natural ecosystems (−0.6 ± 0.7‰). Fine atmospheric particulate matter (PM2.5) had consistently high values of bulk δ15N (15.6 ± 1.4‰), δ15N in NH4+ (22.5 ± 1.6‰), and NO3− (8.8 ± 0.7‰), consistent with equilibrium fractionation with gaseous species. The δ15N in bulk deposition NH4+ varied by more than 40‰, and spatial variation in δ15N within storms exceeded 10‰. Sporadically high values of δ15N were thus consistent with increased particulate N contributions as well as potential N source variation. Despite large differences in reactive N sources, urban and agricultural landscapes are not always strongly reflected in the composition and fluxes of local N deposition—an important consideration for regional-scale ecosystem models

The Phytogeography and Ecology of the Coastal Atacama and Peruvian Deserts

The Atacama and Peruvian Deserts form a continuous belt for more than 3500 km along the western escarpment of the Andes from northern Peru to northernmost Chile. These arid environments are due to a climatic regime dominated by the cool, north-flowing Humboldt (Peruvian) Current. Atmospheric conditions influenced by a stable, subtropical anticyclone result in a mild, uniform coastal climate nearly devoid of rain, but with the regular formation of thick stratus clouds below I 000 m during the winter months. Where coastal topography is low and flat, the clouds dissipate inward over broad areas with little biological impact. However, where isolated mountains or steep coastal slopes intercept the clouds, a fog-zone develops. This moisture allows the development of plant communities termed lomas formations. These floristic assemblages function as islands separated by hyperarid habitat devoid of plant life. Since growth is dependent upon available moisture, an understanding of climatic patterns is essential in efforts to interpret present-day plant distributions. Topography and substrate combine to influence patterns of moisture availability. The ecological requirements and tolerances of individual species ultimately determines community composition. Species endemism exceeds 40% and suggests that the lomas formations have evolved in isolation from their nearest geographic neighbors in the Andes. While the arid environment is continuous, there appears to be a significant barrier to dispersal between 18° and 22°S latitude in extreme northern Chile. Less than 7% of a total flora, estimated at nearly 1000 species, occur on both sides ofthis region. Viable hypotheses concerning the age and origins of these desert floras will require continued study of the ecology and biogeography of their component species