Abstract. Sea salt (NaCl) has recently been proven to be of the utmost importance for ecosystem functioning in Amazon lowland forests because of its impact on herbivory, litter decomposition and, thus, carbon cycling. Sea salt deposition should generally decline as distance from its marine source increases. For the Amazon, a negative east-west gradient of sea salt availability is assumed as a consequence of the barrier effect of the Andes Mountains for Pacific air masses. However, this generalized pattern may not hold for the tropical mountain rainforest in the Andes of southern Ecuador. To analyse sea salt availability, we investigated the deposition of sodium (Na + ) and chloride (Cl − ), which are good proxies of sea spray aerosol. Because of the complexity of the terrain and related cloud and rain formation processes, sea salt deposition was analysed from both, rain and occult precipitation (OP) along an altitudinal gradient over a period between 2004 and 2009. To assess the influence of easterly and westerly air masses on the deposition of sodium and chloride over southern Ecuador, sea salt aerosol concentration data from the Monitoring Atmospheric Composition and Climate (MACC) reanalysis data set and back-trajectory statistical methods were combined. Our results, based on deposition time series, show a clear difference in the temporal variation of sodium and chloride concentration and Na + / Cl − ratio in relation to height and exposure to winds. At higher elevations, sodium and chloride present a higher seasonality and the Na + / Cl − ratio is closer to that of sea salt. Mediumto long-range sea salt transport exhibited a similar seasonality, which shows the link between our measurements at high elevations and the sea salt synoptic transport. Although the influence of the easterlies was predominant regarding the atmospheric circulation, the statistical analysis of trajectories and hybrid receptor models revealed a stronger impact of the north equatorial Atlantic, Caribbean, and Pacific sea salt sources on the atmospheric sea salt concentration in southern Ecuador. The highest concentration in rain and cloud water was found between September and February when air masses originated from the north equatorial Atlantic, the Caribbean Sea and the equatorial Pacific. Together, these sources accounted for around 82.4 % of the sea salt budget over southern Ecuador.
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.
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 being roughly identified in only a few lowland tropical forests. Even scarcer are these type of studies in tropical mountain forests, many of them megadiversity hotspots and especially vulnerable to acidic deposition. Here, the topographic complexity and related streamflow condition 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 of them to the deposition. The main goal of the current study is to evaluate sulfate (SO4−) 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.
Abstract. Salt (NaCl) is recently proven to be of highest importance for ecosystem functioning of the Amazon lowland forests because of its importance for herbivory, litter decomposition and thus, carbon cycling. Salt deposition should generally decline with distance from its marine sources. For tropical South America, a negative east-west salt availability gradient is assumed in the Amazon as a consequence of the barrier effect of the Andes for Pacific air masses. However, this generalized pattern may not hold for the tropical mountain rain forest in the Andes of southern Ecuador. To analyze salt availability, we investigate the deposition of Na+ and Cl- which are good proxies of sea spray aerosol. Because of the complexity of the terrain and related cloud and rain formation processes, salt deposition was analyzed from both, rain and occult precipitation (OP) water along an altitudinal gradient over a period from 2004 to 2009. To assess the influence of Atlantic and Pacific air masses on the locally observed deposition of sodium and chloride, sea-salt aerosol concentration data from the Monitoring Atmospheric Composition and Climate (MACC) reanalysis dataset and back-trajectory statistical methods were combined. Our results based on deposition time series and 2192 generated trajectories show a clear difference in the temporal variation of sodium and chloride concentration due to height and exposure to winds. The sea-salt transport was highly seasonal where higher locations revealed a stronger seasonality. Although the influence of the easterlies were predominant regarding atmospheric circulation, the statistical analysis of trajectories and hybrid receptor models revealed a stronger impact of the Pacific sea-salt sources on the deposition at the study area. The highest concentration in rain and cloud water was found between September and February originating from both, the equatorial Pacific and Atlantic. However, the Pacific sources contributed with up to 25 % to the observed total concentration of Na+ and Cl- at the receptor site although the frequency of occurrence of the respective trajectories is below 10 %. This highlights the great importance of westerly winds from the Pacific for the sea-salt transport to the deposition into the tropical mountain forests at the eastern Andean slopes of southern Ecuador.
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