Dust Impacts on Terrestrial Ecosystems

Atmospherically transported dust originates mostly from eroded soils and secondarily from glacially ground rock material. Globally most dust is generated from desert and desert-fringe areas, but there is almost always a locally derived component often generated by human activity. Compared with average composition of Earth’s crust, dust is enriched in biologically important elements such as phosphorus and nitrogen as well as in elements such as iron and titanium that are concentrated in soils during weathering. Dust can be deposited locally within the same ecosystem or on spatially and climatically distant locations. Most dust particles are <10 µm in diameter and their large surface to volume ratio makes them more susceptible to weathering than coarse-grained host soil material. As a consequence, dust input can be particularly important when soils are first developing on rock or alluvium, where its organic components can support pioneering species and the fine-grained minerals can weather quickly to augment rock-derived nutrients. It can be even more important late in ecosystem development when many soluble nutrients have been depleted and phosphorus is tied up in minimally soluble mineral phases. Thus while dust input supports progressive ecosystem development it can be particularly important in retarding the retrogressive ecosystem processes, because the added nutrients are most likely to counteract deficiencies. As an example, humid tropical forests in tectonically inactive settings can be particularly dependent on nutrient input from dust. Indeed studies of dust inputs to humid forests in rapidly eroding domains demonstrate the importance of nutrient augmentation from distant sources. Although seasonally dry forests and savannas are closer to the main dust sources they may be less impacted by dust augmentation because soils in these areas are less depleted by natural soil development. Human generated dust has substantially increased over the last few hundred years leading to dislocations of nutrient supplies that can be acute when for instance humid forest areas are cleared for agriculture and surface soils lost to erosion. These areas are most dependent of human management of nutrient supply because global sources of nutrient-rich dust to replenish losses are distant. Dust can act as a natural fertilizer to ecosystems but both the rate of addition and the time lag of release by weathering make it unlikely to be a useful balance to anthropogenic disruption to local nutrient cycles.