Significance of atmospheric deposition to freshwater ecosystems in the southern Iberian Peninsula

The Iberian Peninsula is close to the Saharan Desert, which is the biggest source of atmospheric aerosols of the World. Currently, it is recognized that atmospheric deposition of aerosols over ecosystems is a significant source not only of elements with gaseous phases but also of rock-derived ones. In the last years we have been quantifying the atmospheric flux of elements and substances of biogeochemical interest on the aquatic ecosystems of the South Iberian Peninsula, and their impact on their functioning and structure. The results we are obtaining indicate that atmospheric contribution of P and Ca are essential to explain the functioning of high mountain lakes, and that atmospheric input of organic matter partially supports the pelagic food web of these ecosystems. In this article we offer a summary of some of the results obtained to date.La Península Ibérica está próxima al Desierto del Sahara que es la mayor fuente de aerosoles atmosféricos del Planeta. Actualmente, se reconoce que la deposición de aerosoles sobre los ecosistemas es una entrada significativa no sólo de elementos con fases gaseosas sino, también, de elementos derivados de rocas. En los últimos años hemos estado cuantificado el flujo atmosférico de elementos y sustancias de interés biogeoquímico sobre los ecosistemas acuáticos del sur de la Península Ibérica y el impacto sobre su funcionamiento y estructura. Los resultados que estamos obteniendo indican que los aportes atmosféricos de P y Ca son esenciales para explicar el funcionamiento de los lagos de alta montaña y que las entradas atmosféricas de materia orgánica sostienen parcialmente las redes tróficas pelágicas de estos ecosistemas. En este artículo ofrecemos un resumen de algunos de los resultados obtenidos hasta ahora

Microbial food web dynamics in response to a Saharan dust event: results from a mesocosm study in the oligotrophic Mediterranean Sea

BiogeosciencesInternational audienceThe significant impact of dust deposition on het-erotrophic bacterial dynamics in the surface oligotrophic ocean has recently been evidenced. Considering the central role of bacteria in the microbial loop, it is likely that dust deposition also affects the structure and the functioning of the whole microbial food web. In the frame of the DUNE project, aiming to estimate the impact of dust deposition on the oligotrophic Mediterranean Sea through mesocosm ex-periments, the main goal of the present paper was to as-sess how two successive dust deposition events affect the dynamics of the microbial food web. The first dust seeding delivered new P and N to the amended mesocosms and re-sulted in a pronounced stimulation of bacterial respiration. It also induced pronounced, but transient, changes in the bac-terial community composition. No significant effects were observed on the abundances of viruses and heterotrophic nanoflagellates. The second dust seeding also delivered new P and N to the amended mesocosms, but the effect on the microbial food web was very different. Bacterial respira-tion remained constant and bacterial abundance decreased. Compositional changes following the second seeding were minor compared to the first one. The decrease in bacterial abundance coincided with an increase in virus abundance, resulting in higher virus : bacteria ratios throughout the sec-ond seeding period. Our study shows that dust deposition to the surface oligotrophic ocean may involve important mod-ifications of the trophic links among the components of the microbial food web with presumed consequences on C and nutrient cycling

Atmospheric deposition of organic matter at a remote site in the central Mediterranean Sea: implications for the marine ecosystem

Abstract. Atmospheric fluxes of dissolved organic matter (DOM) were studied for the first time on the island of Lampedusa, a remote site in the central Mediterranean Sea (Med Sea), between 19 March 2015 and 1 April 2017. The main goals of this study were to quantify total atmospheric deposition of DOM in this area and to evaluate the impact of Saharan dust deposition on DOM dynamics in the surface waters of the Mediterranean Sea. Our data show high variability in DOM deposition rates without a clear seasonality and a dissolved organic carbon (DOC) input from the atmosphere of 120.7 mmol DOC m−2 yr−1. Over the entire time series, the average dissolved organic phosphorus (DOP) and dissolved organic nitrogen (DON) contributions to the total dissolved pools were 40 % and 26 %, respectively. The data on atmospheric elemental ratios also show that each deposition event is characterized by a specific elemental ratio, suggesting a high variability in DOM composition and the presence of multiple sources. This study indicates that the organic substances transported by Saharan dust on Lampedusa mainly come from a natural sea spray and that Saharan dust can be an important carrier of organic substances even though the load of DOC associated with dust is highly variable. Our estimates suggest that atmospheric input has a larger impact on the Med Sea than on the global ocean. Further, DOC fluxes from the atmosphere to the Med Sea can be up to 6 times larger than total river input. Longer time series combined with modeling would greatly improve our understanding of the response of DOM dynamics in the Med Sea to the change in aerosol deposition pattern due to the effect of climate change

El papel de la deposición atmosférica en la biogeoquímica de laguna de alta montaña (Sierra Nevada, España)

Atmosphere is an important route through which many elements are transported long distances from their sources. Atmospheric particles, known as aerosols, have multiple origins, both natural and anthropogenic. Natural sources, such as sea salt and dust, are responsible for almost 90% of global aerosol emissions (SCHLESINGER, 1997). Arid and semiarid regions are the main sources of soil dust to the atmosphere and, among them, the Sahara desert is the world’s major source of soil dust, with an annual production of 400-700·106 tons per year, almost 50% of the global dust production (SCHÜTZ ET AL. 1981; D’ALMEIDA, 1986; SWAP ET AL. 1996). Every year, large amounts of desert dust are exported from the Sahara to the North Atlantic Ocean and the Mediterranean region. The transport towards Atlantic Ocean is linked to the general atmospheric circulation that has predominant wind directions from west and northwest. By contrast, northward transport of dust over the Mediterranean is influenced by the presence of cyclones (MOULIN ET AL. 1997). The seasonal pattern of African dust transport over the Mediterranean shows a maximum dust load in the central and eastern basins during spring, and in the central and western basins during summer (MOULIN ET AL. 1997). The Iberian Peninsula, located in the western basin, receives African dust mainly during late spring and summer under particular meteorological conditions (RODRIGUEZ ET AL. 2001). Atmospheric deposition can play a major role in biogeochemical cycling in both terrestrial and aquatic ecosystems. Inputs of elements from the atmosphere have sustained the productivity of Hawaiian rainforests during millions of years (CHADWICK ET AL. 1999), and atmospheric deposition can account for 34% of the calcium required for Quercus ilex forest growth in northeastern Spain (AVILA ET AL. 1997). On the other hand, there are growing evidences that atmospheric inputs have an impact on marine chemical cycling and on biological processes in the sea (DUCE ET AL. 1991). Atmospheric deposition is the major input of iron to the open ocean (DUCE & TINDALE, 1991) and atmospheric input of phosphorus can represent up to 14% of total primary production demands in the open western Mediterranean Sea (RIDAME & GUIEU, 2002). The role of atmospheric deposition in the biogeochemistry of freshwater ecosystems has been less explored relative to marine ecosystems and most of the effort has been focused on the effects of acid rain (SULLIVAN ET AL. 1990; KOPAČEK ET AL. 1995; TAIT & THALER, 2000). The contribution of atmospheric inputs of nutrients and Elvira Pulido Manuel de Villena. TESIS DOCTORAL 4 oligoelements to biological processes and chemical properties of lakes has been scantly assessed (PETERS, 1977; GIBSON ET AL. 1995). There are around 50 lakes in the Sierra Nevada mountains (SE Spain) located at elevations of 2800-3100 m above sea level. They are located above tree line in a remote area far from human activity. This location along with their oligotrophic nature make these lakes ideal sites to assess the impact of dust deposition on freshwater ecosystems. In this study, two lakes with contrasting catchments located in the Sierra Nevada mountains were selected. La Caldera Lake is located on rocky terrain, has no inlets and, hence, does not receive any inputs from stream runoff. In contrast, Río Seco Lake is located in a catchment covered by alpine meadows and has temporary inlets that drain water from the catchment. The main goal of this PhD thesis is to assess the influence of atmospheric deposition on the biogeochemistry of these two high mountain lakes. This question is addressed in four different chapters that represent the main topics of this study.Tesis Univ. Granada

El papel de la deposición atmosférica en la biogeoquímica de laguna de alta montaña (Sierra Nevada, España)

Atmosphere is an important route through which many elements are transported long distances from their sources. Atmospheric particles, known as aerosols, have multiple origins, both natural and anthropogenic. Natural sources, such as sea salt and dust, are responsible for almost 90% of global aerosol emissions (SCHLESINGER, 1997). Arid and semiarid regions are the main sources of soil dust to the atmosphere and, among them, the Sahara desert is the world’s major source of soil dust, with an annual production of 400-700·106 tons per year, almost 50% of the global dust production (SCHÜTZ ET AL. 1981; D’ALMEIDA, 1986; SWAP ET AL. 1996). Every year, large amounts of desert dust are exported from the Sahara to the North Atlantic Ocean and the Mediterranean region. The transport towards Atlantic Ocean is linked to the general atmospheric circulation that has predominant wind directions from west and northwest. By contrast, northward transport of dust over the Mediterranean is influenced by the presence of cyclones (MOULIN ET AL. 1997). The seasonal pattern of African dust transport over the Mediterranean shows a maximum dust load in the central and eastern basins during spring, and in the central and western basins during summer (MOULIN ET AL. 1997). The Iberian Peninsula, located in the western basin, receives African dust mainly during late spring and summer under particular meteorological conditions (RODRIGUEZ ET AL. 2001). Atmospheric deposition can play a major role in biogeochemical cycling in both terrestrial and aquatic ecosystems. Inputs of elements from the atmosphere have sustained the productivity of Hawaiian rainforests during millions of years (CHADWICK ET AL. 1999), and atmospheric deposition can account for 34% of the calcium required for Quercus ilex forest growth in northeastern Spain (AVILA ET AL. 1997). On the other hand, there are growing evidences that atmospheric inputs have an impact on marine chemical cycling and on biological processes in the sea (DUCE ET AL. 1991). Atmospheric deposition is the major input of iron to the open ocean (DUCE & TINDALE, 1991) and atmospheric input of phosphorus can represent up to 14% of total primary production demands in the open western Mediterranean Sea (RIDAME & GUIEU, 2002). The role of atmospheric deposition in the biogeochemistry of freshwater ecosystems has been less explored relative to marine ecosystems and most of the effort has been focused on the effects of acid rain (SULLIVAN ET AL. 1990; KOPAČEK ET AL. 1995; TAIT & THALER, 2000). The contribution of atmospheric inputs of nutrients and Elvira Pulido Manuel de Villena. TESIS DOCTORAL 4 oligoelements to biological processes and chemical properties of lakes has been scantly assessed (PETERS, 1977; GIBSON ET AL. 1995). There are around 50 lakes in the Sierra Nevada mountains (SE Spain) located at elevations of 2800-3100 m above sea level. They are located above tree line in a remote area far from human activity. This location along with their oligotrophic nature make these lakes ideal sites to assess the impact of dust deposition on freshwater ecosystems. In this study, two lakes with contrasting catchments located in the Sierra Nevada mountains were selected. La Caldera Lake is located on rocky terrain, has no inlets and, hence, does not receive any inputs from stream runoff. In contrast, Río Seco Lake is located in a catchment covered by alpine meadows and has temporary inlets that drain water from the catchment. The main goal of this PhD thesis is to assess the influence of atmospheric deposition on the biogeochemistry of these two high mountain lakes. This question is addressed in four different chapters that represent the main topics of this study.Tesis Univ. Granada

Dust iron dissolution in seawater: Results from a one-year time-series in the Mediterranean Sea

International audienceA better comprehension of atmospheric iron dissolution in seawater would be a key advance in understanding the atmospheric supply of iron to the ocean and its role on marine biogeochemistry. So far, different studies have demonstrated that dissolution of atmospheric iron depends on physical and chemical properties of the particles, which can be modified during their transport from the source. Here, based on a one-year time-series in the Western Mediterranean Sea, we show that dissolution of iron from a Saharan desert dust sample in seawater follows the seasonal trend of the dissolved organic carbon (DOC) variability in the surface layer. As part of the DOC pool, the role of iron binding ligands, probably derived from bacteria activity, has also been investigated. The dust iron dissolution rates are found to be linearly dependent on iron binding ligands and dissolved organic carbon concentrations (r 2 > 0.65, p < 0.01, n = 9)

Transient fertilizing effect of dust in P-deficient LNLC surface ocean

International audienceIn much of the world's low-nutrient low-chlorophyll (LNLC) oceans, including the Mediterranean Sea, surface dissolved inorganic phosphorus (DIP) is below the detection limit of conventional techniques. Although dust deposition has been generally recognized as a major source of P to the Mediterranean Sea, the lack of DIP data at nanomolar levels has so far precluded a quantification of this effect. This work reports the first one-year time series of surface nanomolar DIP in the Mediterranean Sea. Moreover, by combining nanomolar DIP data from two field studies (the above cited time-series and an experimental addition of Saharan dust to large mesocosms) and one in vitro dust dissolution experiment, we show that dust pulses may indeed provoke transient increases in DIP concentration (up to 80 nM) in P-starved surface waters of this LNLC region. Citation: Pulido-Villena, E., V. Rerolle, and C. Guieu (2010), Transient fertilizing effect of dust in P-deficient LNLC surface ocean, Geophys. Res. Lett., 37, L01603, doi: 10.1029/2009GL041415

Significance of atmospheric inputs of calcium over the southwestern Mediterranean region: High mountain lakes as tools for detection

We quantified dry and wet atmospheric deposition of calcium over the southwest Mediterranean region and we assessed its impact on calcium dynamics of two high mountain lakes differing in morphometry and catchment characteristics. Atmospheric deposition of Ca averaged 40 mmol m(-2) yr(-1), and it showed a seasonal pattern similar to that reported for Saharan dust export to the Mediterranean region, with maxima during spring and summer. Ca enrichment from nonmarine sources was significantly related to the TOMS (Total Ozone Mapping Spectrometer) aerosol index. Atmospheric inputs significantly affected Ca concentration of the selected lakes, which do not presumably receive significant Ca inputs from weathering. The intensity of the effect depended on their corresponding sensitivities to evaporation. Total atmospheric inputs of Ca to each study lake catchment (11300 and 3100 moles) were enough to explain the lake Ca content (5400 and 111 moles, respectively). The results obtained in this study reveal that atmospheric inputs, particularly Saharan dust deposition, may be a significant source of calcium to remote mountain lakes

Evidence of an atmospheric forcing on bacterioplankton and phytoplankton dynamics in a high mountain lake

We quantified dry and wet atmospheric deposition of soluble reactive phosphorus (SRP) to the Southwest Mediterranean region during one year and assessed its effect on bacterial abundance and phytoplankton specific biomass during one ice-free period in a high mountain lake located in an area highly influenced by Saharan dust outbreaks. Dry deposition of SRP represented 79% of total SRP inputs and it showed a seasonal pattern similar to Saharan dust export to this region, with maxima during spring and summer. Bacterial abundance was significantly correlated with SRP atmospheric deposition, suggesting the influence of this input on bacterioplankton dynamics. The field evidence was experimentally corroborated using bacterial regrowth cultures performed with dust-amended lake water. Dust addition significantly increased SRP concentration in lake water and it stimulated bacterial abundance. Regarding phytoplankton community, only one species, the chrysophyte Chromulina nevadensis, was significantly related to SRP inputs and, consequently, there was a significant decrease in phytoplankton species diversity after atmospheric SRP inputs. Since changes in climate will presumably lead to an alteration in dust export, these results point to the need of further studies on the potential effects of this alteration on bacterioplankton and phytoplankton dynamics in remote oligotrophic systems

Chemical signature of Saharan dust on dry and wet atmospheric deposition in the south-western Mediterranean region

We studied if the presence of Saharan dust intrusions and the rains modify the chemical signature of the wet and dry deposition in the southern Iberian Peninsula. We have sorted the 109 sampling weeks by the presence (rainy weeks) or absence (dry weeks) of rain and by the occurrence or not of Saharan dust intrusions. Dry deposition dominated the delivery of particulate material (PM), total phosphorus (TP), soluble reactive phosphorus (SRP), Ca2+, Mg2+ and K+, whereas wet deposition dominated the delivery of Na+, total nitrogen, and. In the dry weeks, the presence of Saharan dust intrusions lead to higher inputs of PM, TP, SRP, Ca2+, Mg2+ and K+ in the dry deposition. Conversely, in the rainy weeks, there were no differences in mean values of dry deposition irrespective of the occurrence of Saharan dust intrusions. Nevertheless, in the presence of Saharan intrusions and some rain, the weekly collection of PM, TP and Ca2+ in dry deposition were significantly higher and increased as rainfall was lower. By contrast, the ions Cl&#x2013; and Na+ in wet deposition were higher in absence of Saharan dust intrusion and increased as rainfall increased