Sources, pathways, and deposition of nutrients and pollutants in an Ecuadorian tropical mountain forest
The element cycle is an important control of the ecosystem functioning such as the provision of supporting and regulating ecosystem services. Human induced alterations of this cycle could have deleterious effects on the ecosystem and its services, as e.g., carbon sequestration and water supply. The...
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|The element cycle is an important control of the ecosystem functioning such as the provision of supporting and regulating ecosystem services. Human induced alterations of this cycle could have deleterious effects on the ecosystem and its services, as e.g., carbon sequestration and water supply. The input of atmospheric elements is a key underlying mechanism of this cycle, supplying new nutrients/pollutants to the ecosystem. Therefore, an in-depth knowledge of the fluxes and the complex factors driving the deposition of ecosystem-relevant elements are indispensable to unravel the impacts of element cycle alterations on the mountain forests function, e.g. by nutrient manipulation experiments.
The current work is the first effort in a TMF with a very intricate terrain to reveal the complex causal relationships between the atmospheric fluxes of ecosystem-relevant nutrients and pollutants, the contributing emission sources and the atmospheric circulation drivers responsible for transport. This investigation has shown that the atmospheric deposition is highly conditioned by the interception of OP by vegetation and ground.
Therefore, in the study area, the atmospheric constituents explored present a high spatial and temporal heterogeneity mainly based on elevation, aspect, and topographic position of the receptor side, as well as the location and height of the surrounding barriers. In general, the higher the terrain features are, the higher is the frequency of clouds touching the ground and thus, the influence of the synoptical circulation and far-range sources is increased. That is on the condition that the surrounding topography does not act as a barrier for the synoptical winds from specific directions.
The exposed findings stress the importance of considering topographical complexity of the receptor site when assessing atmospheric deposition in mountainous areas and should be considered when designing future nutrient manipulation experiments. Due to the importance of the synoptical circulation in the medium to long range transport of nutrient and pollutants, also the location of the sources with respect to the preponderant transport pathways is an important parameter affecting the observed deposition. Additionally, the seasonality, the surface, and the intensity of the emissions are also highly relevant factor determining the state of deposition at the receptor site.
The sources and transport pathways of the investigated atmospheric constituents in the study area are illustrated in a synthesis map at the end of the manuscript. The anthropogenic sources dominate the sulfur and nitrogen cycles, on which a very high influence of the biomass-burning sources was observed, especially on high elevation and vegetated areas well-exposed to the preponderant wind direction. Atmospheric sodium and chloride deposition at the study area is still dominated by natural sources, especially the Caribbean Sea and the equatorial Pacific Ocean, mostly fertilizing areas at high elevations, more exposed to the synoptic winds.