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Combined list of the recent articles of the journal Biogeosciences and the recent discussion forum Biogeosciences Discussions



 



Soil properties impacting denitrifier community size, structure, and activity in New Zealand dairy-grazed pasture

Fri, 22 Sep 2017 11:58:09 +0200

Soil properties impacting denitrifier community size, structure, and activity in New Zealand dairy-grazed pasture
Neha Jha, Surinder Saggar, Donna Giltrap, Russ Tillman, and Julie Deslippe
Biogeosciences, 14, 4243-4253, https://doi.org/10.5194/bg-14-4243-2017, 2017
Denitrification is an anaerobic respiration process that is the primary contributor of the nitrous oxide (N2O) produced from grassland soils. Our objective was to gain insight into the relationships between denitrifier community size, structure, and activity for a range of pasture soils. We collected 10 dairy pasture soils with contrasting soil textures, drainage classes, management strategies (effluent irrigation or non-irrigation), and geographic locations in New Zealand, and measured their physicochemical characteristics. We measured denitrifier abundance by quantitative polymerase chain reaction (qPCR) and assessed denitrifier diversity and community structure by terminal restriction fragment length polymorphism (T-RFLP) of the nitrite reductase (nirS, nirK) and N2O reductase (nosZ) genes. We quantified denitrifier enzyme activity (DEA) using an acetylene inhibition technique. We investigated whether varied soil conditions lead to different denitrifier communities in soils, and if so, whether they are associated with different denitrification activities and are likely to generate different N2O emissions. Differences in the physicochemical characteristics of the soils were driven mainly by soil mineralogy and the management practices of the farms. We found that nirS and nirK communities were strongly structured along gradients of soil water and phosphorus (P) contents. By contrast, the size and structure of the nosZ community was unrelated to any of the measured soil characteristics. In soils with high water content, the richnesses and abundances of nirS, nirK, and nosZ genes were all significantly positively correlated with DEA. Our data suggest that management strategies to limit N2O emissions through denitrification are likely to be most important for dairy farms on fertile or allophanic soils during wetter periods. Finally, our data suggest that new techniques that would selectively target nirS denitrifiers may be the most effective for limiting N2O emissions through denitrification across a wide range of soil types.



Distribution and C / N stoichiometry of dissolved organic matter in the North Sea in summer 2011–12

Fri, 22 Sep 2017 11:58:09 +0200

Distribution and C / N stoichiometry of dissolved organic matter in the North Sea in summer 2011–12
Saisiri Chaichana, Tim Jickells, and Martin Johnson
Biogeosciences Discuss., https//doi.org/10.5194/bg-2017-387,2017
Manuscript under review for BG (discussion: open, 0 comments)
Organic molecules dissolved in the waters of coastal seas (DOM) are a potentially important vector for carbon transport to and storage in the open ocean. DOM carbon and nitrogen concentrations from two consecutive summers in the North Sea show a strong pattern of concentrations decreasing away from land. We also observe significant differences between the years in both the DOM concentration and C : N ratios, indicative of differences either in biogeochemistry or circulation between the years.



Ideas and perspectives: Can we use the soil carbon saturation deficit to quantitatively assess the soil carbon storage potential, or should we explore other strategies?

Fri, 22 Sep 2017 11:58:09 +0200

Ideas and perspectives: Can we use the soil carbon saturation deficit to quantitatively assess the soil carbon storage potential, or should we explore other strategies?
Pierre Barré, Denis A. Angers, Isabelle Basile-Doelsch, Antonio Bispo, Lauric Cécillon, Claire Chenu, Tiphaine Chevallier, Delphine Derrien, Thomas K. Eglin, and Sylvain Pellerin
Biogeosciences Discuss., https//doi.org/10.5194/bg-2017-395,2017
Manuscript under review for BG (discussion: open, 0 comments)
Soil C storage is currently discussed at a high political level. This paper discusses whether the concept of soil C saturation deficit can be appropriate to determine quantitatively the soil C storage potential and contribute to answer operational questions raised by policy makers. After a review of the literature, we conclude that for practical and conceptual reasons, the C saturation deficit is not appropriate for assessing quantitatively the soil total OC storage potential.



Carbon dioxide emissions from the flat bottom and shallow Nam Theun 2 Reservoir: drawdown area as a neglected pathway to the atmosphere

Fri, 22 Sep 2017 11:58:09 +0200

Carbon dioxide emissions from the flat bottom and shallow Nam Theun 2 Reservoir: drawdown area as a neglected pathway to the atmosphere
Chandrashekhar Deshmukh, Frédéric Guérin, Axay Vongkhamsao, Sylvie Pighini, Phetdala Oudone, Saysoulinthone Sopraseuth, Arnaud Godon, Wanidaporn Rode, Pierre Guédant, Priscia Oliva, Stéphane Audry, Cyril Zouiten, Corinne Galy-Lacaux, Henri Robain, Olivier Ribolzi, Arun Kansal, Vincent Chanudet, Stéphane Descloux, and Dominique Serça
Biogeosciences Discuss., https//doi.org/10.5194/bg-2017-380,2017
Manuscript under review for BG (discussion: open, 0 comments)
Based on an intense monitoring of CO2 concentrations and Organic and inorganic carbon in the reservoir, in the rivers upstream and downstream and of CO2 emissions from the drawdown area, we confirmd the importance of the flooded stock of organic matter as a source of C fuelling emissions and we show that the drawdown area contributes, depending on the year, from 50 % to 75 % of total annual gross emissions in the flat and shallow Nam Theun 2 Reservoir.



Impacts of droughts and extreme temperature events on gross primary production and ecosystem respiration: a systematic assessment across ecosystems and climate zones

Fri, 22 Sep 2017 11:58:09 +0200

Impacts of droughts and extreme temperature events on gross primary production and ecosystem respiration: a systematic assessment across ecosystems and climate zones
Jannis von Buttlar, Jakob Zscheichler, Anja Rammig, Sebastian Sippel, Markus Reichstein, Alexander Knohl, Martin Jung, Olaf Menzer, M. Altaf Arain, Nina Buchmann, Alessandro Cescatti, Damiano Gianelle, Gerard Kieley, Beverly E. Law, Vincenzo Magliulo, Hank Margolis, Harry McCaughey, Lutz Merbold, Mirco Migliavacca, Leonardo Montagnani, Walter Oechel, Marian Pavelka, Matthias Peichl, Serge Rambal, Antonio Raschi, Russell L. Scott, Francesco P. Vaccari, Eva van Gorsel, Andrej Varlagin, Georg Wohlfahrt, and Miguel D. Mahecha
Biogeosciences Discuss., https//doi.org/10.5194/bg-2017-393,2017
Manuscript under review for BG (discussion: open, 0 comments)
Extreme climatic events, such as droughts and heat stress induce anomalies in ecosystem-atmosphere CO2 fluxes, such as gross primary production (GPP) and ecosystem respiration (Reco), and, hence, can change the net ecosystem carbon balance. However, despite our increasing understanding of the underlying mechanisms, the magnitudes of the impacts of different types of extremes on GPP and Reco within and between ecosystems remain poorly predicted. Here we aim to identify the major factors controlling the amplitude of extreme event impacts on GPP, Reco, and the resulting net ecosystem production (NEP). We focus on the impacts of heat and drought and their combination. We identified hydrometeorological extreme events in consistently downscaled water availability and temperature measurements over a 30 year time period. We then used FLUXNET eddy-covariance flux measurements to estimate the CO2 flux anomalies during these extreme events across dominant vegetation types and climate zones. Overall, our results indicate that short-term heat extremes increased respiration more strongly than they down-regulated GPP, resulting in a moderate reduction of the ecosystem’s carbon sink potential. In the absence of heat stress, droughts tended to have smaller and similarly dampening effects on both GPP and Reco, and, hence, often resulted in neutral NEP responses. The combination of drought and heat typically led to a strong decrease in GPP, whereas heat and drought impacts on respiration partially offset each other. Taken together, compound heat and drought events led to the strongest C sink reduction compared to any single-factor extreme. A key insight of this paper, however, is that duration matters most: for heat stress during droughts, the magnitude of impacts systematically increased with duration, whereas under heat stress without drought, the response of Reco over time turned from an initial increase to a down-regulation after about two weeks. This confirms earlier theories that not only the magnitude but also the duration of an extreme event determines its impact. Our study corroborates the results of several local site-level case studies, but as a novelty generalizes these findings at the global scale. Specifically, we find that the different response functions of the two antipodal land-atmosphere fluxes GPP and Reco can also result in increasing NEP during certain extreme conditions. Apparently counterintuitive findings of this kind bear great potential for scrutinizing the mechanisms implemented in state-of-the-art terrestrial biosphere models and provide a benchmark for future model development and testing.



Effects of shrub and tree cover increase on the near-surface atmosphere in northern Fennoscandia

Thu, 21 Sep 2017 11:58:09 +0200

Effects of shrub and tree cover increase on the near-surface atmosphere in northern Fennoscandia
Johanne H. Rydsaa, Frode Stordal, Anders Bryn, and Lena M. Tallaksen
Biogeosciences, 14, 4209-4227, https://doi.org/10.5194/bg-14-4209-2017, 2017
We investigate the atmospheric sensitivity to an expansion in shrub and tree cover in the northern Fennoscandia region. We applied a regional weather and climate model in evaluating biophysical effects of increased shrub cover at a fine resolution. We find that shrub cover increase causes a warming that is sensitive to the shrub and tree heights. Cooling effects include increased snow cover, cloud cover, and precipitation. We show that the net warming will likely increase in the future.



Process-based modelling of NH3 exchange with grazed grasslands

Thu, 21 Sep 2017 11:58:09 +0200

Process-based modelling of NH3 exchange with grazed grasslands
Andrea Móring, Massimo Vieno, Ruth M. Doherty, Celia Milford, Eiko Nemitz, Marsailidh M. Twigg, László Horváth, and Mark A. Sutton
Biogeosciences, 14, 4161-4193, https://doi.org/10.5194/bg-14-4161-2017, 2017
This study describes and evaluates a new ammonia (NH3) exchange model for grazed fields (GAG_field). GAG_field is able to simulate the main features of the observed NH3 fluxes. A sensitivity analysis for the non-meteorological model parameters showed that the sensitivity of the NH3 fluxes to a parameter varies among urine patches. Moreover, the fluxes modelled with a dynamic soil pH are similar if a constant pH 7.5 is used, suggesting a useful simplification for regional-scale model application.



Biogeochemical cycling at the aquatic–terrestrial interface is linked to parafluvial hyporheic zone inundation history

Thu, 21 Sep 2017 11:58:09 +0200

Biogeochemical cycling at the aquatic–terrestrial interface is linked to parafluvial hyporheic zone inundation history
Amy E. Goldman, Emily B. Graham, Alex R. Crump, David W. Kennedy, Elvira B. Romero, Carolyn G. Anderson, Karl L. Dana, Charles T. Resch, Jim K. Fredrickson, and James C. Stegen
Biogeosciences, 14, 4229-4241, https://doi.org/10.5194/bg-14-4229-2017, 2017
The history of river inundation influences shoreline sediment biogeochemical cycling and microbial dynamics. Sediment exhibited a binary respiration response to rewetting, in which respiration from less recently saturated sediment was suppressed relative to more recently saturated sediment, likely due to inhibition of fungal metabolic activity. River shorelines should likely be integrated as a distinct environment into hydrobiogeochemical models to predict watershed biogeochemical function.



Soil water content drives spatiotemporal patterns of CO2 and N2O emissions from a Mediterranean riparian forest soil

Thu, 21 Sep 2017 11:58:09 +0200

Soil water content drives spatiotemporal patterns of CO2 and N2O emissions from a Mediterranean riparian forest soil
Sílvia Poblador, Anna Lupon, Santiago Sabaté, and Francesc Sabater
Biogeosciences, 14, 4195-4208, https://doi.org/10.5194/bg-14-4195-2017, 2017
This study quantified, for the first time, simultaneous rates of carbon dioxide (CO2) and nitrous oxide (N2O) from a Mediterranean riparian forest. Our results showed a strong linkage between riparian hydrology, soil microbial processes, and greenhouse gas (GHG) emissions. High CO2 effluxes occurred all year long, while N2O emissions were generally low and confined to saturated soils. Overall, this study shows that riparian soils can be hotspots of GHG emissions within Mediterranean catchment.



Inverse-model estimates of the ocean's coupled phosphorus, silicon, and iron cycles

Thu, 21 Sep 2017 11:58:09 +0200

Inverse-model estimates of the ocean's coupled phosphorus, silicon, and iron cycles
Benoît Pasquier and Mark Holzer
Biogeosciences, 14, 4125-4159, https://doi.org/10.5194/bg-14-4125-2017, 2017
We construct a model of the ocean's coupled phosphorus, silicon, and iron cycles and optimize its biogeochemical parameters. State estimates for widely differing iron sources are consistent with observations because of compensation between sources and sinks. Export production and the patterns of export supported by each iron source type (aeolian, sedimentary, hydrothermal) are well constrained. The fraction of export supported by each iron type varies systematically with its fractional source.



Water, Energy, and Carbon with Artificial Neural Networks (WECANN): a statistically based estimate of global surface turbulent fluxes and gross primary productivity using solar-induced fluorescence

Wed, 20 Sep 2017 11:58:09 +0200

Water, Energy, and Carbon with Artificial Neural Networks (WECANN): a statistically based estimate of global surface turbulent fluxes and gross primary productivity using solar-induced fluorescence
Seyed Hamed Alemohammad, Bin Fang, Alexandra G. Konings, Filipe Aires, Julia K. Green, Jana Kolassa, Diego Miralles, Catherine Prigent, and Pierre Gentine
Biogeosciences, 14, 4101-4124, https://doi.org/10.5194/bg-14-4101-2017, 2017
Water, Energy, and Carbon with Artificial Neural Networks (WECANN) is a statistically based estimate of global surface latent and sensible heat fluxes and gross primary productivity. The retrieval uses six remotely sensed observations as input, including the solar-induced fluorescence. WECANN provides estimates on a 1° × 1° geographic grid and on a monthly time scale and outperforms other global products in capturing the seasonality of the fluxes when compared to eddy covariance tower data.



On the potential causes of the recent Pelagic Sargassum blooms events in the tropical North Atlantic Ocean

Wed, 20 Sep 2017 11:58:09 +0200

On the potential causes of the recent Pelagic Sargassum blooms events in the tropical North Atlantic Ocean
Sandrine Djakouré, Moacyr Araujo, Aubains Hounsou-Gbo, Carlos Noriega, and Bernard Bourlès
Biogeosciences Discuss., https//doi.org/10.5194/bg-2017-346,2017
Manuscript under review for BG (discussion: open, 0 comments)
Since 2011, unprecedented and repetitive blooms and large mass strandings of the floating brown macroalgæ, Sargassum natans and Sargassum fluitans have been reported along the West Indies, the Caribbean, the Brazilian and the West Africa coasts. Recent studies have highlighted a new tank of Sargassum: the North Equatorial Recirculation Region of the Atlantic Ocean. This region is located off the northeast of Brazil, approximately between the equator and 10° N and from 50° W to 25° W. The potential causes of these recent blooms and mass strandings are still poorly understood. Observational datasets and modelling outputs involving hydrological parameters and climate events are examined focusing on their potential feedback on the observed blooms and mass strandings. The results show that combined conditions have been in favor of these recent changes. High anomalously unprecedented positive sea surface temperature observed in the tropical Atlantic in 2010–2011 could have induced favorable temperature conditions for Sargassum blooms. These favorable conditions were then fed by additional continental nutrients inputs, principally from the Amazon River. These continental nutrients load are the consequences of deforestation, agroindustrial and urban activities in the Amazonian forest. The results also suggest that subsurface intake of nutrients from the equatorial upwelling could also contribute to the blooms of the Sargassum seaweed in the Atlantic Ocean but further studies are needed to confirm these additional inputs.



Marine Phytoplankton Stoichiometry Mediates Nonlinear Interactions Between Nutrient Supply, Temperature, and Atmospheric CO2

Wed, 20 Sep 2017 11:58:09 +0200

Marine Phytoplankton Stoichiometry Mediates Nonlinear Interactions Between Nutrient Supply, Temperature, and Atmospheric CO2
Allison R. Moreno, George I. Hagstrom, Francois W. Primeau, Simon A. Levin, and Adam C. Martiny
Biogeosciences Discuss., https//doi.org/10.5194/bg-2017-367,2017
Manuscript under review for BG (discussion: open, 0 comments)
To determine the missing links between variation in marine elemental stoichiometry and carbon cycling, we embed four environmentally controlled stoichiometric models into an ocean box model. We found that environmentally driven shifts in stoichiometry make the biological pump more influential. We have thus shown that variation in stoichiometry can lead to nonlinear and counterintuitive controls on pCO2, suggesting the need for further studies of ocean C : P and the impact on ocean carbon cycling.



The pyrogeography of eastern boreal Canada from 1901 to 2012 simulated with the LPJ-LMfire model

Wed, 20 Sep 2017 11:58:09 +0200

The pyrogeography of eastern boreal Canada from 1901 to 2012 simulated with the LPJ-LMfire model
Emeline Chaste, Martin P. Girardin, Jed O. Kaplan, Jeanne Portier, Yves Bergeron, and Christelle Hély
Biogeosciences Discuss., https//doi.org/10.5194/bg-2017-350,2017
Manuscript under review for BG (discussion: open, 0 comments)
A vegetation model was used to reconstruct fire activity from 1901 to 2012 in relation to changes in lightning ignition, climate and vegetation in eastern Canada's boreal forest. The model correctly simulated the history of fire activity. The results showed that fire activity is ignition-limited but is also greatly affected by both climate and vegetation. This research aims to develop a vegetation model that could be used to predict the future impacts of climate changes on fire activity.



Interannual drivers of the seasonal cycle of CO2 fluxes in the Southern Ocean

Wed, 20 Sep 2017 11:58:09 +0200

Interannual drivers of the seasonal cycle of CO2 fluxes in the Southern Ocean
Luke Gregor, Schalk Kok, and Pedro M. S. Monteiro
Biogeosciences Discuss., https//doi.org/10.5194/bg-2017-363,2017
Manuscript under review for BG (discussion: open, 0 comments)
The Southern Ocean accounts for a large portion of the variability in oceanic CO2 uptake. However, the drivers of these changes are not understood due to lack of observations. In this study, we used an ensemble of gap-filling methods to estimate surface CO2. We found that winter was a more important driver of longer term variability driven by changes in wind stress. Summer variability of CO2 was driven primarily by increases in primary production.



Variability in copepod trophic levels and in feeding selectivity based on stable isotope analysis in Gwangyang Bay off the southern coast of Korea

Wed, 20 Sep 2017 11:58:09 +0200

Variability in copepod trophic levels and in feeding selectivity based on stable isotope analysis in Gwangyang Bay off the southern coast of Korea
Mianrun Chen, Dongyoung Kim, Hongbin Liu, and Chang-Keun Kang
Biogeosciences Discuss., https//doi.org/10.5194/bg-2017-364,2017
Manuscript under review for BG (discussion: open, 0 comments)
Trophism (i.e., food resources and trophic levels) of different copepod groups was assessed along a salinity gradient in the temperate estuarine Gwangyang Bay of Korea, based on seasonal investigation of taxonomic results in 2015 and stable isotope analysis incorporating multiple linear regression models. Our results depict a simple energy flow of the planktonic food web of Gwangyang Bay.



Does denitrification occur within porous carbonate sand grains?

Tue, 19 Sep 2017 11:58:09 +0200

Does denitrification occur within porous carbonate sand grains?
Perran Louis Miall Cook, Adam John Kessler, and Bradley David Eyre
Biogeosciences, 14, 4061-4069, https://doi.org/10.5194/bg-14-4061-2017, 2017
Nitrogen is the key nutrient that typically limits productivity in coastal waters. One of the key controls on the amount of bioavailable nitrogen is the process of denitrification, which converts nitrate (bioavailable) into nitrogen gas. Previous studies suggest high rates of denitrification may take place within carbonate sediments, and one explanation for this is that this process may take place within the sand grains. Here we show evidence to support this hypothesis.



Tracing the origin of the oxygen-consuming organic matter in the hypoxic zone in a large eutrophic estuary: the lower reach of the Pearl River Estuary, China

Tue, 19 Sep 2017 11:58:09 +0200

Tracing the origin of the oxygen-consuming organic matter in the hypoxic zone in a large eutrophic estuary: the lower reach of the Pearl River Estuary, China
Jianzhong Su, Minhan Dai, Biyan He, Lifang Wang, Jianping Gan, Xianghui Guo, Huade Zhao, and Fengling Yu
Biogeosciences, 14, 4085-4099, https://doi.org/10.5194/bg-14-4085-2017, 2017
We provide direct and quantitative assessments showing the marine organic matter from eutrophication-induced primary production dominated oxygen consumption in the hypoxic zone, while the terrestrially sourced organic matter also significantly contributed to the formation and maintenance of hypoxia in the lower Pearl River Estuary (PRE) and the adjacent coastal water.



A zero-power warming chamber for investigating plant responses to rising temperature

Tue, 19 Sep 2017 11:58:09 +0200

A zero-power warming chamber for investigating plant responses to rising temperature
Keith F. Lewin, Andrew M. McMahon, Kim S. Ely, Shawn P. Serbin, and Alistair Rogers
Biogeosciences, 14, 4071-4083, https://doi.org/10.5194/bg-14-4071-2017, 2017
Experiments that manipulate the temperature of plants and ecosystems are used to improve understanding of how they will respond to climate change. In logistically challenging locations passive warming using solar energy is the the only viable option for warming experiments. Unfortunately current passive warming approaches can only raise air temperature by about 1.5 °C. We have developed a novel approach that doubles the warming possible using solar energy and requires no power.



The devil's in the disequilibrium: sensitivity of ocean carbon storage to climate state and iron fertilization in a general circulation model

Tue, 19 Sep 2017 11:58:09 +0200

The devil's in the disequilibrium: sensitivity of ocean carbon storage to climate state and iron fertilization in a general circulation model
Sarah Eggleston and Eric D. Galbraith
Biogeosciences Discuss., https//doi.org/10.5194/bg-2017-328,2017
Manuscript under review for BG (discussion: open, 0 comments)
To better understand why atmospheric carbon dioxide has changed over the course of Earth's history, we analyze carbon dissolved in the ocean in a state-of-the-art model. While primary producers in the surface ocean are important to the global carbon cycle, the carbon in the ocean and atmosphere are not in equilibrium in most places, and our results indicate that the degree of this disequilibrium, which has previously been largely ignored in similar studies, could be just as significant.