Natural or anthropogenic? On the origin of atmospheric sulfate deposition in the Andes of southeastern Ecuador

Abstract

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.

Classification of Tree Functional Types in a Megadiverse Tropical Mountain Forest from Leaf Optical Metrics and Functional Traits for Two Related Ecosystem Functions

“…The area is affected by climate change because significant warminghas been observed during the last decades [29]. Biomass burning in the Amazon has led to the long-range transport of aerosols and, thus, to the atmospheric depositions of plant nutrients (e.g., N) into the area, which increase with altitude [33,34]. The forest structure and tree species composition change with elevation, not only due to strong topographical differences (ravines and ridges) [35] but also due to pronounced climatic differences in the study area (Table S1).…”

Atmospheric salt deposition in a tropical mountain rain forest at the eastern Andean slopes of South Ecuador – Pacific or Atlantic origin?

“…Correlations were tested for the various elevations within the MACC data set. MACC1 (0.03-0.5 µm) MACC2 (0.5-5 µm) MACC3 (5-20 µm) The PSCF (Malm et al, 1986;Pekney et al, 2006;Zeng and Hopke, 1989) calculates the probability that a source of aerosol or pollutant observed at the ground measurement site is located at a specific cell in the geographic space and is defined by…”