Abstract:
Atmospheric sulfur deposition above certain limits
can represent a threat to tropical forests, causing nutrient
imbalances and mobilizing toxic elements that impact biodiversity
and forest productivity. Atmospheric sources of sulfur
deposited by precipitation have been roughly identified in
only a few lowland tropical forests. Even scarcer are studies
of this type in tropical mountain forests, many of them megadiversity
hotspots and especially vulnerable to acidic deposition.
In these places, the topographic complexity and related
streamflow conditions affect the origin, type, and intensity of
deposition. Furthermore, in regions with a variety of natural
and anthropogenic sulfur sources, like active volcanoes and
biomass burning, no source emission data has been used for
determining the contribution of each source to the deposition.
The main goal of the current study is to evaluate sulfate
(SO?
4 ) deposition by rain and occult precipitation at two topographic
locations in a tropical mountain forest of southern
Ecuador, and to trace back the deposition to possible emission
sources applying back-trajectory modeling. To link upwind
natural (volcanic) and anthropogenic (urban/industrial
and biomass-burning) sulfur emissions and observed sulfate
deposition, we employed state-of-the-art inventory and satellite
data, including volcanic passive degassing as well. We
conclude that biomass-burning sources generally dominate
sulfate deposition at the evaluated sites. Minor sulfate transport
occurs during the shifting of the predominant winds
to the north and west. Occult precipitation sulfate deposition
and likely rain sulfate deposition are mainly linked to
biomass-burning emissions from the Amazon lowlands. Volcanic
and anthropogenic emissions from the north and west
contribute to occult precipitation sulfate deposition at the
mountain crest Cerro del Consuelo meteorological Station and to rain-deposited sulfate at the upriver mountain pass El
Tiro meteorological station.
