Impacts of vegetation dynamics on the redistribution of sediment, nutrients, and contaminants by wind and water

Background/Question/Methods

Aeolian and fluvial processes are fundamental drivers of earth surface dynamics and play an important role in the redistribution of sediment, nutrients, and contaminants.  Projected increases in both land-use intensity and drought frequency for many arid and semiarid environments are likely to alter land-surface dynamics through differential changes in dust emissions, water-driven sediment production, and soil degradation associated with wind and water erosion.  The redistribution of sediment, nutrients, and contaminants near the soil surface can be largely affected by interactions between aeolian and fluvial processes, as well as the structure and distribution of vegetation, yet most studies to date have evaluated these processes independently and in isolation of one another.  We report time-series field measurements of wind- and water-driven sediment transport and evaluated both types of transport under baseline conditions and under disturbed conditions associated with fire, drought, and grazing.  In addition, we evaluated rates of horizontal dust flux at scales ranging from individual plants up to plot-scale vegetation patches and shrub clusters to assess the effects of vegetation dynamics on the capture and redistribution of sediment, nutrients, and contaminants.

Results/Conclusions

Climate variability associated with protracted drought, in conjunction with land management practices such as prescribed fire and livestock grazing, had a large effect on the relative rates of wind- and water-driven sediment transport.  Grazing and especially fire amplified the rates of both types of sediment transport; however, rates of aeolian sediment transport increased to a greater extent than fluvial transport under protracted drought conditions.  Our results also indicate that differences in the structure and distribution of vegetation play a fundamental role in the capture and redistribution of wind-blown sediment, nutrients, and contaminants.  Differences among vegetation patch types indicate that shrub clusters capture more sediment than individual shrubs and herbaceous patches, and importantly, that bare patches serve as amplified sediment sources following disturbance.  Our results have direct implications for desertification and nutrient redistribution, as well as contaminant transport issues associated with landfills, mine tailings, and other land use activities.  More generally, our results highlight the need to more fully integrate aeolian and fluvial processes to assess their relative roles in the redistribution of sediment, nutrients, and contaminants in response to disturbance and changing climate.