Articles | Volume 17, issue 4
Atmos. Chem. Phys., 17, 2673–2687, 2017

Special issue: Amazon Tall Tower Observatory (ATTO) Special Issue

Atmos. Chem. Phys., 17, 2673–2687, 2017
Research article
22 Feb 2017
Research article | 22 Feb 2017

Soluble iron nutrients in Saharan dust over the central Amazon rainforest

Joana A. Rizzolo1, Cybelli G. G. Barbosa1, Guilherme C. Borillo1, Ana F. L. Godoi1, Rodrigo A. F. Souza2, Rita V. Andreoli2, Antônio O. Manzi3, Marta O. Sá3, Eliane G. Alves3, Christopher Pöhlker4, Isabella H. Angelis4, Florian Ditas4, Jorge Saturno4, Daniel Moran-Zuloaga4, Luciana V. Rizzo5, Nilton E. Rosário5, Theotonio Pauliquevis5, Rosa M. N. Santos2, Carlos I. Yamamoto6, Meinrat O. Andreae4, Paulo Artaxo7, Philip E. Taylor8, and Ricardo H. M. Godoi1 Joana A. Rizzolo et al.
  • 1Environmental Engineering Department, Federal University of Parana, Curitiba, PR, Brazil
  • 2Meteorology Department, State University of Amazonas – UEA, Manaus, AM, Brazil
  • 3Instituto Nacional de Pesquisas da Amazônia, Programa de Grande Escala Biosfera Atmosfera na Amazônia, Manaus, AM, Brazil
  • 4Biogeochemistry Department, Max Planck Institute for Chemistry, Mainz, Germany
  • 5Universidade Federal de São Paulo, Instituto de Ciências Ambientais, Químicas e Farmacêuticas, Diadema, SP, Brazil
  • 6Chemical Engineering Department, Federal University of Parana, Curitiba, PR, Brazil
  • 7Institute of Physics, University of São Paulo, São Paulo, SP, Brazil
  • 8Deakin University, CCMB and CMMR, School of Life and Environmental Sciences, Geelong, VIC, Australia

Abstract. The intercontinental transport of aerosols from the Sahara desert plays a significant role in nutrient cycles in the Amazon rainforest, since it carries many types of minerals to these otherwise low-fertility lands. Iron is one of the micronutrients essential for plant growth, and its long-range transport might be an important source for the iron-limited Amazon rainforest. This study assesses the bioavailability of iron Fe(II) and Fe(III) in the particulate matter over the Amazon forest, which was transported from the Sahara desert (for the sake of our discussion, this term also includes the Sahel region). The sampling campaign was carried out above and below the forest canopy at the ATTO site (Amazon Tall Tower Observatory), a near-pristine area in the central Amazon Basin, from March to April 2015. Measurements reached peak concentrations for soluble Fe(III) (48 ng m−3), Fe(II) (16 ng m−3), Na (470 ng m−3), Ca (194 ng m−3), K (65 ng m−3), and Mg (89 ng m−3) during a time period of dust transport from the Sahara, as confirmed by ground-based and satellite remote sensing data and air mass backward trajectories. Dust sampled above the Amazon canopy included primary biological aerosols and other coarse particles up to 12 µm in diameter. Atmospheric transport of weathered Saharan dust, followed by surface deposition, resulted in substantial iron bioavailability across the rainforest canopy. The seasonal deposition of dust, rich in soluble iron, and other minerals is likely to assist both bacteria and fungi within the topsoil and on canopy surfaces, and especially benefit highly bioabsorbent species. In this scenario, Saharan dust can provide essential macronutrients and micronutrients to plant roots, and also directly to plant leaves. The influence of this input on the ecology of the forest canopy and topsoil is discussed, and we argue that this influence would likely be different from that of nutrients from the weathered Amazon bedrock, which otherwise provides the main source of soluble mineral nutrients.

Short summary
Particles collected from the air above the Amazon Basin during the wet season were identified as Saharan dust. Soluble minerals were analysed to assess the bioavailability of iron. Dust deposited onto the canopy and topsoil can likely benefit organisms such as fungi and lichens. The ongoing deposition of Saharan dust across the Amazon rainforest provides an iron-rich source of essential macronutrients and micronutrients to plant roots, and also directly to plant leaves during the wet season.
Final-revised paper