References

ADGEO

Advances in Geosciences

ADGEO

Adv. Geosci.

1680-7359

Copernicus Publications

Göttingen, Germany

10.5194/adgeo-22-85-2009

Sahara dust, ocean spray, volcanoes, biomass burning: pathways of nutrients into Andean rainforests

Fabian

¹ Rollenbeck

¹ ² Spichtinger

¹ Brothers

³ Dominguez

³ Thiemens

Technical University of Munich (TUM), TUM Life Science Center Weihenstephan, Am Hochanger 13, 85354 Freising, Germany

Laboratory for Climatology and Remote Sensing (LCRS), University of Marburg, Germany

Department of Chemistry, University of California San Diego (UCSD), USA

13 10 2009

22 85 94

2009

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The full text article is available as a PDF file from https://adgeo.copernicus.org/articles/22/85/2009/adgeo-22-85-2009.pdf

Regular rain and fogwater sampling in the Podocarpus National Park, on the humid eastern slopes of the Ecuadorian Andes, along an altitude profile between 1960 and 3180 m, has been carried out since 2002. The samples, accumulated over about 1-week intervals, were analysed for pH, conductivity and major ions (K+, Na+, NH4+, Ca2+, Mg2+, Cl−, SO42−, NO3−, PO43−). About 35% of the weekly samples had very low ion contents, with pH mostly above 5 and conductivity below 10 μS/cm. 10-days back trajectories (FLEXTRA) showed that respective air masses originated in pristine continental areas, with little or no obvious pollution sources. About 65%, however, were significantly loaded with cations and anions, with pH as low as 3.5 to 4.0 and conductivity up to 50 μS/cm. The corresponding back trajectories clearly showed that air masses had passed over areas of intense biomass burning, active volcanoes, and the ocean, with episodic Sahara and/or Namib desert dust interference. Enhanced SO42− and NO3+ were identified, by combining satellite-based fire pixel observations with back trajectories, as predominantly resulting from biomass burning. Analyses of oxygen isotopes 16O, 17O, and 18O in nitrate show that nitrate in the samples is indeed a product of atmospheric conversion of precursors. Some SO42−, about 10% of the total input, could be identified to originate from active volcanoes, whose plumes were encountered by about 10% of all trajectories. Enhanced Na+, K+, and Cl− were found to originate from ocean spray sources. They were associated with winds providing Atlantic air masses to the receptor site within less than 5 days. Episodes of enhanced Ca2+ and Mg2+ were found to be associated with air masses from African deserts. Satellite aerosol data confirm desert sources both on the Northern (Sahara) as on the Southern Hemisphere (Namib), depending on the season. A few significant PO43− peaks are related with air masses originating from North African phosphate mining fields.

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