FIRST SURVEY OF AIRBORNE PHYTOLITHS IN MAR DEL PLATA (ARGENTINA)

LATORRE, FABIANA; OSTERRIETH, MARGARITA; FERNÁNDEZ HONAINE, MARIANA

Mar del Plata

Otro; 7 th International Meeting on Phytolith Research; 2008

A first analysis of airborne phytoliths was carried out in Mar del Plata (38º03'S, 57º33'W), Argentina. The primary aim was to characterize the phytolith morphotypes present in the atmosphere, to quantify their abundance and to detect if exists a seasonal variation exists throughout the year. The final goal was to evaluate the plant-opal transport by current air and so to contribute to interpret the origin of particles deposited into sediments. For the analysis, year 1993 was selected because of its driest characteristics in relation to mean rainfall values from the previous 30-years (difference of 100mm); temperature was also on average 0.6ºC colder than the mean values previously registered. These climatic conditions could favour the presence of these biomineralizations in the air. We have analized the seasonal conditions of climate and the changes in land use as possible factor influencing the type and abundance of airborne phytoliths throughout the year. The standard method for monitoring airborne particulate matter implies the use of Hirst-type suction bioaerosol samplers based on the impact principle. In this work, a Burkard 7-day recording volumetric trap was used. The sampler was placed 15m high on the Universidad Nacional de Mar del Plata building. The trap operates continuously with a flow rate of 10 liters/min, ensuring the provision of both hourly and daily data. Airborne particles were deposited onto Melinex tape coated with an adhesive substance. After exposure, the tape was cut into daily (48 mm) segments. The tape was adhered to a microscope slide with a 10% Gelvatol solution and a few drops of glycerin jelly stained with basic fuchsin. The counting method involved a subsampling unit, consisting of three longitudinal transverse under a magnification of 400x, that upon conversion represents the average concentration of particles during the 24 hour period (p/m3). Wind speed data were obtained from our local meterological station located next to the sampler, and rainfall data were provided by Meteorological National Service located at the local airport. We selected the windiest days belonging to May and November (high accumulated rainfall values), February and April (low values), and October (intermediate values). Considering eight days of survey, the concentration of phytoliths in the air was of 1543 p/m3; it was composed by 61% of isolated and 1% of articulated types, the rest were unknown or unidentified phytoliths (38%). This high percentage is in part attributable to the mounting media and to the fact that the material was fixed. Most abundant morphotypes were elongate psilate with 634 p/m3, followed by rondels with 153 p/m3. A significative and negative correlation was found between wind speed and phytoliths (Spearman non-parametric coefficient rs=-0.714; p=0.0465). These preliminary results showed a relation between phytoliths and the agricultural practices of the area. Months with higher phytolith concentrations coincided with the period where soils are without plant cover due to agricultural management. These practices include burnings of pastures, which occur in the east-northeast area, and blowing of typical crops, common in north and west-southwest area of Mar del Plata.