scholarly journals Long-term trends in the chemistry of atmospheric deposition in Northwestern Italy: the role of increasing Saharan dust deposition

Tellus B ◽  
2004 ◽  
Vol 56 (5) ◽  
pp. 426-434 ◽  
Author(s):  
M. Rogora ◽  
R. Mosello ◽  
A. Marchetto
2014 ◽  
Vol 11 (2) ◽  
pp. 425-442 ◽  
Author(s):  
C. Guieu ◽  
F. Dulac ◽  
C. Ridame ◽  
P. Pondaven

Abstract. The main goal of project DUNE was to estimate the impact of atmospheric deposition on an oligotrophic ecosystem based on mesocosm experiments simulating strong atmospheric inputs of eolian mineral dust. Our mesocosm experiments aimed at being representative of real atmospheric deposition events onto the surface of oligotrophic marine waters and were an original attempt to consider the vertical dimension after atmospheric deposition at the sea surface. This introductory paper describes the objectives of DUNE and the implementation plan of a series of mesocosm experiments conducted in the Mediterranean Sea in 2008 and 2010 during which either wet or dry and a succession of two wet deposition fluxes of 10 g m−2 of Saharan dust have been simulated based on the production of dust analogs from erodible soils of a source region. After the presentation of the main biogeochemical initial conditions of the site at the time of each experiment, a general overview of the papers published in this special issue is presented. From laboratory results on the solubility of trace elements in dust to biogeochemical results from the mesocosm experiments and associated modeling, these papers describe how the strong simulated dust deposition events impacted the marine biogeochemistry. Those multidisciplinary results are bringing new insights into the role of atmospheric deposition on oligotrophic ecosystems and its impact on the carbon budget. The dissolved trace metals with crustal origin – Mn, Al and Fe – showed different behaviors as a function of time after the seeding. The increase in dissolved Mn and Al concentrations was attributed to dissolution processes. The observed decrease in dissolved Fe was due to scavenging on sinking dust particles and aggregates. When a second dust seeding followed, a dissolution of Fe from the dust particles was then observed due to the excess Fe binding ligand concentrations present at that time. Calcium nitrate and sulfate were formed in the dust analog for wet deposition following evapocondensation with acids for simulating cloud processing by polluted air masses under anthropogenic influence. Using a number of particulate tracers that were followed in the water column and in the sediment traps, it was shown that the dust composition evolves after seeding by total dissolution of these salts. This provided a large source of new dissolved inorganic nitrogen (DIN) in the surface waters. In spite of this dissolution, the typical inter-elemental ratios in the particulate matter, such as Ti / Al or Ba / Al, are not affected during the dust settling, confirming their values as proxies of lithogenic fluxes or of productivity in sediment traps. DUNE experiments have clearly shown the potential for Saharan wet deposition to modify the in situ concentrations of dissolved elements of biogeochemical interest such as Fe and also P and N. Indeed, wet deposition yielded a transient increase in dissolved inorganic phosphorus (DIP) followed by a very rapid return to initial conditions or no return to initial conditions when a second dust seeding followed. By transiently increasing DIP and DIN concentrations in P- and N-starved surface waters of the Mediterranean Sea, wet deposition of Saharan dust can likely relieve the potential P and/or N limitation of biological activity; this has been directly quantified in terms of biological response. Wet deposition of dust strongly stimulated primary production and phytoplanktonic biomass during several days. Small phytoplankton (< 3 μm) was more stimulated after the first dust addition, whereas the larger size class (> 3 μm) significantly increased after the second one, indicating that larger-sized cells need further nutrient supply in order to be able to adjust their physiology and compete for resource acquisition and biomass increase. Among the microorganisms responding to the atmospheric inputs, diazotrophs were stimulated by both wet and dry atmospheric deposition, although N2 fixation was shown to be only responsible for a few percent of the induced new production. Dust deposition modified the bacterial community structure by selectively stimulating and inhibiting certain members of the bacterial community. The microbial food web dynamics were strongly impacted by dust deposition. The carbon budget indicates that the net heterotrophic character (i.e., ratio of net primary production to bacteria respiration < 1) of the tested waters remained (or was even increased) after simulated wet or dry deposition despite the significant stimulation of autotrophs after wet events. This indicates that the oligotrophic tested waters submitted to dust deposition are a net CO2 source. Nonetheless, the system was able to export organic material, half of it being associated with lithogenic particles through aggregation processes between lithogenic particles and organic matter. These observations support the "ballast" hypothesis and suggest that this "lithogenic carbon pump" could represent a major contribution of the global carbon export to deep waters in areas receiving high rates of atmospheric deposition. Furthermore, a theoretical microbial food web model showed that, all other things being equal, carbon, nitrogen and phosphorus stoichiometric mismatch along the food chain can have a substantial impact on the ecosystem response to nutrient inputs from dusts, with changes in the biomass of all biological compartments by a factor of ~ 2–4, and shifts from net autotrophy to net heterotrophy. Although the model was kept simple, it highlights the importance of stoichiometric constrains on the dynamics of microbial food webs.


2014 ◽  
Vol 11 (19) ◽  
pp. 5621-5635 ◽  
Author(s):  
C. Guieu ◽  
C. Ridame ◽  
E. Pulido-Villena ◽  
M. Bressac ◽  
K. Desboeufs ◽  
...  

Abstract. By bringing new nutrients and particles to the surface ocean, atmospheric deposition impacts biogeochemical cycles. The extent to which those changes are modifying the carbon balance in oligotrophic environments such as the Mediterranean Sea that receives important Saharan dust fluxes is unknown. The DUNE (DUst experiment in a low Nutrient, low chlorophyll Ecosystem) project provides the first attempt to evaluate the changes induced in the carbon budget of a large body of oligotrophic waters after simulated Saharan dust wet or dry deposition events, allowing us to measure (1) the metabolic fluxes while the particles are sinking and (2) the particulate organic carbon export. Here we report the results for the three distinct artificial dust seeding experiments simulating wet or dry atmospheric deposition onto large mesocosms (52 m3) that were conducted in the oligotrophic waters of the Mediterranean Sea in the summers of 2008 and 2010. Although heterotrophic bacteria were found to be the key players in the response to dust deposition, net primary production increased about twice in case of simulated wet deposition (that includes anthropogenic nitrogen). The dust deposition did not produce a shift in the metabolic balance as the tested waters remained net heterotrophic (i.e., net primary production to bacteria respiration ratio <1) and in some cases the net heterotrophy was even enhanced by the dust deposition. The change induced by the dust addition on the total organic carbon pool inside the mesocosm over the 7 days of the experiments, was a carbon loss dominated by bacteria respiration that was at least 5–10 times higher than any other term involved in the budget. This loss of organic carbon from the system in all the experiments was particularly marked after the simulation of wet deposition. Changes in biomass were mostly due to an increase in phytoplankton biomass but when considering the whole particulate organic carbon pool it was dominated by the organic carbon aggregated to the lithogenic particles still in suspension in the mesocosm at the end of the experiment. Assuming that the budget is balanced, the dissolved organic carbon (DOC) pool was estimated by the difference between the total organic carbon and the particulate organic carbon (POC) pool. The partitioning between dissolved and particulate organic carbon was dominated by the dissolved pool with a DOC consumption over 7 days of ∼1 μmol C L−1 d−1 (dry deposition) to ∼2–5 μmol C L−1 d−1 (wet deposition). This consumption in the absence of any allochthonous inputs in the closed mesocosms meant a small <10% decrease of the initial DOC stock after a dry deposition but a ∼30–40% decrease of the initial DOC stock after wet deposition. After wet deposition, the tested waters, although dominated by heterotrophy, were still maintaining a net export (corrected from controls) of particulate organic carbon (0.5 g in 7 days) even in the absence of allochthonous carbon inputs. This tentative assessment of the changes in carbon budget induced by a strong dust deposition indicates that wet deposition by bringing new nutrients has higher impact than dry deposition in oligotrophic environments. In the western Mediterranean Sea, the mineral dust deposition is dominated by wet deposition and one perspective of this work is to extrapolate our numbers to time series of deposition during similar oligotrophic conditions to evaluate the overall impact on the carbon budget at the event and seasonal scale in the surface waters of the northwestern Mediterranean Sea. These estimated carbon budgets are also highlighting the key processes (i.e., bacterial respiration) that need to be considered for an integration of atmospheric deposition in marine biogeochemical modeling.


2020 ◽  
Vol 727 ◽  
pp. 138519
Author(s):  
Carmen Pérez-Martínez ◽  
Kathleen M. Rühland ◽  
John P. Smol ◽  
Vivienne J. Jones ◽  
José M. Conde-Porcuna

1990 ◽  
Vol 66 (1) ◽  
pp. 32-34 ◽  
Author(s):  
Roger A. Sedjo

This paper examines the role of Canada in world forest resource production. A broad overview of global timber supply is presented together with an overview of likely future sources. The discussion covers both regions of supply as well as the nature of the forest resource — old growth, second growth, and plantation forest. Within this broad perspective some long-term trends and tendencies are identified. The growing role of plantation and intensively managed forestry is discussed. Canada's strengths and liabilities as a forest resource supplier are discussed within this context. It is argued that Canada cannot compete successfully with semi-tropical regions in intensive forest management. Rather, Canada appears to have the features necessary to compete in world wood markets using a strategy of extensive forestry that takes advantage of Canada's vast forest land areas.


2007 ◽  
Vol 41 (2) ◽  
pp. 291-315 ◽  
Author(s):  
Michael Jandl

This article examines the consequences of the latest round of EU-Enlargement in May 2004 on irregular migration across Central and Eastern Europe. Drawing on a unique collection of both quantitative and qualitative data related to irregular migration and human smuggling, the article first presents some long-term trends in irregular migration across the region before taking up more recent developments in 2003 and 2004. While border apprehensions have broadly declined since about 2000 there is ample evidence for an increasing role of human smugglers in facilitating irregular migration. In addition, there are noticeable changes in the modus operandi of human smugglers.


Hydrobiologia ◽  
2006 ◽  
Vol 562 (1) ◽  
pp. 17-40 ◽  
Author(s):  
M. Rogora ◽  
R. Mosello ◽  
S. Arisci ◽  
M. C. Brizzio ◽  
A. Barbieri ◽  
...  

2015 ◽  
Vol 60 (2) ◽  
pp. 629-640 ◽  
Author(s):  
T. Miyazako ◽  
H. Kamiya ◽  
T. Godo ◽  
Y. Koyama ◽  
Y. Nakashima ◽  
...  

2015 ◽  
Vol 8 (7) ◽  
pp. 2801-2811 ◽  
Author(s):  
B. Laurent ◽  
R. Losno ◽  
S. Chevaillier ◽  
J. Vincent ◽  
P. Roullet ◽  
...  

Abstract. Deposition is one of the key terms of the mineral dust cycle. However, dust deposition remains poorly constrained in transport models simulating the atmospheric dust cycle. This is mainly due to the limited number of relevant deposition measurements. This paper aims to present an automatic collector (CARAGA), specially developed to sample the total (dry and wet) atmospheric deposition of insoluble dust in remote areas. The autonomy of the CARAGA can range from 25 days to almost 1 year depending on the programmed sampling frequency (from 1 day to 2 weeks respectively). This collector is used to sample atmospheric deposition of Saharan dust on the Frioul islands in the Gulf of Lions in the Western Mediterranean. To quantify the mineral dust mass in deposition samples, a weighing and ignition protocol is applied. Almost 2 years of continuous deposition measurements performed on a weekly sampling basis on Frioul Island are presented and discussed with air mass trajectories and satellite observations of dust. Insoluble mineral deposition measured on Frioul Island was 2.45 g m−2 for February to December 2011 and 3.16 g m−2 for January to October 2012. Nine major mineral deposition events, measured during periods with significant MODIS aerosol optical depths, were associated with air masses coming from the southern Mediterranean Basin and North Africa.


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