Widespread dust deposition on North American peatlands coincident with European land-clearance

Ecosystems around the world are being subjected to numerous human disturbances. Climate change and land degradation are the most obvious of these disturbances and have received much attention. However, easily overlooked, indirect disturbances can also alter ecosystem structure and function. Dust deposition is a prime example of an easily overlooked disturbance process. We hypothesized that historic European settlement and land-clearance in eastern North America led to widespread wind erosion of upland soils and subsequent dust deposition onto otherwise undisturbed peatlands, potentially fertilizing these naturally nutrient-poor ecosystems and causing shifts in plant communities. We tested these hypotheses by analyzing 11 peat profiles collected across a broad region of eastern North America. We documented a strong correlation between the concentrations of Ambrosia pollen grains and microscopic mineral particles, interpreting this as a signal of dust deposition coincident with European settlement and land-clearance. Analysis of Sphagnum macrofossils revealed substantial site-to-site variability in both the degree and the direction of ecological response to dust deposition, but suggested that increasing magnitude of dust deposition increased the likelihood of a decline in the relative abundance of Sphagnum. Results also suggested that raised bogs were more sensitive to dust deposition than kettle peatlands. We conclude that European settlement and land-clearance resulted in widespread dust deposition on peatlands, leading to ecological changes in some of these ecosystems, and leaving behind a coherent dust horizon in the late-Holocene peatland stratigraphy of eastern North America. This easily overlooked indirect disturbance process could be ongoing today in areas of widespread soil disturbance and could potentially further alter dust-receiving ecosystems.