Abstract
Phosphorus (P) availability constrains both carbon uptake and loss in some of the world's most productive ecosystems. In some of these regions, atmospheric aerosols appear to be an important, if not dominant, source of new P inputs. For example, previous work suggests that mineral aerosols from North Africa bring significant amounts of new phosphorus to the P‐impoverished soils of the Amazon Basin. Here we use recent observations and atmospheric transport modeling to show that the Amazon Basin itself appears to be losing atmospheric phosphorus to neighboring regions as a consequence of biomass burning emissions, anthropogenic sources of mineral aerosols and primary biogenic particles. Observations suggest that biomass burning emissions and human disturbance are responsible for ∼23% of the phosphorus flux in the Amazon. Although biomass burning and disturbance may bring new phosphorus into nondisturbed regions, as a whole the Amazon appears to be losing phosphorus through the atmosphere. Phosphorus lost via atmospheric transport from the Amazon is deposited in the adjacent oceans and in other regions downwind. These results suggest that land use change within the Amazon may substantially increase phosphorus availability to the remaining undisturbed forests, and that this fertilization mechanism could potentially contribute to recent changes in carbon uptake measured in undisturbed stands, as well as fertilizing downwind ocean regions.
Highlights
As part of our analysis, we examine the role of humans in perturbing the atmospheric phosphorus cycle, a topic that has not been addressed in previous studies
In order to verify that our results are not sensitive to this approach, we show results using multicomponent regressions, where we regress the phosphorus onto aluminum, black carbon and potassium, and determine the slopes simultaneously
[27] The results described in section 3.1 suggest that even in the absence of significant human disturbance, combustion and biogenic sources of atmospheric phosphorus within the Amazon may contribute to atmospheric phosphorus deposition more than long-range transport of mineral aerosols
Summary
[2] Tropical forests account for at least one-third of annual terrestrial biosphere-atmosphere carbon dioxide (CO2) exchange [Field et al, 1998], and can modify climate and atmospheric composition at a global scale [e.g., Dickinson and Henderson-Sellers, 1988; Shukla et al, 1990; Townsend et al, 1992; Malhi and Grace, 2000; Clark, 2002]. The widespread distribution of low-P soils in tropical latitudes has, in turn, caused atmospheric inputs of aerosol-bound phosphorus to be linked with the long-term productivity of these forests [e.g., Swap et al, 1992; Chadwick et al, 1999; Wardle et al, 2004]. Atmospheric inputs of phosphorus in mineral aerosols are typically quite low for most ecosystems, they are thought to be an important source of new phosphorus to moist tropical forests on geologic timescales [Swap et al, 1992; Chadwick et al., GB4030. While mineral inputs may well be important at long timescales, recent observations over tropical forest regions do not support the dominance of mineral aerosols for the atmospheric phosphorus cycle in these areas.
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