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

Clases de tamaño, grupos quimiotaxonómicos y propiedades bio-ópticas del fitoplancton a lo largo de un transecto desde el mar Mediterráneo al SO del océano Atlántico

The relationships between the structure of the phytoplankton community and the bio-optical properties of surface waters were studied during the TransPEGASO cruise along a transect across the Atlantic Ocean that covered seven biogeographical provinces, from the Alborán Sea (SW Mediterranean) to the Patagonian Shelf. We characterized the composition of the phytoplankton community by means of high-performance liquid chromatography and CHEMTAX pigment analyses applied to whole water and two filtration size classes ( 0.5 mg m-3) with a single Mediterranean (MEDI) sample and those from the southwestern Atlantic Shelf (SWAS). According to CHEMTAX, the most important taxa in the tropical and subtropical Atlantic were Prochlorococcus, haptophytes and Synechoccoccus, while the MEDI and SWAS were dominated by diatoms and haptophytes. Both the VU and HI algorithms, which are based on pigment composition or Chl a concentration, predicted for SWAS a high proportion of nano- and microphytoplankton, while the SFF indicated dominance of the 0.5 mg m-3) con una sola muestra mediterránea (MEDI) y las de la plataforma patagónica, en el sudoeste del Atlántico (SWAS). Según CHEMTAX, los taxones más importantes en el Atlántico tropical y subtropical fueron Prochlorococcus, haptofitos y Synechoccoccus, mientras que las provincias MEDI y SWAS estuvieron dominadas por diatomeas y haptofitos. Tanto los algoritmos VU como los HI, que se basan en la composición de pigmentos o en la concentración de Chl a, predijeron para SWAS una alta proporción de nano y microfitoplancton, mientras que la SFF indicó un dominio de la clase de tamaño < 3 μm. Por otra parte, los resultados de CHEMTAX indicaron que, en promedio, la contribución de las diatomeas era importante en esta provincia. Sin embargo, en varias estaciones de SWAS para las que CHEMTAX estimaba una elevada contribución de diatomeas, las observaciones microscópicas encontraron solamente escasas concentraciones de células de diatomeas de tamaño nano- o microplanctónico. Esta discrepancia parece deberse a la presencia, confirmada por microscopía electrónica de barrido, de pequeñas células (< 3 μm) de la diatomea Minidiscus sp. y de Parmales (un grupo que comparte la composición pigmentaria con las diatomeas). Estos hallazgos advierten contra una asignación rutinaria de los pigmentos de las diatomeas a la clase de tamaño de microplancton. La absorción total (sin contar la propia del agua) en la columna de agua estuvo dominada por CDOM. En promedio, la contribución de la absorción de fitoplancton para las diferentes provincias osciló de 19.3% en MEDI a 45.7% en SWAS y 47% en la provincia del Atlántico Tropical Occidental (WTRA). La absorción del fitoplancton por unidad de Chl a [aph*(443), m2 mg-1] fue menor en MEDI y SWAS que en las provincias oligotróficas. aph*(443) se correlacionó negativamente con el primer componente derivado de un análisis de los componentes principales basado en la concentración de los pigmentos más importantes y no se correlacionó con indicadores de la estructura de tamaños de la comunidad fitoplanctónica tales como la proporción de Chl a en la clase < 3 μm o un índice de tamaño (SI) derivado de la distribución de clases de tamaño obtenida mediante el algoritmo VU. Estas observaciones indican que la variabilidad observada en aph*(443) se relacionaba principalmente con diferencias en la composición pigmentaria y posiblemente también con procesos de fotoaclimatación del fitoplancton, y que cualquier efecto de empaquetamiento debido al tamaño de las células quedaba probablemente enmascarado por otros factores. Este último resultado puede estar relacionado con una influencia relativamente pequeña del tamaño dentro del estrecho rango de concentraciones de Chl a considerado en nuestro estudio (todas eran ≤2.4 mg m-3)

Uncoupled seasonal variability of transparent exopolymer and Coomassie stainable particles in coastal Mediterranean waters: Insights into sources and driving mechanisms

Transparent exopolymer particles (TEP) and Coomassie stainable particles (CSP) are gel-like particles, ubiquitous in the ocean, that affect important biogeochemical processes including organic carbon cycling by planktonic food webs. Despite much research on both groups of particles (especially TEP) over many years, whether they exist as distinctly stainable fractions of the same particles or as independent particles, each with different driving factors, remains unclear. To address this question, we examined the temporal dynamics of TEP and CSP over 2 complete seasonal cycles at 2 coastal sites in the Northwestern Mediterranean Sea, the Blanes Bay Microbial Observatory (BBMO) and the L’Estartit Oceanographic Station (EOS), as well as their spatial distribution along a coast-to-offshore transect. Biological, chemical, and physical variables were measured in parallel. Surface concentrations (mean + standard deviation [SD]) of TEP were 36.7 + 21.5 µg Xanthan Gum (XG) eq L–1 at BBMO and 36.6 + 28.3 µg XG eq L–1 at EOS; for CSP, they were 11.9 + 6.1 µg BSA eq L–1 at BBMO and 13.0 + 5.9 µg BSA eq L–1 at EOS. Seasonal variability was more evident at EOS, where surface TEP and CSP concentrations peaked in summer and spring, respectively, and less predictable at the shore-most station, BBMO. Vertical distributions between surface and 80 m, monitored at EOS, showed highest TEP concentrations within the surface mixed layer during the stratification period, whereas CSP concentrations were highest before the onset of summer stratification. Phytoplankton were the main drivers of TEP and CSP distributions, although nutrient limitation and saturating irradiance also appeared to play important roles. The dynamics and distribution of TEP and CSP were uncoupled both in the coastal sites and along the transect, suggesting that they are different types of particles produced and consumed differently in response to environmental variability

Turnover time of fluorescent dissolved organic matter in the dark global ocean

Research articleMarine dissolved organic matter (DOM) is one of the largest reservoirs of reduced carbon on Earth. In the dark ocean (4200 m), most of this carbon is refractory DOM. This refractory DOM, largely produced during microbial mineralization of organic matter, includes humic-like substances generated in situ and detectable by fluorescence spectroscopy. Here we show two ubiquitous humic-like fluorophores with turnover times of 435±41 and 610±55 years, which persist significantly longer than the B350 years that the dark global ocean takes to renew. In parallel, decay of a tyrosine-like fluorophore with a turnover time of 379±103 years is also detected. We propose the use of DOM fluorescence to study the cycling of resistant DOM that is preserved at centennial timescales and could represent a mechanism of carbon sequestration (humic-like fraction) and the decaying DOM injected into the dark global ocean, where it decreases at centennial timescales (tyrosine-like fraction).Versión del editor10,015

Nitrogen Limitation of the Summer Phytoplankton and Heterotrophic Prokaryote Communities in the Chukchi Sea

Major changes to Arctic marine ecosystems have resulted in longer growing seasons with increased phytoplankton production over larger areas. In the Chukchi Sea, the high productivity fuels intense benthic denitrification creating a nitrogen (N) deficit that is transported through the Arctic to the Atlantic Ocean, where it likely fuels N fixation. Given the rapid pace of environmental change and the potentially globally significant N deficit, we conducted experiments aimed at understanding phytoplankton and microbial N utilization in the Chukchi Sea. Ship-board experiments tested the effect of nitrate (NO3-) additions on both phytoplankton and heterotrophic prokaryote abundance, community composition, photophysiology, carbon fixation and NO3- uptake rates. Results support the critical role of NO3- in limiting summer phytoplankton communities to small cells with low production rates. NO3- additions increased particulate concentrations, abundance of large diatoms, and rates of carbon fixation and NO3- uptake by cells &gt;1 μm. Increases in the quantum yield and electron turnover rate of photosystem II in +NO3- treatments suggested that phytoplankton in the ambient dissolved N environment were N starved and unable to build new, or repair damaged, reaction centers. While some increases in heterotrophic prokaryote abundance and production were noted with NO3- amendments, phytoplankton competition or grazers likely dampened these responses. Trends toward a warmer more stratified Chukchi Sea will likely enhance summer oligotrophic conditions and further N starve Chukchi Sea phytoplankton communities

Organic matter distribution and dynamics in marine ecosystems. Field, experimental and remote sensing approaches

Incluye Resumen y Conclusiones en españolTesis Univ. Granada. Departamento de Ecología. Leída el 3 de octubre de 200

Size fractionation, chemotaxonomic groups and bio-optical properties of phytoplankton along a transect from the Mediterranean Sea to the SW Atlantic Ocean

International audienc

Effects of dissolved organic matter photoproducts and mineral nutrient supply on bacterial growth in mediterranean inland waters

Sunlight reacts with dissolved organic matter (DOM) modifying its availability as bacterial substrate. We assessed the impact of DOM photoproducts and mineral nutrient supply on bacterial growth in seven inland waters from the South of Spain, where DOM is characterized by low chromophoric content and long residence time. Factorial experiments were performed with presence vs absence of DOM photoproducts and mineral nutrient supply. In six of the seven experiments, we found a significant and negative effect of DOM photoproducts on bacterial growth and a significant and positive effect of mineral nutrient supply. The interaction of these two factors leaded to a compensation of negative effects of photoproducts by availability of mineral nutrients. Dissolved organic matter diagenetic status and the ionic environment where organic carbon is dissolved can be influencing bacterial DOM processing

Seasonal dynamics of transparent exopolymer particles (TEP) and their drivers in the coastal NW Mediterranean Sea

International audienceTransparent Exopolymer Particles (TEPs) are a subclass of organic particles with high impact in biogeochemical and ecological processes, such as the biological carbon pump, air-sea interactions, or the microbial loop. However, the complexity in production and consumption makes TEP dynamics hardly predictable, calling for the need of descriptive studies about the in situ dynamics of these particles. We followed monthly TEP dynamics and combined them with a dataset of environmental variables during three years in a coastal site of the oligotrophic North Western Mediterranean (Blanes Bay). TEP concentration, ranging from 11.3 to 289.1 μg XG eq L−1 (average 81.7 ± 11.7 μg XG eq L−1), showed recurrent peaks in early summer (June–July). TEP were temporally disconnected from chlorophyll a maxima, that occurred in late winter and early spring (maxima 1.21 μg L−1), but they were significantly related to the abundance of specific phytoplankton groups (diatoms and dinoflagellates) and also coincided with periods of low nutrient concentrations. The fraction of particulate organic carbon in the form of TEP (the TEP:POC and TEP:PM ratios) were also highest in early summer, indicating that TEP-enriched particles of low density accumulate in surface waters during stratified periods. We hypothesize that the accumulation of these particles affects the microbial food web by enhancing the activity of specific prokaryotic extracellular enzymes (esterase, β-glucosidase and alkaline phosphatase) and promoting the abundance of heterotrophic nanoflagellate

Microbiology of the Rapidly Changing Polar Environments

Marine and freshwater polar environments are characterized by intense physical forces and strong seasonal variations. The persistent cold and sometimes inhospitable conditions create unique ecosystems and habitats for microbial life. Polar microbial communities are diverse productive assemblages, which drive biogeochemical cycles and support higher food-webs across the Arctic and over much of the Antarctic. Recent studies on the biogeography of microbial species have revealed phylogenetically diverse polar ecotypes, suggesting adaptation to seasonal darkness, sea-ice coverage and high summer irradiance. Because of the diversity of habitats related to atmospheric and oceanic circulation, and the formation and melting of ice, high latitude oceans and lakes are ideal environments to investigate composition and functionality of microbial communities. In addition, polar regions are responding more dramatically to climate change compared to temperate environments and there is an urgent need to identify sensitive indicators of ecosystem history, that may be sentinels for change or adaptation. For instance, Antarctic lakes provide useful model systems to study microbial evolution and climate history. Hence, it becomes essential and timely to better understand factors controlling the microbes, and how, in turn, they may affect the functioning of these fragile ecosystems. Polar microbiology is an expanding field of research with exciting possibilities to provide new insights into microbial ecology and evolution. With this Research Topic we seek to bring together polar microbiologists studying different aquatic systems and components of the microbial food web, to stimulate discussion and reflect on these sensitive environments in a changing world perspective