Wet deposition in the remote western and central Mediterranean as a source of trace metals to surface seawater

This study reports the only recent characterisation of two contrasted wet deposition events collected during the PEACETIME cruise in the Mediterranean open seawater, and their impact on trace metals (TMS) marine stocks. Rain samples were analysed for Al, 12 trace metals (TMs hereafter, including Co, Cd, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Ti, V and Zn) and nutrients (N, P, DOC) concentrations. The first rain sample collected in the Ionian Sea (rain ION) was a wet typical regional background deposition event whereas the second rain collected in the Algerian Basin (rain FAST) was a Saharan dust wet deposition. The concentrations of TMs in the two rain samples were significantly lower compared to concentrations in rains collected at coastal sites reported in the literature, suggesting either less anthropogenic influence in the remote Mediterranean environment, or decreased emissions during the last decades in the Mediterranean Sea. The TMs inventories in the surface microlayer and mixed layer (0–20 m) at ION and FAST stations before and after the events, compared to atmospheric fluxes, showed that the atmospheric inputs were a significant source of particulate TMs for both layers. At the scale of the western and central Mediterranean, the atmospheric inputs were of the same order of magnitude as marine stocks within the ML for dissolved Fe, Co and Zn, underlining the role of the atmosphere in their biogeochemical cycle in the stratified Mediterranean Sea. In case of intense wet dust deposition event, the contribution of atmospheric inputs could be critical for dissolved stocks of the majority of TMs.

Canopy Exchange and Modification of Nitrogen Fluxes in Forest Ecosystems

Purpose of Review We provide an overview of the main processes occurring during the interactions between atmospheric nitrogen and forest canopies, by bringing together what we have learned in recent decades, identifying knowledge gaps, and how they can be addressed with future research thanks to new technologies and approaches. Recent Findings There is mounting evidence that tree canopies retain a significant percentage of incoming atmospheric nitrogen, a process involving not only foliage, but also branches, microbes, and epiphytes (and their associated micro-environments). A number of studies have demonstrated that some of the retained nitrogen can be assimilated by foliage, but more studies are needed to better quantify its contribution to plant metabolism and how these fluxes vary across different forest types. By merging different approaches (e.g., next-generation sequence analyzes and stable isotopes, particularly oxygen isotope ratios) it is now possible to unveil the highly diverse microbial communities hidden in forest canopies and their ability to process atmospheric nitrogen through processes such as nitrification and nitrogen fixation. Future work should address the contribution of both foliar nitrogen uptake and biological transformations within forest canopies to whole ecosystem nitrogen cycling budgets. Summary Scientists have studied for decades the role of forest canopies in altering nitrogen derived from atmospheric inputs before they reach the forest floor, showing that tree canopies are not just passive filters for precipitation water and dissolved nutrients. We now have the technological capability to go beyond an understanding of tree canopy itself to better elucidate its role as sink or source of nutrients, as well as the epiphytes and microbial communities hidden within them.

Diversity and Sources of Airborne Eukaryotic Communities (AEC) in the Global Dust Belt over the Red Sea

Airborne eukaryotic communities (AEC), rank among the least studied aerobiological components, despite their adverse impacts on human health and the environment. Here, we describe the AECs in the global dust belt, the area between the west coast of North Africa and Central Asia, which supports the highest dust fluxes on the planet. We sampled atmospheric dust over 14 months (fall 2015–fall 2016) from onshore and offshore locations of the Red Sea, the only waterbody that entirely encompassed in the global dust belt. We also sampled surface water samples to determine the potential transfer of taxa across the air-sea interface. To target the eukaryotes, we performed Miseq sequencing of atmospheric dust and surface water samples. Analysis of amplicon sequencing indicates a total pool of 18,816 sequence variants (SVs). Among 33 unique eukaryotic phyla in the AEC over the Red Sea, the most dominant taxa were Streptophyta, Apicomplexa, and Ascomycota. Aerosol eukaryotes originated from various sources and formed more diverse communities than eukaryotic communities of the Red Sea surface water. AECs were dominated by phylotypes released from plant material and soils, and including taxa reported to be harmful to human health. The AEC composition was significantly influenced by sampling locations and seasonal conditions but not by the origin of the air masses nor dust loads. This work is original and uses state-of-the-art methods and very powerful NGS- bioinformatics and statistical approaches. The selected study site has high interest and it has been well chosen because of the unique combination of high loads of dust deposition, being the only fully contained seawater body in the area acting as a sink for the atmospheric dust, and the lack of riverine inputs and watershed effects empathizing the role of atmospheric inputs in the ecology of the system.

Atmospheric inputs of volcanic iron around Heard and McDonald Islands, Southern ocean

Increased atmospheric Fe loading and solubility was attributed to emissions from Heard Island volcano (Kerguelen plateau), emphasizing the need for models to consider volcanoes as a source of aeolian Fe to remote oceanic regions.

Comparative Study of 16 Clear-Sky Radiative Transfer Models to Estimate Direct Normal Irradiance (DNI) in Botucatu, Brazil

The interest of the direct normal irradiation (DNI) estimation is important in the evaluation of the solar potential and, consequently, for data correction and expansion of the historical series. In this study, a review of the performance of 16 models of radiative transfer was performed. These models are used to estimate DNI on a clear day in Botucatu/SP region located in Brazil. The revised models are categorized into two classes: simple models (11 models: ASH, MAJ, ALLEN, GH, P1, HLJ, FU, KU, H1, IP, and INC) and complex models (five models: BIRD, IQ, MRM5, P2, and YANG). The evaluation methodology used here is consistent with the literature. The input parameters were estimated and a statistical analysis using relative-mean-bias-error (rMBE), root-mean-square-error (rRMSE), and mean absolute percentage error (MAPE) indicators were performed to validate those models. The results indicate that the complex models (that require more atmospheric inputs) generally performed better than simpler models. Despite the consistent limitations in the use of estimated parameters, the performance of the models can be considered satisfactory. The best performances are highlighted for models MRM5 and YANG. Simple models ASH and IP performed similar to complex models. These results were confirmed using frequency distribution and the cumulative frequency analysis. These results are important for engineers of solar systems to use the best model and select the most suitable locations for installing a small or large solar plant.

An explicit estimate of the atmospheric nutrient impact on global oceanic productivity

State-of-the-art global nutrient deposition fields are here coupled to the biogeochemistry model PISCES to investigate the effect on ocean biogeochemistry in the context of atmospheric forcings for preindustrial, present, and future periods. Present-day atmospheric deposition fluxes of inorganic N, Fe, and P over the global ocean are accounted equal to ~40 Tg-N yr−1, ~0.28 Tg-Fe yr−1 and ~0.10 Tg-P yr−1. The resulting globally integrated primary production of roughly 47 Pg-C yr−1 is well within the range of satellite-based estimates and other modeling predictions. Preindustrial atmospheric nutrient deposition fluxes are lower compared to present-day (~51 %, ~36 %, and ~40 % for N, Fe, and P, respectively), resulting here in a lower marine primary production by ~3 % globally. Future changes in air pollutants under the RCP8.5 scenario result in a modest decrease of the bioaccessible nutrients input into the global ocean compared to present-day (~13 %, ~14 % and ~20 % for N, Fe and P, respectively), without significantly affecting the projected primary production in the model. The global mean nitrogen-fixation rates changed only marginally from preindustrial to future conditions (111 ± 0.6 Tg-N yr−1). With regard to the atmospheric inputs to the ocean, sensitivity model simulations indicate that the contribution of nutrients' organic fraction results in an increase in primary production by about 2.4 %. This estimate is almost equal to the effect of emissions and atmospheric processing on the oceanic biogeochemistry since preindustrial times in the model when only the inorganic fraction of the nutrients is considered. Although the impact of the atmospheric organic nutrients may imply a relatively weak response of marine productivity on a global scale, stronger regional effects up to ~20 % are calculated in the oligotrophic subtropical gyres. Overall, this work provides a first explicit assessment of the contribution of the organic forms of atmospheric nutrients, highlighting the importance of their representation in biogeochemistry models and thus the oceanic productivity estimates.

Unraveling Aquatic Quality Controls of a Nearly Undisturbed Mediterranean Island (Samothraki, Greece)

Due to its rough, mountainous relief, Samothraki remains one of the last minimally disturbed islands in the Mediterranean. This paper examines the hydrogeochemical regime of the island’s surface waters as it results from geological, morphological, and hydro(geo)logical controls within a frame of minimally disturbed environmental conditions. Shallow, fractured groundwater aquifers, in combination with steep slopes and predominant weathering resistant rocks, bring about flashy stream regimes with remarkably low solute concentrations. Streams and springs revealed hydrochemical similarities. Contrary to streams chiefly draining sedimentary rocks, streams underlined by granite and ophiolite rocks do not respond hydrochemically to geochemical differences. Using ion proportions instead of concentrations, geochemical fingertips of magmatic stream basins were detected. Atmospheric inputs largely affect stream and spring composition, e.g., by 75% regarding sodium. Only 20% of dissolved oxygen and pH variance was assigned to biological activity, while nutrient levels were consistent with the undisturbed conditions of the island, except nitrate. Small mountainous springs and brooks fed by restricted, fractured groundwater aquifers with perennial flow, despite scarce summer rainfalls, may be fueled by cloud and fog condensation. High night-day stream flow differences, high atmospheric humidity predominately occurring during the night, and low stream water travel times point out toward this phenomenon.