Articles | Volume 14, issue 9
Research article 10 May 2017
Research article | 10 May 2017
Nitrogen input 15N signatures are reflected in plant 15N natural abundances in subtropical forests in China
Geshere Abdisa Gurmesa et al.
No articles found.
Wendell W. Walters, Linlin Song, Jiajue Chai, Yunting Fang, Nadia Colombi, and Meredith G. Hastings
Atmos. Chem. Phys., 20, 11551–11567,Short summary
This article details new field observations of the nitrogen stable isotopic composition of ammonia emitted from vehicles conducted in the US and China. Vehicle emissions of ammonia may be a significant source to urban regions with important human health and environmental implications. Our measurements have indicated a consistent isotopic signature from vehicle ammonia emissions. The nitrogen isotopic composition of ammonia may be a useful tool for tracking vehicle emissions.
Yunhua Chang, Yan-Lin Zhang, Jiarong Li, Chongguo Tian, Linlin Song, Xiaoyao Zhai, Wenqi Zhang, Tong Huang, Yu-Chi Lin, Chao Zhu, Yunting Fang, Moritz F. Lehmann, and Jianmin Chen
Atmos. Chem. Phys., 19, 12221–12234,Short summary
The present work underscores the value of cloud water dissolved inorganic nitrogen isotopes as carriers of quantitative information on regional NOx and NH3 emissions. It sheds light on the origin and production pathways of nitrogenous species in clouds and emphasizes the importance of biomass-burning-derived nitrogenous species as cloud condensation nuclei in China’s troposphere. Moreover, it highlights the rapid evolution of NOx emissions in China.
Susan J. Cheng, Peter G. Hess, William R. Wieder, R. Quinn Thomas, Knute J. Nadelhoffer, Julius Vira, Danica L. Lombardozzi, Per Gundersen, Ivan J. Fernandez, Patrick Schleppi, Marie-Cécile Gruselle, Filip Moldan, and Christine L. Goodale
Biogeosciences, 16, 2771–2793,Short summary
Nitrogen deposition and fertilizer can change how much carbon is stored in plants and soils. Understanding how much added nitrogen is recovered in plants or soils is critical to estimating the size of the future land carbon sink. We compared how nitrogen additions are recovered in modeled soil and plant stocks against data from long-term nitrogen addition experiments. We found that the model simulates recovery of added nitrogen into soils through a different process than found in the field.
Chongjuan Chen, Yufu Jia, Yuzhen Chen, Imran Mehmood, Yunting Fang, and Guoan Wang
Biogeosciences, 15, 369–377,Short summary
The south slope of Tian Shan differs from the north slope in environment. The study showed that leaf δ15N, soil δ15N and △δ15Nleaf-soil on the south slope were greater than those on the north slope. The significant influential factors of leaf and soil δ15N on the south slope were different from those on the north slope. The results suggested that the south slope has higher soil N transformation rates than the north slope and relationships between leaf and soil δ15N and environment are localized.
Dongwei Liu, Weixing Zhu, Xiaobo Wang, Yuepeng Pan, Chao Wang, Dan Xi, Edith Bai, Yuesi Wang, Xingguo Han, and Yunting Fang
Biogeosciences, 14, 989–1001,Short summary
The use of 15N natural abundance of soil ammonium and nitrate demonstrates a clear shifting contribution from abiotic to biotic controls on N cycling along a 3200 km dryland transect in northern China, with a threshold at mean annual precipitation of 100 mm. Abiotic factors were the main driver below threshold, shown by the accumulation of atmospheric N and NH3 losses. In the area above threshold, soil N cycling was controlled mainly by biological factors, e.g., plant uptake and denitrification.
Mianhai Zheng, Tao Zhang, Lei Liu, Weixing Zhu, Wei Zhang, and Jiangming Mo
Biogeosciences, 13, 3503–3517,
Weili Liu, Lin Qi, Yunting Fang, and Jian Yang
Revised manuscript not acceptedShort summary
Wildfire is a major disturbance in boreal forest ecosystem and strongly affects ecosystem N cycling. We find that even 5 years after a wildfire, isotopic signatures of soil and plant N pools are still different from those in unburned areas in a Chinese boreal forest. Our results show persistent legacy effects in the form of increased N losses following wildfires. The fire-induced increases in NH3 volatilization may greatly contribute to the increased δ15N values in plant and soil.
W. Zhang, X. Zhu, Y. Luo, R. Rafique, H. Chen, J. Huang, and J. Mo
Biogeosciences, 11, 4941–4951,
H. Chen, W. Zhang, F. Gilliam, L. Liu, J. Huang, T. Zhang, W. Wang, and J. Mo
Biogeosciences, 10, 6609–6616,
X. Lu, F. S. Gilliam, G. Yu, L. Li, Q. Mao, H. Chen, and J. Mo
Biogeosciences, 10, 3931–3941,
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Zhongjie Yu and Emily M. Elliott
Biogeosciences, 18, 805–829,Short summary
In this study, we demonstrated distinct nitrogen isotope effects for nitric oxide (NO) production from major microbial and chemical NO sources in an agricultural soil. These results highlight characteristic bond-forming and breaking mechanisms associated with microbial and chemical NO production and implicate that simultaneous isotopic analyses of NO and nitrous oxide (N2O) can lead to unprecedented insights into the sources and processes controlling NO and N2O emissions from agricultural soils.
Daniel A. Frick, Rainer Remus, Michael Sommer, Jürgen Augustin, Danuta Kaczorek, and Friedhelm von Blanckenburg
Biogeosciences, 17, 6475–6490,Short summary
Silicon is taken up by some plants to increase structural stability and to develop stress resistance and is rejected by others. To explore the underlying mechanisms, we used the stable isotopes of silicon that shift in their relative abundance depending on the biochemical transformation involved. On species with a rejective (tomato, mustard) and active (wheat) uptake mechanism, grown in hydroculture, we found that the transport of silicic acid is controlled by the precipitation of biogenic opal.
Quentin Charbonnier, Julien Bouchez, Jérôme Gaillardet, and Éric Gayer
Biogeosciences, 17, 5989–6015,Short summary
The abundance and isotope composition of the trace metal barium (Ba) allows us to track and quantify nutrient cycling throughout the Amazon Basin. In particular, we show that the Ba biological fingerprint evolves from that of a strong net nutrient uptake in the mountainous area of the Andes towards efficient nutrient recycling on the plains of the Lower Amazon. Our study highlights the fact that the geochemical signature of rock-derived nutrients transported by the Amazon is scarred by life.
Ajinkya G. Deshpande, Thomas W. Boutton, Ayumi Hyodo, Charles W. Lafon, and Georgianne W. Moore
Biogeosciences, 17, 5639–5653,Short summary
Wetland forests in the southern USA are threatened by changing climate and human-induced pressures. We used tree ring widths and C isotopes as indicators of forest growth and physiological stress, respectively, and compared these to past climate data. We observed that vegetation growing in the drier patches is susceptible to stress, while vegetation growth and physiology in wetter patches is less sensitive to unfavorable environmental conditions, highlighting the importance of optimal wetness.
Dominika Lewicka-Szczebak, Maciej Piotr Lewicki, and Reinhard Well
Biogeosciences, 17, 5513–5537,Short summary
We present the first validation of N2O isotopic approaches for estimating N2O source pathways and N2O reduction. These approaches are widely used for tracing soil nitrogen cycling, but the results of these estimations are very uncertain. Here we report the results from parallel treatments allowing for precise validation of these approaches, and we propose the best strategies for results interpretation, including the new idea of an isotope model integrating three isotopic signatures of N2O.
Markus Raitzsch, Claire Rollion-Bard, Ingo Horn, Grit Steinhoefel, Albert Benthien, Klaus-Uwe Richter, Matthieu Buisson, Pascale Louvat, and Jelle Bijma
Biogeosciences, 17, 5365–5375,Short summary
The isotopic composition of boron in carbonate shells of marine unicellular organisms is a popular tool to estimate seawater pH. Usually, many shells need to be dissolved and measured for boron isotopes, but the information on their spatial distribution is lost. Here, we investigate two techniques that allow for measuring boron isotopes within single shells and show that they yield robust mean values but provide additional information on the heterogeneity within and between single shells.
Florian Einsiedl, Anja Wunderlich, Mathieu Sebilo, Ömer K. Coskun, William D. Orsi, and Bernhard Mayer
Biogeosciences, 17, 5149–5161,Short summary
Nitrate pollution of freshwaters and methane emissions into the atmosphere are crucial factors in deteriorating the quality of drinking water and in contributing to global climate change. Here, we report vertical concentration and stable isotope profiles of CH4, NO3-, NO2-, and NH4+ in the water column of Fohnsee (southern Bavaria, Germany) that may indicate linkages between nitrate-dependent anaerobic methane oxidation and the anaerobic oxidation of ammonium.
Ruifang C. Xie, Frédéric A. C. Le Moigne, Insa Rapp, Jan Lüdke, Beat Gasser, Marcus Dengler, Volker Liebetrau, and Eric P. Achterberg
Biogeosciences, 17, 4919–4936,Short summary
Thorium-234 (234Th) is widely used to study carbon fluxes from the surface ocean to depth. But few studies stress the relevance of oceanic advection and diffusion on the downward 234Th fluxes in nearshore environments. Our study in offshore Peru showed strong temporal variations in both the importance of physical processes on 234Th flux estimates and the oceanic residence time of 234Th, whereas salinity-derived seawater 238U activities accounted for up to 40 % errors in 234Th flux estimates.
Ralf A. Oeser and Friedhelm von Blanckenburg
Biogeosciences, 17, 4883–4917,Short summary
We present a novel strategy to decipher the relative impact of biogenic and abiotic drivers of weathering. We parameterized the nutrient fluxes in four ecosystems along a climate and vegetation gradient situated on the Chilean Coastal Cordillera. We investigated how nutrient demand by plants drives weathering. We found that the increase in biomass nutrient demand is accommodated by faster nutrient recycling rather than an increase in the weathering–release rates.
Tito Arosio, Malin M. Ziehmer, Kurt Nicolussi, Christian Schlüchter, and Markus Leuenberger
Biogeosciences, 17, 4871–4882,Short summary
Stable isotopes in tree-ring cellulose are tools for climatic reconstructions, but interpretation is challenging due to nonclimate trends. We analyzed the tree-age trends in tree-ring isotopes of deciduous larch and evergreen cembran pine. Samples covering the whole Holocene were collected at the tree line in the Alps. For cambial ages over 100 years, we prove the absence of age trends in δD, δ18O, and δ13C for both species. For lower cambial ages, trends differ for each isotope and species.
Yu-Te Hsieh, Walter Geibert, E. Malcolm S. Woodward, Neil J. Wyatt, Maeve C. Lohan, Eric P. Achterberg, and Gideon M. Henderson
Revised manuscript accepted for BGShort summary
The South Atlantic near 40 °S is one of the high productivity and most dynamic nutrient regions in the oceans, but the sources and fluxes of trace elements (TEs) to this region remain unclear. This study investigates seawater Ra-228 and provides important constraints on ocean mixing and dissolved TE fluxes to this region. Vertical mixing is a more important source than aeolian or shelf inputs in this region, but particulate or winter deep-mixing inputs may be required to balance the TE budgets.
Yuyang He, Xiaobin Cao, and Huiming Bao
Biogeosciences, 17, 4785–4795,Short summary
Different carbon sites in a large organic molecule have different isotope compositions. Different carbon sites may not have the chance to exchange isotopes at all. The lack of appreciation of this notion might be blamed for an unsettled debate on the thermodynamic state of an organism. Here we demonstrate using minerals, N2O, and acetic acid that the dearth of exchange among different carbon sites renders them as independent as if they were different elements in organic molecules.
Felix M. Spielmann, Albin Hammerle, Florian Kitz, Katharina Gerdel, and Georg Wohlfahrt
Biogeosciences, 17, 4281–4295,Short summary
Carbonyl sulfide (COS) can be used as a proxy for plant photosynthesis on an ecosystem scale. However, the relationships between COS and CO2 fluxes and their dependence on daily to seasonal changes in environmental drivers are still poorly understood. We examined COS and CO2 ecosystem fluxes above an agriculturally used mountain grassland for 6 months. Harvesting of the grassland disturbed the otherwise stable COS-to-CO2 uptake ratio. We even found the canopy to release COS during those times.
Getachew Agmuas Adnew, Thijs L. Pons, Gerbrand Koren, Wouter Peters, and Thomas Röckmann
Biogeosciences, 17, 3903–3922,Short summary
We measured the effect of photosynthesis, the largest flux in the carbon cycle, on the triple oxygen isotope composition of atmospheric CO2 at the leaf level during gas exchange using three plant species. The main factors that limit the impact of land vegetation on the triple oxygen isotope composition of atmospheric CO2 are identified, characterized and discussed. The effect of photosynthesis on the isotopic composition of CO2 is commonly quantified as discrimination (ΔA).
Moritz Schroll, Frank Keppler, Markus Greule, Christian Eckhardt, Holger Zorn, and Katharina Lenhart
Biogeosciences, 17, 3891–3901,Short summary
Fungi have recently been identified to produce the greenhouse gas methane. Here, we investigated the stable carbon isotope values of methane produced by saprotrophic fungi. Our results show that stable isotope values of methane from fungi are dependent on the fungal species and the metabolized substrate. They cover a broad range and overlap with stable carbon isotope values of methane reported for methanogenic archaea, the thermogenic degradation of organic matter, and other eukaryotes.
Pranav Hirave, Guido L. B. Wiesenberg, Axel Birkholz, and Christine Alewell
Biogeosciences, 17, 2169–2180,Short summary
Sediment input into water bodies is a prominent threat to freshwater ecosystems. We tested the stability of tracers employed in freshwater sediment tracing based on compound-specific isotope analysis during early degradation in soil. While bulk δ13C values showed no stability, δ13C values of plant-derived fatty acids and n-alkanes were stably transferred to the soil without soil particle size dependency after an early degradation in organic horizons, thus indicating their suitability as tracers.
Caroline Thaler, Amandine Katz, Magali Bonifacie, Bénédicte Ménez, and Magali Ader
Biogeosciences, 17, 1731–1744,Short summary
Paleoenvironment reconstructions, retrieved from δ18O and Δ47 values measured in carbonate, are compromised when crystallization occurs in isotopic disequilibrium. We show that some paleoenvironmental information can still be retrieved from these paired disequilibrium Δ47 and δ18O values. The possibility of retrieving information on paleowaters, sediments' interstitial waters, or organisms' body water at the carbonate precipitation loci will help understand past Earth and life evolution.
Guillaume Humbert, Mathieu Sébilo, Justine Fiat, Longqi Lang, Ahlem Filali, Véronique Vaury, Mathieu Spérandio, and Anniet M. Laverman
Biogeosciences, 17, 979–993,Short summary
Mitigating emissions of the greenhouse gas N2O requires understanding of the relative contribution of its producing processes in response to environmental variables. We show, using isotopic analysis, that N2O emissions from a nitrifying system were sensitive to oxygenation, temperature and NH4+ concentrations with nitrite reduction being the main N2O source. Temperature appears to be the main control on N2O production, due to its dissimilar effects on ammonium and nitrite oxidizing activities.
Oguz Yigiterhan, Ebrahim Mohd Al-Ansari, Alex Nelson, Mohamed Alaa Abdel-Moati, Jesse Turner, Hamood Abdulla Alsaadi, Barbara Paul, Ibrahim Abdullatif Al-Maslamani, Mehsin Abdulla Al-Ansi Al-Yafei, and James W. Murray
Biogeosciences, 17, 381–404,Short summary
We analyze net-tow samples of plankton and associated particulate matter from the Exclusive Economic Zone, Qatar, Arabian Gulf, using net tows with mesh sizes of 50 and 200 μm to examine the composition of plankton populations. We also focus on the role and composition of the atmospheric dust, representative of terrigenous material, deposited in the Gulf. We concluded that Al, Fe, Cr, Co, Mn, Ni, Pb, and Li are of dust origin and As, Cd, Cu, Mo, Zn, and Ca are of anthropogenic/biogenic origin.
Clare Woulds, James B. Bell, Adrian G. Glover, Steven Bouillon, and Louise S. Brown
Biogeosciences, 17, 1–12,Short summary
Sedimented hydrothermal vents occur where heated, mineral-rich (hydrothermal) water seeps through seafloor sediments. They host chemosynthetic microbes, which use chemical energy to fix dissolved carbon dioxide into sugars (chemosynthesis). We conducted carbon tracing experiments, and observed chemosynthesis at both vent and non-vent sites. Thus, chemosynthesis occurred over a much larger area than expected, suggesting it is more widespread than previously thought.
Cara C. Manning, Rachel H. R. Stanley, David P. Nicholson, Brice Loose, Ann Lovely, Peter Schlosser, and Bruce G. Hatcher
Biogeosciences, 16, 3351–3376,Short summary
We measured rates of biological activity and gas exchange in a Canadian estuary during ice melt. We quantified gas exchange using inert, deliberately released tracers and found that the gas transfer rate at > 90 % ice cover was 6 % of the rate for nearly ice-free conditions. We measured oxygen concentration and isotopic composition and used the data to detect changes in the rates of photosynthesis and respiration (autotrophy and heterotrophy) as the ice melted.
Marlène Lavrieux, Axel Birkholz, Katrin Meusburger, Guido L. B. Wiesenberg, Adrian Gilli, Christian Stamm, and Christine Alewell
Biogeosciences, 16, 2131–2146,Short summary
A fingerprinting approach using compound-specific stable isotopes was applied to a lake sediment core to reconstruct erosion processes over the past 150 years in a Swiss catchment. Even though the reconstruction of land use and eutrophication history was successful, the observation of comparatively low δ13C values of plant-derived fatty acids in the sediment suggests their alteration within the lake. Thus, their use as a tool for source attribution in sediment cores needs further investigation.
Luciana A. Pereira, Roberto V. Santos, Marília Hauser, Fabrice Duponchelle, Fernando Carvajal, Christophe Pecheyran, Sylvain Bérail, and Marc Pouilly
Biogeosciences, 16, 1781–1797,Short summary
This study presents the first step for a chemical origin certification of pirarucu fishery in the Amazon. A preliminary isotopic tool to improve the actual tracking system integrates ecological, social, and economic aspects of Amazon dynamics. The geographic origin validation of farmed and wild fishes contributes to environmental and social practices, secures food and income to communities, helps manage endangered species, reinforces aquaculture, and combats illegal fisheries.
Sarah Conrad, Johan Ingri, Johan Gelting, Fredrik Nordblad, Emma Engström, Ilia Rodushkin, Per S. Andersson, Don Porcelli, Örjan Gustafsson, Igor Semiletov, and Björn Öhlander
Biogeosciences, 16, 1305–1319,Short summary
Iron analysis of the particulate, colloidal, and truly dissolved fractions along the Lena River freshwater plume showed that the particulate iron dominates close to the coast. Over 99 % particulate and about 90 % colloidal iron were lost, while the truly dissolved phase was almost constant. Iron isotopes suggest that the shelf acts as a sink for particles and colloids with negative iron isotope values, while colloids with positive iron isotope values travel further out into the Arctic Ocean.
Elizabeth Verhoeven, Matti Barthel, Longfei Yu, Luisella Celi, Daniel Said-Pullicino, Steven Sleutel, Dominika Lewicka-Szczebak, Johan Six, and Charlotte Decock
Biogeosciences, 16, 383–408,Short summary
This study utilized state-of-the-art measurements of nitrogen isotopes to evaluate nitrogen cycling and to assess the biological sources of the potent greenhouse gas, N2O, in response to water-saving practices in rice systems. Water-saving practices did emit more N2O, and high N2O production had a lower 15N isotope signature. Modeling and visual interpretation indicate that these emissions mostly came from denitrification or nitrifier denitrification, controlled upstream by nitrification rates.
Feifei Deng, Gideon M. Henderson, Maxi Castrillejo, Fiz F. Perez, and Reiner Steinfeldt
Biogeosciences, 15, 7299–7313,Short summary
To better use Pa / Th to reconstruct deep water ventilation rate, we assessed controls on 230Th and 231Pa in the northern North Atlantic. With extended optimum multi-parameter analysis and CFC-based water-mass age, we found the imprint of young overflow water on Th and Pa and enhanced scavenging near the seafloor. A significantly higher advective loss of Pa to the south relative to Th in the Atlantic was estimated, supporting the use of Pa / Th for assessing basin-scale meridional transport.
Anne L. Morée, Jörg Schwinger, and Christoph Heinze
Biogeosciences, 15, 7205–7223,Short summary
Changes in the distribution of the carbon isotope 13C can be used to study the climate system if the governing processes (ocean circulation and biogeochemistry) are understood. We show the Southern Ocean importance for the global 13C distribution and that changes in 13C can be strongly influenced by biogeochemistry. Interpretation of 13C as a proxy for climate signals needs to take into account the effects of changes in biogeochemistry in addition to changes in ocean circulation.
Douglas G. Russell, Wei Wen Wong, and Perran L. M. Cook
Biogeosciences, 15, 7225–7234,Short summary
Nitrogen is an important nutrient in marine environments and is continually converted from one form to another. One way these processes can be investigated is by looking at the ratio of the 15N and 14N stable isotopes of different nitrogen-containing compounds. To date few studies have compared these ratios in seagrass beds, their associated sediments and the porewater NH4+ pool. The strong relationship between these nitrogen pools suggests that nitrogen is tightly recycled within seagrass beds.
Bharat Rastogi, Max Berkelhammer, Sonia Wharton, Mary E. Whelan, Frederick C. Meinzer, David Noone, and Christopher J. Still
Biogeosciences, 15, 7127–7139,Short summary
Carbonyl sulfide (OCS) has gained prominence as an independent tracer for gross primary productivity, which is usually modelled by partitioning net CO2 fluxes. Here, we present a simple empirical model for estimating ecosystem-scale OCS fluxes for a temperate old-growth forest and find that OCS sink strength scales with independently estimated CO2 uptake and is sensitive to the the fraction of downwelling diffuse light. We also examine the response of OCS and CO2 fluxes to sequential heat waves.
Fumiko Nakagawa, Urumu Tsunogai, Yusuke Obata, Kenta Ando, Naoyuki Yamashita, Tatsuyoshi Saito, Shigeki Uchiyama, Masayuki Morohashi, and Hiroyuki Sase
Biogeosciences, 15, 7025–7042,Short summary
To clarify the biological processing of nitrate within temperate forested catchments using unprocessed atmospheric nitrate exported from each catchment as a tracer, we continuously monitored stream nitrate concentrations and stable isotopic compositions in three forested catchments for more than 2 years. We concluded that the export flux of unprocessed atmospheric nitrate relative to the deposition flux in each forest ecosystem is applicable as an index for nitrogen saturation.
Lucie Cassarino, Christopher D. Coath, Joana R. Xavier, and Katharine R. Hendry
Biogeosciences, 15, 6959–6977,Short summary
Using a simple model, we show that the silicon isotopic composition of sponges can be used to estimate the silicic acid concentration of seawater, a key parameter linked to nutrient and carbon cycling. However, our data illustrate that skeletal type and growth rate also control silicon isotopic composition of sponges. Our study demonstrates the paleoceanographic utility of sponges as an archive for ocean silica content provided that suitable skeleton types are selected.
Laurie C. Hofmann and Svenja Heesch
Biogeosciences, 15, 6139–6149,Short summary
The ability of marine macroalgae to adapt to changing ocean chemistry will depend on the flexibility of their inorganic carbon uptake mechanisms across biogeographic ranges. Therefore, we investigated the plasticity of inorganic carbon uptake mechanisms in north Atlantic rhodoliths – free-living calcifying red algae that form important benthic habitats in coastal environments. We observed flexible mechanisms related to seawater DIC concentrations, indicating the potential for adaptation.
Jacqueline Bertlich, Dirk Nürnberg, Ed C. Hathorne, Lennart J. de Nooijer, Eveline M. Mezger, Markus Kienast, Steffanie Nordhausen, Gert-Jan Reichart, Joachim Schönfeld, and Jelle Bijma
Biogeosciences, 15, 5991–6018,
Jill N. Sutton, Gregory F. de Souza, Maribel I. García-Ibáñez, and Christina L. De La Rocha
Biogeosciences, 15, 5663–5676,Short summary
The silicon stable isotope distribution determined from samples collected from the North Atlantic Ocean indicates that water mass subduction and circulation are the dominant processes controlling the distribution of dissolved silicon in this region. In addition, these data provide a clear view of the direct interaction between northern and southern water masses and the extent to which the silicon isotope composition of these silica-poor waters is influenced by hydrography.
Maxi Castrillejo, Núria Casacuberta, Marcus Christl, Christof Vockenhuber, Hans-Arno Synal, Maribel I. García-Ibáñez, Pascale Lherminier, Géraldine Sarthou, Jordi Garcia-Orellana, and Pere Masqué
Biogeosciences, 15, 5545–5564,Short summary
The investigation of water mass transport pathways and timescales is important to understand the global ocean circulation. Following earlier studies, we use artificial radionuclides introduced to the oceans in the 1950s to investigate the water transport in the subpolar North Atlantic (SPNA). For the first time, we combine measurements of the long-lived iodine-129 and uranium-236 to confirm earlier findings/hypotheses and to better understand shallow and deep ventilation processes in the SPNA.
Gustaf Granath, Håkan Rydin, Jennifer L. Baltzer, Fia Bengtsson, Nicholas Boncek, Luca Bragazza, Zhao-Jun Bu, Simon J. M. Caporn, Ellen Dorrepaal, Olga Galanina, Mariusz Gałka, Anna Ganeva, David P. Gillikin, Irina Goia, Nadezhda Goncharova, Michal Hájek, Akira Haraguchi, Lorna I. Harris, Elyn Humphreys, Martin Jiroušek, Katarzyna Kajukało, Edgar Karofeld, Natalia G. Koronatova, Natalia P. Kosykh, Mariusz Lamentowicz, Elena Lapshina, Juul Limpens, Maiju Linkosalmi, Jin-Ze Ma, Marguerite Mauritz, Tariq M. Munir, Susan M. Natali, Rayna Natcheva, Maria Noskova, Richard J. Payne, Kyle Pilkington, Sean Robinson, Bjorn J. M. Robroek, Line Rochefort, David Singer, Hans K. Stenøien, Eeva-Stiina Tuittila, Kai Vellak, Anouk Verheyden, James Michael Waddington, and Steven K. Rice
Biogeosciences, 15, 5189–5202,Short summary
Peat constitutes a long-term archive for climate reconstruction by using the isotopic composition of carbon and oxygen. We analysed isotopes in two peat moss species across North America and Eurasia. Peat (moss tissue) isotope composition was predicted by soil moisture and isotopic composition of the rainwater but differed between species. Our results suggest that isotope composition can be used on a large scale for climatic reconstructions but that such models should be species-specific.
Joshua A. Haslun, Nathaniel E. Ostrom, Eric L. Hegg, and Peggy H. Ostrom
Biogeosciences, 15, 3873–3882,Short summary
N2O δ15N and δ18O values changed non-linearly during in vitro N2O production by bacterial denitrification of NO3−, an argument against their use in N2O apportionment. We present a novel approach for describing non-linear isotopic behaviour, which may be applied to other multi-step reactions. We also show that the intramolecular distribution of 15N in N2O, used to apportion N2O emissions to denitrification and nitrification, is unaffected by electron donor source and electron donor concentration.
Linas Balčiauskas, Raminta Skipitytė, Marius Jasiulionis, Laima Balčiauskienė, and Vidmantas Remeikis
Biogeosciences, 15, 3883–3891,Short summary
Effects of an expanding great cormorant colony on small mammals were evaluated. An increase of the number of bird pairs led to decreased δ13C and increased δ15N values in mice hair after the first year of nest appearance. Differences in isotopic signatures were related to species of rodents, pointing to the differences in their diet. Cormorant influence was indirect, the result of biological pollution from guano on rodent foods. Scaring cormorants from the colonies may have the opposite effect.
Wu Sun, Kadmiel Maseyk, Céline Lett, and Ulli Seibt
Biogeosciences, 15, 3277–3291,Short summary
Carbonyl sulfide (COS) is an emerging tracer to probe land photosynthesis at canopy to global scales, but the relationship between leaf COS and CO2 fluxes needed for this application is poorly quantified. With in situ leaf fluxes of COS and CO2 measured in a freshwater marsh, we show that light and vapor deficit control the relationship between leaf COS and CO2 fluxes by regulating stomatal conductance. Our findings support the use of COS as a tracer for canopy photosynthesis.
Anne Alexandre, Amarelle Landais, Christine Vallet-Coulomb, Clément Piel, Sébastien Devidal, Sandrine Pauchet, Corinne Sonzogni, Martine Couapel, Marine Pasturel, Pauline Cornuault, Jingming Xin, Jean-Charles Mazur, Frédéric Prié, Ilhem Bentaleb, Elizabeth Webb, Françoise Chalié, and Jacques Roy
Biogeosciences, 15, 3223–3241,Short summary
There is a lack of proxies suitable for reconstructing, in a quantitative way, past changes in continental atmospheric humidity, which is a key climate parameter. Here, we demonstrate through climate chamber and climate transect calibrations that the triple oxygen isotope composition of phytoliths offers a potential for reconstructing changes in relative humidity.
Philip M. Riekenberg, Joanne M. Oakes, and Bradley D. Eyre
Biogeosciences, 15, 2873–2889,Short summary
Shallow coastal waters are increasingly experiencing increased nutrient loading. Sediment algae within these systems are responsible for a large portion of C production, but we have limited knowledge of what happens to sediment microbial processing of MPB-C under increased nutrient conditions. This work examines how C-processing pathways change after increased short-term nutrient exposure, finding shifts in processing between microbial groups and increased export of algal C from the sediment.
Jill N. Sutton, Yi-Wei Liu, Justin B. Ries, Maxence Guillermic, Emmanuel Ponzevera, and Robert A. Eagle
Biogeosciences, 15, 1447–1467,Short summary
The boron isotope composition of marine biogenic carbonates has been studied as a proxy for monitoring past changes in seawater pH and carbonate chemistry. We highlight the potential utility of the boron isotope composition of marine biogenic carbonates as a proxy of calcifying site pH for a wide range of calcifying taxa and the importance of using species-specific seawater-pH–boron isotope calibrations when reconstructing seawater pH from the boron isotope composition of biogenic carbonates.
Emil Kristensen, Mikkel Madsen-Østerbye, Philippe Massicotte, Ole Pedersen, Stiig Markager, and Theis Kragh
Biogeosciences, 15, 1203–1216,Short summary
We propose a novel modelling approach enabling swift hydrological surveys based on multiple conservative and non-conservative tracers to estimate water retention time, groundwater discharge sites, fractions of water originating from the discharge sites, groundwater recharge sites and sites that are especially important in regard to groundwater recharge. Thus we provide a whole lake hydrological survey while pinpointing sources of pollutants like colored dissolved organic matter and nutrients.
Chao Wang, Benjamin Z. Houlton, Dongwei Liu, Jianfeng Hou, Weixin Cheng, and Edith Bai
Biogeosciences, 15, 987–995,Short summary
Soil contains a large amount of organic carbon and plays a crucial role in regulating Earth's C cycle and climate system. In this study, we collected soil-carbon isotope data within a 1 m depth globally and provided an isotope-based approach for understanding soil carbon decomposition rate. Compared with other methods, utilization of C isotope composition ratios in the soil profile provides an independent approach that does not rely on disruption of plant-soil-microbe interactions.
Chris J. Curtis, Jan Kaiser, Alina Marca, N. John Anderson, Gavin Simpson, Vivienne Jones, and Erika Whiteford
Biogeosciences, 15, 529–550,Short summary
Few studies have investigated the atmospheric deposition of nitrate in the Arctic or its impacts on Arctic ecosystems. We collected late-season snowpack from three regions in western Greenland from the coast to the edge of the ice sheet. We found major differences in nitrate concentrations (lower at the coast) and deposition load (higher). Nitrate in snowpack undergoes losses and isotopic enrichment which are greatest in inland areas; hence deposition impacts may be greatest at the coast.
Birgit Gaye, Anna Böll, Joachim Segschneider, Nicole Burdanowitz, Kay-Christian Emeis, Venkitasubramani Ramaswamy, Niko Lahajnar, Andreas Lückge, and Tim Rixen
Biogeosciences, 15, 507–527,Short summary
The Arabian Sea has one of the most severe oxygen minima of the world's oceans between about 100 and 1200 m of water depth and is therefore a major oceanic nitrogen sink. Stable nitrogen isotopic ratios in sediments record changes in oxygen concentrations and were studied for the last 25 kyr. Oxygen concentrations dropped at the end of the last glacial and became further reduced during the Holocene, probably due to the increasing age of the low-oxygen water mass.
Calla M. Schmidt, Tamara E. C. Kraus, Megan B. Young, and Carol Kendall
Biogeosciences, 15, 353–367,Short summary
In this study we measured phytoplankton use of nitrogen from wastewater treatment plant effluent in a river. The project was designed to test a new technique for isolating phytoplankton from river water prior to isotopic analysis in order to use trace nitrogen source use under environmental conditions. This study helps us understand the fate of anthropogenic nitrogen in aquatic ecosystems, which is essential to establishing effective nutrient management plans.
Jassin Petersen, Christine Barras, Antoine Bézos, Carole La, Lennart J. de Nooijer, Filip J. R. Meysman, Aurélia Mouret, Caroline P. Slomp, and Frans J. Jorissen
Biogeosciences, 15, 331–348,Short summary
In Lake Grevelingen, a coastal ecosystem, foraminifera experience important temporal variations in oxygen concentration and in pore water manganese. The high resolution of LA-ICP-MS allows us to analyse the chambers of foraminiferal shells separately and to obtain signals from a series of calcification events. We estimate the variability in Mn/Ca observed within single shells due to biomineralization and show that a substantial part of the signal is related to environmental variability.
Juliane Meyer, Claudia Wrozyna, Albrecht Leis, and Werner E. Piller
Biogeosciences, 14, 4927–4947,Short summary
Isotopic signatures of ostracods from Florida correlate with their host water, implying a regional influence of temperature and precipitation. Calculated monthly configurations of a theoretical calcite formed in rivers were compared to ostracod isotope compositions. The data suggest a seasonal shell formation during early spring that is coupled to the hydrological cycle of the region. The surprising seasonality of the investigated ostracods is of importance for paleontological interpretation.
Na Zhao, Ping Meng, Yabing He, and Xinxiao Yu
Biogeosciences, 14, 3431–3444,Short summary
Few researchers have investigated post-photosynthetic 13C fractionation happening in leaves. Potted saplings were cultivated under orthogonal treatments of CO2 concentration and soil water content. The 13C fractionation from mesophyll conductance and post-carboxylation both contributed to the total 13C fractionation that was determined by δ13C of water-soluble compounds and gas-exchange measurements.
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We measured the abundance of a nitrogen (N) isotope (15N) in two subtropical forests in China to study the cycling of input N (deposition and addition). Plant leaves in both forests were 15N-depleted relative to the atmospheric standard, likely as an imprint from 15N-depleted deposition. Plant 15N changed into 15N of the added N, indicating incorporation of N into plants. Thus, interpretations of ecosystem 15N from high-N-deposition regions need to include data on the 15N deposition signature.
We measured the abundance of a nitrogen (N) isotope (15N) in two subtropical forests in China to...